Structure Sensitivity Study of Propane Dehydrogenation on Cobalt Catalysts: HCP versus FCC
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In heterogeneous catalysis, it is crucial to understand the structure sensitivity in order to elucidate the reaction mechanism and rationally design optimal catalysts. In this work, propane dehydrogenation (PDH) and side reactions (cracking and deep dehydrogenation) were studied by density functional theory calculations on Co catalysts with different crystallographic structures: face-centered cubic (FCC) and hexagonal closed packed (HCP). Wulff construction reveals that the most stable facet of each crystallographic structure, viz. Co(111) and Co(0001), cover 76.2% and 19.4% of the exposed surface. Various reaction pathways for PDH, deep dehydrogenation, and cracking were explored on Co(111) and Co(0001). Microkinetic simulation results suggest that PDH proceeds through both dehydrogenation pathways (via 1-propyl or 2-propyl intermediate) on Co(111), while it favors path A (via 1-propyl intermediate) on Co(0001). At typical reaction conditions of PDH, Co(111) is more active than Co(0001) by 1.3 times, while the latter is more selective toward propylene production and more resistive to coke formation. Compared to Pt(111), both Co surfaces are more active for PDH while Co(0001) is also more selective toward propylene formation. This work provides fundamental insights into the crystallographic structure sensitivity of propane dehydrogenation on a Co catalyst and useful guidance to achieve better catalytic performance for a Co catalyst.Keywords:
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The yields and selectivities in both the catalyzed and non-catalyzed oxidative dehydrogenation of propane were found to increase with increasing pressure. The results showed that the maximum yields of valuable ODH products could be obtained by adjusting only reactants' partial pressure, while keeping their ratio constant.
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Abstract Dehydrogenation plays a very important role in both nature and human civilization. In chemical industry, dehydrogenations are used to produce propene, butene, butadiene, isobutene, and isopropene from the corresponding alkanes. In living organisms (both animals and plants), respiration is actually a process of oxidation wherein some steps involve dehydrogenation. Almost all dehydrogenation reactions require a catalyst. Catalysts for dehydrogenation can be classified into two main categories: conventional catalysts (including inorganic and organic) and enzymes. This article focuses on the application of biological catalysts in dehydrogenation and oxidation reactions occurring in nature. Biological dehydrogenation is illustrated from two aspects: chemistry of biocatalytic dehydrogenation and biocatalysts of dehydrogenation. Biological dehydrogenation reactions usually occur at very mild conditions and have very high selectivity. The catalysts for these processes are usually enzymes (or cells producing these enzymes). Enzymes having dehydrogenation capacities are usually dehydrogenases, oxidases, etc., and most of them need a coenzyme or a cofactor to work with them.
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The presence of Bi 2 O 3 in the lattice or on the surface of ZrO 2 -based materials provokes creation of coordinatively unsaturated Zr 4+ cations under reductive conditions. Such sites are catalytically active for non-oxidative dehydrogenation of propane.
Propane
Oxidative addition
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Propene is a colorless combustible unsaturated gaseous hydrocarbon. Domestic and foreign development of preparing propene by propane dehydrogenation is outlined in this paper. Thermodynamics of propane dehydrogenation is analysed and it is reported that the reaction is reversible,moleculeincreasing and intensely thermonegative;catalyst of good selectivity must be adopted in order to increase propane selectivity. Several methods of preparing propane are summarized, which include propane dehydrogenation in membrane reactor and oxidative dehydrogenation where oxygen and carbon dioxide are used as oxidant.
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Abstract This study investigated non-oxidative propane dehydrogenation over TiH2. It was found that H2 co-feeding positively affected dehydrogenation, improving the propylene formation rate. In situ spectroscopic characterization of TiH2 in the presence of H2 indicated that partially dehydrogenated titanium hydrides are active for dehydrogenation.
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