Hydrogen adsorbed titanium

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. 

Helium [7440-59-7] M 4.0. Dried by passage through a column of Linde 5A molecular sieves and CaS04, then passed through an activated-charcoal trap cooled in liquid N2, to adsorb N2, argon, xenon and krypton. Passed over CuO pellets at 300° to remove hydrogen and hydrocarbons, over Ca chips at 600° to remove oxygen, and then over titanium chips at 700° to remove N2 [Arnold and Smith 7 Chem Soc, Faraday Trans 2 77 861 1981]. 

Figure 1 shows the FT-1R spectra of samples dispersed in KBr. All the spectra display a strong band at 960 cm 1. This band has been assigned to Si-O-Ti bonds [14] or to Si-OH groups [15, 16]. It is usually taken as the evidence for isomorphous substitution of Si by Ti, but it cannot be used to determine quantitatively the content of titanium into the framework of mesoporous materials [17]. In addition, the broad pattern between 3700 and 3000 cm 1, originated from hydrogen-bonded surface OH groups as well as from adsorbed H20 [18], decreases dramatically in the silylated samples. 

When Bandi and Kuhne studied the reduction of C02 to methanol at mixed Ru02 + Ti02 electrodes (ratio 3 1) produced by coating titanium foil [65], in a C02-saturated KHC03 solution at a current density of 5 mA cm 2, only minimal C02 reduction was observed. However, the addition of electrodeposited Cu led to faradaic efficiencies of up to 30% for methanol at potentials of approximately -0.972V (versus SCE). Trace amounts of formic acid and ethanol were also observed. In this case, the rate-limiting step was surmised to be the surface recombination of adsorbed hydrogen and C02 to yield adsorbed COOH". 

Here we report a technique of direct synthesis of the photocatalytically active mesoporous composites Ti02/M (M = Cu, Ni, Co, Fe, Zn, Ag etc.) via photochemical reduction of the metal cations adsorbed on highly developed surface of a mesoporous titanium dioxide. The Ti02/M composites were found to be efficient photocatalysts of hydrogen evolution from water-alcohol mixtures. 

The pre-edge intensity very often increases only upon removal of any adsorbed water vapor [64]. The water vapor acts as a ligand, which changes the intensity of the pre-edge peak. This is crucial for the understanding of how the oxidation catalysis works, since TS-1 is mostly used in aqueous solutions with hydrogen peroxide. It has been suggested that EXAFS can show the presence of titanium peroxo species on TS-1 [65]. 

The mechanism proposed involves adsorption of propene onto gold, and the reaction of the adsorbed species with oxygen species (hydroperoxo and peroxo species) formed at the interface between the gold particles and the titanium support, through the reductive activation of oxygen with hydrogen [36j]. Scheme 6.7 shows the reaction mechanism proposed in the literature [37b,g,h]. 

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