Hydrogen decomposition

From the equation showing the mechanism it is evident that 1 mol of lithium aluminum hydride can reduce as many as four molecules of a carbonyl compound, aldehyde or ketone. The stoichiometric equivalent of lithium aluminum hydride is therefore one fourth of its molecule, i.e. 9.5 g/mol, as much as 2 g or 22.4 liters of hydrogen. Decomposition of 1 mol of lithium aluminum hydride with water generates four molecules of hydrogen, four hydrogens from the hydride and four from water. 

The clear solutions of the polyhydrofuUerenes in various organic solvents become inhomogeneous upon the formation of a precipitate. This, together with the broad peaks in the NMR spectra, shows the instability of these CjqH s. Thermal treatment of CjqH in the solid state at 550 °C leads to a complete reversion to Cjq (Scheme 5.3). Sublimation ofC oHjg and CjqHjj at lower temperatures (273 12 °C) was accompanied by partial loss of hydrogen. Decomposition of CjqHjj was confirmed to be a stepwise process with formation of CggHjg as an intermediate product [64]. 

The rapid kinetics of Reaction 1, the high volumetric hydrogen storage densities, and the wide range of hydrogen decomposition pressures of the AB5 hydrides initiated proposals to use them as chemical compressors, cryogenic... 

The use of AB5 hydrides as chemically or thermally driven heat pumps is intriguing (6). Since two different AB5 alloys are involved, the relationship between their respective hydrogen decomposition pressures, as a function of temperature, is the key parameter that determines the thermodynamics of heat pump action. 

It is crucial to discover the relationship between chemical compositions and hydrogen decomposition pressures of the AB5 compounds. Intermetallic compounds of lanthanide and transition metals form an interesting class of structures. The AB5 series crystallize in the hexagonal CaCus (P6/mmm) structure (see Figure 1). Generally, radius ratios (raAb) greater than 1.30 form the CaCus-type... 

Using the cell volume-decomposition pressure correlation, one predicts that aluminum substitutions in LaNis should lower the hydrogen decomposition pressures by one order of magnitude for every two-A3 increase in cell volume (12). 

Hydrogen decomposition desorption recombination (HDDR) process is the only top-down industrial process used for the preparation of coercive nanoparticles. This process applied to rare-earth transition-metal (RE-TM) alloys consists in heating the concerned alloy under hydrogen until it decomposes into a fine mixture of RE-hydride and TM. The hard magnetic phase is recombined with a much finer microstructure. This process was first developed to convert 100 microns sized cast Nd2Fei4B grains into 200-300 nm crystallites [18, 19]. Later, it has been applied to other RE-TM alloys [20, 21]. Recently, a new variation of this process has been developed towards developing texture in the final materials [22], It is briefly described below. 

A large series of complexes of the type MHx(H2)y (M = alkali metal, transition metal, and uranium) has been prepared by Andrews and coworkers by codeposition of laser-ablated metal atoms with neat hydrogen at low temperatures, typically 4K. An excellent example is WH4(H2)4 (Figure 5.12), which has been studied by matrix isolation IR spectroscopy in solid hydrogen (decomposition occurs above 7K).166... 

Mendelsohn, M.H., Gruen, D.M. and Dwight, A.E., Effect on hydrogen decomposition pressures of group lllA and IVA element substitutions for Ni in LaNi5 alloys. Materials Research Bulletin, 1978, 13(11) p. 1221-1224. 

Hydrogen reduction, chemical transport, hydrogen decomposition, metal organic CVD, plasma CVD... 

In addition to many bimolecular reactions of the radical, the uni-molecular hydrogen decomposition reaction is important in many combustion models. Seery and Bowman, McKellar and Norrish, and Fifer have all found the reaction HCO 4- M -> H 4- CO + M to be important in analytical models that describe the oxidation of formaldehyde. 

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