Effect of Li additive on CO2 hydrogenation reactivity of zeolite supportedRh catalysts

We performed CO2 hydrogenation over Li-promoted Rh ion-exchanged zeolite ca talysts (Li/RhY). As the amount of added Li increased, the main product tra nsformed from methane to CO. Simultaneously, we observed promotion of ethan ol production, as well as methanol production. Moreover, when 1.8% of CO wa s mixed with the reactant gas, the selectivity for ethanol was increased to as high as 13% on Li/RhY (Li/Rh=10), but no influence was observed on Rh i on-exchanged zeolite catalyst (RhY). We studied the mechanism of the promot ion effect of Li by means of in situ FT-IR observations. IR spectra of CO/C O2 adsorption and those for subsequent TPR were observed. On RhY, CO2 molec ules were adsorbed as terminal CO species which were the same as those foun d in CO adsorption. However, on Li/RhY, a new peak appeared at 1618 cm(-1) by CO2 adsorption and relatively stable species were formed on Li/RhY (Li/R h=10). The results indicate that the Li additives created a new reaction pa th on the catalyst surface, where CO2 adsorption enhancement as well as sta bilization of adsorbed CO species occurred. (C) 1998 Elsevier Science B.V. All rights reserved.