ACTIVE-SITES OF SOLID ACIDIC CATALYSTS .3. INFRARED STUDY OF THE WATER GAS CONVERSION REACTION ON ALUMINA

The water gas conversion reaction (CO2 + H2 CO + H2O) on alumina was investigated by infrared spectroscopy over a temperature range between 200 and 600 °C, following the kinetic study reported as Part II of this series, ir spectra were recorded during the reaction which proceeded unidirectionally at a steady rate. Thus formate ion was found on the surface in both forward and backward reactions. The results also showed that the concentration of the surface formate ion responded quickly to the change of the reactant pressure and that the rates of the decomposition of the surface formate were in reasonable agreement with those of the overall reaction at the same surface coverage. It was therefore concluded that the surface formate ion found in this study is the intermediate of the water gas conversion reaction on alumina. Some formate ions, however, are so strongly held on the surface that they do not participate in the reaction below 500 °C. Although the rate-determining step of the CO2 + H2 reaction is the decomposition of the surface formate ion in the absence of water, the rate-determining step is shifted to the formation of formate ion in the presence of water. © 1979.