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1
Siffert, B., und A. Naidja. „Decarboxylation catalytique de l'acide oxaloacetique en presence de montmorillonite“. Clay Minerals 22, Nr. 4 (Dezember 1987): 435–46. http://dx.doi.org/10.1180/claymin.1987.022.4.07.
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ResumeLa décarboxylation de l'acide oxaloacétique en acide pyruvique a été étudiée en présence de montmorillonite saturée en cations différents et des mêmes cations à l'état libre (non incorporés). L'action catalytique dépend de la nature du cation, cést-à-dire de sa facilité à former des complexes avec l'acide oxaloacétique. Le réseau argileux intervient dans la catalyse essentiellement par les atomes d'aluminium (ou de fer) situés sur les bords des feuillets argileux. Il joue le rôle d'un métalloenzyme biologique. Le calcul des énergies d'activation pour les différents systèmes met bien en évidence l'activité catalytique de l'argile. En présence du phyllosilicate, la réaction a lieu avec un bon rendement jusqu'à une température de 60°C.
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D'Hont, M., und J. C. Jungers. „Contribution à l'étude du mécanisme de la catalyse hétérogène: L'Activation de l'Azote par le fer et le Nickel“. Bulletin des Sociétés Chimiques Belges 58, Nr. 10-12 (01.09.2010): 450–59. http://dx.doi.org/10.1002/bscb.19490581004.
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Jurkowski, Artur, und Zofia Lendzion-Bieluń. „Determination of Fe2+/Fe3+ mole ratio based on the change of precursor lattice parameters of wustite based iron catalysts for the ammonia synthesis“. Polish Journal of Chemical Technology 21, Nr. 3 (01.09.2019): 48–52. http://dx.doi.org/10.2478/pjct-2019-0029.
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Abstract In the presented article, oxide forms of iron catalysts with the wustite structure and with a R = Fe2+/Fe3+ molar ratio in the range from 3.78 to 8.16 were investigated. The chemical composition of the tested catalyst precursors was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The X-ray diffraction (XRD) technique was used to determine the phase composition and location of reflections characteristic of the Fe1−xO phase. The molar ratio of iron ions R = Fe2+/Fe3+ was determined by manganometric titration. The distribution of promoters in the structure of iron catalyst precursors with different R = Fe2+/Fe3+ ratio was determined by a selective etching method. The dependence of the lattice parameter ao value in the crystal structure Fe1−xO on the molar ratio R = Fe2+/Fe3+ was determined. On the basis of the determined dependence, R can easily be calculated in catalyst precursors of the wustite structure.
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Sun, Xinhui, Antonios Arvanitis, Devaiah Damma, Noe T. Alvarez, Vesselin Shanov, Panagiotis G. Smirniotis und Junhang Dong. „Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions“. Catalysts 10, Nr. 8 (12.08.2020): 927. http://dx.doi.org/10.3390/catal10080927.
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A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.
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Gholami, Fatemeh, Zahra Gholami, Martin Tomas, Veronika Vavrunkova, Somayeh Mirzaei und Mohammadtaghi Vakili. „Promotional Effect of Manganese on Selective Catalytic Reduction of NO by CO in the Presence of Excess O2 over M@La–Fe/AC (M = Mn, Ce) Catalyst“. Catalysts 10, Nr. 11 (13.11.2020): 1322. http://dx.doi.org/10.3390/catal10111322.
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The catalytic performance of a series of La-Fe/AC catalysts was studied for the selective catalytic reduction (SCR) of NO by CO. With the increase in La content, the Fe2+/Fe3+ ratio and amount of surface oxygen vacancies (SOV) in the catalysts increased; thus the catalytic activity improved. Incorporating the promoters to La3-Fe1/active carbon (AC) catalyst could affect the catalyst activity by changing the electronic structure. The increase in Fe2+/Fe3+ ratio after the promoter addition is possibly due to the extra synergistic interaction of M (Mn and Ce) and Fe through the redox equilibrium of M3+ + Fe3+ ↔ M4+ + Fe2+. This phenomenon could have improved the redox cycle, enhanced the SOV formation, facilitated NO decomposition, and accelerated the CO-SCR process. The presence of O2 enhanced the formation of the C(O) complex and improved the activation of the metal site. Mn@La3-Fe1/AC catalyst revealed an excellent NO conversion of 93.8% at 400 °C in the presence of 10% oxygen. The high catalytic performance of MnOx and double exchange behavior of Mn3+ and Mn4+ can increase the number of SOV and improve the catalytic redox properties.
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Wang, Yizhou, Zheng Wang, Qiuyue Zhang, Yanping Ma, Gregory A. Solan, Yang Sun und Wen-Hua Sun. „Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis“. Catalysts 14, Nr. 3 (21.03.2024): 213. http://dx.doi.org/10.3390/catal14030213.
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Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me2Ph Fe1, 2,6-Et2Ph Fe2, 2,6-i-Pr2Ph Fe3, 2,4,6-Me3Ph Fe4, and 2,6-Et2-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 106 g (PE) mol−1 (Fe) h−1 seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (Mw/Mn = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol−1 and MAO: 4.9 kg mol−1), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol−1 and MAO: 72.4–95.5 kg mol−1). Moreover, analysis of these polyethylenes by 1H and 13C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.
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Lin, Y. T., und M. C. Lu. „Catalytic action of goethite in the oxidation of 2-chlorophenols with hydrogen peroxide“. Water Science and Technology 55, Nr. 12 (01.06.2007): 101–6. http://dx.doi.org/10.2166/wst.2007.386.
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The use of goethite and hydrogen peroxide was recently found to effectively oxidise organic compounds. This research was to investigate the effect of adsorption, pH, Fe2 + and Fe3 + on 2-CP oxidation. Results indicated that 2-CP can be decomposed with hydrogen peroxide catalysed by goethite and the oxidation rate increased with decreasing goethite particle size. The optimum oxidation rate was observed at the pH below 3.0.Addition of Fe2 + and Fe3 + can enhance the catalytic oxidation rate of 2-CP very efficiently. The main mechanism of goethite catalysing hydrogen peroxide to oxidise 2-CP may be due to the catalysis of ferrous ions and goethite surface.
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Gowri Krishnan, Shamala, Fei Ling Pua, Kumaran Palanisamy und Sharifah Nabihah. „Preparation of Oil Palm EFB Derived Solid Acid Catalyst for Esterification Reaction: Effect of Calcination Temperature“. Key Engineering Materials 701 (Juli 2016): 117–21. http://dx.doi.org/10.4028/www.scientific.net/kem.701.117.
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Oil palm empty fruit bunch (EFB) is one of the palm biomass produced in abundance after oil extraction in Malaysia. This study was focused to utilize this waste biomass as a beneficial raw materials. EFB was used to prepare new solid acid catalyst for biodiesel production. EFB was converted into solid catalyst via direct impregnation method and it was used to catalyse esterification of oleic acid. Transition metal sulfide salt, Fe2(SO4)3 was impregnated on EFB fibres. Effect of different calcination temperature was studied on the properties of catalyst. The result shows that Fe2(SO4)3 based solid acid catalyst which calcined at 500°C exhibited the highest catalytic activity with 93.90% esterification rate was achieved. The morphology and surface chemistry and function group determination for the solid acid catalyst were characterized by SEM-EDX and FTIR.
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Boscá, Lisardo, und Antonio Castrillo. „Nitric oxide, vascular function and exercise“. Biochemist 34, Nr. 3 (01.06.2012): 28–32. http://dx.doi.org/10.1042/bio03403028.
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NO (nitric oxide) is a diffusible gas molecule produced intracellularly by three distinct nitric oxide synthase (NOS) enzymes that are highly conserved in mammalian species. The NOS enzymes are haemcontaining proteins that catalyse a fiveelectron oxidation process of the guanidino nitrogen of arginine and in the presence of O2. NOS activity is, in fact, a tandem of two consecutive reactions: a reductase step catalysed by a moiety of NOS homologous with the cytochrome P450 reductase, including the NADPH and flavin nucleotide cofactorbinding domains, and an oxygenase step coupling the reduction of Fe3+ to Fe2+ in the haem to the release of NO and citrulline from arginine and molecular oxygen. The reaction requires several cofactors, including tetrahydrobiopterin and calcium/calmodulin.
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Hu, Sihai, Yaoguo Wu, Hairui Yao, Cong Lu und Chengjun Zhang. „Enhanced Fenton-like removal of nitrobenzene via internal microelectrolysis in nano zerovalent iron/activated carbon composite“. Water Science and Technology 73, Nr. 1 (15.09.2015): 153–60. http://dx.doi.org/10.2166/wst.2015.467.
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The efficiency of Fenton-like catalysis using nano zerovalent iron (nZVI) is limited by nZVI aggregation and activity loss due to inactive ferric oxide forming on the nZVI surface, which hinders electron transfer. A novel iron–carbon composite catalyst consisting of nZVI and granular activated carbon (GAC), which can undergo internal iron–carbon microelectrolysis spontaneously, was successfully fabricated by the adsorption–reduction method. The catalyst efficiency was evaluated in nitrobenzene (NB) removal via the Fenton-like process (H2O2-nZVI/GAC). The results showed that nZVI/GAC composite was good for dispersing nZVI on the surface of GAC, which permitted much better removal efficiency (93.0%) than nZVI (31.0%) or GAC (20.0%) alone. Moreover, iron leaching decreased from 1.28 to 0.58 mg/L after reaction of 240 min and the oxidation kinetic of the Fenton-like reaction can be described well by the second-order reaction kinetic model (R2 = 0.988). The composite catalyst showed sustainable catalytic ability and GAC performed as a medium for electron transfer in internal iron–carbon microelectrolysis to promote Fe2+ regeneration and Fe3+/Fe2+ cycles. Therefore, this study represents an important method to design a low cost and high efficiency Fenton-like catalyst in practical application.
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Ghosh, Shishir, Graeme Hogarth, Nathan Hollingsworth, Katherine B. Holt, Shariff E. Kabir und Ben E. Sanchez. „Hydrogenase biomimetics: Fe2(CO)4(μ-dppf)(μ-pdt) (dppf = 1,1′-bis(diphenylphosphino)ferrocene) both a proton-reduction and hydrogen oxidation catalyst“. Chem. Commun. 50, Nr. 8 (2014): 945–47. http://dx.doi.org/10.1039/c3cc46456c.
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The diiron complex Fe2(CO)4(μ-dppf)(μ-pdt) is an active catalyst for both the reduction of protons to give hydrogen and also the reverse oxidation of hydrogen and thus mimics hydrogenases which are able to catalyse both reactions.
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Belaroui, L. S., und A. Bengueddach. „Study of the catalytic activity of Al-Fe pillared clays in the Baeyer–Villiger oxidation“. Clay Minerals 47, Nr. 2 (Juni 2012): 275–84. http://dx.doi.org/10.1180/claymin.2012.047.2.10.
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AbstractThree types of AlFePILCs pillared clays have been prepared from Algerian clay precursors. They have been characterized and tested in the Baeyer–Villiger oxidation of cyclohexanone to caprolactone using benzaldehyde and oxygen as oxidant at room temperature. The structural and textural properties of the catalyst have been determined by X-ray diffraction, nitrogen adsorption-desorption isotherms and Mössbauer spectroscopy.The different activities of the clays have been related to their Fe contents and accessible surface areas. The induction period observed before the reaction started has been attributed to the dissolution of a portion of the Fe3+ cations, mediated by either the perbenzoic acid intermediate or the benzoic acid co-product. The reaction was indeed catalysed by a few ppm of dissolved iron cations and the catalysis of the Baeyer–Villiger oxidation reaction should mechanistically be considered as homogeneous.
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Giulivi, C., und E. Cadenas. „One- and two-electron reduction of 2-methyl-1,4-naphthoquinone bioreductive alkylating agents: kinetic studies, free-radical production, thiol oxidation and DNA-strand-break formation“. Biochemical Journal 301, Nr. 1 (01.07.1994): 21–30. http://dx.doi.org/10.1042/bj3010021.
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The one- and two-electron enzymic reduction of the bioreductive alkylating agents 2-methylmethoxynaphthoquinone (quinone I) and 2-chloromethylnaphthoquinone (quinone II) was studied with purified NADPH-cytochrome P-450 reductase and DT-diaphorase respectively, and characterized in terms of kinetic constants, oxyradical production, thiol oxidation and DNA-strand-break formation. The catalytic-centre activity values indicated that DT-diaphorase catalysed the reduction of quinone I far more efficiently than NADPH-cytochrome P-450 reductase, although the Km values of the two enzymes for this quinone were similar (1.2-3.0 microM). The one-electron-transfer flavoenzyme also catalysed the reduction of quinone II, but the behaviour of DT-diaphorase towards this quinone did not permit calculation of kinetic constants. A salient feature of the redox transitions caused by the one- and two-electron catalysis of these quinones was the different contributions of disproportionation and autoxidation reactions respectively. In the former case, about 26% of NADPH consumed was accounted for in terms of autoxidation (as H2O2 formation), whereas in the latter, the autoxidation component accounted for most (98%) of the NADPH consumed. This difference was abrogated by superoxide dismutase, which enhanced autoxidation during NADPH-cytochrome P-450 catalysis to a maximal value. E.s.r. analysis indicated the formation of superoxide radicals, the signal of which was suppressed by superoxide dismutase and unaffected by catalase. The one- and two-electron reduction of these quinones in the presence of GSH was accompanied by formation of thiyl radicals. Although superoxide dismutase suppressed the thiol radical e.s.r. signal in both instances, the enzyme enhanced GSSG accumulation during NADPH-cytochrome P-450 catalysis of quinone I, whereas it inhibited GSSG formation during reduction of the quinone by DT-diaphorase. One- and two-electron reduction of quinone I led to calf thymus DNA-strand-break formation, a process that (a) was substantially decreased in experiments performed with dialysed DNA and in the presence of desferal and (b) was partially sensitive to superoxide dismutase and/or catalase. These findings are rationalized in terms of the occurrence of metal ions ligated to DNA, protecting against the toxic effects of superoxide radicals generated during enzymic reduction of quinones.
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Formica, Michele, Tatiana Rogova, Heyao Shi, Naoto Sahara, Branislav Ferko, Alistair J. M. Farley, Kirsten E. Christensen, Fernanda Duarte, Ken Yamazaki und Darren J. Dixon. „Catalytic enantioselective nucleophilic desymmetrization of phosphonate esters“. Nature Chemistry 15, Nr. 5 (Mai 2023): 714–21. http://dx.doi.org/10.1038/s41557-023-01165-6.
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AbstractMolecules that contain a stereogenic phosphorus atom are crucial to medicine, agrochemistry and catalysis. While methods are available for the selective construction of various chiral organophosphorus compounds, catalytic enantioselective approaches for their synthesis are far less common. Given the vastness of possible substituent combinations around a phosphorus atom, protocols for their preparation should also be divergent, providing facile access not only to one but to many classes of phosphorus compounds. Here we introduce a catalytic and enantioselective strategy for the preparation of an enantioenriched phosphorus(V) centre that can be diversified enantiospecifically to a wide range of biologically relevant phosphorus(V) compounds. The process, which involves an enantioselective nucleophilic substitution catalysed by a superbasic bifunctional iminophosphorane catalyst, can accommodate a wide range of carbon substituents at phosphorus. The resulting stable, yet versatile, synthetic intermediates can be combined with a multitude of medicinally relevant O-, N- and S-based nucleophiles.
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Zarkadoulas, Athanasios, Ioanna Zgouleta, Nikolaos V. Tzouras und Georgios C. Vougioukalakis. „Traceless Directing Groups in Sustainable Metal-Catalyzed C–H Activation“. Catalysts 11, Nr. 5 (27.04.2021): 554. http://dx.doi.org/10.3390/catal11050554.
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Sustainable transformations towards the production of valuable chemicals constantly attract interest, both in terms of academic and applied research. C–H activation has long been scrutinized in this regard, given that it offers a straightforward pathway to prepare compounds of great significance. In this context, directing groups (DG) have paved the way for chemical transformations that had not been achievable using traditional reactions. Few steps, high yields, selectivity and activation of inert substrates are some of the invaluable assets of directed catalysis. Additionally, the employment of traceless directing groups (TDG) greatly improves and simplifies this strategy, enabling the realization of multi-step reactions in one-pot, cascade procedures. Cheap, abundant, readily available transition metal salts and complexes can catalyze a plethora of reactions employing TDGs, usually under low catalyst loadings—rarely under stoichiometric amounts, leading in greater atom economy and milder conditions with increased yields and step-economy. This review article summarizes all the work done on TDG-assisted catalysis with manganese, iron, cobalt, nickel, or copper catalysts, and discusses the structure-activity relationships observed, by presenting the catalytic pathways and range of transformations reported thus far.
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Hsueh, C. L., Y. H. Huang, C. C. Wang und 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, Nr. 6 (01.03.2006): 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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Liu, Hua Zhang, Xia Zhen Yang, Ya Qing Cen und Hao Dong Tang. „A Novel Fe 1-xO-Based Fused Iron Catalyst for Fischer-Tropsch Synthesis with the High Olefine Selectivity“. Advanced Materials Research 512-515 (Mai 2012): 2207–11. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.2207.
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The performance and stability for FTS was studied on novel Fe1-xO-based iron catalyst (FIC) in agitated slurry reactor (ASR) and fixed bed reactor (FBR), and compared with precipitation-iron catalyst (PIC). The studied results indicate that novel Fe1-xO-based iron catalyst has the high conversion and high stability, especially, the high alkene selectivity in C2 ~ C4 products that the ratios of olefines and paraffines the more than 9 and the low cost, the preparation process and the high mechanical intensity. The catalyst can be used at FBR or ASR, and FTS at high temperature or low temperature.
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Ettwig, Katharina F., Baoli Zhu, Daan Speth, Jan T. Keltjens, Mike S. M. Jetten und Boran Kartal. „Archaea catalyze iron-dependent anaerobic oxidation of methane“. Proceedings of the National Academy of Sciences 113, Nr. 45 (24.10.2016): 12792–96. http://dx.doi.org/10.1073/pnas.1609534113.
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Anaerobic oxidation of methane (AOM) is crucial for controlling the emission of this potent greenhouse gas to the atmosphere. Nitrite-, nitrate-, and sulfate-dependent methane oxidation is well-documented, but AOM coupled to the reduction of oxidized metals has so far been demonstrated only in environmental samples. Here, using a freshwater enrichment culture, we show that archaea of the order Methanosarcinales, related to “Candidatus Methanoperedens nitroreducens,” couple the reduction of environmentally relevant forms of Fe3+ and Mn4+ to the oxidation of methane. We obtained an enrichment culture of these archaea under anaerobic, nitrate-reducing conditions with a continuous supply of methane. Via batch incubations using [13C]methane, we demonstrated that soluble ferric iron (Fe3+, as Fe-citrate) and nanoparticulate forms of Fe3+ and Mn4+ supported methane-oxidizing activity. CO2 and ferrous iron (Fe2+) were produced in stoichiometric amounts. Our study connects the previous finding of iron-dependent AOM to microorganisms detected in numerous habitats worldwide. Consequently, it enables a better understanding of the interaction between the biogeochemical cycles of iron and methane.
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Muñiz, Kilian. „Metal-free catalytic vicinal diamination of alkenes“. Pure and Applied Chemistry 85, Nr. 4 (27.03.2013): 755–61. http://dx.doi.org/10.1351/pac-con-12-10-23.
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The development of an intramolecular vicinal diamination protocol using metal-free conditions is discussed. The reaction uses a bromide source to generate a Br(I) catalyst in situ from a benign terminal oxidant such as sodium chlorite. The reaction is of great scope and surpasses the transition-metal catalyses developed so far for these types of reactions.
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Wang, Ziyun, Hai-Feng Wang und P. Hu. „Possibility of designing catalysts beyond the traditional volcano curve: a theoretical framework for multi-phase surfaces“. Chemical Science 6, Nr. 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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Kukielka, E., und A. I. Cederbaum. „DNA strand cleavage as a sensitive assay for the production of hydroxyl radicals by microsomes: role of cytochrome P4502E1 in the increased activity after ethanol treatment“. Biochemical Journal 302, Nr. 3 (15.09.1994): 773–79. http://dx.doi.org/10.1042/bj3020773.
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There is increasing interest in the role of reactive oxygen radicals in the hepatotoxicity associated with ethanol consumption. Reactive oxygen intermediates interact with DNA and can cause single-strand breaks of supercoiled DNA. Experiments were carried out to evaluate the utility of this system as a sensitive assay for the detection of potent oxidants generated by rat liver microsomes isolated from pair-fed control rats and rats treated chronically with ethanol. DNA strand cleavage was assayed by monitoring the migration of the supercoiled and open circular forms in agarose. Microsomes catalysed DNA strand breakage with either NADPH or NADH as cofactors; iron was required to catalyse the reaction and various ferric complexes were effective in promoting the reaction. DNA strand cleavage was prevented by catalase, superoxide dismutase, GSH and hydroxyl-radical-scavenging agents, suggesting that a hydroxyl-radical-like species was the oxidant responsible for the breakage. This assay system proved to be much more sensitive in detecting hydroxyl radicals than are other methods, such as e.s.r. spectroscopy or oxidation of chemical scavenging agents with respect to the amount of microsomal protein and the nature and concentration of the iron catalyst required. Microsomes from ethanol-treated rats were more reactive than control microsomes in catalysing the DNA strand cleavage with either NADPH or NADH; increased catalytic activity was observed with various ferric complexes and was sensitive to the above antioxidants. Compared with preimmune IgG, anti-(cytochrome P4502E1) IgG had no effect on DNA strand cleavage by the control microsomes, but completely prevented the NADPH- and the NADH-dependent increased activity found with microsomes from the ethanol-treated rats. Inhibitors of cytochrome P4502E1, such as diethyl dithiocarbamate and tryptamine, also lowered the extent of increase of DNA strand cleavage produced by microsomes from the ethanol-treated rats. These results indicate that DNA strand cleavage is a very sensitive assay for detecting the production of hydroxyl radicals by microsomes and to demonstrate increased activity by microsomes after chronic ethanol treatment. This increased activity with NADPH and NADH is due, at least in part, to induction of cytochrome P4502E1.
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Du, Yunchen, Di Guo, Meiling Xiong, Yanwu Qi, Chenkui Cui, Jun Ma, Xijiang Han und 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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Tichá, Iveta Chena, Simona Hybelbauerová und Jindřich Jindřich. „New α- and β-cyclodextrin derivatives with cinchona alkaloids used in asymmetric organocatalytic reactions“. Beilstein Journal of Organic Chemistry 15 (01.04.2019): 830–39. http://dx.doi.org/10.3762/bjoc.15.80.
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The preparation of new organocatalysts for asymmetric syntheses has become a key stage of enantioselective catalysis. In particular, the development of new cyclodextrin (CD)-based organocatalysts allowed to perform enantioselective reactions in water and to recycle catalysts. However, only a limited number of organocatalytic moieties and functional groups have been attached to CD scaffolds so far. Cinchona alkaloids are commonly used to catalyze a wide range of enantioselective reactions. Thus, in this study, we report the preparation of new α- and β-CD derivatives monosubstituted with cinchona alkaloids (cinchonine, cinchonidine, quinine and quinidine) on the primary rim through a CuAAC click reaction. Subsequently, permethylated analogs of these cinchona alkaloid–CD derivatives also were synthesized and the catalytic activity of all derivatives was evaluated in several enantioselective reactions, specifically in the asymmetric allylic amination (AAA), which showed a promising enantiomeric excess of up to 75% ee. Furthermore, a new disubstituted α-CD catalyst was prepared as a pure AD regioisomer and also tested in the AAA. Our results indicate that (i) the cinchona alkaloid moiety can be successfully attached to CD scaffolds through a CuAAC reaction, (ii) the permethylated cinchona alkaloid–CD catalysts showed better results than the non-methylated CDs analogues in the AAA reaction, (iii) promising enantiomeric excesses are achieved, and (iv) the disubstituted CD derivatives performed similarly to monosubstituted CDs. Therefore, these new CD derivatives with cinchona alkaloids effectively catalyze asymmetric allylic aminations and have the potential to be successfully applied in other enantioselective reactions.
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Kobayashi, Yasukazu, und Riki Hikosaka. „Analyzing Loose Contact Oxidation of Diesel Engine Soot and Ag/CeO2 Catalyst Using Nonlinear Regression Analysis“. Bulletin of Chemical Reaction Engineering & Catalysis 12, Nr. 1 (30.04.2017): 14. http://dx.doi.org/10.9767/bcrec.12.1.606.14-23.
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<p>Loose contact (LC) oxidation kinetics of carbon black (CB) model soot and Ag/CeO<sub>2</sub> catalyst was deduced from thermogravimetric analysis (TG) experiments. In the LC mode at ≧750 K, CB particles were likely to be combusted also by non-catalyzed oxidation, especially those particles located far from the catalyst surface, as well as Ag/CeO<sub>2</sub>-catalyed oxidation. Since the non-catalyzed oxidation is not due to catalytic activity, in order to deduce the catalytic activity from TG data, a nonlinear regression analysis method was proposed in this study to extract only the catalyzed oxidation part of the TG data. It was verified that this was successfully done with the equations used by the very good curve fits to the experimental TG data, and the catalytic activity was correctly obtained from LC samples with various degrees of physical contact between the CB and catalyst. Copyright © 2016 BCREC GROUP. All rights reserved</p><p><em>Received: 18th July 2016; Revised: 12nd September 2016; Accepted: 20th September 2016</em></p><p><strong>How to Cite</strong>: Kobayashi, Y., Hikosaka, R. (2017). Analyzing Loose Contact Oxidation of Diesel Engine Soot and Ag/CeO<sub>2</sub> Catalyst Using Nonlinear Regression Analysis.<em> Bulletin of Chemical Reaction Engineering & Catalysis</em>, 12 (1): 14-23 (doi:10.9767/bcrec.12.1.606.14-23)</p><p><strong>Permalink/DOI:</strong> http://dx.doi.org/10.9767/bcrec.12.1.606.14-23</p><p> </p>
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Rindler, Paul M., Angela Cacciola, Michael Kinter und Luke I. Szweda. „Catalase-dependent H2O2consumption by cardiac mitochondria and redox-mediated loss in insulin signaling“. American Journal of Physiology-Heart and Circulatory Physiology 311, Nr. 5 (01.11.2016): H1091—H1096. http://dx.doi.org/10.1152/ajpheart.00066.2016.
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We have recently demonstrated that catalase content in mouse cardiac mitochondria is selectively elevated in response to high dietary fat, a nutritional state associated with oxidative stress and loss in insulin signaling. Catalase and various isoforms of glutathione peroxidase and peroxiredoxin each catalyze the consumption of H2O2. Catalase, located primarily within peroxisomes and to a lesser extent mitochondria, has a low binding affinity for H2O2relative to glutathione peroxidase and peroxiredoxin. As such, the contribution of catalase to mitochondrial H2O2consumption is not well understood. In the current study, using highly purified cardiac mitochondria challenged with micromolar concentrations of H2O2, we found that catalase contributes significantly to mitochondrial H2O2consumption. In addition, catalase is solely responsible for removal of H2O2in nonrespiring or structurally disrupted mitochondria. Finally, in mice fed a high-fat diet, mitochondrial-derived H2O2is responsible for diminished insulin signaling in the heart as evidenced by reduced insulin-stimulated Akt phosphorylation. While elevated mitochondrial catalase content (∼50%) enhanced the capacity of mitochondria to consume H2O2in response to high dietary fat, the selective increase in catalase did not prevent H2O2-induced loss in cardiac insulin signaling. Taken together, our results indicate that mitochondrial catalase likely functions to preclude the formation of high levels of H2O2without perturbing redox-dependent signaling.
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Boubnov, Alexey, Henning Lichtenberg, Stefan Mangold und Jan-Dierk Grunwaldt. „Identification of the iron oxidation state and coordination geometry in iron oxide- and zeolite-based catalysts using pre-edge XAS analysis“. Journal of Synchrotron Radiation 22, Nr. 2 (25.02.2015): 410–26. http://dx.doi.org/10.1107/s1600577514025880.
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Analysis of the oxidation state and coordination geometry using pre-edge analysis is attractive for heterogeneous catalysis and materials science, especially forin situand time-resolved studies or highly diluted systems. In the present study, focus is laid on iron-based catalysts. First a systematic investigation of the pre-edge region of the FeK-edge using staurolite, FePO4, FeO and α-Fe2O3as reference compounds for tetrahedral Fe2+, tetrahedral Fe3+, octahedral Fe2+and octahedral Fe3+, respectively, is reported. In particular, high-resolution and conventional X-ray absorption spectra are compared, considering that in heterogeneous catalysis and material science a compromise between high-quality spectroscopic data acquisition and simultaneous analysis of functional properties is required. Results, which were obtained from reference spectra acquired with different resolution and quality, demonstrate that this analysis is also applicable to conventionally recorded pre-edge data. For this purpose, subtraction of the edge onset is preferentially carried out using an arctangent and a first-degree polynomial, independent of the resolution and quality of the data. For both standard and high-resolution data, multiplet analysis of pre-edge features has limitations due to weak transitions that cannot be identified. On the other hand, an arbitrary empirical peak fitting assists the analysis in that non-local transitions can be isolated. The analysis of the oxidation state and coordination geometry of the Fe sites using a variogram-based method is shown to be effective for standard-resolution data and leads to the same results as for high-resolution spectra. This method, validated by analysing spectra of reference compounds and their well defined mixtures, is finally applied to track structural changes in a 1% Fe/Al2O3and a 0.5% Fe/BEA zeolite catalyst during reduction in 5% H2/He. The results, hardly accessible by other techniques, show that Fe3+is transformed into Fe2+, while the local Fe–O coordination number of 4–5 is maintained, suggesting that the reduction involves a rearrangement of the oxygen neighbours rather than their removal. In conclusion, the variogram-based analysis of FeK-edge spectra proves to be very useful in catalysis research.
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Ghorbel, Mouna, Kaouthar Feki, Sana Tounsi, Najla Haddaji, Moez Hanin und Faiçal Brini. „The Activity of the Durum Wheat (Triticum durum L.) Catalase 1 (TdCAT1) Is Modulated by Calmodulin“. Antioxidants 11, Nr. 8 (29.07.2022): 1483. http://dx.doi.org/10.3390/antiox11081483.
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Plant catalases (CAT) are involved in the cellular scavenging of the reactive oxygen species during developmental processes and in response to abiotic and biotic stresses. However, little is known about the regulation of the CAT activity to ensure efficient antioxidant function. Using bioinformatic analyses, we showed that durum wheat catalase 1 (TdCAT1) harbors highly conserved cation-binding and calmodulin binding (CaMBD) domains which are localized at different positions of the protein. As a result, the catalytic activity of TdCAT1 is enhanced in vitro by the divalent cations Mn2+ and Fe2+ and to a lesser extent by Cu2+, Zn2+, and Mg2+. Moreover, the GST-pull down assays performed here revealed that TdCAT1 bind to the wheat CaM (TdCaM1.3) in a Ca2+-independent manner. Furthermore, the TdCaM1.3/Ca2+ complex is stimulated in a CaM-dose-dependent manner by the catalytic activity of TdCAT1, which is further increased in the presence of Mn2+ cations. The catalase activity of TdCAT1 is enhanced by various divalent cations and TdCaM1.3 in a Ca-dependent manner. Such effects are not reported so far and raise a possible role of CaM and cations in the function of CATs during cellular response to oxidative stress.
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Tromp, Moniek. „Catalysis seen in action“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, Nr. 2036 (06.03.2015): 20130152. http://dx.doi.org/10.1098/rsta.2013.0152.
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Synchrotron radiation techniques are widely applied in materials research and heterogeneous catalysis. In homogeneous catalysis, its use so far is rather limited despite its high potential. Here, insights in the strengths and limitations of X-ray spectroscopy technique in the field of homogeneous catalysis are given, including new technique developments. A relevant homogeneous catalyst, used in the industrially important selective oligomerization of ethene, is taken as a worked-out example. Emphasis is placed on time-resolved operando X-ray absorption spectroscopy with outlooks to novel high energy resolution and emission techniques. All experiments described have been or can be done at the Diamond Light Source Ltd (Didcot, UK).
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Wang, Zheng, Gregory A. Solan, Yanping Ma, Qingbin Liu, Tongling Liang und Wen-Hua Sun. „Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity“. Research 2019 (16.10.2019): 1–15. http://dx.doi.org/10.34133/2019/9426063.
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The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II) chlorides (aryl = 2,6-Me2C6H3Fe1; 2,6-Et2C6H3Fe2; 2,6-i-Pr2C6H3Fe3; 2,4,6-Me3C6H2Fe4; and 2,6-Et2-4-Me2C6H2Fe5) have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione, FeCl2·4H2O, and the appropriate aniline in acetic acid. All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy. In addition, the structure of Fe3 has been determined by single crystal X-ray diffraction, which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six- and seven-membered carbocycles to be cis-configured. In combination with either MAO or MMAO, Fe1–Fe5 exhibited exceptionally high activities for ethylene polymerization (up to 15.86×106 gPE mol−1 Fe h−1 at 40°C (MMAO) and 9.60×106 gPE mol−1 Fe h−1 at 60°C (MAO)) and produced highly linear polyethylene (HLPE, Tm≥128°C) with a wide range in molecular weights; in general, the MMAO-promoted polymerizations were more active. Irrespective of the cocatalyst employed, the 2,6-Me2-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr2Fe3 the least but afforded the highest molecular weight polyethylene (Mw: 65.6–72.6 kg mol-1). Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40°C showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace (Mw/Mn=13.4). By contrast, using Fe4/MAO at 60°C a vinyl-terminated polymer of lower molecular weight (Mw=14.2 kg mol−1) was identified that exhibited a unimodal distribution (Mw/Mn=3.8). Moreover, the amount of aluminoxane cocatalyst employed, temperature, and run time were also found to be influential on the modality of the polymer.
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Melki, Rafik, Nadia Aïcha Laoufi und Abdelkader Mouheb. „Effects of iron ions, doping methods and nanotubular morphology on TiO2 solar photocatalytic performance“. Water Science and Technology 83, Nr. 12 (10.05.2021): 3020–32. http://dx.doi.org/10.2166/wst.2021.182.
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Abstract The effects of Fe2+ and Fe3+ as TiO2 cocatalysts were studied, and the experimental results showed that Fe3+ was more efficient than Fe2+, which needed an intermediate reaction to produce hydroxyl radicals. TiO2 was modified with the aim of improving its structural, optical, and adsorption properties, thus improving its photocatalytic performance. The light range of the catalyst activation process was expanded, which increased the catalyst's ability to absorb visible light. Consequently, this study exploits solar energy in photocatalysis by Fe ion doping using different methods, including impregnation, photodeposition, solvothermal doping, and hydrothermal doping, and evaluates the influence of each doping method on TiO2 optical properties and photocatalytic activity. Enhancing the catalyst adsorption capacity by morphologically modifying TiO2 nanoparticles into nanotubes using the hydrothermal method increases the catalyst surface area from 55 to 294 m2/g, as shown in the SEM and BET results. The effect of combining morphological changes and Fe3+ doping on TiO2 activity was evaluated. We observed a reduction in the TiO2 band gap from 3.29 to 3.01 eV, absorption edge widening, and an increase in the specific surface area up to 279 m2/g; thus, the synthesized catalyst eliminated Cefixime in 120 min.
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Korichi, Noussaiba, Olivier Aubry, Hervé Rabat, Benoît Cagnon und Dunpin Hong. „Paracetamol Degradation by Catalyst Enhanced Non-Thermal Plasma Process for a Drastic Increase in the Mineralization Rate“. Catalysts 10, Nr. 9 (21.08.2020): 959. http://dx.doi.org/10.3390/catal10090959.
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In order to remediate the very poor mineralization of paracetamol in water, even when well degraded by using a Non-Thermal Plasma (NTP) process at a very low dissipated power, a plasma-catalyst coupling process was tested and investigated. A homemade glass fiber supported Fe3+ catalyst was immersed in the liquid to be treated in a Dielectric Barrier Discharge plasma reactor. The plasma-catalysis process, at the same low dissipated power, achieved a mineralization rate of 54% with a full conversion rate of paracetamol at 25 mg L−1 in initial concentration after 60 min treatment, thanks to Fenton-like effects. The synergetic effects of the plasma-catalysis coupling process also improved the Energy Yield by a factor of two. The catalyst before and after use for treatment was characterized by Brunauer-Emmett-Teller and Thermogravimetric analysis. High-Performance Liquid Chromatography was used to measure the concentration of treated solution and to investigate the intermediates. Two of them, namely 1,4-hydroquinone and 1,4-benzoquinone, were formally identified. Some intermediates are presented in this paper as a function of treatment time and their UV absorbance spectra. NTP processes with and without catalyst coupling were compared in terms of acidity, conductivity, and nitrate concentrations in the treated solution.
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Yang, Ruiguang, Guiying Li und Changwei Hu. „The preparation of Fe/wood-based activated carbon catalyst for phenol hydroxylation from Fe2+ and Fe3+ precursors“. Catalysis Science & Technology 5, Nr. 4 (2015): 2486–95. http://dx.doi.org/10.1039/c4cy01705f.
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Hernandez-Aldave, Sandra, und Enrico Andreoli. „Fundamentals of Gas Diffusion Electrodes and Electrolysers for Carbon Dioxide Utilisation: Challenges and Opportunities“. Catalysts 10, Nr. 6 (26.06.2020): 713. http://dx.doi.org/10.3390/catal10060713.
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Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO2 conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has emerged as the Achilles heel of CO2 electrolysis. Too often, catalysts are assessed in electrochemical settings that are far removed from industrially relevant operational conditions, where CO2 mass transport limitations should be minimised. To overcome this issue, gas diffusion electrodes and gas-fed electrolysers need to be developed and applied, presenting new challenges and opportunities to the CO2 electrolysis community. In this review, we introduce the reader to the fundamentals of gas diffusion electrodes and gas-fed electrolysers, highlighting their advantages and disadvantages. We discuss in detail the design of gas diffusion electrodes and their operation within gas-fed electrolysers in both flow-through and flow-by configurations. Then, we correlate the structure and composition of gas diffusion electrodes to the operational performance of electrolysers, indicating options and prospects for improvement. Overall, this study will equip the reader with the fundamental understanding required to enhance and optimise CO2 catalysis beyond the laboratory scale.
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Milgrom, Lionel. „Why is catalase so fast?“ International Journal of High Dilution Research - ISSN 1982-6206 15, Nr. 4 (18.08.2021): 38. http://dx.doi.org/10.51910/ijhdr.v15i4.865.
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ded network of hydrogen-bonded water and H2O2 molecules, stretching out far beyond the enzymes’ active sites, into the cell's internal aqueous medium. As catalases function, they provide coherent oxidative ‘pulses’, which rapidly spread throughout the H-bonded network, effectively ‘unzipping’ H2O2 molecules as far as they extend from the enzyme.
Result/discussion: This 'memory-of-water'-like mechanism predicts catalase H2O2 disproportionation should occur outside the enzyme. An experimental protocol is proposed to test this prediction. If successful, it would suggest a) holistic re-appraisal of the conventional mechanistic framework of enzyme kinetics is required, and b) should encourage more research into understanding the biochemical effects of CAM therapies.
Keywords: Holistic biochemistry; catalase enzymes; hydrogen peroxide disproportionation; hydrogen-bonded networks; memory of water.
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Tsai, Meng-Che, Yohannes Ayele Awoke, Wei-Nien Su und Bing Joe Hwang. „Value-Added Electrolysis Hydrogen Production Via Methanol Oxidation over a Synergetic Pt1-W Dual-Site Catalyst“. ECS Meeting Abstracts MA2024-01, Nr. 35 (09.08.2024): 1923. http://dx.doi.org/10.1149/ma2024-01351923mtgabs.
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Electrochemical water splitting is a promising way of generating hydrogen for future sustainable green energy source technology options to replace nonrenewable and environmentally pollutant hydrocarbon energy sources. However, due to its high overpotential in oxygen evolution reaction (OER) and low-value product O2, some candidate anodic reactions with low potential should be proposed to replace OER, such as alcohol oxidation. Unlike fuel cell applications, partial oxidation is preferred to achieve high-value products rather than complete oxidation. For this purpose, we design a synergistic effect Pt1-W site on the dual-doped TiO2 support (Ti0.8W0.2NxOy) to catalyze alkaline methanol oxidation and gain 90% selectivity of formate production. Comparing the case of the Pt nanoparticles (69% selectivity of formaldehyde), the Pt single-atom catalyst controls selectivity and enhances the reactivity and stability attributed to the strong catalyst-support interaction. As a result, this work shows a novel strategy for electrochemical hydrogen production at far lower anodic potential by designing a stable and efficient Pt-based single-atom catalyst.
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Jia, Xianbo, Jichen Chen, Chenqiang Lin und Xinjian Lin. „Cloning, Expression, and Characterization of a Novel Thermophilic Monofunctional Catalase fromGeobacillussp. CHB1“. BioMed Research International 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/7535604.
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Catalases are widely used in many scientific areas. A catalase gene (Kat) fromGeobacillussp. CHB1 encoding a monofunctional catalase was cloned and recombinant expressed inEscherichia coli(E. coli), which was the first time to clone and express this type of catalase ofgenus Geobacillusstrains as far as we know. ThisKatgene was 1,467 bp in length and encoded a catalase with 488 amino acid residuals, which is only 81% similar to the previously studiedBacillussp. catalase in terms of amino acid sequence. Recombinant catalase was highly soluble inE. coliand made up 30% of the totalE. coliprotein. Fermentation broth of the recombinantE. colishowed a high catalase activity level up to 35,831 U/mL which was only lower than recombinantBacillussp. WSHDZ-01 among the reported catalase production strains. The purified recombinant catalase had a specific activity of 40,526 U/mg andKmof 51.1 mM. The optimal reaction temperature of this recombinant enzyme was 60°C to 70°C, and it exhibited high activity over a wide range of reaction temperatures, ranging from 10°C to 90°C. The enzyme retained 94.7% of its residual activity after incubation at 60°C for 1 hour. High yield and excellent thermophilic properties are valuable features for this catalase in industrial applications.
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Khanh, Huynh Hoang Nhu, Vo Thi Dieu Trang, Pham Duc Thinh und Pham Trung San. „CATALYTIC CONDITIONS OF FUCOIDAN DEGRADING ENZYMES FROM VASTICARDIUM FLAVUM“. Vietnam Journal of Science and Technology 57, Nr. 1 (18.02.2019): 28. http://dx.doi.org/10.15625/2525-2518/57/1/12249.
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The fucoidanase from the digestive glands of the marine shell Vasticardium flavum was studied. The fucoidanase catalysed the hydrolysis of 1→3-L-fucan from sea cucumbers Stichopus variegatus, Holothuria spinifera, did not catalyze the hydrolysis of fucoidan from F. evanescens and F. vesiculosus containing alternating α-1→4 and α-1→3 glycoside bonds. This enzyme also did not catalyze the hydrolysis of fucoidan from U. pinnatifida, S. mcclurei, which belong to the galactofucan group. Optima of pH and time incubation were at 3-4 and 24 hours, respectively. The enzyme activity was significantly increased in the presence of the Ca2+, Ba2+, Co2+ and Mg2+ cations, but the Cu2+, Sn2+, Fe2+ and Al3+ cations partially inactivated the enzyme. The enzyme was completely inactivated after 5 min of incubation at 65° C.
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Palumbo, A., G. Misuraca, M. D'Ischia und G. Prota. „Effect of metal ions on the kinetics of tyrosine oxidation catalysed by tyrosinase“. Biochemical Journal 228, Nr. 3 (15.06.1985): 647–51. http://dx.doi.org/10.1042/bj2280647.
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The conversion of tyrosine into dopa [3-(3,4-dihydroxyphenyl)alanine] is the rate limiting step in the biosynthesis of melanins catalysed by tyrosinase. This hydroxylation reaction is characterized by a lag period, the extent of which depends on various parameters, notably the presence of a suitable hydrogen donor such as dopa or tetrahydropterin. We have now found that catalytic amounts of Fe2+ ions have the same effect as dopa in stimulating the tyrosine hydroxylase activity of the enzyme. Kinetic experiments showed that the shortening of the induction time depends on the concentration of the added metal and the nature of the buffer system used and is not suppressed by superoxide dismutase, catalase, formate or mannitol. Notably, Fe3+ ions showed only a small delaying effect on tyrosinase activity. Among the other metals which were tested, Zn2+, Co2+, Cd2+ and Ni2+ had no detectable influence, whereas Cu2+ and Mn2+ exhibited a marked inhibitory effect on the kinetics of tyrosine oxidation. These findings are discussed in the light of the commonly accepted mechanism of action of tyrosinase.
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Nasuha, Norhaslinda, und B. H. Hameed. „Effects of Substituted Transition Metals (Me:Cr3+, Mn3+, Fe3+ and Mo) on the Fe2+/Modified Silica in the Oxidative Degradation of Reactive Black 5“. Applied Mechanics and Materials 802 (Oktober 2015): 531–36. http://dx.doi.org/10.4028/www.scientific.net/amm.802.531.
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The Fe2+/modified silica catalysts have been substituted with four types of transition metals such as Fe3+, Cr3+, Mn3+ and Mo. The catalytic activity of these catalysts has been tested for the oxidative degradation of Reactive Black 5 (RB5) at 30°C and pH 4.5. The substituted Fe2+/modified silica with Fe3+ (Fe2+:Fe3+/ m-SiO2) exhibited the highest catalytic performance compared to others transition metals by degrading the RB5 nearly to 95%. This catalyst possessed on high stability by maintaining its performance during the three successive cycles of reaction. These findings can be ascribed to the plausible enhancement in the formation of hydroxyl radicals (HO●) due to the effective redox between Fe2+ and Fe3+
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Tisa, Farhana, Abdul Aziz Abdul Raman und Wan Mohd Ashri Wan Daud. „Simulation for Supporting Scale-Up of a Fluidized Bed Reactor for Advanced Water Oxidation“. Scientific World Journal 2014 (2014): 1–17. http://dx.doi.org/10.1155/2014/348974.
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Simulation of fluidized bed reactor (FBR) was accomplished for treating wastewater using Fenton reaction, which is an advanced oxidation process (AOP). The simulation was performed to determine characteristics of FBR performance, concentration profile of the contaminants, and various prominent hydrodynamic properties (e.g., Reynolds number, velocity, and pressure) in the reactor. Simulation was implemented for 2.8 L working volume using hydrodynamic correlations, continuous equation, and simplified kinetic information for phenols degradation as a model. The simulation shows that, by using Fe3+and Fe2+mixtures as catalyst, TOC degradation up to 45% was achieved for contaminant range of 40–90 mg/L within 60 min. The concentration profiles and hydrodynamic characteristics were also generated. A subsequent scale-up study was also conducted using similitude method. The analysis shows that up to 10 L working volume, the models developed are applicable. The study proves that, using appropriate modeling and simulation, data can be predicted for designing and operating FBR for wastewater treatment.
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Huang, Yao-Hui, Chun-Ping Huang, Yu-Wen Lu und Chun-Yu Lo. „Oxidation and immobilization of iron and manganese by a fluidized bed reactor“. Water Supply 9, Nr. 6 (01.12.2009): 619–25. http://dx.doi.org/10.2166/ws.2009.677.
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An iron and manganese species immobilization technology was developed in a fluidized bed reactor (FBR) with a new fluidized media, immobilized iron oxide (namely FeOx-30). The FeOx-30 catalyst exhibited excellent performance as a catalyst for the oxidation of Mn2 + . About 95% and 30% of the manganese species were immobilized on FeOx-30 and silica sand in FBR, respectively. The oxidation rates of Fe2 + and Mn2 + and the immobilization efficiencies of iron and manganese oxides strongly depend on pH value. Usually during oxidization the pH values of the solution containing Fe2 + must be above 7, and Mn2 + must be above 9. During this study, large amounts of iron species leached from the surface of FeOx-30 only when manganese was in the system. The surface of the FeOx-30 became fragile in a single system. However, the removal of iron and manganese species simultaneously was better than only the removal of manganese in an FBR. In the binary system, the optimum pH condition for immobilization of both iron and manganese species was pHi 9. The higher catalyst loading in the binary system led to a higher removal efficiency of iron and manganese.
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Amiri, Mohammad Javad, Mohaddeseh Afshari, Mohammad Dinari und Mohammad Arshadi. „Activation of Peroxymonosulfate by Fe0 for the Degradation of BTEX: Effects of Aging Time and Interfering Ions“. Sustainability 14, Nr. 22 (17.11.2022): 15247. http://dx.doi.org/10.3390/su142215247.
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Resolving three environmental challenges simultaneously—recycling bone waste, aggregation, oxidation of bare nZVI and benzene, toluene, ethylbenzene, and p-xylene (BTEX) contamination—was conducted by fabricating a highly stable and efficient activator of peroxymonosulfate. In this work, a novel heterogeneous catalyst, ostrich bone ash-supported nanoscale zero-valent iron (Fe0-OBA) prepared by pyrolysis of animal bones and reduced Fe2+ on the surface of it, was used for the activation of peroxymonosulfate (PMS). Advantageous properties such as extensive availability, low production cost, and high thermal stability make OBA an appealing carbonaceous material for heterogeneous catalysis. The TEM and SEM results revealed that the black ball-shaped nZVI particles were uniformly dispersed on the surface of OBA. The Fe0-OBA composite had a porous structure with a specific surface area of 109 m2 g−1 according to BET analysis. With BTEX as the refractory pollutant, the PMS-based Fe0-OBA system shows great degradation performance as compared to the homogeneous Fe2+/PMS system. The effects of various parameters, such as initial pH (2–9), temperature (25–45 °C), initial BTEX concentration (50–200 mg L−1), PMS dosage (0.5–1.25 mM), time of reaction (0–60 min), and Fe0-OBA dosage (0.5–5 g L−1) on the BTEX degradation, have been discussed in detail. The pseudo-first-order kinetic model can describe the BTEX degradation by the PMS-based Fe0-OBA system. The excellent stability of Fe0-OBA even after 10 years, while maintaining the degradation efficiency, shows the high potential of it in a wide range of practical applications. This study illustrated that Fe0-OBA could be an effective activator of PMS for the degradation of stubborn organic contaminants in water and wastewater.
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Tesser, R., R. Vitiello, G. Carotenuto, C. Garcia Sancho, A. Vergara, P. J. Maireles Torres, Changzhu Li und M. Di Serio. „Niobia supported on silica as a catalyst for Biodiesel production from waste oil“. Catalysis for Sustainable Energy 2, Nr. 1 (30.04.2015): 33–42. http://dx.doi.org/10.1515/cse-2015-0002.
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AbstractThe activity and stability of niobia supported on silica catalyst have been tested in continuous micro-pilot reactors, for biodiesel production starting from acid vegetable oils. A catalyst was prepared by the impregnation of silica pellets with a loading of 12% of Nb and was extensively characterized. The activity of this catalyst in both esterification and transesterification was tested in a continuous micro-pilot laboratory plant in which acid oil was fed (FFA 10% w/w) at a temperature of 220°C and at a pressure of 60 bar. The niobia based catalyst resulted in a very active catalyst in both esterification (FFA conversion = 95-90%) and transesterification reactions (FAME yield = 80-90%), and the activity remained quite constant for more than 100 h on stream. Notwithstanding this stability, a non-negligible leaching phenomena has been detected, in the case of long-time continuous runs, as the Nb concentration on the spent catalyst resulted lower than that on the fresh one. The obtained result confirms that the leaching of the active specie is one of the most strong problem in heterogeneous catalysis for biodiesel production.
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SONG, Donna D., und Nicholas A. JACQUES. „Purification and enzymic properties of the fructosyltransferase of Streptococcus salivarius ATCC 25975“. Biochemical Journal 341, Nr. 2 (08.07.1999): 285–91. http://dx.doi.org/10.1042/bj3410285.
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The recombinant fructosyltransferase (Ftf) of Streptococcus salivarius was expressed in Escherichia coli and purified to electrophoretic homogeneity after a combination of adsorption, ion-exchange and gel-filtration chromatography. The N-terminal signal sequence of the Ftf was removed by E. coli at the same site as in its natural host. The purified Ftf exhibited maximum activity at pH 6.0 and 37 °C, was activated by Ca2+, but inhibited by the metal ions Cu2+, Zn2+, Hg2+ and Fe3+. The enzyme catalysed the transfer of the fructosyl moiety of sucrose to a number of acceptors, including water, glucose and sucrose via a Ping Pong mechanism involving a fructosyl-enzyme intermediate. While this mechanism of catalysis is utilized by the levansucrases of Bacillus subtilis and Acetobacter diazotrophicus and the values of the kinetic constants for the three enzymes are similar, sucrose was a far more efficient fructosyl-acceptor for the Ftf of S. salivarius than for the two other enzymes.
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Li, Zhen, Huihui Zhang, Deshi Yang, Zhipeng Hu, Fengqiang Wang und Zhijun Zhang. „Efficient Conversion of Lignin to Aromatics via Catalytic Fast Pyrolysis over Niobium-Doped HZSM-5“. Molecules 28, Nr. 10 (22.05.2023): 4245. http://dx.doi.org/10.3390/molecules28104245.
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A niobium-doped HZSM-5 (H[Nb]ZSM-5) was prepared by a hydrothermal synthesis method. The morphology, phase structure, composition, pore structure, and acid content of the catalyst were characterized using a series of analysis techniques such as scanning electron microscope (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption, and temperature programmed desorption measurements (NH3-TPD). The H[Nb]ZSM-5 catalyst fully remained within the crystal framework and pore structure of HZSM-5. Meanwhile, introduction of niobium (V) endowed the catalyst with both Lewis acid and Bronsted acid sites. Catalytic fast pyrolysis (CFP) of alkali lignin was carried out through a pyrolysis and gas chromatography-mass spectrometry (Py-GC/MS) at 650 °C and atmospheric pressure. The results indicated that H[Nb]ZSM-5 can efficiently and selectively convert lignin into monoaromatic hydrocarbons (MAHs), compared to the control HZSM-5. Catalyzed by H[Nb]ZSM-5, the content of MAHs and aliphatic hydrocarbons reached 43.4% and 20.8%, respectively; while under the catalysis of HZSM-5, these values were 35.5% and 3.2%, respectively. H[Nb]ZSM-5 remarkably lowered the phenol content to approximately 2.8%, which is far lower than the content (24.9%) obtained under HZSM-5 catalysis.
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Porter, A. J., C. H. Botchway, B. Kwakye-Awuah, C. Hernandez-Tamargo, S. K. Matam, S. L. McHugh, I. P. Silverwood, N. H. de Leeuw und A. J. O'Malley. „Local and nanoscale methanol mobility in different H-FER catalysts“. Catalysis Science & Technology 12, Nr. 5 (2022): 1663–77. http://dx.doi.org/10.1039/d1cy02001c.
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Methanol dynamics in commercial and natural kaolin synthesised FER zeolite catalysts were probed using quasielastic neutron scattering and molecular modelling. Significant differences are observed due to the induced changes in catalyst composition.
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Futó, Judit Edit, und Anna Lovász. „The Long Road Towards Women’s Equality in the Labour Market : Claudia Goldin’s Research on Historical Trends and Contributing Factors“. Financial and Economic Review 23, Nr. 1 (2024): 135–54. http://dx.doi.org/10.33893/fer.23.1.135.
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Claudia Goldin won the 2023 Nobel Prize in Economics for her research on women in the labour market. Her body of work provides a broad, data-driven, historical overview of gender inequalities and evidence of the impacts of specific changes and institutional elements. We review her main findings regarding the evolution of women’s employment and earnings in light of key historical events. She documented a U-shaped labour supply curve over time, which challenged past notions of a monotonous positive relationship between economic development and women’s labour supply. Her work brought attention to complex forces that shaped the past, such as the rise of factory jobs, service-sector jobs and the contraceptive pill. Her research also points to remaining causes of inequalities, such as high-earning professions that disproportionately favour long work hours and continuous job attachment. Her work contributes to our knowledge of this social issue and has catalysed new areas of research.
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Khazzal Hummadi, Khalid, Karim H. Hassan und Phillip C. H. Mitchell. „Selectivity and Activity of Iron Molybdate Catalysts in Oxidation of Methanol“. Journal of Engineering Research [TJER] 6, Nr. 1 (01.06.2009): 1. http://dx.doi.org/10.24200/tjer.vol6iss1pp1-7.
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The selectivity and activity of iron molybdate catalysts prepared by different methods are compared with those of a commercial catalyst in the oxidation of methanol to formaldehyde in a continuous tubular bed reactor at 200-350 oC (473-623 oK), 10 atm (1013 kPa), with a methanol-oxygen mixture fixed at 5.5% by volume methanol: air ratio. The iron(III) molybdate catalyst prepared by co-precipitation and filtration had a selectivity towards formaldehyde in methanol oxidation comparable with a commercial catalyst; maximum selectivity (82.3%) was obtained at 573oK when the conversion was 59.7%. Catalysts prepared by reacting iron (III) and molybdate by kneading or precipitation followed by evaporation, omitting a filtration stage, were less active and less selective. The selectivity-activity relationships of these catalysts as a function of temperature were discussed in relation to the method of preparation, surface areas and composition. By combing this catalytic data with data from the patent literature we demonstrate a synergy between iron and molybdenum in regard to methanol oxidation to formaldehyde; the optimum composition corresponded to an iron mole fraction 0.2-0.3. The selectivity to formaldehyde was practically constant up to an iron mole fraction 0.3 and then decreased at higher iron concentrations. The iron component can be regarded as the activity promoter. The iron molybdate catalysts can thus be related to other two-component MoO3-based selective oxidation catalysts, e.g. bismuth and cobalt molybdates. The iron oxide functions as a relatively basic oxide abstracting, in the rate-controlling step, a proton from the methyl of a bound methoxy group of chemisorbed methanol. It was proposed that a crucial feature of the sought after iron(III) molybdate catalyst is the presence of -O-Mo-O-Fe-O-Mo-O- groups as found in the compound Fe2(MoO4)3 and for Fe3+ well dispersed in MoO3 generally. At the higher iron(III) concentrations the loss of selectivity is due to the presence of iron oxide patches or particles which catalyze the total oxidation of methanol, and the loss of activity to blocking of molybdenum sites.
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Chen, Wei, Mei Zeng und Junjiao Yang. „Preparation of Fenton Catalysts for Water Treatment“. Catalysts 13, Nr. 11 (30.10.2023): 1407. http://dx.doi.org/10.3390/catal13111407.
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In the heterogeneous Fenton reaction, a solid catalyst reacts with H2O2 to generate highly oxidizing free radicals, that degrade organic pollutants in aqueous solutions. In this study, impregnation calcination was used to modify activated carbon and load it with various metal compounds. The synergistic catalysis of the various metal compounds showed improved catalytic activity, and the prepared heterogeneous Fenton catalyst exhibited high catalytic activity, a wide pH range, and good stability. The concentration ratios of the Fenton catalyst impregnation solutions-were as follows: Fe3+, Cu2+, Mn2+, and Ce3+ at 0.45, 0.72, 0.19, and 0.11 mol/L, respectively. The optimal sintering temperature of AC impregnation was determined through TGA/DSC, SEM, SEM-EDS, XPS, and XRD testing. At a final calcination temperature of 900 °C, the degradation efficiency of 10 ppm methylene blue reached 98.25% at pH 5 with 5 mM H2O2. After ten soaking cycles, the degradation efficiency exceeded 90%. The structure and performance of the catalysts were characterized using EPR, BET, ICP, and UV spectroscopy, demonstrating the excellent performance of the catalyst and providing an improved treatment plan for solving wastewater problems.
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Huszár, Bianka, Réka Henyecz, Zoltán Mucsi und György Keglevich. „MW-Promoted Cu(I)-Catalyzed P–C Coupling Reactions without the Addition of Conventional Ligands; an Experimental and a Theoretical Study“. Catalysts 11, Nr. 8 (30.07.2021): 933. http://dx.doi.org/10.3390/catal11080933.
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An experimental and a theoretical study on the so far less investigated Cu(I) salt-catalyzed Hirao reaction of iodobenzene and diarylphosphine oxides (DAPOs) revealed that Cu(I)Br or Cu(I)Cl is the most efficient catalyst under microwave irradiation. The optimum conditions included 165 °C and a 1:2 molar ratio for DAPOs and triethylamine. The possible ligations of Cu(I) were studied in detail. Bisligated P---Cu(I)---P (A), P---Cu(I)---N (B) and N---Cu(I)---N (C) complexes were considered as the catalysts. Calculations on the mechanism suggested that complexes A and B may catalyze the P–C coupling, but the latter one is more advantageous both according to experiments and calculations pointing out the Cu(I) → Cu(III) conversion in the oxidative addition step. The P–C coupling cannot take place with PhBr, as in this case, the catalyst complex cannot be regenerated.