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1
Ma, Yubo, Zhixian Gao, Tao Yuan et Tianfu Wang. « Kinetics of Dicyclopentadiene Hydroformylation over Rh–SiO2 Catalysts ». Progress in Reaction Kinetics and Mechanism 42, no 2 (mai 2017) : 191–99. http://dx.doi.org/10.3184/146867817x14821527549013.
Texte intégralRésumé :
The hydroformylation of dicyclopentadiene (DCPD) to monoformyltricyclodecenes (MFTD) represents a key intermediate step in the conversion of the C5 fraction derived from the petrochemical process to value-added fine chemicals, for example, diformyltricyclodecanes and tricyclodecanedimethylol. Although both heterogeneous and homogeneous catalysts can catalyse this reaction, the heterogeneously catalysed pathway has received significantly less attention due to its lower catalytic activities. We demonstrate in this work that a low Rh loaded heterogeneous 0.1% Rh–SiO2 catalyst can present a similar performance relative to the homogeneous Rh(PPh3)Cl, a reference catalyst for this reaction. Furthermore, an extensive kinetic study of DCPD hydroformylation to MFTD using heterogeneous 0.1% Rh–SiO2 catalysts has been performed. A series of kinetic experiments was carried out over a broad range of conditions (temperature: 100–120 °C; pressure: 1.5–5 MPa; catalyst-to-reactant mass ratio: 0.02–0.05; PPh3 concentration: 5–12.5 g L−1). A kinetic analysis was carried out, indicating the activation energy for the reaction to be 84.7 kJ mol−1. DCPD conversion and MFTD yield could be optimised to be as high as 99% at 0.1% Rh loading, a DCPD/catalyst mass ratio of 25, a PPh3 concentration of 10 g L−1, a reaction time of 4 h and a reaction pressure of 4 MPa.
2
Lomic, Gizela, Erne Kis, Goran Boskovic et Radmila Marinkovic-Neducin. « Application of scanning electron microscopy in catalysis ». Acta Periodica Technologica, no 35 (2004) : 67–77. http://dx.doi.org/10.2298/apt0435067l.
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A short survey of various information obtained by scanning electron microscopy (SEM) in the investigation of heterogeneous catalysts and nano-structured materials have been presented. The capabilities of SEM analysis and its application in testing catalysts in different fields of heterogeneous catalysis are illustrated. The results encompass the proper way of catalyst preparation, the mechanism of catalyst active sites formation catalysts changes and catalyst degradation during their application in different chemical processes. Presented SEM pictures have been taken on a SEM JOEL ISM 35 over 25 years of studies in the field of heterogeneous catalysis.
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Khan, Haris Mahmood, Tanveer Iqbal, Saima Yasin, Muhammad Irfan, Muhammad Mujtaba Abbas, Ibham Veza, Manzoore Elahi M. Soudagar, Anas Abdelrahman et Md Abul Kalam. « Heterogeneous Catalyzed Biodiesel Production Using Cosolvent : A Mini Review ». Sustainability 14, no 9 (22 avril 2022) : 5062. http://dx.doi.org/10.3390/su14095062.
Texte intégralRésumé :
Biodiesel is gaining recognition as a good replacement for typical diesel owing to its renewability, sustainability, and eco-friendly nature. Transesterification is the leading route for biodiesel generation, which occurs during homogeneous/heterogeneous/enzymatic catalysis. Besides this, the usage of heterogeneous catalysts is considered more advantageous over homogeneous catalysts due to the easy catalyst recovery. Consequently, numerous heterogeneous catalysts have been synthesized from multiple sources with the intention of making the manufacturing process more efficient and cost-effective. Alongside this, numerous researchers have attempted to improve the biodiesel yield using heterogeneous catalysts by introducing cosolvents, such that phase limitation between oil and alcohol can be minimized. This short review is aimed at examining the investigations performed to date on heterogeneously catalyzed biodiesel generation in the presence of different cosolvents. It encompasses the techniques for heterogeneous catalyst synthesis, reported in the literature available for heterogeneous catalyzed biodiesel generation using cosolvents and their effects. It also suggests that the application of cosolvent in heterogeneously catalyzed three-phase systems substantially reduces the mass transfer limitation between alcohol and oil phases, which leads to enhancements in biodiesel yield along with reductions in values of optimized parameters, with catalyst weight ranges from 1 to 15 wt. %, and alcohol/oil ratio ranges from 5.5 to 20. The reaction time for getting the maximum conversion ranges from 10 to 600 min in the presence of different cosolvents. Alongside this, most of the time, the biodiesel yield remained above 90% in the presence of cosolvents.
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Kaplunenko, Volodymyr, et Mykola Kosinov. « Electric field - induced catalysis. Laws of field catalysis ». InterConf, no 26(129) (18 octobre 2022) : 332–51. http://dx.doi.org/10.51582/interconf.19-20.10.2022.037.
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Abstract.The article explores a new type of catalysis - electric field catalysis. The laws of field catalysis are given. The characteristics of the electric field are determined, which set the values of the characteristics of the field catalysis. Field catalysis and field catalyst do not fit into the traditional definition of catalysis and catalyst, which may require a revision of the terminology of catalysis. The field is a more versatile catalyst compared to material catalysts, both in terms of its application to a wider range of chemical reactions, and in the ability to control the rate and selectivity. It is shown that a common donor-acceptor mechanism of catalysis is realized in heterogeneous and field catalysis. Generalized formulas are obtained, from which, as partial results, the laws of heterogeneous and field catalysis follow. New definitions of catalyst and field catalysis are given. The class of material catalysts has been expanded and supplemented with field catalysts.
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Liu, Jingyue. « Advanced Electron Microscopy Characterization of Nanostructured Heterogeneous Catalysts ». Microscopy and Microanalysis 10, no 1 (22 janvier 2004) : 55–76. http://dx.doi.org/10.1017/s1431927604040310.
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Heterogeneous catalysis is one of the oldest nanosciences. Although model catalysts can be designed, synthesized, and, to a certain degree, characterized, industrial heterogeneous catalysts are often chemically and physically complex systems that have been developed through many years of catalytic art, technology, and science. The preparation of commercial catalysts is generally not well controlled and is often based on accumulated experiences. Catalyst characterization is thus critical to developing new catalysts with better activity, selectivity, and/or stability. Advanced electron microscopy, among many characterization techniques, can provide useful information for the fundamental understanding of heterogeneous catalysis and for guiding the development of industrial catalysts. In this article, we discuss the recent developments in applying advanced electron microscopy techniques to characterizing model and industrial heterogeneous catalysts. The importance of understanding the catalyst nanostructure and the challenges and opportunities of advanced electron microscopy in developing nanostructured catalysts are also discussed.
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Latos, Piotr, Anna Wolny et Anna Chrobok. « Supported Ionic Liquid Phase Catalysts Dedicated for Continuous Flow Synthesis ». Materials 16, no 5 (5 mars 2023) : 2106. http://dx.doi.org/10.3390/ma16052106.
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Heterogeneous catalysis, although known for over a century, is constantly improved and plays a key role in solving the present problems in chemical technology. Thanks to the development of modern materials engineering, solid supports for catalytic phases having a highly developed surface are available. Recently, continuous-flow synthesis started to be a key technology in the synthesis of high added value chemicals. These processes are more efficient, sustainable, safer and cheaper to operate. The most promising is the use of heterogeneous catalyst with column-type fixed-bed reactors. The advantages of the use of heterogeneous catalyst in continuous flow reactors are the physical separation of product and catalyst, as well as the reduction in inactivation and loss of the catalyst. However, the state-of-the-art use of heterogeneous catalysts in flow systems compared to homogenous ones remains still open. The lifetime of heterogeneous catalysts remains a significant hurdle to realise sustainable flow synthesis. The goal of this review article was to present a state of knowledge concerning the application of Supported Ionic Liquid Phase (SILP) catalysts dedicated for continuous flow synthesis.
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Du, Yuan-Peng, et Jeremy S. Luterbacher. « Designing Heterogeneous Catalysts for Renewable Catalysis Applications Using Metal Oxide Deposition ». CHIMIA International Journal for Chemistry 73, no 9 (18 septembre 2019) : 698–706. http://dx.doi.org/10.2533/chimia.2019.698.
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Heterogeneous catalysis has long been a workhorse for the chemical industry and will likely play a key role in the emerging area of renewable chemistry. However, renewable molecule streams pose unique challenges for heterogeneous catalysis due to their high oxygen content, frequent low volatility and the near constant presence of water. These constraints can often lead to the need for catalyst operation in harsh liquid phase conditions, which has compounded traditional catalyst deactivation issues. Oxygenated molecules are also frequently more reactive than petroleum-derived molecules, which creates a need for highly selective catalysts. Synthetic control over the nanostructured environment of catalytic active sites could facilitate the creation of both more stable and selective catalysts. In this review, we discuss the use of metal oxide deposition as an emerging strategy that can be used to synthesize and/or modify heterogeneous catalysts to introduce tailored nanostructures. Several important applications are reviewed, including the synthesis of high surface area mesoporous metal oxides, the enhancement of catalyst stability, and the improvement of catalyst selectivity.
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Holzwarth, Arnold, et Wilhelm F. Maier. « Catalytic Phenomena in Combinatorial Libraries of Heterogeneous Catalysts ». Platinum Metals Review 44, no 1 (1 janvier 2000) : 16–21. http://dx.doi.org/10.1595/003214000x4411621.
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Combinatorial catalysis is becoming a significant method for investigating the activities of large numbers of potential catalysts. A very important prerequisite for making use of combinatorial catalysis research is a reliable, fast and efficient technique for monitoring the catalytic activities. Emissivity-corrected infrared thermography, which monitors the heat changes resulting from the heat of reaction on catalyst surfaces, is such a technique. In this article we describe emissivity-corrected infrared thermography and demonstrate its performance, over time, in monitoring the catalytic activities of catalyst libraries. It is shown that not only can static relative activity be displayed, but also that catalyst-specific time-dependent properties, such as activation and deactivation phenomena can be demonstrated.
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Miceli, Mariachiara, Patrizia Frontera, Anastasia Macario et Angela Malara. « Recovery/Reuse of Heterogeneous Supported Spent Catalysts ». Catalysts 11, no 5 (1 mai 2021) : 591. http://dx.doi.org/10.3390/catal11050591.
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The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.
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Jakab-Nácsa, Alexandra, Attila Garami, Béla Fiser, László Farkas et Béla Viskolcz. « Towards Machine Learning in Heterogeneous Catalysis—A Case Study of 2,4-Dinitrotoluene Hydrogenation ». International Journal of Molecular Sciences 24, no 14 (14 juillet 2023) : 11461. http://dx.doi.org/10.3390/ijms241411461.
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Utilization of multivariate data analysis in catalysis research has extraordinary importance. The aim of the MIRA21 (MIskolc RAnking 21) model is to characterize heterogeneous catalysts with bias-free quantifiable data from 15 different variables to standardize catalyst characterization and provide an easy tool to compare, rank, and classify catalysts. The present work introduces and mathematically validates the MIRA21 model by identifying fundamentals affecting catalyst comparison and provides support for catalyst design. Literature data of 2,4-dinitrotoluene hydrogenation catalysts for toluene diamine synthesis were analyzed by using the descriptor system of MIRA21. In this study, exploratory data analysis (EDA) has been used to understand the relationships between individual variables such as catalyst performance, reaction conditions, catalyst compositions, and sustainable parameters. The results will be applicable in catalyst design, and using machine learning tools will also be possible.
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Xu, Jun Qiang, Fang Guo, Jun Li, Xiu Zhi Ran et Yan Tang. « Synthesis of the Cu/Flokite Catalysts and their Performances for Catalytic Wet Peroxide Oxidation of Phenol ». Advanced Materials Research 560-561 (août 2012) : 869–72. http://dx.doi.org/10.4028/www.scientific.net/amr.560-561.869.
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The supported Cu/Flokite catalysts were prepared by conventional incipient wetness impregnation. The catalysis oxidation degradation of phenol was carried out in heterogeneous catalyst and H2O2 process. The results indicated that the reaction system with catalyst and hydrogen peroxide was more benefit to degradation of phenol. When the phenol initial concentration was 100 mg/L, the phenol removal over the 2.5%Cu -2.5% Fe/Flokite catalyst could reach 96%. The peroxide catalytic oxidation process over the enhanced heterogeneous catalyst would be a novel technique for the treatment of phenol wastewater.
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Crozier, P. A., et M. Pan. « Quantitative nano-characterization of heterogeneous catalysts ». Proceedings, annual meeting, Electron Microscopy Society of America 53 (13 août 1995) : 398–99. http://dx.doi.org/10.1017/s0424820100138361.
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Heterogeneous catalysts can be of varying complexity ranging from single or double phase systems to complicated mixtures of metals and oxides with additives to help promote chemical reactions, extend the life of the catalysts, prevent poisoning etc. Although catalysis occurs on the surface of most systems, detailed descriptions of the microstructure and chemistry of catalysts can be helpful for developing an understanding of the mechanism by which a catalyst facilitates a reaction. Recent years have seen continued development and improvement of various TEM, STEM and AEM techniques for yielding information on the structure and chemistry of catalysts on the nanometer scale. Here we review some quantitative approaches to catalyst characterization that have resulted from new developments in instrumentation.HREM has been used to examine structural features of catalysts often by employing profile imaging techniques to study atomic details on the surface. Digital recording techniques employing slow-scan CCD cameras have facilitated the use of low-dose imaging in zeolite structure analysis and electron crystallography. Fig. la shows a low-dose image from SSZ-33 zeolite revealing the presence of a stacking fault.
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Singh, B., Faizal Bux et Y. C. Sharma. « Comparison of homogeneous and heterogeneous catalysis for synthesis of biodiesel from M. indica oil ». Chemical Industry and Chemical Engineering Quarterly 17, no 2 (2011) : 117–24. http://dx.doi.org/10.2298/ciceq100902061s.
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Biodiesel was developed by transesterification of Madhuca indica oil by homogeneous and heterogeneous catalysis. KOH and CaO were taken as homogeneous and heterogeneous catalyst respectively. It was found that the homogeneous catalyst (KOH) took 1.0 h of reaction time, 6:1 methanol to oil molar ratio, 0.75 wt% of catalyst amount, 55?0.5?C reaction temperature for completion of the reaction. The heterogeneous catalyst (CaO) was found to give optimum yield in 2.5 h of reaction time at 8:1 methanol to oil molar ratio, 2.5 wt% of catalyst amount, at 65?0.5?C. A high yield (95-97%) and conversion (>96.5%) was obtained from both the catalysts. CaO was found to leach to some extent in the reactants and a biodiesel conversion of 27-28% was observed as a result of leaching.
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Rabelo, S. N., L. S. Oliveira et A. S. França. « BIODIESEL PRODUCTION FROM MICROWAVE IRRADIATED REACTOR USING HOMOGENEOUS AND HETEROGENEOUS CATALYSIS ». Revista de Engenharia Térmica 17, no 1 (30 juin 2018) : 18. http://dx.doi.org/10.5380/reterm.v17i1.62254.
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Biodiesel was successful produced in a microwave irradiation reactor using homogeneous and heterogeneous catalysis. The biodiesel was production by the trasesterification reaction of soybean oil using metanol. Sodium methylate (30% solution in metanol) was used for the homogeneous catalyst and the heterogeneous catalyst was developed using wasted eggshells. The eggshells were calcined and tested pure and doped with potassium hydroxide in 10, 30 and 50% of weight. The power and temperature of the microwave were kept constant in every reaction being 800W and 200º Celsius, respectively. The reaction time was significantly reduced using microwave compared to the conventional process. In only one minute of reaction, the methyl ester (FAME) conversion obtained was 98.9% with the homogeneous catalyst and within 15 minutes, the heterogeneous catalysis accomplished 100%. For heterogeneous catalyst, the best results were acquired when the doped catalyst contained 50% of KOH. The results indicated that the eggshells treated with KOH has a great potential to be used for microwave-assisted transesterification reactions of oils with mild operations conditions: molar ratio oil/alcochol 1:6 and just 5% of catalyst. In addition, the heterogenous catalyst was recovered and reused in other reactions with a relatively satisfying results. The physico-chemical properties of the catalysts were characterized by X-ray diffraction and thermogravimectric analysis.
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Xu, Jun Qiang, Fang Guo, Shu Shu Zou et Xue Jun Quan. « Optimization of the Catalytic Wet Peroxide Oxidation of Phenol over the Fe/NH4Y Catalyst ». Materials Science Forum 694 (juillet 2011) : 640–44. http://dx.doi.org/10.4028/www.scientific.net/msf.694.640.
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The heterogeneous NH4Y zeolite-supported iron catalysts were prepared by incipient wetness impregnation. The catalysis oxidation degradation of phenol was carried over the heterogeneous catalyst in the peroxide catalytic oxidation process. Compared with the homogeneous Fenton process, the Fe/ NH4Y-acid catalyst can effectively degrade contaminants with high catalytic activity and easy catalyst separation from the solution. The phenol removal efficiency could reach 96% in the optimum experimental conditions. These process conditions were as follows: iron content is 5%, reaction time was 60 min, reaction temperature was 70 oC, the catalyst dosage was 1g/L, the H2O2 concentration was 1.65g/L.
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Du, Yunchen, Di Guo, Meiling Xiong, Yanwu Qi, Chenkui Cui, Jun Ma, Xijiang Han et Ping Xu. « Fe3+-Exchanged Titanate Nanotubes : A New Kind of Highly Active Heterogeneous Catalyst for Friedel-Crafts Type Benzylation ». Journal of Nanomaterials 2015 (2015) : 1–9. http://dx.doi.org/10.1155/2015/738089.
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Heterogeneous catalysis for Friedel-Crafts type benzylation has received much attention in recent years due to its characteristic of environmental benefits. In this paper, titanate nanotubes (TNTs) were employed as heterogeneous catalyst support, and a new kind of Fe3+-exchanged titanate nanotubes (Fe-TNTs) catalyst with highly dispersed ferric sites was constructed by an ion exchange technique. The obtained catalyst was systematically characterized by XRD, TEM, N2adsorption, XPS, and UV-vis spectra. As expected, Fe-TNTs showed excellent catalytic activities in the benzylation of benzene and benzene derivatives. The recycling tests for Fe-TNTs were also carried out, where the reason for the gradually decreased activity was carefully investigated. Superior to some reported catalysts, the catalytic ability of used Fe-TNTs could be easily recovered by ion exchange again, indicating that Fe-TNTs herein were a highly active and durable heterogeneous catalyst for Friedel-Crafts type benzylation. These results might be helpful for the design and preparation of novel heterogeneous catalysts by combining the structural advantages of titanate nanotubes and active metal ions.
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Wong, W.-Y., S. Lim, Y.-L. Pang, C.-H. Lim, F.-L. Pua et G. Pua. « Response surface optimisation of biodiesel synthesis using biomass derived green heterogeneous catalyst ». IOP Conference Series : Materials Science and Engineering 1257, no 1 (1 octobre 2022) : 012010. http://dx.doi.org/10.1088/1757-899x/1257/1/012010.
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Abstract Although homogeneous alkali-catalysed transesterification is the typical process used in biodiesel production, it caused complications in downstream separation processes and an oversupply of glycerol as a by-product. The present work studied the synthesis of a novel sulfonated biomass-derived solid acid catalyst and its application in biodiesel production via interesterification of oleic acid. Solid acid catalysts were prepared by direct sulfonation via thermal treatment with concentrated sulfuric acid. The design of experiments was conducted via four-factors central composite design (CCD) coupled with response surface methodology (RSM) analysis. The parameters considered for optimisation included carbonisation and sulfonation temperatures, catalyst loading and reaction time, each varied at five levels. The maximum yield of fatty acid methyl ester (FAME) was obtained using optimum parameters as carbonisation temperature of 586 °C, sulfonation temperature of 110 °C, catalyst loading of 10.5 wt.% and reaction time of 7 h was 54.3 % based on the theoretical ester formation. A quadratic mathematical model in RSM was successfully established that can make effective predictions about the anticipated biodiesel yield. This study proved that the low-cost heterogeneous catalyst derived from biomass waste with a simple production route could catalyse the interesterification process under moderate process conditions.
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Jin, Jia Min. « Catalysis Mechanism and Application of Carbon Gasification Reaction-A Comparison of Two Heterogeneous Catalysis Mechanisms ». International Journal of Chemistry 14, no 1 (14 avril 2022) : 23. http://dx.doi.org/10.5539/ijc.v14n1p23.
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This article is a brief summary article of research. The results of the three times experiments are reviewed. two heterogeneous catalysis mechanisms are introduced, namely: Chemical Reaction Mode Cyclic Catalysis Mechanism-CRM and Electron Cyclic Donate-Accept Catalysis Mechanism-ECDAM or Electron Orbital Deformation-Recovery Cyclic Catalysis Mechanism -EODRM. Some difficulties encountered by CRM are listed. The author clearly points out that the CRM is not credible. This false theory has misled us for more than 100 years.
About ECDAM, the article also gives a brief description. The main point of ECDAM is that the catalysis phenomenon are physical rather than chemical phenomenon. The catalysts do not participate in chemical reactions. It's just contact, electron cyclic donate-accept or electron orbital deformation-recovery cycle. The theory contains three viewpoints:
1. There is a boundary between the catalyst and the poison.
2. The active of the catalyst or the degree of toxicity of the poison is closely related to ihe electronegative value of the catalyst or poison.
3. The active of catalyst is closely related to the chemical state of the catalyst
The selectivity of catalyst is also related to electronegative or energy level
According to ECDAM, the author considers that there are several problems worth studying in production and scientific research. such as: alumina is a poison in the Fe ammonia synthesis catalyst. The Cordierite (2MgO·2Al2O3·5SiO2) ceramic honeycomb support is also a poison in automotive exhaust purification catalyst. The Cordierite ceramic honeycomb is retardant in wall flow filter for diesel vehicles. Activated carbon is a poison in the Ruthenium catalyst for ammonia synthesis. Alumina and activated carbon all are a poison to noble metal catalysts, and so on.
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Zhao, Da, Roland Petzold, Jiyao Yan, Dieter Muri et Tobias Ritter. « Tritiation of aryl thianthrenium salts with a molecular palladium catalyst ». Nature 600, no 7889 (15 décembre 2021) : 444–49. http://dx.doi.org/10.1038/s41586-021-04007-y.
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AbstractTritium labelling is a critical tool for investigating the pharmacokinetic and pharmacodynamic properties of drugs, autoradiography, receptor binding and receptor occupancy studies1. Tritium gas is the preferred source of tritium for the preparation of labelled molecules because it is available in high isotopic purity2. The introduction of tritium labels from tritium gas is commonly achieved by heterogeneous transition-metal-catalysed tritiation of aryl (pseudo)halides. However, heterogeneous catalysts such as palladium supported on carbon operate through a reaction mechanism that also results in the reduction of other functional groups that are prominently featured in pharmaceuticals3. Homogeneous palladium catalysts can react chemoselectively with aryl (pseudo)halides but have not been used for hydrogenolysis reactions because, after required oxidative addition, they cannot split dihydrogen4. Here we report a homogenous hydrogenolysis reaction with a well defined, molecular palladium catalyst. We show how the thianthrene leaving group—which can be introduced selectively into pharmaceuticals by late-stage C–H functionalization5—differs in its coordinating ability to relevant palladium(II) catalysts from conventional leaving groups to enable the previously unrealized catalysis with dihydrogen. This distinct reactivity combined with the chemoselectivity of a well defined molecular palladium catalyst enables the tritiation of small-molecule pharmaceuticals that contain functionality that may otherwise not be tolerated by heterogeneous catalysts. The tritiation reaction does not require an inert atmosphere or dry conditions and is therefore practical and robust to execute, and could have an immediate impact in the discovery and development of pharmaceuticals.
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Takabatake, Moe, et Ken Motokura. « Montmorillonite-based heterogeneous catalysts for efficient organic reactions ». Nano Express 3, no 1 (1 mars 2022) : 014004. http://dx.doi.org/10.1088/2632-959x/ac5ac3.
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Abstract In this review, we give a brief overview of recently developed montmorillonite-based heterogeneous catalysts used for efficient organic reactions. Cation-exchanged montmorillonite catalysts, metal catalysts supported on montmorillonite, and an interlayer design used for selective catalysis are introduced and discussed. In traditional syntheses, homogeneous acids and metal salts were used as catalysts, but the difficulty in separation of catalysts from products was a bottleneck when considering industrialization. The use of solid heterogeneous catalysts is one of the major solutions to overcome this problem. Montmorillonite can be used as a heterogeneous catalyst and/or catalyst support. This clay material exhibits strong acidity and a stabilizing effect on active species, such as metal nanoparticles, due to its unique layered structure. These advantages have led to the development of montmorillonite-based heterogeneous catalysts. Acidic montmorillonite, such as proton-exchanged montmorillonite, exhibits a high catalytic activity for the activation of electrophiles, such as alcohols, alkenes, and even alkanes. The montmorillonite interlayer/surface also functions as a good support for various metal species used for oxidation and carbon-carbon bond forming reactions. The use of an interlayer structure enables selective reactions and the stabilization of catalytically active species.
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Encinar, José María, Juan Félix González, Gloria Martínez et Sergio Nogales-Delgado. « Use of NaNO3/SiAl as Heterogeneous Catalyst for Fatty Acid Methyl Ester Production from Rapeseed Oil ». Catalysts 11, no 11 (20 novembre 2021) : 1405. http://dx.doi.org/10.3390/catal11111405.
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The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction takes place. For this purpose, different catalysts are used, including a wide range of possibilities. In this research the use of NaNO3/SiAl as a heterogeneous catalyst for FAME production through transesterification of rapeseed oil with methanol is considered. A thorough characterization of the catalyst (including XDR and XPS analysis, SEM microscopy, lixiviation and reusability tests, among others), specific optimization of transesterification by using the final catalyst (considering catalyst amount, stirring rate, methanol/oil ratio, and temperature), and quality determination of the final biodiesel (following the UNE-EN 14214 standard) were carried out. In conclusion, 20 mmolNa·gsupport−1 (that is, NaNO3/SiAl 20/1) offered the best results, with a high activity (exceeding 99% w/w of FAMEs) without requiring higher impregnation amounts. The best chemical conditions for this heterogeneous catalyst were 5% w/w catalyst, 700 rpm, 9:1 methanol/oil ratio, and 65 °C, obtaining Ea = 73.3 kJ·mol−1 and a high-quality biodiesel, similar to those obtained through homogeneous catalysis. Consequently, this catalyst could be a suitable precursor for FAME production.
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Quevedo, Rodolfo, Camilo Perdomo et Sonia Moreno. « Heterogeneous Catalysts in Pictet-Spengler-Type Reactions ». Journal of Chemistry 2013 (2013) : 1–5. http://dx.doi.org/10.1155/2013/125302.
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Several solid catalysts were evaluated as an alternative for 1,2,3,4-tetrahydroisoquinoline synthesis by means of the Pictet-Spengler reaction. The reaction catalysed by a mixed oxide (Mg and Al) led to the best yield and good regioselectivity; using an Al-pillared bentonite led to good yields and total regioselectivity. The results revealed no direct relationship between catalyst acidity and yield.
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Liu, J., et J. R. Ebner. « Nano-Characterization of Industrial Heterogeneous Catalysts ». Microscopy and Microanalysis 4, S2 (juillet 1998) : 740–41. http://dx.doi.org/10.1017/s1431927600023825.
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Catalyst characterization plays a vital role in new catalyst development and in troubleshooting of commercially catalyzed processes. The ultimate goal of catalyst characterization is to understand the structure-property relationships associated with the active components and supports. Among many characterization techniques, only electron microscopy and associated analytical techniques can provide local information about the structure, chemistry, morphology, and electronic properties of industrial heterogeneous catalysts. Three types of electron microscopes are usually used for characterizing industrial supported catalysts: 1) scanning electron microscope (SEM), 2) scanning transmission electron microscope (STEM), and 3) transmission electron microscope (TEM). Each type of microscope has its unique capabilities. However, the integration of all electron microscopic techniques has proved invaluable for extracting useful information about the structure and the performance of industrial catalysts.Commercial catalysts usually have a high surface area with complex geometric structures to enable reacting gases or fluids to access as much of the active surface of the catalyst as possible.
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Shinde, Preeti S., Pradnya S. Suryawanshi, Kanchan K. Patil, Vedika M. Belekar, Sandeep A. Sankpal, Sagar D. Delekar et Sushilkumar A. Jadhav. « A Brief Overview of Recent Progress in Porous Silica as Catalyst Supports ». Journal of Composites Science 5, no 3 (6 mars 2021) : 75. http://dx.doi.org/10.3390/jcs5030075.
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Porous silica particles have shown applications in various technological fields including their use as catalyst supports in heterogeneous catalysis. The mesoporous silica particles have ordered porosity, high surface area, and good chemical stability. These interesting structural or textural properties make porous silica an attractive material for use as catalyst supports in various heterogeneous catalysis reactions. The colloidal nature of the porous silica particles is highly useful in catalytic applications as it guarantees better mass transfer properties and uniform distribution of the various metal or metal oxide nanocatalysts in solution. The catalysts show high activity, low degree of metal leaching, and ease in recycling when supported or immobilized on porous silica-based materials. In this overview, we have pointed out the importance of porous silica as catalyst supports. A variety of chemical reactions catalyzed by different catalysts loaded or embedded in porous silica supports are studied. The latest reports from the literature about the use of porous silica-based materials as catalyst supports are listed and analyzed. The new and continued trends are discussed with examples.
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Mazaheri, Hoora, Hwai Chyuan Ong, Zeynab Amini, Haji Hassan Masjuki, M. Mofijur, Chia Hung Su, Irfan Anjum Badruddin et T. M. Yunus Khan. « An Overview of Biodiesel Production via Calcium Oxide Based Catalysts : Current State and Perspective ». Energies 14, no 13 (1 juillet 2021) : 3950. http://dx.doi.org/10.3390/en14133950.
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Biodiesel is a clean, renewable, liquid fuel that can be used in existing diesel engines without modification as pure or blend. Transesterification (the primary process for biodiesel generation) via heterogeneous catalysis using low-cost waste feedstocks for catalyst synthesis improves the economics of biodiesel production. Heterogeneous catalysts are preferred for the industrial generation of biodiesel due to their robustness and low costs due to the easy separation and relatively higher reusability. Calcium oxides found in abundance in nature, e.g., in seashells and eggshells, are promising candidates for the synthesis of heterogeneous catalysts. However, process improvements are required to design productive calcium oxide-based catalysts at an industrial scale. The current work presents an overview of the biodiesel production advancements using calcium oxide-based catalysts (e.g., pure, supported, and mixed with metal oxides). The review discusses different factors involved in the synthesis of calcium oxide-based catalysts, and the effect of reaction parameters on the biodiesel yield of calcium oxide-based catalysis are studied. Further, the common reactor designs used for the heterogeneous catalysis using calcium oxide-based catalysts are explained. Moreover, the catalytic activity mechanism, challenges and prospects of the application of calcium oxide-based catalysts in biodiesel generation are discussed. The study of calcium oxide-based catalyst should continue to be evaluated for the potential of their application in the commercial sector as they remain the pivotal goal of these studies.
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Wang, Ziyun, Hai-Feng Wang et P. Hu. « Possibility of designing catalysts beyond the traditional volcano curve : a theoretical framework for multi-phase surfaces ». Chemical Science 6, no 10 (2015) : 5703–11. http://dx.doi.org/10.1039/c5sc01732g.
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The current theory of catalyst activity in heterogeneous catalysis is mainly obtained from the study of catalysts with mono-phases, while most catalysts in real systems consist of multi-phases, the understanding of which is far short of chemists' expectation.
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Suryanto, Andi, Ummu Kalsum, Lailatul Qadariya et Mahfud Mahfud. « Production of Methyl ester from Coconut Oil using Heterogeneous K/Al2O3 under Microwave Irradiation ». Journal of Chemical Process Engineering 5, no 2 (20 décembre 2020) : 23–29. http://dx.doi.org/10.33536/jcpe.v5i2.754.
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Methyl esters derived from coconut oil are very interesting to study because they contain free fatty acids with a medium carbon chain structure (C12-C14), so most methyl esters (70%) can be bio-kerosene and the rest can be biodiesel. The process of preparing methyl ester by reaction of Trans-esterification triglyceride generally using a homogeneous KOH catalyst but this process requires a long catalyst separation process through washing and drying process. The use of heterogeneous catalysts in the production of methyl esters can remove the washing and drying processes, but trans-esterification reactions with heterogeneous catalysts require severe conditions (high pressure and high temperature), whereas at low temperatures and atmospheric conditions, the methyl ester yield is relatively low. Using microwave-irradiated trans-esterification reactions with heterogeneous catalysts, it is expected to be much faster and can obtained higher yields. Therefore, in this study we prepare a heterogeneous catalyst K/Al2O3 using solution KOH that impregnated in catalyst support Al2O3, and catalyst obtained are caracterized by XRD, BET dan SEM. Our objective was to compare the yield of methyl esters obtained through the trans-esterification process of coconut oil assisted by microwave using a heterogeneous K / Al2O3 catalyst with yield obtained using a homogeneous KOH catalyst. Experimental equipment consists of a batch reactor placed in a microwave oven equipped with a condenser, agitator and temperature controller. The batch process was carried out at atmospheric pressure with variation of K/Al2O3 catalyst concentration (0.5, 1.0, 1.5, 2.0, 2.5%) and microwave power (100, 264 and 400 W). In general, the process of producing methyl esters by heterogeneous catalysts will get three layers, wherein the first layer is the product of methyl ester, the second layer is glycerol and the third layer is the catalyst. The experimental results show that the methyl ester yield increases with increasing of microwave power, catalyst concentration and reaction time. The results obtained with K /Al2O3 catalysts are generally slightly lower than those obtained using a homogeneous KOH catalyst. However, the yield of methyl esters obtained by the K / Al2O3 heterogeneous catalyst process are relatively easy to separate rather than using a homogeneous KOH catalyst.
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Pan, Dipika, et Jhuma Ganguly. « Assessment of Chitosan Based Catalyst and their Mode of Action ». Current Organocatalysis 6, no 2 (24 juin 2019) : 106–38. http://dx.doi.org/10.2174/2213337206666190327174103.
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Introduction:The popularity of chitosan is increasing among the researchers due to its environment friendly nature, high activity and easy approachability. Chitosan based catalysts are not only the most active and selective in catalytic reaction, but their “green” accessibility also makes them promising in organic catalysis. Chitosan is commonly extracted from chitin by alkaline deacetylation and it is the second abundant biopolymer in nature after cellulose. Chitosan based catalysts are advantageous by means of non-metallic activation as it involves small organic molecules. The robustness, nontoxicity, the lack of metal leaching possibility, inertness towards moisture and oxygen, easy handling and storage are the main advantages of organocatalysts. Traditional drawbacks associated with the metal-based heterogeneous catalysts, like longer reaction times during any synthesis, metal-leaching after every reaction and structural instability of the catalyst for prolonged recycling experiments are also very negligible for chitosan based catalysts. Besides, these catalysts can contribute more in catalysis due to their reusability and these special features increase their demand as the functionalized and profitable catalysts.Objective:The thorough description about the preparation of organocatalysts from chitosan and their uniqueness and novel activities in various famous reactions includes as the main aim of this review. Reusable and recycle nature of chitosan based organocatalysts gain the advantages over traditional and conventional catalyst which is further discussed over here.Methods and Discussions:In this article only those reactions are discussed where chitosan has been used both as support in heterogeneous catalysts or used as a catalyst itself without any co-catalyst for some reactions. Owing to its high biodegradability, nontoxicity, and antimicrobial properties, chitosan is widely-used as a green and sustainable polymeric catalyst in vast number of the reactions. Most of the preparations of catalyst have been achieved by exploring the complexation properties of chitosan with metal ions in heterogeneous molecular catalysis. Organocatalysis with chitosan is primarily discussed for carbon-carbon bond-forming reactions, carbon dioxide fixation through cyclo- addition reaction, condensation reaction and fine chemical synthesis reactions. Furthermore, its application as an enantioselective catalyst is also considered here for the chiral, helical organization of the chitosan skeleton. Moreover, another advantage of this polymeric catalyst is its easy recovery and reusability for several times under solvent-free conditions which is also explored in the current article.Conclusion:Important organocatalyzed reactions with either native chitosan or functionalized chitosan as catalysts have attracted great attention in the recent past. Also, chitosan has been widely used as a very promising support for the immobilization of catalytic metals for many reactions. In this review, various reactions have been discussed which show the potentiality of chitosan as catalyst or catalyst support.
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Guo, Fang, Jun Qiang Xu et Jun Li. « Kinetics Studies for Catalytic Oxidation of Methyl Orange over the Heterogeneous Fe/Beta Catalysts ». Advanced Materials Research 807-809 (septembre 2013) : 361–64. http://dx.doi.org/10.4028/www.scientific.net/amr.807-809.361.
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The Fe/Beta catalysts were prepared by conventional incipient wetness impregnation. The catalysis oxidation degradation of methyl orange was carried out in catalyst and H2O2 process. The results indicated that the catalyst and hydrogen peroxide were more benefit to degradation of methyl orange. The reaction condition was optimized. The optimum reaction process was as follow: iron amount of catalyst was 1.25%, the catalyst dosage and H2O2 concentration was 1 mg/L and 1.5 mg/L, and reaction temperature was 70 °C. The apparent activation energy (65 KJ/mol) was obtained according to the arrhenius formula, which was benefit to study the reaction mechanism.
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Tan, Yie Hua, Mohammad Omar Abdullah et Cirilo Nolasco Hipolito. « Comparison of Biodiesel Production between Homogeneous and Heterogeneous Base Catalysts ». Applied Mechanics and Materials 833 (avril 2016) : 71–77. http://dx.doi.org/10.4028/www.scientific.net/amm.833.71.
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Homogeneous base catalyst has wide acceptability in biodiesel production because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Heterogeneous base catalyst is developed to cater these problems. The advantages of heterogeneous catalyst are their high basicity and non-toxicity. This work compared the production of biodiesel using two different kind of catalysts that is homogeneous catalyst (sodium hydroxide, NaOH and potassium hydroxide, KOH) and heterogeneous catalysts (calcium, oxide, CaO catalyst derived from chicken and ostrich eggshells). Transesterification of waste cooking oil (WCO) and methanol in the presence of heterogeneous base catalyst was conducted at an optimal reaction condition (calcination temperature for catalyst: 1000 °C; catalyst loading amount: 1.5 wt%; methanol/oil molar ratio: 10:1; reaction temperature: 65 °C; reaction time: 2 hours) with 97% biodiesel yield was obtained. While, the homogeneous base catalyst gave higher biodiesel yield of 98% at optimum operating condition (catalyst concentration: 0.75 wt%; methanol/oil molar ratio: 6:1; reaction temperature: 65 °C; reaction time: 1 hours). The slight difference in the biodiesel yield was due to the stronger basic strength in the homogeneous catalyst and were not statistically not different (p=0.05). However, despite these advances, the ultimate aim of producing biodiesel at affordable low cost and minimal-environmental-impact is yet to be realized.
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Li, Siyi, Shuo Cheng et Jeffrey S. Cross. « Homogeneous and Heterogeneous Catalysis Impact on Pyrolyzed Cellulose to Produce Bio-Oil ». Catalysts 10, no 2 (3 février 2020) : 178. http://dx.doi.org/10.3390/catal10020178.
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Effectively utilizing catalytic pyrolysis to upgrade bio-oil products prepared from biomass has many potential benefits for the environment. In this paper, cellulose (a major component of plants and a biomass model compound) is pyrolyzed and catalyzed with different catalysts: Ni2Fe3, ZSM-5, and Ni2Fe3/ZSM-5. Two different pyrolysis processes are investigated to compare homogeneous and heterogeneous catalysis influence on the products. The results indicate that the Ni2Fe3 cluster catalyst shows the best activity as a homogeneous catalysis. It can also be recycled repeatedly, increases the yield of bio-oil, and improves the quality of the bio-oil by decreasing the sugar concentration. Furthermore, it also catalyzes the formation of a small amount of hydrocarbon compounds. In the case of Ni2Fe3/ZSM-5 catalyst, it shows a lower yield of bio-oil but also decreases the sugar concentration significantly. Ni2Fe3, not only can it be used as homogeneous catalysis mixed with cellulose but also shows catalytic activity as a supported catalyst on ZSM-5, with higher catalytic activity than ZSM-5. These results indicate that the Ni2Fe3 catalyst has significant activity for potential use in industry to produce high quality bio-oil from biomass.
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Hsueh, C. L., Y. H. Huang, C. C. Wang et C. Y. Chen. « Photooxidation of azo dye Reactive Black 5 using a novel supported iron oxide : heterogeneous and homogeneous approach ». Water Science and Technology 53, no 6 (1 mars 2006) : 195–201. http://dx.doi.org/10.2166/wst.2006.197.
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Photooxidation of azo dye Reactive Black 5 (RB5) by H2O2 was performed with a novel supported iron oxide in a batch reactor in the range of pH 2.5–6.0. The iron oxide was prepared through a fluidized-bed reactor (FBR) and much cheaper than the Nafion-based catalysts. Experimental results indicate that the iron oxide can significantly accelerate the degradation of RB5 under the irradiation of UVA light (λ=365 nm). An advantage of the catalyst is its long-term stability, which was confirmed through using the catalyst for multiple runs in the degradation of RB5. In addition, this study focused mainly on determining the proportions of homogeneous catalysis and heterogeneous catalysis in the batch reactor. Conclusively, although heterogeneous catalysis contributes primarily to the oxidation of RB5 during pH 4.5-6.0, the homogeneous catalysis is of increasing importance below pH 4.0 because of the Fe ions leaching from the catalyst to solution.
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Tišler, Zdeněk, Pavla Vondrová, Kateřina Hrachovcová, Kamil Štěpánek, Romana Velvarská, Jaroslav Kocík et Eliška Svobodová. « Aldol Condensation of Cyclohexanone and Furfural in Fixed-Bed Reactor ». Catalysts 9, no 12 (14 décembre 2019) : 1068. http://dx.doi.org/10.3390/catal9121068.
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Aldol condensation reaction is usually catalysed using homogeneous catalysts. However, the heterogeneous catalysis offers interesting advantages and the possibility of cleaner biofuels production. Nowadays, one of the most used kinds of heterogeneous catalysts are hydrotalcites, which belong to a group of layered double hydroxides. This paper describes the aldol condensation of cyclohexanone (CH) and furfural (F) using Mg/Al mixed oxides and rehydrated mixed oxides in order to compare the catalyst activity after calcination and rehydration, as well as the possibility of its regeneration. The catalysts were synthesized by calcination and subsequent rehydration of the laboratory-prepared and commercial hydrotalcites, with Mg:Al molar ratio of 3:1. Their structural and chemical properties were determined by several analytical methods (inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), specific surface area (BET), thermogravimetric analysis (TGA), temperature programmed desorption (TPD)). F-CH aldol condensation was performed in a continuous fixed-bed reactor at 80 °C, CH:F = 5:1, WHSV 2 h−1. The rehydrated laboratory-prepared catalysts showed a 100% furfural conversion for more than 55 h, in contrast to the calcined ones (only 24 h). The yield of condensation products FCH and F2CH was up to 68% and 10%, respectively. Obtained results suggest that Mg/Al mixed oxides-based heterogeneous catalyst is suitable for use in the aldol condensation reaction of furfural and cyclohexanone in a fixed-bed reactor, which is an interesting alternative way to obtain biofuels from renewable sources.
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Widayat, W., Marcelinus Christwardana, S. Syaiful, Hantoro Satriadi, Akhmad Khaibar Khaibar et Mukhammad Mujahid Almaki. « Development of Heterogeneous Alkali Methoxide Catalyst from Fly Ash and Limestone ». Chemistry & ; Chemical Technology 14, no 4 (15 décembre 2020) : 521–30. http://dx.doi.org/10.23939/chcht14.04.521.
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This study is aimed to use fly ash and limestone as raw materials for preparing alkali methoxide heterogeneous catalysts for transesterification of palm oil into biodiesel. The heterogeneous catalyst was synthesized from fly ash and limestone through wet and dry methods and calcined within 1073–1273 K. X-ray diffraction and scanning electron microscopy analyses indicated the well-dispersed presence of the Ca(OCH3)2 crystal over the fly ash and limestone framework, which was mixed using wet method and calcined at 1073 K (W-800). Results showed that W-800 exhibited larger surface area and more uniform active sites than the other catalysts. About 88.6 % of biodiesel was produced from commercial palm oil with W-800 as the catalyst. The product possesses physicochemical characteristics, such as density, kinematic viscosity and free fatty acid content, which satisfy the international biodiesel standard. The catalyst was used for biodiesel production for four cycles, and the biodiesel yield was maintained up to 91.87 % from the initial value.
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Bagheri, Samira, Nurhidayatullaili Muhd Julkapli et Sharifah Bee Abd Hamid. « Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis ». Scientific World Journal 2014 (2014) : 1–21. http://dx.doi.org/10.1155/2014/727496.
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The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO2) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO2supported metal catalysts have attracted interest due to TiO2nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO2was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO2supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO2as a support material for heterogeneous catalysts and its potential applications.
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Chandra Kishore, Somasundaram, Suguna Perumal, Raji Atchudan, Ashok K. Sundramoorthy, Muthulakshmi Alagan, Sambasivam Sangaraju et Yong Rok Lee. « A Review of Biomass-Derived Heterogeneous Catalysts for Biodiesel Production ». Catalysts 12, no 12 (23 novembre 2022) : 1501. http://dx.doi.org/10.3390/catal12121501.
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The scientific community is being forced to consider alternative renewable fuels such as biodiesel as a result of the sharp increases in the price of petroleum and the increased demand for petroleum-derived products. Transesterification is a technique used to create biodiesel where a variety of edible oils, non-edible oils, and animal fats are used. For this, either a homogeneous or heterogeneous catalyst is utilized. An appropriate catalyst is chosen based on the quantity of free fatty acid content in the oil. The main distinction between homogeneous and heterogeneous catalysts is that compared to the heterogeneous catalyst, the homogeneous catalyst is not affected by the quantity of free fatty acids in the oil. Early methods of producing biodiesel relied on homogeneous catalysts, which have drawbacks such as high flammability, toxicity, corrosion, byproducts such as soap and glycerol, and high wastewater output. The majority of these issues are solved by heterogeneous catalysts. Recent innovations use novel heterogeneous catalysts that are obtained from biomass and biowaste resources. Numerous researchers have documented the use of biomass-derived heterogeneous catalysts in the production of high-quality, pure biodiesel as a potentially greener manufacturing method. The catalysts were significantly altered through conventional physical processes that were both cost- and energy-effective. The present review is intended to analyze catalysts from biowaste for making biodiesel at a minimal cost. The most recent methods for creating diverse kinds of catalysts—including acidic, basic, bifunctional, and nanocatalysts—from various chemicals and biomass are highlighted in this review. Additionally, the effects of various catalyst preparation methods on biodiesel yield are thoroughly explored.
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Gupta, Raman, Monika Gupta, Satya Paul et Rajive Gupta. « Silica-supported ZnCl2 — A highly active and reusable heterogeneous catalyst for the one-pot synthesis of dihydropyrimidinones–thiones ». Canadian Journal of Chemistry 85, no 3 (1 mars 2007) : 197–201. http://dx.doi.org/10.1139/v07-018.
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A novel silica-supported zinc chloride catalyst was prepared and investigated for the Biginelli reaction. The key features of the catalyst include rapid reaction with 100% conversion of aldehyde, good catalyst recyclability, and high stability under the reaction conditions (passes hot filtration test successfully). A low catalyst loading (12 mol% of ZnCl2) was required to achieve a quantitative reaction. Other catalysts such as SiO2–AlCl2, SiO2–AlCl2–ZnCl2 were also prepared and their activity was compared with SiO2–ZnCl2 for the Biginelli reaction.Key words: silica gel, zinc chloride, Biginelli compounds, heterogeneous catalysis, reusability.
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Gates, Bruce C. « Concluding remarks : progress toward the design of solid catalysts ». Faraday Discussions 188 (2016) : 591–602. http://dx.doi.org/10.1039/c6fd00134c.
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The 2016 Faraday Discussion on the topic “Designing New Heterogeneous Catalysts” brought together a group of scientists and engineers to address forefront topics in catalysis and the challenge of catalyst design—which is daunting because of the intrinsic non-uniformity of the surfaces of catalytic materials. “Catalyst design” has taken on a pragmatic meaning which implies the discovery of new and better catalysts on the basis of fundamental understanding of the catalyst structure and performance. The presentations and discussion at the meeting illustrate the rapid progress in this understanding linked with improvements in spectroscopy, microscopy, theory, and catalyst performance testing. The following text includes a statement of recurrent themes in the discussion and examples of forefront science that evidences progress toward catalyst design.
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Maru, Minaxi S., Parth Patel, Noor-ul H. Khan et Ram S. Shukla. « Copper Hydrotalcite (Cu-HT) as an Efficient Catalyst for the Hydrogenation of CO2 to Formic Acid ». Current Catalysis 9, no 1 (10 septembre 2020) : 59–71. http://dx.doi.org/10.2174/2211544709999200413110411.
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: Hydrogenation of CO2 to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Herein, hydrotalcite supported copper metal has shown activity and efficiency to produce formic acid from the hydrogenation of CO2, without adding any additional base or promoter and was effectively recycled 4 times after separating by simple filtration without compromising the formic acid yield. Hydrotalcite supported copper-based catalyst (Cu-HT) was synthesized through the coprecipitation method and used as a heterogeneous catalyst for the hydrogenation of CO2. The precise copper metal content determined by ICP in Cu-HT is 0.00944 mmol. The catalyst afforded maximum TOF, 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol:water (5:1, v/v) solvent. Cu-HT catalyst was synthesised and thoroughly characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area. The first-order kinetic dependence with respect to the catalyst amount, partial pressures of CO2, and of H2 was observed and a plausible reaction mechanism is suggested. Background: CO2 hydrogenation to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Objective: he aim is to investigate the heterogeneous catalyst systems, using solid soft base hydrotalcite supported Cu metal-based catalyst for effective and selective hydrogenation of CO2 to formic acid. Methods: The Cu –HT catalyst was synthesized and characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area in which the precise copper content was 0.00944 mmol. The Cu-HT catalysed hydrogenation of CO2 was carried out in the autoclave. Results: The Cu-HT catalyst afforded maximum TOF of 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol: water (5:1, v/v) solvent, without adding any additional base or promoter and was recycled 4 times by simple filtration without compromising the formic acid yield. Formation of formic acid was observed to depend on the amount of the catalyst, partial pressures of CO2 and H2, total pressure, temperature and time. Conclusion: Cu-HT based heterogeneous catalyst was found to be efficient for selective hydrogenation of CO2 to formic acid and was effectively recycled four times after elegantly separating by simple filtration.
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Ertl, Gerhard, Maria Zielińska, Małgorzata Rajfur et Maria Wacławek. « Elementary steps in heterogeneous catalysis : The basis for environmental chemistry ». Chemistry-Didactics-Ecology-Metrology 22, no 1-2 (1 décembre 2017) : 11–41. http://dx.doi.org/10.1515/cdem-2017-0001.
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Abstract Catalysis is an alternative way for reaching an immediate formation of a product, because of a lower energy barrier (between the molecules and the catalysts). Heterogeneous catalysis comprises the acceleration of a chemical reaction through interaction of the molecules involved with the surface of a solid. It is a discipline, which involves all the different aspects of chemistry: inorganic and analytical chemistry in order to characterize the catalysts and the forms of these catalysts. The industrial chemistry puts all these things together to understand the solid chemical handling, chemical reaction and energy engineering and the heat and mass transfer in these catalytic processes. Very often there are more than one, but several products, then the role of the catalyst is not so much related to activity, but to selectivity. The underlying elementary steps can now be investigated down to the atomic scale as will be illustrated mainly with two examples: the oxidation of carbon monoxide (car exhaust catalyst) and the synthesis of ammonia (the basis for nitrogen fertilizer). There is a huge market for the catalysts themselves despite of their high costs. A large fraction is used for petroleum refineries, automotive and industrial cleaning processes. The catalytic processes is a wide field and there are still many problems concerning energy conservation and energy transformation, so there is much to do in the future.
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Lawer-Yolar, Gideon, Benjamin Dawson-Andoh et Emmanuel Atta-Obeng. « Synthesis of Biodiesel from Tall Oil Fatty Acids by Homogeneous and Heterogeneous Catalysis ». Sustainable Chemistry 2, no 1 (10 mars 2021) : 206–21. http://dx.doi.org/10.3390/suschem2010012.
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This study compared the yield of biodiesel produced from tall oil fatty acids (TOFA) via (i) homogeneous catalyst (sulfuric acid) and (ii) a heterogeneous catalyst (Amberlyst® BD20, together with Ambersep BD 19 (Midcontinental Chemical Co., Olathe, KS, USA)® using a batch reactor. The effect of operation conditions including temperature, catalyst concentration, methanol: oil ratio and reaction time on esterification yield were investigated. Gas chromatographic data showed that the major fatty acids present in the TOFA are oleic acid (C18:1n9) and linoleic acid (C18:2n6). Homogenous catalysis yielded 96.76% biodiesel compared to 90.24% for heterogeneous catalysis. Optimized conditions for homogenous catalysis were at a catalyst concentration of 0.5 w/w%, 15:1 methanol: oil mass ratio at 55 °C for 60 min. FTIR results also showed that the homogeneous catalyst yielded a more complete reaction toward biodiesel production in a shorter time (60 min) compared to the heterogeneous catalyst (4.7 h). For heterogeneous catalysis, the highest yield and the lowest acid value were achieved after a second recycling because the reactants were not fully in contact with the catalyst during the first recycling. The catalyst did not show a reduction in catalytic activity even after the fourth recycling. However, the acid value was higher than that for ASTM standards for biodiesel.
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Mardina, Primata, Hesti Wijayanti, Abubakar Tuhuloula, Erita Hijriyati et Sarifah. « Corncob residue as heterogeneous acid catalyst for green synthesis of biodiesel : A short review ». Communications in Science and Technology 6, no 2 (31 décembre 2021) : 60–68. http://dx.doi.org/10.21924/cst.6.2.2021.460.
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The utilization of an appropriate catalyst in biodiesel production depends on the free fatty acid content of vegetable oil as a feedstock. Recently, heterogeneous acid catalysts are widely chosen for biodiesel production. However, these catalysts are non-renewable, highly expensive and low stability. Due to the aforementioned drawbacks of commercial heterogeneous acid catalyst, a number of efforts have been made to develop renewable green solid acid catalysts derived from biomass. Published literature revealed that the application of the biomass derived solid acid catalysts can achieve up to 98% yield of biodiesel. This article focused on corncob as raw material in solid acid catalyst preparation for biodiesel production. The efficient preparation method and performance comparation are discussed here. The corncob derived heterogeneous acid catalysts provides an environmentally friendly and green synthesis for biodiesel production.
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Pua, Fei Ling, Kah Thong Looi, Shamala Gowri Krishnan et Sharifah Nabihah. « Synthesis and Characterization of Different Transition Metal-Alginate Based Heterogeneous Catalyst for Esterification Reaction ». Key Engineering Materials 709 (septembre 2016) : 57–60. http://dx.doi.org/10.4028/www.scientific.net/kem.709.57.
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In recent years, attention has been drawn to produce heterogeneous catalyst to replace homogeneous catalyst in biodiesel industry. This study was focused on the synthesis of three different types of alginate based heterogeneous catalyst (Ferric-alginate, Copper-alginate, and Nickel alginate) and the effect of the catalyst on esterification of oleic acid. Morphology and elemental analysis was conducted to investigate the properties of the catalyst. The new heterogeneous catalysts were used to catalyze the esterification of oleic acid at reaction temperature of 60°C and 2 hours reaction time. Fe-alginate has achieved the highest free fatty acids (FFAs) conversation rate of 82.03%. The results and findings proved that transition metal-alginate heterogeneous catalyst has the potential and ability to esterify the free fatty acids prior biodiesel production from high free fatty acids feedstock.
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He, Zhenhong, Qingli Qian, Zhaofu Zhang, Qinglei Meng, Huacong Zhou, Zhiwei Jiang et Buxing Han. « Synthesis of higher alcohols from CO 2 hydrogenation over a PtRu/Fe 2 O 3 catalyst under supercritical condition ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 373, no 2057 (28 décembre 2015) : 20150006. http://dx.doi.org/10.1098/rsta.2015.0006.
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Hydrogenation of CO 2 to alcohols is of great importance, especially when producing higher alcohols. In this work, we synthesized heterogeneous PtRu/Fe 2 O 3 , in which the Pt and Ru bimetallic catalysts were supported on Fe 2 O 3 . The catalyst was used to catalyse CO 2 hydrogenation to alcohols. It was demonstrated that the activity and selectivity could be tuned by the bimetallic composition, and the catalyst with a Pt to Ru molar ratio of 1:2 (Pt 1 Ru 2 /Fe 2 O 3 ) had high activity and selectivity at 200°C, which is very low for heterogeneous hydrogenation of CO 2 to produce higher alcohols. The conversion and the selectivity increased with increasing pressures of CO 2 and/or H 2 . The catalyst could be reused at least five times without any obvious change in activity or selectivity.
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Lee, Suk Joong, et Jong Ho Yoon. « Use of Porphyrin Containing Porous Materials in Heterogeneous Catalyst ». ECS Meeting Abstracts MA2022-01, no 14 (7 juillet 2022) : 957. http://dx.doi.org/10.1149/ma2022-0114957mtgabs.
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Due to their potential applications in catalysis, separation, gas storage, drug delivery, and biosensing, porous materials (PMs) such as porous organic polymers (POPs), polymers with intrinsic microporosity (PIMs), porous coordination polymers (PCPs), and metal–organic frameworks (MOFs), have received much attention. Various building blocks have been prepared and demonstrated various functional materials. Among the various organic building blocks, porphyrin has become one of the most important building blocks for the construction of such materials witnessed by a wide range of molecular architectures using porphyrin derivatives with various applications. Mn(III)- and Fe(III)-containing metalloporphyrins are often used to fabricate various functional molecular architectures and to mimic the extraordinary behavior of enzymes in both homogeneous and heterogeneous catalytic systems. In the case of homogeneous catalysis, Mn(III)- and Fe(III)-containing metalloporphyrins have frequent trouble with fast catalytic degradation because of µ-oxo dimer formation or ligand oxidation. To avoid the catalyst degradation, the immobilization and/or site-isolation of homogeneous catalysts using supporters such as polymers, membranes, and MOFs, are widely used strategy. In addition, they are often used to modify the surface of porous silica materials such as SBA-15, MCM-41 and MCM-48, because these porous silica materials exhibit narrow pore size distributions, high thermal stability and easy accessibility. In this presentation, we like to show the use of metalloporphyrins in various porous materials and their use as heterogeneous catalysts. References D. Y. Shin, J. H. Yoon, S. H. Kim, H. Baik, S. J. Lee,* "Immobilization of Porphyrinic Mn(III) Catalyst on a New Class of Silica Support Comprising Three-Dimensionally Interconnected Network with Two Different Sizes of Pores", Catal. Sci. Technol. 2018, 8, 6306-6310. J. Yi, H. Y. Jeong, D. Y. Shin, C. Kim, S. J. Lee,* "Mn(III)-Porphyrin Containing Heterogeneous Catalyst based on Microporous Polymeric Constituents as a New Class of Catalyst Support", ChemCatChem 2018, 10, 3974-3977. J. Yoon, H. M. Choi, S. J. Lee,* "Cu(II)Cl2 containing bispyridine-based porous organic polymer support prepared via alkyne–azide cycloaddition as a heterogeneous catalyst for oxidation of various olefins", New J. Chem. 2020, 44, 9149-9152. H. M. Choi, Y. J. Kim, E. T. Choi, S. J. Lee,* "Selective Photocatalytic Oxidative Detoxification of a Chemical Warfare Agent Simulant by Porphyrin-Containing Polymers of Intrinsic Microporocity." ACS Appl. Polym. Mater.2021, submitted .
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Hülsey, Max J., Chia Wei Lim et Ning Yan. « Promoting heterogeneous catalysis beyond catalyst design ». Chemical Science 11, no 6 (2020) : 1456–68. http://dx.doi.org/10.1039/c9sc05947d.
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Gaide, Ieva, Violeta Makareviciene, Egle Sendzikiene et Kiril Kazancev. « Natural Rocks–Heterogeneous Catalysts for Oil Transesterification in Biodiesel Synthesis ». Catalysts 11, no 3 (16 mars 2021) : 384. http://dx.doi.org/10.3390/catal11030384.
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Some of the more recent methods to produce biodiesel are based on heterogeneous catalysis, which has the advantage of easy separation of catalyst from the final product. In this paper, the heterogeneous transesterification of rapeseed oil with methanol is studied. The aim of this work was to investigate the possibilities of using natural catalysts in biodiesel synthesis and to determine the optimal conditions for this process. After the evaluation of catalytic effectiveness of rocks containing calcium and magnesium carbonates, it was determined that dolomite is the most effective catalyst in heterogeneous biodiesel synthesis. The optimal conditions of dolomite preparation are the following: heating at 850 °C for 5 h. The rapeseed oil transesterification was optimized by the application response surface methodology. Optimal conditions for the production of rapeseed methyl esters using dolomite as catalyst are the following: molar ratio of methanol to rapeseed oil of 11.94:1, reaction temperature of 64 °C, dolomite content of 6 wt%, reaction time of 5 h.
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Tyufekchiev, Maksim, Jordan Finzel, Ziyang Zhang, Wenwen Yao, Stephanie Sontgerath, Christopher Skangos, Pu Duan, Klaus Schmidt-Rohr et Michael T. Timko. « A New Method for Solid Acid Catalyst Evaluation for Cellulose Hydrolysis ». Sustainable Chemistry 2, no 4 (15 novembre 2021) : 645–69. http://dx.doi.org/10.3390/suschem2040036.
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A systematic and structure-agnostic method for identifying heterogeneous activity of solid acids for catalyzing cellulose hydrolysis is presented. The basis of the method is preparation of a supernatant liquid by exposing the solid acid to reaction conditions and subsequent use of the supernatant liquid as a cellulose hydrolysis catalyst to determine the effects of in situ generated homogeneous acid species. The method was applied to representative solid acid catalysts, including polymer-based, carbonaceous, inorganic, and bifunctional materials. In all cases, supernatant liquids produced from these catalysts exhibited catalytic activity for cellulose hydrolysis. Direct comparison of the activity of the solid acid catalysts and their supernatants could not provide unambiguous detection of heterogeneous catalysis. A reaction pathway kinetic model was used to evaluate potential false-negative interpretation of the supernatant liquid test and to differentiate heterogeneous from homogeneous effects on cellulose hydrolysis. Lastly, differences in the supernatant liquids obtained in the presence and absence of cellulose were evaluated to understand possibility of false-positive interpretation, using structural evidence from the used catalysts to gain a fresh understanding of reactant–catalyst interactions. While many solid acid catalysts have been proposed for cellulose hydrolysis, to our knowledge, this is the first effort to attempt to differentiate the effects of heterogeneous and homogeneous activities. The resulting supernatant liquid method should be used in all future attempts to design and develop solid acids for cellulose hydrolysis.
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Li, Haobo, Jianping Xiao, Qiang Fu et Xinhe Bao. « Confined catalysis under two-dimensional materials ». Proceedings of the National Academy of Sciences 114, no 23 (22 mai 2017) : 5930–34. http://dx.doi.org/10.1073/pnas.1701280114.
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Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces.
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Sumarlan, Iwan, et Rona B. Mentari. « Esterification of Waste Cooking Oil using Heterogeneous Catalyst from Pearl Shell ». Jurnal Akademika Kimia 9, no 3 (28 août 2020) : 183–90. http://dx.doi.org/10.22487/j24775185.2020.v9.i3.pp183-190.
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Biodiesel is a renewable and environmentally friendly energy source. The process of using a homogeneous catalyst has several disadvantages, such as: removing a lot of waste water from washing the catalyst residue and cannot be reused. This catalyst is also low in corrosion and is more environmentally friendly. The purpose of this study was to study the preparation of heterogeneous catalysts from pearl shells applied to the cooking oil esterification reaction. The oil was then characterized by the XRD, XRF, SEM, and FTIR. The results of GCMS for reaction without catalysts yield only 27.07% by weight of alkyl ester, whereas using a catalyst is 93.4%. The influence of time, in the 60th minute, was the optimal time for the esterification reaction, and the effect of the weight of the catalyst which was 1% the optimal weight. This shows that pearl oyster shell catalyst can act as an esterification catalyst for used cooking oil and can be used as an alternative to a homogeneous catalyst substitute catalyst.