Titanium hydrogen chemisorption

Cremaschi P and Whitten J L 1987 The effect of hydrogen chemisorption on titanium surface bonding Theor. Chim. Acta. 72 485-96... 

Burch and Flambard (113) have recently studied the H2 chemisorption capacities and CO/H2 activities of Ni on titania catalysts. They attributed the enhancement of the catalytic activities for the CO/H2 reaction (after activation in H2 at 450°C) to an interfacial metal-support interaction (IFMSI). This interaction is between large particles of Ni and reduced titanium ions the Ti3+ is promoted by hydrogen spillover from Ni to the support, as pictured in Fig. 8. The IFMSI state differs from the SMSI state since hydrogen still chemisorbs in a normal way however, if the activation temperature is raised to 650°C, both the CO/H2 activity and the hydrogen chemisorption are suppressed. They define this condition as a total SMSI state. Between the temperature limits, they assumed a progressive transition from IFMSI to SMSI. Such an intermediate continuous sequence had been... 

The latest experimental evidence suggest the presence of titanyl groups (Ti=0) in the structure188 (Scheme 9.3). H202 is activated via chemisorption on these groups with the formation of a surface titanium peroxo complex (13). It may exist in the hydrated or open diradical form and initiates hydrogen abstraction. Rapid... 

The relative ease with which hydrogen chemisorbs on the surface of a metal oxide surface mainly depends on the chemical nature of the oxide and on the O-vacancies. Thus, hydrogen adsorbs dissociatively on a perfect titanium oxide surface [10,11]. The energetically most favorable mode for the adsorption of atomic hydrogen is the adsorption on the outermost O atom, accompanied by the reduction of a Ti atom. In this mode, protons are formally adsorbed while an equivalent amount of Ti(IV) atoms are reduced to Ti(III). Theoretical calculations have demonstrated that H adsorption is less favorable on a defective surface than on a perfect surface. However, the best adsorption mode for the atomic chemisorption on a defective surface is heterolytic adsorption, which involves two different adsorption sites one H+/0= and one H on the surface. This adsorption mode is best on irreducible oxides such as MgO however, it is less favorable than adsorption on the perfect Ti02 surface [10]. The heat of atomic adsorption in all cases is very weak and dissociation onto the surface is unlikely. The molecular adsorption (physisorption), thus, remains the most stable system. 

W. J. Lo, Y. W. Chung, and G. A. Somoijai, Electron spectroscopy studies of the chemisorption of oxygen, hydrogen and water on the titanium dioxide (100) surfaces with varied stoichiometry evidence for the photogeneration of titanium (3+) and for its importance in chemisorption. Surf. Sci. 77 199 (1978). 

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