Catalysis by heteropoly compounds. VIII. Reduction-oxidation and catalytic properties of 12-molybdophosphoric acid and its alkali salts. The role of redox carriers in the bulk
Catalysis by heteropoly compounds. VIII. Reduction-oxidation and catalytic properties of 12-molybdophosphoric acid and its alkali salts. The role of redox carriers in the bulk
复制标题
杂多化合物催化。
DOI：
10.1021/j100247a021
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
M. Misono
中科院分区：
文献类型：
--
作者：
N. Mizuno;Tetsuji Watanabe;M. Misono
The catalytic oxidationof CO and H2 over 12-molybdophosphoric acid and its Cs and Na salts has been studied at 350 C in a closed circulating system. By the quantitative comparison of these rates with the rates of stoichiometric reduction of catalysts by CO and H2 and reoxidation by 02, it was demonstrated that (i) these catalytic oxidationsproceeded by a redox mechanism, and (ii) in these reactions the difference in the redox carriers in the bulk was closely reflected, as was found previously for stoichiometric reactions. For example, the rate of catalytic oxidation of CO was proportional to the surface area of catalyst, while the rate of catalytic oxidation of H2 depended very little on the surface area. In the oxidation of CO, the surface polyanions are mainly involved in catalysis, owing toslow diffusion of the lattice oxideion, ie, the redox carrier. On the other hand, in the latter reaction, the redox carriers are protons and electrons which migrate in the bulk, so that all polyanions in the bulk can take part in the redox cycles. Therefore, although the orderof the catalytic activity differed considerably between the two reactions, it decreased monotonously with the alkali content (bothNa and Cs) when the rate of CO oxidation was normalized to the surface area and the rate of H2 oxidation to the weight. It was further found that linear relationships exist respectively for CO and H2 between the rate of catalyticoxidation and the rate of stoichiometric reduction. These results were discussed on the basis of a redox mechanism.
