Bonding and Charge Transfer in Group VIII-Ti Systems

Bonding and Charge Transfer in Group VIII-Ti Systems 

Our own X-ray absorption measurements of Rh-Ti compounds exhibit suggestive similarities with the reduced Rh/Ti02 catalysts. First of all, as described above, the EXAFS analysis of high-temperature-reduced Rh/Ti02 (100% dispersed) catalyst provides evidence for the formation of 

Metal-Support Interactions In Other Oxide Supports and Related Phenomena 

A vaguely defined metal-support interaction has frequently been used to describe modifications of metal properties observed when oxide-supported catalysts are thermally treated. After the original report by Tauster et al. (13) on the SMSI effect in Ti02-supported catalysts, the same authors (32) extended their operational definition to other reducible oxides. Consequently, several investigations were conducted using reducible oxide supports such as vanadia (87, 106, 154-156), niobia (157-162), or ceria (95). In general, the same characteristic features of Ti02 were obtained for these oxides, i.e., suppression in H2 and CO chemisorption capacity, suppression of catalytic activity for several reactions, promotion of the CO/H2 reaction, and reversibility by oxidation. 

In a recent international conference, Kunimori et al. (162a) reported that the Rh-Nb205 interaction increases with the temperature of calcination as evidenced by the formation of a RhNb04 phase, identified by X-ray diffraction, when Nb205-promoted Rh/Si02 catalysts are calcined at 973 K. Subsequent TPR studies indicate that as the Rh-Nb205 interaction increases, the Rh becomes more difficult to reduce. 

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