REGULATION OF REACTION INTERMEDIATE BY REACTANT IN THE WATER GAS SHIFT REACTION ON CEO2, IN RELATION TO REACTANT-PROMOTED MECHANISM

Reaction regulation by intermediate-reactant interaction in the water-gas shift reaction (H2O + CO → H2 + CO2; WGSR) on CeO2 was investigated in relation to the reactant-promoted mechanism on MgO and ZnO by FT-IR. Terminal OH groups on partially reduced CeO2 reacted with CO to produce bridge formates. Bridge formates were converted to bidentate formates above 443 K, and this transformation occurred at room temperature when water coexisted. The decomposition of the surface formates was affected by the water molecule; 70% of the bidentate formates decomposed to OH + CO (backward decomposition) and 30% of them decomposed to H2 + CO2 (forward decompose to H2 and unidentate carbonates. The decomposition of the unidentate carbonates to CO2 was promoted by coadsorbed water. The results are also discussed in comparison with the formates increased from 94 kJ mol-1 without water to 193 kJ mol-1 with water. Isotope effects were observed on the hydrogen atoms of both formate and hydroxyl, giving a proposed transition state in the reaction mechanism. The bidentate formates reacted with the adjacent hollow-site OH to decompose to H2 and unidentate carbonates. The decomposition of the unidentate carbonates to CO2 was promoted by coadsorbed water. The results are also discussed in comparison with the results for WGSR on MgO and ZnO. © 1992.