Gallium doping reaction with

Fig. 30. Differential heats of reaction at 30°C of a stoichiometric mixture (CO + 02) at the surface of a freshly prepared sample of gallium-doped nickel oxide. Reprinted from (53) with permission J. Chim. Phys.

Carbonates, diaryl, reactions with cyclohepta-amylose, 23 240 Carbon dioxide adsorption, 21 44 on chromia, 20 27 on gallium-doped NiO, 22 247-251 on nickel catalysts, 22 87-96 dissociative, 22 93-96... 

The calorimetric study of interactions on the surface of gallium-doped nickel oxide therefore yields results which are similar to those obtained on pure Ni0(250°), although the incorporation of trivalent ions changes somewhat the surface affinity toward oxygen. In both cases, two reaction mechanisms for the production of gaseous carbon dioxide are probable. In mechanism II, a reaction intermediate, C03-(ads) is formed whereas, in mechanism I, gaseous carbon dioxide is produced directly by the interaction of carbon monoxide with adsorbed... 

It is equally possible to impart n-type conductivity to an insulator by suitable doping. An example is provided by the reaction of small amounts of gallium oxide, Ga203, with zinc oxide, ZnO. In this case, Ga ions substitute for Zn ions in the zinc oxide structure to form Ga tZni To maintain charge neutrality, one electron must be added to balance each Ga + ion in the structure. It is generally believed that these rest on Zn ions to generate... 

Thus the weakly Bronsted acidic boron zeolites allow acid-catalyzed reactions to be carried out with high selectivity. Gallium substitution gives effective, sulfur-resistant catalysts for the synthesis of aromatics from lower alkanes, without the need for noble metal doping [8], The nonacidic titanium siUcalite exhibits very interesting properties in selective oxidation reactions with H2O2 [T32]. 

The products of the reactions of silanetriols with gallium [41] and indium alkyls [42] are very similar to those obtained from aluminum alkyls described above. The interest in Ga containing siloxanes stems from the known catalytic activity of Ga-doped zeolites in the dehydrogenation reactions of alkanes. The reactions of silanetriols 15 and 16 with GaMej or InMes in refluxing hexane/1,4-dioxane lead to the cubic Ga/In siloxanes [RSi03M-THF]4 (M = Ga 38, 39 In 40, 41), respectively. In the resulting products, the Ga and In centers are coordinated to a dioxane solvent molecule These compounds have a very similar structure to that of aluminosiloxanes 30-33 shown in Scheme 7. 

On metal electrodes, the transfer coefficients typically approach 0.5. Generally, the transfer coefficients for redox reactions on moderately doped diamond electrodes are smaller than 0.5 their sum a +p, less than 1. We recall that an ideal semiconductor electrode must demonstrate a rectification effect in particular, on p-type semiconductors, reactions proceeding via the valence band have the transfer coefficients a = 0, P = 1, and thus, a +p = 1 [7]. Actually, the ideal behavior is rarely the case even with single crystal semiconductor materials manufactured by use of advanced technologies ( like germanium, silicon, gallium arsenide, etc.). The departure from the ideal semiconductor behavior is likely to be caused by the fact that the interfacial potential drop appears essentially localized, even in part, in the Helmholtz layer, due, e.g., to a high density of surface states, or the surface states directly participate in the electrochemical reactions. As a result, the transfer coefficients a and p have intermediate values, between those characteristic of semiconductors (O or 1) and metals (-0.5). Semiconductor diamond falls in with this peculiarity. However, for heavily doped electrodes, the redox reactions often proceed as reversible, and the transfer coefficients approach 0.5 ( metaMike behavior). 

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