Dehydrogenation mechanism in catalyst-activatedMg H 2
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A small amount of ${\mathrm{Nb}}_{2}{\mathrm{O}}_{5}$ catalyst is known to substantially improve the desorption thermodynamics and kinetics of $\mathrm{Mg}{\mathrm{H}}_{2}$. Using density functional theory in combination with ab initio molecular dynamics simulation, we provide theoretical understanding of the mechanism of dehydrogenation in Nb doped $\mathrm{Mg}{\mathrm{H}}_{2}$. We show that the substitution of Nb at the Mg site followed by the clustering of H around Nb is a likely pathway for hydrogen desorption. We also find that dehydrogenation from the vicinity of Mg vacancies is exothermic. However, the vacancies are not likely to play a significant role in hydrogen desorption due to their high formation energy $(3.87\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$.Keywords:
Exothermic reaction
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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.
Propene
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Alkali-metal hydrazinidoboranes have been recently investigated as a new stable high-capacity material for hydrogen storage, necessitating an exploration of the dehydrogenation mechanism for further developments in this field. Herein, we present a first systematic study of the structure and dehydrogenation mechanism of sodium hydrazinidoborane (NaHB) with three possible pathways considered: pathway A, corresponding to unimolecular dehydrogenation; pathway B, featuring dehydrogenation of the (NaHB) 2 dimer via two different sub-pathways, and pathway C, corresponding to direct dehydrogenation (as compared to B). The calculated rate of the most probable dehydrogenation pathway (B, 3.28[Formula: see text]min[Formula: see text] is similar to that obtained experimentally (12.26[Formula: see text]min[Formula: see text], supporting the validity of our findings.
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The development of preparing propene by propane dehydrogenation is outlined in this paper,including catalytic dehydrogenation,oxidative dehydrogenation and dehydrogenation in the membrane reactor.Although,catalytic dehydrogenation of propane has been commercialized,the performance of catalysts needs to be further improved.The catalytic systems and their main results of propane oxidative dehydrogenation to propylene are viewed.Compared with the traditional dehydrogenation,the membrane reactor has its advantages in propane dehydrogenation.If the activity and stability of catalysts for propane dehydrogenation and the hydrogen perm-selectivity of the membrane reactor can be further improved,the membrane reactor is a promising method for the dehydrogenation of propane.
Propane
Propene
Membrane reactor
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The development of preparing propene by propane dehydrogenation is outlined,and catalytic dehydrogenation,oxidative dehydrogenation and dehydrogenation in the membrane reactor is summarized and analyzed.Although,catalytic dehydrogenation of propane has been commercialized,the performance of catalysts needs to be further improved.The catalytic systems and their main results of propane oxidative dehydrogenation to propylene are viewed.Compared with the traditional dehydrogenation,the membrane reactor has its advantages in propane dehydrogenation.If the activity and stability ofcatalysts for propane dehydrogenation and the hydrogen perm-selectivity of the membrane reactor can be further improved,the membrane reactor is a promising method for the dehydrogenation of propane.
Propane
Propene
Membrane reactor
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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.
Propane
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The use of a membrane reactor for shifting equilibrium controlled dehydrogenation reactions results in increased conversion, lower reaction temperatures and fewer by-products. Results will be presented on a palladium membrane reactor system for dehydrogenation of 1-butene to butadiene, with oxidation of permeating hydrogen to water on the permeation side. The heat released by the exothermic oxidation reaction is utilized for the endothermic dehydrogenation reaction.
Exothermic reaction
Endothermic process
Membrane reactor
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