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Dagorne, Samuel. "Recent Developments on N-Heterocyclic Carbene Supported Zinc Complexes: Synthesis and Use in Catalysis". Synthesis 50, n. 18 (28 giugno 2018): 3662–70. http://dx.doi.org/10.1055/s-0037-1610088.
Testo completoAbstract (sommario):
The present contribution reviews the synthesis, reactivity, and use in catalysis of NHC–Zn complexes reported since 2013. NHC-stabilized Zn(II) species typically display enhanced stability relative to common organozinc species (such as Zn dialkyls), a feature of interest for the mediation of various chemical processes and the stabilization of reactive Zn-based species. Their use in catalysis is essentially dominated by reduction reactions of various unsaturated small molecules (including CO2), thus primarily involving Zn–H and Zn–alkyl derivatives as catalysts. Simple NHC adducts of Zn(II) dihalides also appear as effective catalysts for the reduction amination of CO2 and borylation of alkyl/aryl halides. Stable and well-defined Zn alkoxides have also been prepared and behave as effective catalysts in the polymerization of cyclic esters/carbonates for the production of well-defined biodegradable materials. Overall, the attractive features of NHC-based Zn(II) species include ready access, a reasonable stability/reactivity balance, and steric/electronic tunability (through the NHC source), which should promote their further development.1 Introduction2 NHC-Supported Zinc Alkyl/Aryl Species2.1 Synthesis2.2 Reactivity and Use in Catalysis3 NHC-Supported Zinc Hydride Species3.1 Synthesis3.2 Reactivity and Use in Catalysis4 NHC-Supported Zinc Amido/Alkoxide Species4.1 Synthesis4.2 Use in Catalysis5 NHC-Supported Zinc Dihalide Species5.1 Synthesis5.2 Use in Catalysis6 Other NHC-Stabilized Zn Species7 Conclusion
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Crawford, Jennifer, e Matthew Sigman. "Conformational Dynamics in Asymmetric Catalysis: Is Catalyst Flexibility a Design Element?" Synthesis 51, n. 05 (8 gennaio 2019): 1021–36. http://dx.doi.org/10.1055/s-0037-1611636.
Testo completoAbstract (sommario):
Traditionally, highly selective low molecular weight catalysts have been designed to contain rigidifying structural elements. As a result, many proposed stereochemical models rely on steric repulsion for explaining the observed selectivity. Recently, as is the case for enzymatic systems, it has become apparent that some flexibility can be beneficial for imparting selectivity. Dynamic catalysts can reorganize to maximize attractive non-covalent interactions that stabilize the favored diastereomeric transition state, while minimizing repulsive non-covalent interactions for enhanced selectivity. This short review discusses catalyst conformational dynamics and how these effects have proven beneficial for a variety of catalyst classes, including tropos ligands, cinchona alkaloids, hydrogen-bond donating catalysts, and peptides.1 Introduction2 Tropos Ligands3 Cinchona Alkaloids4 Hydrogen-Bond Donating Catalysts5 Peptide Catalysts6 Conclusion
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Newman, R. A., J. A. Blazy, T. G. Fawcett, L. F. Whiting e R. A. Stowe. "Use of the Dow-Developed DSC/XRD/MS in the Study of Several Model Copper-Based Catalyst Systems". Advances in X-ray Analysis 30 (1986): 493–502. http://dx.doi.org/10.1154/s0376030800021650.
Testo completoAbstract (sommario):
Due to the difficulty of analyzing materials at high temperatures and in reactive atmospheres, solid-state catalysts have often been developed with little knowledge of the true chemical behavior of the catalyst, except on a bulk scale. In the field of solid-state catalysis research, a great deal of time and effort is presently being spent to better characterize the chemical and physical properties which determine a particular catalyst‘s efficiency, lifetime, and selectivity. Recently, we have undertaken a study of model copper catalysts at The Dow Chemical Company in an effort to better understand the chemical and physical properties which determine the efficiency, regenerability, and lifetime of this type of solid state catalyst.
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Kaplunenko, Volodymyr, e Mykola Kosinov. "Electric field - induced catalysis. Laws of field catalysis". InterConf, n. 26(129) (18 ottobre 2022): 332–51. http://dx.doi.org/10.51582/interconf.19-20.10.2022.037.
Testo completoAbstract (sommario):
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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Lomic, Gizela, Erne Kis, Goran Boskovic e Radmila Marinkovic-Neducin. "Application of scanning electron microscopy in catalysis". Acta Periodica Technologica, n. 35 (2004): 67–77. http://dx.doi.org/10.2298/apt0435067l.
Testo completoAbstract (sommario):
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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Liu, Jingyue. "Advanced Electron Microscopy Characterization of Nanostructured Heterogeneous Catalysts". Microscopy and Microanalysis 10, n. 1 (22 gennaio 2004): 55–76. http://dx.doi.org/10.1017/s1431927604040310.
Testo completoAbstract (sommario):
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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Guerrero Fajardo, Carlos Alberto, Yvonne N’Guyen, Claire Courson e Anne Cécile Roger. "Fe/SiO2 catalysts for the selective oxidation of methane to formaldehyde". Ingeniería e Investigación 26, n. 2 (1 maggio 2006): 37–44. http://dx.doi.org/10.15446/ing.investig.v26n2.14735.
Testo completoAbstract (sommario):
Selective oxidation of methane to formaldehyde was analysed with iron catalysts supported on silica prepared by the sol-gel method, leading to obtaining a large support surface area facilitating high dispersion of iron on silica’s amorphous surface. Seven catalysts were prepared; one of them corresponded to the silica support and another five having an iron load 0.1-0.5% in weight. Catalyst 7 (0.5% Fe in weight) was prepared with neutral pH control and had the most homogeneous characteristics since it did not present isolated iron species, corroborated by SEM and TEM analysis. The highest BET areas were 1,757 and 993 m2.g-1 for 0.5% Fe catalysts, having an average 36% microporosity and 43% mesoporosity. X-ray diffraction confirmed the catalyst’s amorphous structure. Catalytic activity was carried out with catalyser 7 at atmospheric pressure in a quartz reactor using a CH4/O2/N2=7.5/1/4 reaction mixture at 400-750°C temperature range. Reaction products were analysed by gas chromatography with TCD. The heterogeneous catalysts displayed greater methane conversion (but with methanol selectivity) whereas homogenous catalyst 7 gave better results regarding formaldehyde. The highest conversion percentage (8.60% mol) for catalyser 7 was presented at 650°C. Formaldehyde selectivity was 50% mol in the 600-650°C range and maximum yield (0.31g HCHO/Kg catalyst) was found in this range; it was thus considered that 650°C for the reaction was thereby the best operating temperature.
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Trigoura, Leslie, Yalan Xing e Bhanu P. S. Chauhan. "Recyclable Catalysts for Alkyne Functionalization". Molecules 26, n. 12 (9 giugno 2021): 3525. http://dx.doi.org/10.3390/molecules26123525.
Testo completoAbstract (sommario):
In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis.
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Yap, Daryl Q. J., Raju Cheerlavancha, Renecia Lowe, Siyao Wang e Luke Hunter. "Investigation of cis- and trans-4-Fluoroprolines as Enantioselective Catalysts in a Variety of Organic Transformations". Australian Journal of Chemistry 68, n. 1 (2015): 44. http://dx.doi.org/10.1071/ch14129.
Testo completoAbstract (sommario):
Stereoselective fluorination is known to rigidify the ring structure of l-proline, as a result of a combination of electrostatic and hyperconjugative effects associated with the C–F bond. This is a potential strategy for enhancing the enantioselectivity of proline-catalysed reactions. In this study, cis- and trans-4-fluoroprolines were investigated as catalysts in five different organic transformations, including examples of both enamine and iminium ion catalysis. Some significant differences in enantioselectivity were observed between the cis- and trans-isomers of the fluorinated catalysts, confirming that the ring pucker is important. However, no substantial improvements were observed relative to the parent catalyst, l-proline.
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Gai, P. L., K. Kourtakis, H. Dindi e S. Ziemecki. "Novel Xerogel Catalyst Materials for Hydrogenation Reactions and the Role of Atomic Scale Interfaces". Microscopy and Microanalysis 5, S2 (agosto 1999): 704–5. http://dx.doi.org/10.1017/s1431927600016846.
Testo completoAbstract (sommario):
We are developing a new family of heterogeneous catalysts for hydrogenation catalysis. Catalyst synthesis is accomplished using colloidal polymerization chemistry which produce high surface area xerogel catalysts. These xerogels have been synthesized by one-step sol gel chemistry. These catalysts contain ruthenium and modifiers such as gold occluded or incorporated in a titanium oxide matrix. The materials, especially the modified systems exhibit favorable performance in microreactor evaluations for hydrogenation reactions and exhibit high activities. Nanostructural studies have revealed that the materials contain dispersed catalyst clusters which are desirable microstructures for the catalysis since the majority of the atoms are exposed to catalysis and are potentially active sites.The composition and atomic structure of the xerogel catalysts containing ruthenium and other metals have been examined using our in-house developments of environmental high resolution electron microscopy (EHREM) the atomic scale [1-3] and low voltage high resolution SEM (LVSEM)[4] methods.
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Zhao, Xiaodan, e Lihao Liao. "Modern Organoselenium Catalysis: Opportunities and Challenges". Synlett 32, n. 13 (11 maggio 2021): 1262–68. http://dx.doi.org/10.1055/a-1506-5532.
Testo completoAbstract (sommario):
AbstractOrganoselenium catalysis has attracted increasing interest in recent years. This Cluster highlights recent key advances in this area regarding the functionalization of alkenes, alkynes, and arenes by electrophilic selenium catalysis, selenonium salt catalysis, selenium-based chalcogen-bonding catalysis, and Lewis basic selenium catalysis. These achievements might inspire and help future research.1 Introduction2 Electrophilic Selenium Catalysis3 Selenonium Salt Catalysis4 Selenium-Based Chalcogen-Bond Catalysis5 Lewis Basic Selenide Catalysis6 Conclusion
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Testa, Maria Luisa, e Valeria La Parola. "Sulfonic Acid-Functionalized Inorganic Materials as Efficient Catalysts in Various Applications: A Minireview". Catalysts 11, n. 10 (23 settembre 2021): 1143. http://dx.doi.org/10.3390/catal11101143.
Testo completoAbstract (sommario):
Acid catalysis is widely used in the chemical industry, and nowadays many efforts are being focused on replacing the more common homogeneous catalysts with heterogeneous ones in order to make greener the industrial processes. In this perspective, sulfonic solid acid materials represent a valid alternative to the homogenous mineral acid in several acid catalyzed reactions. In this minireview, an overview of the recent advances on the preparation, stability and application of these materials is reported. Special attention is addressed to the sustainability of the considered processes, starting from the catalyst’s preparation, the use of green solvents and reducing the possible reaction steps. Ways to tackle the main drawback represented by easy leaching of acid groups are described. For an easy catalyst recovery, the use of a magnetic core in a catalyst particle, with the related synthetic approaches, is also illustrated. Finally, a section is dedicated to the principal characterization techniques to identify the structural properties of the catalysts.
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Motokura, Ken, e Kyogo Maeda. "Recent Advances in Heterogeneous Ir Complex Catalysts for Aromatic C–H Borylation". Synthesis 53, n. 18 (9 aprile 2021): 3227–34. http://dx.doi.org/10.1055/a-1478-6118.
Testo completoAbstract (sommario):
AbstractAromatic C–H borylation catalyzed by an Ir complex is among the most powerful methods for activating inert bonds. The products, i.e., arylboronic acids and their esters, are usable chemicals for the Suzuki–Miyaura cross-coupling reaction, and significant effort has been directed toward the development of homogeneous catalysis chemistry. In this short review, we present a recent overview of current heterogeneous Ir-complex catalyst developments for aromatic C–H borylation. Not only have Ir complexes been immobilized on support surfaces with phosphine and bipyridine ligands, but Ir complexes incorporated within solid materials have also been developed as highly active and reusable heterogeneous Ir catalysts. Their catalytic activities and stabilities strongly depend on their surface structures, including linker length and ligand structure.1 Introduction and Homogeneous Ir Catalysis2 Heterogeneous Ir Complex Catalysts for C–H Borylation Reactions3 Other Heterogeneous Metal Complex Catalysts for C–H Borylation Reactions4 Summary and Outlook
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Cottone, Grazia, Sergio Giuffrida, Stefano Bettati, Stefano Bruno, Barbara Campanini, Marialaura Marchetti, Stefania Abbruzzetti et al. "More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function". Catalysts 9, n. 12 (4 dicembre 2019): 1024. http://dx.doi.org/10.3390/catal9121024.
Testo completoAbstract (sommario):
Catalysis makes chemical and biochemical reactions kinetically accessible. From a technological point of view, organic, inorganic, and biochemical catalysis is relevant for several applications, from industrial synthesis to biomedical, material, and food sciences. A heterogeneous catalyst, i.e., a catalyst confined in a different phase with respect to the reagents’ phase, requires either its physical confinement in an immobilization matrix or its physical adsorption on a surface. In this review, we will focus on the immobilization of biological catalysts, i.e., enzymes, by comparing hard and soft immobilization matrices and their effect on the modulation of the catalysts’ function. Indeed, unlike smaller molecules, the catalytic activity of protein catalysts depends on their structure, conformation, local environment, and dynamics, properties that can be strongly affected by the immobilization matrices, which, therefore, not only provide physical confinement, but also modulate catalysis.
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Qin, Helen. "Evaluation of Hydrogen-Oxygen Recombiner Catalysts Under Various Conditions for Nuclear and Non-Nuclear Hydrogen Safety". STEM Fellowship Journal 2, n. 1 (1 luglio 2016): 12–16. http://dx.doi.org/10.17975/sfj-2016-003.
Testo completoAbstract (sommario):
Hydrogen plays an important role in nuclear and non-nuclear safety, as the unsafe manipulation of hydrogen can lead to dangerous accidents. This concern has led the Hydrogen Isotopes Technology Branch at the Canadian Nuclear Laboratories to develop catalysts in order to aid in the recombination of hydrogen and oxygen. This research project evaluates catalysts with different compositions under various conditions (i.e. dry, humid) in a spinning basket reactor (SBR). Results suggest that catalysts with lower wetproof coating loading have higher activity levels after being exposed to water vapour or immersed in liquid water compared to catalysts with higher amounts of wetproof coating. The specific activity levels were 1.91 cm3 H2/s·gCAT and 1.57 cm3 H2/s·gCAT, normalized to the benchmark catalyst’s activity in humid conditions, for catalysts with low and high amounts of wetproof coating, respectively. Normalization was performed so that the activity levels of the benchmark catalyst in humid conditions was equal to one, thus assigning the other activity level values based on their relation to the benchmark catalyst’s activity levels in humid conditions. For the benchmark catalyst, activity levels in water vapour and immersion conditions were about the same, whereas activity levels for the newly developed catalysts (with low and high wetproofing agent loadings) varied depending on the water exposure levels of the test. Thus, despite the wetproofing, the amount of water exposure had an effect on catalyst activity levels. This trend demonstrates that the benchmark catalyst was well wetproofed and suggests that further improvement is needed in the wetproofing method used for the new catalyst.
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Choudhury, Joyanta, e Shrivats Semwal. "Emergence of Stimuli-Controlled Switchable Bifunctional Catalysts". Synlett 29, n. 02 (19 dicembre 2017): 141–47. http://dx.doi.org/10.1055/s-0036-1591741.
Testo completoAbstract (sommario):
Can a single catalyst perform more than one ‘type’ of reaction? If we consider traditional design of catalysts, then the answer would probably be ‘no’. However, with the advancement of catalyst design concepts, chemists have been able to demonstrate the above task, thanks to ‘stimuli-switchable bifunctional catalysts’. Within the nascent research area of ‘artificial switchable catalysis’, this new type of system offers the potential to achieve complex functions which are otherwise difficult or impossible. This Synpacts article highlights the rise of these new-generation catalysts.1 Introduction2 Key Advances3 Conclusion
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Wang, Ziyun, Hai-Feng Wang e P. Hu. "Possibility of designing catalysts beyond the traditional volcano curve: a theoretical framework for multi-phase surfaces". Chemical Science 6, n. 10 (2015): 5703–11. http://dx.doi.org/10.1039/c5sc01732g.
Testo completoAbstract (sommario):
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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Mazaheri, Hoora, Hwai Chyuan Ong, Zeynab Amini, Haji Hassan Masjuki, M. Mofijur, Chia Hung Su, Irfan Anjum Badruddin e T. M. Yunus Khan. "An Overview of Biodiesel Production via Calcium Oxide Based Catalysts: Current State and Perspective". Energies 14, n. 13 (1 luglio 2021): 3950. http://dx.doi.org/10.3390/en14133950.
Testo completoAbstract (sommario):
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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Jurczak, Janusz, Maciej Majdecki, Patryk Niedbała e Agata Tyszka-Gumkowska. "Assisted by Hydrogen-Bond Donors: Cinchona Quaternary Salts as Privileged Chiral Catalysts for Phase-Transfer Reactions". Synthesis 53, n. 16 (1 aprile 2021): 2777–86. http://dx.doi.org/10.1055/a-1472-7999.
Testo completoAbstract (sommario):
AbstractThis short review is devoted to asymmetric phase-transfer reactions that employ hybrid ammonium Cinchona catalysts supported by possessing hydrogen-bond donor groups. We present recent advances utilizing this type of catalyst in the field of biphasic reaction systems. The main emphasis is placed on the advantages of additional functional groups present in the structure of the catalyst, such as hydroxy, amide, (thio)urea or squaramide.1 Introduction2 Phase-Transfer Hybrid Cinchona Catalysts with a Free Hydroxy Group3 (Thio)urea Hybrid Cinchona Catalysts4 Hybrid Amide-Based Catalysts Bearing a Cinchona Scaffold5 Conclusions
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Baráth, Eszter. "Selective Reduction of Carbonyl Compounds via (Asymmetric) Transfer Hydrogenation on Heterogeneous Catalysts". Synthesis 52, n. 04 (2 gennaio 2020): 504–20. http://dx.doi.org/10.1055/s-0039-1691542.
Testo completoAbstract (sommario):
Based on the ever-increasing demand for optically pure compounds, the development of efficient methods to produce such products is very important. Homogeneous asymmetric catalysis occupies a prominent position in the ranking of chemical transformations, with transition metals coordinated to chiral ligands being applied extensively for this purpose. However, heterogeneous catalysts have the ability to further extend the field of asymmetric transformations, because of their beneficial properties such as high stability, ease of separation and regeneration, and the possibility to apply them in continuous processes. The main challenge is to find potential synthetic routes that can provide a chemically and thermally stable heterogeneous catalyst having the necessary chiral information, whilst keeping the catalytic activity and enantioselectivity equally high (or even higher) than the corresponding homogeneous counterpart. Within this short review, the most relevant immobilization modes and preparative strategies depending on the support material used are summarized. From the reaction scope viewpoint, metal catalysts supported on the various solid materials studied in (asymmetric) transfer hydrogenation of carbonyl compounds are selected and represent the main focus of the second part of this overview.1 Introduction2 Synthesis of Chiral Heterogeneous Catalysts2.1 Immobilization of Homogeneous Asymmetric Catalysts2.1.1 Immobilization on Inorganic Supports2.1.2 Immobilization on Organic Polymers as Supports2.1.3 Immobilization on Dendrimer-Type Materials as Supports2.1.4 Self-Supported Chiral Catalysts: Coordination Polymers2.1.5 Immobilization Using Non-Conventional Media2.2 Chirally Modified Metal Surfaces for Heterogeneous Asymmetric Catalysis3 Examples of Transfer Hydrogenation on Heterogeneous Catalysts3.1 Silicon-Immobilized Catalysts3.2 Carbon-Material-Immobilized Catalysts3.3 Polymer-Immobilized Catalysts3.4 Magnetic-Nanoparticle-Immobilized Catalysts4 Conclusions
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Dadashi-Silab, Sajjad, e Krzysztof Matyjaszewski. "Iron Catalysts in Atom Transfer Radical Polymerization". Molecules 25, n. 7 (3 aprile 2020): 1648. http://dx.doi.org/10.3390/molecules25071648.
Testo completoAbstract (sommario):
Catalysts are essential for mediating a controlled polymerization in atom transfer radical polymerization (ATRP). Copper-based catalysts are widely explored in ATRP and are highly efficient, leading to well-controlled polymerization of a variety of functional monomers. In addition to copper, iron-based complexes offer new opportunities in ATRP catalysis to develop environmentally friendly, less toxic, inexpensive, and abundant catalytic systems. Despite the high efficiency of iron catalysts in controlling polymerization of various monomers including methacrylates and styrene, ATRP of acrylate-based monomers by iron catalysts still remains a challenge. In this paper, we review the fundamentals and recent advances of iron-catalyzed ATRP focusing on development of ligands, catalyst design, and techniques used for iron catalysis in ATRP.
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Wu, Jingyun. "Two-step synthesis and oxidizing power assessment of novel pyrylium". Theoretical and Natural Science 6, n. 1 (3 agosto 2023): 1–7. http://dx.doi.org/10.54254/2753-8818/6/20230107.
Testo completoAbstract (sommario):
Photoredox catalysis is a relatively new concept, and it involves the absorption of light for more productive use of lower energy radiation and to catalyze selective reactions. Traditionally, catalysts used for oxidation or reduction reactions were metal catalysts, such as iridium. However, these metal catalysts are not environmentally friendly and are expensive, prompting the use of organic catalysts. Pyrylium salt, an organic catalyst, can be used as a catalyst. However, the oxidizing ability of basic pyrylium is not that good and can still be improved. In this project, a pyrylium salt with substituents that include fluorine and chlorine (halogens) was synthesized to boost its oxidizing ability in an alcohol oxidation reaction due to its electron-withdrawing groups. Despite unsuccessful oxidation, there is still much research to prove that it can substitute for metal catalysts.
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Zhang, Meng. "A Novel Energy Band Match Method and a Highly Efficient CuO–Co3O4@SiO2 Catalyst for Dimethyl Carbonate Synthesis from CO2". Science of Advanced Materials 13, n. 1 (1 gennaio 2021): 115–22. http://dx.doi.org/10.1166/sam.2021.3848.
Testo completoAbstract (sommario):
The present research on dimethyl carbonate (DMC) synthesis from CO2 was short of effective theoretical guidance and catalyst design was also blind. A kind of regular relationship was found from catalyst structure calculation and activity experiments. Therefore, a novel energy band matching method was proposed. After substantial verification experiments, it was proved to be correct. Whether one certain catalyst has catalytic activity can be judged predictably according to this novel method. Novel and efficient catalysts can be designed or selected on the basis of designer's wishes. Based on this method, three efficient catalysts were prepared and CuO–Co3O4@SiO2 catalyst had the best catalytic performance. In a word, once it is applied in catalysts research, there will be a huge progress in catalysis and materials science fields.
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Pan, Dipika, e Jhuma Ganguly. "Assessment of Chitosan Based Catalyst and their Mode of Action". Current Organocatalysis 6, n. 2 (24 giugno 2019): 106–38. http://dx.doi.org/10.2174/2213337206666190327174103.
Testo completoAbstract (sommario):
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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Su, Shu Hua, Shi Ye Feng, Yuan Fang Zhao, Qiang Lu, Wei Liang Cheng e Chang Qing Dong. "Comparison of Three Types of NH3-SCR Catalysts". Applied Mechanics and Materials 130-134 (ottobre 2011): 418–21. http://dx.doi.org/10.4028/www.scientific.net/amm.130-134.418.
Testo completoAbstract (sommario):
The selective catalysis reduction (SCR) is one of the most promising technologies for NOx reduction at present. There are three types of NH3-SCR catalysts in the market, honeycomb catalyst, plate-types catalyst and corrugated catalyst. This paper firstly describes the preparation of the three types of catalysts, and then analyzes their performance. The analysis indicates the catalyst structure plays an important role on their performance. The honeycomb catalyst and plate-type catalyst are widely utilized in world’s coal power station, which should be due to their excellent capabilities of ash prevention, wear resistance and anti-poisoning.
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Lendzion-Bieluń, Zofia. "The effect of manganese on the structural and surface properties of nanocrystalline cobalt catalyst for ammonia synthesis". Open Chemistry 10, n. 2 (1 aprile 2012): 327–31. http://dx.doi.org/10.2478/s11532-011-0147-y.
Testo completoAbstract (sommario):
AbstractBased on the active surface model of the iron catalyst for ammonia synthesis, the assumptions which led to obtaining the cobalt catalyst for ammonia synthesis were described. The incorporation into the system small amounts of manganese, an element which binds oxygen stronger than cobalt, has influence the development of the catalyst’s specific surface area. The activity of manganese modified catalysts is higher than that of cobalt catalyst without manganese addition. The obtained catalysts were characterized with the following methods: ICP-OES, XRD, BET
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Jakab-Nácsa, Alexandra, Attila Garami, Béla Fiser, László Farkas e Béla Viskolcz. "Towards Machine Learning in Heterogeneous Catalysis—A Case Study of 2,4-Dinitrotoluene Hydrogenation". International Journal of Molecular Sciences 24, n. 14 (14 luglio 2023): 11461. http://dx.doi.org/10.3390/ijms241411461.
Testo completoAbstract (sommario):
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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Du, Yuan-Peng, e Jeremy S. Luterbacher. "Designing Heterogeneous Catalysts for Renewable Catalysis Applications Using Metal Oxide Deposition". CHIMIA International Journal for Chemistry 73, n. 9 (18 settembre 2019): 698–706. http://dx.doi.org/10.2533/chimia.2019.698.
Testo completoAbstract (sommario):
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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Miceli, Mariachiara, Patrizia Frontera, Anastasia Macario e Angela Malara. "Recovery/Reuse of Heterogeneous Supported Spent Catalysts". Catalysts 11, n. 5 (1 maggio 2021): 591. http://dx.doi.org/10.3390/catal11050591.
Testo completoAbstract (sommario):
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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Aceto, Domenico, Maria Carmen Bacariza, Arnaud Travert, Carlos Henriques e Federico Azzolina-Jury. "Thermal and Plasma-Assisted CO2 Methanation over Ru/Zeolite: A Mechanistic Study Using In-Situ Operando FTIR". Catalysts 13, n. 3 (27 febbraio 2023): 481. http://dx.doi.org/10.3390/catal13030481.
Testo completoAbstract (sommario):
CO2 methanation is an attractive reaction to convert CO2 into a widespread fuel such as methane, being the combination of catalysts and a dielectric barrier discharge (DBD) plasma responsible for synergistic effects on the catalyst’s performances. In this work, a Ru-based zeolite catalyst, 3Ru/CsUSY, was synthesized by incipient wetness impregnation and characterized by TGA, XRD, H2-TPR, N2 sorption and CO2-TPD. Catalysts were tested under thermal and plasma-assisted CO2 methanation conditions using in-situ operando FTIR, with the aim of comparing the mechanism under both types of catalysis. The incorporation of Ru over the CsUSY zeolite used as support induced a decrease of the textural properties and an increase of the basicity and hydrophobicity, while no zeolite structural damage was observed. Under thermal conditions, a maximum CO2 conversion of 72% and CH4 selectivity above 95% were registered. These promising results were ascribed to the presence of small Ru0 nanoparticles over the support (16 nm), catalyst surface hydrophobicity and the presence of medium-strength basic sites in the catalyst. Under plasma-catalytic conditions, barely studied in similar setups in literature, CO2 was found to be excited by the plasma, facilitating its adsorption on the surface of 3Ru/CsUSY in the form of oxidized carbon species such as formates, aldehydes, carbonates, or carbonyls, which are afterwards progressively hydrogenated to methane. Adsorption and surface reaction of key intermediates, namely formate and aldehydic groups, was observed even on the support alone, an occurrence not reported before for thermal catalysis. Overall, similar reaction mechanisms were proposed for both thermal and plasma-catalysis conditions.
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Leitner, Walter. "Recent advances in catalyst immobilization using supercritical carbon dioxide". Pure and Applied Chemistry 76, n. 3 (1 gennaio 2004): 635–44. http://dx.doi.org/10.1351/pac200476030635.
Testo completoAbstract (sommario):
Homogeneous organometallic catalysts have a great potential for the development of sustainable synthetic processes. There is, however, an urgent need for the development of new techniques to separate products and catalysts efficiently, allowing for recycling and reuse of the precious catalyst. The unique solvent properties of supercritical carbon dioxide offer new approaches for the immobilization of organometallic catalysts, many of which are suitable for efficient continuous-flow operation. Recent research in this field tries to combine the molecular nature of organometallic catalysts with the reaction-engineering aspect of multiphase catalysis.
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Liang, Yannan, Christopher Watson, Thomas Malinski, Justin Tepera e David E. Bergbreiter. "Soluble polymer supports for homogeneous catalysis in flow reactions". Pure and Applied Chemistry 88, n. 10-11 (1 novembre 2016): 953–60. http://dx.doi.org/10.1515/pac-2016-0801.
Testo completoAbstract (sommario):
AbstractThe use of polyisobutylene and poly(4-dodecylstyrene) bound catalysts that contain transition metal or organocatalysts for cyclopropanation, ring-closing metathesis, and nucleophilic catalysis in flow chemistry schemes is described and compared with similar catalysts used in batch reactions. These Rh(II) carboxylate catalysts, N-heterocyclic carbene-ligated Ru(II) benzylidene catalysts, and analogs of 4-dimethylaminopyridine catalysts were used in reactions in heptane in flow and then separated in a gravity based liquid/liquid separation using a biphasic heptane/acetonitrile mixture. The less dense catalyst-containing phase in that separation was continuously used in flow with fresh substrate solution. Leaching of catalysts, yields, and turnover frequencies in these flow reactions were comparable with prior results obtained with the same phase isolable catalysts in batch reactions.
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BOUSBA, DALILA, CHAFIA SOBHI, AMNA ZOUAOUI e SOUAD BOUASLA. "Synthesis of activated carbon sand their application in the synthesis of monometallic and bimetallic supported catalysts". Algerian Journal of Signals and Systems 5, n. 4 (15 dicembre 2020): 190–96. http://dx.doi.org/10.51485/ajss.v5i4.116.
Testo completoAbstract (sommario):
Biomass-derived porous carbons are attractive materials for the synthesis of carbon-supported catalysts, carbonaceous catalysts are environmentally benign and could provide an important competitive advantage as compared to existing heterogeneous catalysts, however the surface properties of carbon materials and excellent physical and chemical properties are compatible with diverse catalysis reactions including organic transformations. Currently, activated carbons are one of well known carbonaceous materials for their catalytic properties and for use as support in heterogeneous catalysis. The supported catalysts have been successfully used in the chemical industries for a long time, in which carbon supported catalysts have allowed to a new chemical catalytic process, on the other hand Heterogeneous catalysis plays a key role in the manufacture of essential products in different fields. In this paper, we present a comparative study, between two main different methods for activated carbons (ACs) preparation namely, physical and chemical activations. Latter was prepared from agro-industrial biomass and used as a support to prepare monometallic (dry impregnation and excess impregnation) and bimetallic catalyst (successive impregnation and co impregnation).
34
Chen, Huihui, Zhenhua Dong e Jun Yue. "Advances in Microfluidic Synthesis of Solid Catalysts". Powders 1, n. 3 (4 agosto 2022): 155–83. http://dx.doi.org/10.3390/powders1030011.
Testo completoAbstract (sommario):
Heterogeneous catalysis plays a central role in the chemical and energy fields, owing to the high and tunable activities of solid catalysts that are essential to achieve the favorable reaction process efficiency, and their ease of recycle and reuse. Numerous research efforts have been focused on the synthesis of solid catalysts towards obtaining the desired structure, property and catalytic performance. The emergence and development of microfluidic reactor technology provide a new and attractive platform for the controllable synthesis of solid catalysts, primarily because of its superior mixing performance and high heat/mass transfer efficiency. In this review, the recent research progress on the synthesis of solid catalysts based on microfluidic reactor technology is summarized. The first section deals with the synthesis strategies for solid catalysts, including conventional methods in batch reactors and microfluidic alternatives (based on single- and two-phase flow processing). Then, different kinds of solid catalysts synthesized in microflow are discussed, especially with regard to the catalyst type, synthetic process, structure and property, and catalytic performance. Finally, challenges in the microreactor operation and scale-up, as well as future perspectives in terms of the synthesis of more types of catalysts, catalyst performance improvement, and the combination of catalyst synthesis process and catalytic reaction in microreactors, are provided.
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Clerici, Mario G. "Zeolites for Fine Chemical Production State of Art and Perspectives". Eurasian Chemico-Technological Journal 3, n. 4 (10 luglio 2017): 231. http://dx.doi.org/10.18321/ectj573.
Testo completoAbstract (sommario):
The paper analyses the role of catalysis and that of renewable resources in the frame of a sustainable development. The possible uses of natural feedstocks for chemical production and the application of catalytic<br />methods to their transformations are reviewed, with emphasis on carbohydrates and vegetable oils and on zeolite catalysts, respectively. The problems arising from the embedment of active sites on the catalyst<br />surface are discussed, with the aid of specific examples taken from oxidation and acid catalysed reactions.
36
Tišler, Zdeněk, Pavla Vondrová, Kateřina Hrachovcová, Kamil Štěpánek, Romana Velvarská, Jaroslav Kocík e Eliška Svobodová. "Aldol Condensation of Cyclohexanone and Furfural in Fixed-Bed Reactor". Catalysts 9, n. 12 (14 dicembre 2019): 1068. http://dx.doi.org/10.3390/catal9121068.
Testo completoAbstract (sommario):
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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Zhao, Da, Roland Petzold, Jiyao Yan, Dieter Muri e Tobias Ritter. "Tritiation of aryl thianthrenium salts with a molecular palladium catalyst". Nature 600, n. 7889 (15 dicembre 2021): 444–49. http://dx.doi.org/10.1038/s41586-021-04007-y.
Testo completoAbstract (sommario):
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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Patil, Siddappa A., Shivaputra A. Patil e Renukadevi Patil. "Magnetic Nanoparticles Supported Carbene and Amine Based Metal Complexes in Catalysis". Journal of Nano Research 42 (luglio 2016): 112–35. http://dx.doi.org/10.4028/www.scientific.net/jnanor.42.112.
Testo completoAbstract (sommario):
Catalysis is one of the hottest research topics in chemistry. In recent years, metal complexes attracted great interest as catalysts towards various types of organic reactions. However, these catalysts, in most cases, suffer from the deficits during their recovery, recycling and the difficulty in separation of catalysts from the products. Therefore, the design and synthesis of recoverable and recyclable catalyst is very important aspect in catalysis. The aim of this review article is to highlight the speedy growth in the synthesis and catalytic applications of magnetic nanoparticles (Fe3O4, MNPs) supported N-heterocyclic carbene (NHC) and amine based metal complexes in various organic reactions. Furthermore, these catalysts can be easily separated from the reaction media with the external magnet and reused various times without a substantial loss of catalytic activity.
39
Shi, Chunjie, Xiaofeng Yu, Wei Wang, Haibing Wu, Ai Zhang e Shengjin Liu. "The Activity and Cyclic Catalysis of Synthesized Iron-Supported Zr/Ti Solid Acid Catalysts in Methyl Benzoate Compounds". Catalysts 13, n. 6 (2 giugno 2023): 971. http://dx.doi.org/10.3390/catal13060971.
Testo completoAbstract (sommario):
The catalytic activity and cyclic catalysis of different methyl benzoates were studied by using a series of Lewis solid acid catalysts. The iron-supported zirconium/titanium solid acid catalysts were characterized using FTIR, SEM, XRD, and BET. The details of catalytic activity and cyclic catalysis verified that the catalyst catalyzed the reactions of 31 benzoic acids with different substituents and methanol. In addition, the mechanism was revealed according to the microstructure, acid strength, and specific surface area of the catalysts, and the yields of methyl benzoates by the GC-MS. Zr ions had significant effects on the catalytic activity of the catalyst. A certain proportion of Fe and Ti ions additionally enhanced the catalytic activity of the catalyst, with the catalyst-specific composition of Fe:Zr: Ti = 2:1: 1 showing optimal catalytic activity. A variety of substituents in the benzene ring, such as the electron-withdrawing group, the electron-donating group, large steric hindrance, and the position of the group on the benzene ring, had regular effects on the catalytic activity of the methyl benzoates. An increase in the catalyst activity occurred owing to the increases in the catalyst surface and the number of acid sites after the Fe ion was added. The catalytic activity remained unchanged after the facile recycling method was performed.
40
Pacultová, Bílková, Klegova, Karásková, Fridrichová, Jirátová, Kiška et al. "Co-Mn-Al Mixed Oxides Promoted by K for Direct NO Decomposition: Effect of Preparation Parameters". Catalysts 9, n. 7 (9 luglio 2019): 593. http://dx.doi.org/10.3390/catal9070593.
Testo completoAbstract (sommario):
Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst’s properties?
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Bergbreiter, David E., Andrew Kippenberger e Zhenqi Zhong. "Catalysis with palladium colloids supported in poly(acrylic acid)-grafted polyethylene and polystyrene". Canadian Journal of Chemistry 84, n. 10 (1 ottobre 2006): 1343–50. http://dx.doi.org/10.1139/v06-076.
Testo completoAbstract (sommario):
Grafts of poly(acrylic acid) on polyethylene powder (PE-g-PAA) or polystyrene (PS-g-PAA) can be used to support Pd(0) crystallites that function like a homogeneous Pd(0) catalyst in some reactions. These Pd–PE-g-PAA catalysts were active in allylic substitution reactions in the presence of added phosphine ligand. A catalyst analogous to the Pd–PE-g-PAA powder catalyst on polystyrene (Pd–PS-g-PAA) was similarly active for allylic substitution and could also be used in Heck reactions at 80–100 °C in N,N-dimethylacetamide (DMA). Analysis of the product solutions for Pd leachate and a correlation of the Pd leaching with product formation in the allylic substitution chemistry for both types of catalysts suggests that the active catalysts in these reactions are leached from the support. In the case of the allylic substitution reaction, external triphenylphosphine and substrate together are required for the chemistry and Pd leaching.Key words: catalysis, palladium, allylic substitution, grafted polystyrene, supported catalysts.
42
Rasaq, Waheed A., Charles Odilichukwu R. Okpala, Chinenye Adaobi Igwegbe e Andrzej Białowiec. "Catalyst-Enhancing Hydrothermal Carbonization of Biomass for Hydrochar and Liquid Fuel Production—A Review". Materials 17, n. 11 (27 maggio 2024): 2579. http://dx.doi.org/10.3390/ma17112579.
Testo completoAbstract (sommario):
The research impact of catalysts on the hydrothermal carbonization (HTC) process remains an ongoing debate, especially regarding the quest to enhance biomass conversion into fuels and chemicals, which requires diverse catalysts to optimize bio-oil utilization. Comprehensive insights and standardized analytical methodologies are crucial for understanding HTC’s potential benefits in terms of biomass conversion stages. This review seeks to understand how catalysts enhance the HTC of biomass for liquid fuel and hydrochar production, drawing from the following key sections: (a) catalyst types applied in HTC processes; (b) biochar functionality as a potential catalyst; (c) catalysts increasing the success of HTC process; and (d) catalyst’s effect on the morphological and textural character of hydrochar. The performance of activated carbon would greatly increase via catalyst action, which would progress the degree of carbonization and surface modification, alongside key heteroatoms. As catalytic HTC technology advances, producing carbon materials for thermochemical activities will become more cost-effective, considering the ever-growing demands for high-performance thermochemical technologies.
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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.
Testo completoAbstract (sommario):
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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Imrich, Biehler, Maichle-Mössmer e Ziegler. "Carbohydrate-Based Chiral Iodoarene Catalysts: A Survey through the Development of an Improved Catalyst Design". Molecules 24, n. 21 (28 ottobre 2019): 3883. http://dx.doi.org/10.3390/molecules24213883.
Testo completoAbstract (sommario):
Iodoarene catalysts can be applied in versatile reactions, for instance in the construction of complex chiral molecules via dearomatization of simple aromatic compounds. Recently, we reported the synthesis of the first carbohydrate-based chiral iodoarene catalysts and their application in asymmetric catalysis. Here we describe the synthesis of some new and improved catalysts. An account on how we got to the improved catalyst design, as well as the X-ray structure of one of the carbohydrate-based iodoarenes, is given.
45
Zhang, Yujun, Hui Teng, Junpeng Chen, Rui Xia, Yujun Zhou, Kunlin Xie e Zhiyong Chen. "Application of Palladium Single Atoms in C−C Coupling Reactions of Pharmaceutical Synthesis". Advances in Computer and Engineering Technology Research 1, n. 1 (8 dicembre 2023): 192. http://dx.doi.org/10.61935/acetr.1.1.2023.p192.
Testo completoAbstract (sommario):
Designing highly active and structurally well-defined catalysts while reducing the amount of catalyst has become a key issue in heterogeneous catalytic reactions. In this study, palladium single-atom catalysts were prepared for efficient catalysis in the Suzuki cross-coupling reaction of iodobenzene and phenylboronic acid, which was prepared by one-step high-temperature pyrolysis. The palladium single-atom catalysts have high activity as well as stability in Suzuki cross-coupling reactions and have great potential in catalyzing organic reactions.
46
Deng, Jianghai, e Qiuyun Zhou. "The Semi-Closed Molten Salt-Assisted One-Step Synthesis of N-P-Fe Tridoped Porous Carbon Nanotubes for an Efficient Oxygen Reduction Reaction". Catalysts 13, n. 5 (29 aprile 2023): 824. http://dx.doi.org/10.3390/catal13050824.
Testo completoAbstract (sommario):
Transition metal and heteroatom co-doped carbon nanomaterials (TM-H-C) are considered to be the most promising candidates to replace the expensive platinum-based catalysts for oxygen reduction reactions (ORR). Herein, we report a semi-closed molten salt-assisted one-step strategy for fabricating N-P-Fe-tridoped porous carbon nanotube (CNT) catalysts by using the evaporation of ZnCl2 and the catalysis of iron ions to control the heteroatoms doping process and CNT formation. The resultant densely packed porous CNT structure imparts final catalysts with an enhanced mass transfer ability for electron and ORR-involved species, ensuring a high performance in catalyzing the ORR. Significantly, the optimal catalysts show a half-wave potential of 0.89 V (vs. RHE), which is better than commercial platinum-based catalysts and most reported TM-H-C ORR catalysts. Impressively, when applied to a primary inc-oxygen (Zn–O2) battery, the synthesized catalyst comprehensively outperforms the state-of-the-art platinum-based catalyst in both its maximum power density and specific capacity.
47
Gomes, Ruan, Denilson Costa, Roberto Junior, Milena Santos, Cristiane Rodella, Roger Fréty, Alessandra Beretta e Soraia Brandão. "Dry Reforming of Methane over NiLa-Based Catalysts: Influence of Synthesis Method and Ba Addition on Catalytic Properties and Stability". Catalysts 9, n. 4 (30 marzo 2019): 313. http://dx.doi.org/10.3390/catal9040313.
Testo completoAbstract (sommario):
CO2 reforming of CH4 to produce CO and H2 is a traditional challenge in catalysis. This area is still very active because of the potentials offered by the combined utilization of two green-house gases. The development of active, stable, and economical catalysts remains a key factor for the exploitation of natural gas (NG) with captured CO2 and biogas to produce chemicals or fuels via syngas. The major issue associated with the dry reforming process is catalyst deactivation by carbon deposition. The development of suitable catalyst formulations is one strategy for the mitigation of coking which becomes especially demanding when noble metal-free catalysts are targeted. In this work NiLa-based catalyst obtained from perovskite precursors La1−xBaxNiO3 (x = 0.0; 0.05; 0.1 and 0.2) and NiO/La2O3 were synthesized, characterized by in situ and operando XRD and tested in the dry reforming of methane. The characterization results showed that the addition of barium promoted BaCO3 segregation and changes in the catalyst structure. This partly affected the activity; however, the incorporation of Ba improved the catalyst resistance to deactivation process. The Ba-containing and Ba-free NiLa-based catalysts performed significantly better than NiO/La2O3 catalysts obtained by wet impregnation.
48
Li, Gui Hua, e An Feng Wang. "Oxidative Esterification of Methacrolein to Methyl Methacrylate over La Doped Catalyst". Advanced Materials Research 512-515 (maggio 2012): 2390–93. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.2390.
Testo completoAbstract (sommario):
In this present work, rare earth elements La was added to catalysts for the oxidative esterification of methacrolein (MAL) to methyl methacrylate(MMA). Catalysts were characterized by means of BET techniques. Effects of La proportion, material liquid pH and catalyst amount on catalytic performance were investigated. The results indicated that the addation of La in appropriate proportion could improve the catalyst’s activity. 1.0% was found to be the optimum La additional amount. Under the condition of reation temperature 323K, w%(catalyst) 3.6%, proportion of La in the catalyst 1%, pH of material liquid 10.0 the MMA yield could reached up to 89.8%.
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Takabatake, Moe, e Ken Motokura. "Montmorillonite-based heterogeneous catalysts for efficient organic reactions". Nano Express 3, n. 1 (1 marzo 2022): 014004. http://dx.doi.org/10.1088/2632-959x/ac5ac3.
Testo completoAbstract (sommario):
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.
50
Liu, Ning, Sha Cui, Zheyu Jin, Zhong Cao, Hui Liu, Shuqing Yang, Xianmin Zheng e Luhui Wang. "Highly Dispersed and Stable Ni/SiO2 Catalysts Prepared by Urea-Assisted Impregnation Method for Reverse Water–Gas Shift Reaction". Processes 11, n. 5 (28 aprile 2023): 1353. http://dx.doi.org/10.3390/pr11051353.
Testo completoAbstract (sommario):
The nickel-based catalyst was more active in the reverse water-gas shift reaction, but it is easy to sinter and deactivate in high temperature reaction (≥600 °C). A urea-assisted impregnation method was utilized to create a Ni/SiO2-N catalyst to increase the catalytic stability of Ni-based catalysts. For at least 20 h, the Ni/SiO2-N catalyst in the reverse water-gas shift process at 700 °C remained stable, and in the high temperature RWGS reaction, the conversion rate of CO2 of the catalyst is close to the equilibrium conversion rate. The catalysts were characterized by BET, XRD, H2-TPR, and TEM, and the results demonstrate that the Ni particles had a small particle size and exhibited strong interaction with the SiO2 support in the Ni/SiO2-N catalyst, which led to the catalyst’s good activity and stability. Urea-assisted impregnation is a facile method to prepare stable Ni/SiO2 catalysts with high Ni dispersion.