Titanium hydrogen role

Thus, for similar values of ns, the entropy at infinite dilution for TiMo/H2 is about 3.4 eu/H more negative than that for 0-Ti/H2. An explanation for this difference might be that the molybdenum atoms in the metal lattice block potentially available interstitial sites for hydrogen occupation, resulting in nonrandom occupation of sites at low hydrogen content. Rudman (24) proposed such a role for aluminum in titanium. We presently are gathering more data for alloys of varying molybdenum composition to test this hypothesis. 

In nonaqueous, aprotic media, the hydrogen overvoltage does not play any role. Commonly used cathode materials are lead, aluminum, copper, titanium, steel, and carbon of all kinds. 

Study of these new catalysts is intensive. Small molecular-weight distribution was demonstrated by Petrova (112) and by Baulin et al. (113). In addition, polymer substrates have been used (114-116) in order to increase lifetime and activity. As shown by Suzuki (36), stabilization is caused by inhibition of reduction by polymeric ligands. Karol (117, 118) described the reaction of chromocene with silica to form highly active catalysts sensitive to hydrogen. An unknown role is played by the structure mt—CH2—CH2—mt which is formed with ethylene and reduced forms of titanium (119). For soluble systems, it has been shown that the mt—CH2—CH2—mt structure is formed in a biomolecular reaction with /3-hydrogen transfer (120). It was considered that this slow, but unavoidable, reaction is the reason for changes in activity during reaction and that the only way to avoid it is to prevent bimolecular reaction of two alkylated species. 

Clerici and Bellussi" have shown that hexane in methanol can be selectively oxidized to 2-hexanol, 3-hexanol, 2-hexanone and 3-hexanone using a mixture of oxygen and hydrogen at 25 - 30 . The reactions were run in the presence of HCl for 20 - 24 hours. Several titanium silicalite catalysts containing Pd (0.01 mol ratio to Ti02) were prepared and used in these reactions. Presumably, hydrogen plays the role of an electron-donor activating the Ti catalyst. However, no explanations were offered. 

The critical role played by the Ti catalyst in helping hydrogen cycling in alanates has been an on-going research subject for theoreticians. Ti-doped NaAlH4 system has been most studied as a prototypical system for materials of similar structures. The exact nature of the titanium catalyst action and the location of the Ti atoms still remain unclear however, several different theories have been elucidated to explain the observed reaction dynamics. Three doping hypotheses have been applied to study the catalytic effects with DFT simulations. One is to search for evidence of whether Ti exists as a bulk dopant on the sodium alanate and if... 

Therefore, the promoting effect of titanium oxide species might be described as a synergistic effect on both CO and H2. In the next section we discuss the role of hydrogen in the metal-support interaction, which perhaps may be related to its role in the promotion of the CO-H2 reaction. 

The exact role of catalysts, such as titanium, scandium, or cerium, in improving the hydrogen kinetics in NaAlH4 is not completely understood. The local structure of scandium and the formation of different species in ScCla-doped NaAlH4 by Na, Al, and " Sc NMR was studied by Ver-kuijlen et... 

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