Effect of Li additive on CO2 hydrogenation reactivity of zeolite supported Rh catalysts Original Research Article

We performed CO2 hydrogenation over Li-promoted Rh ion-exchanged zeolite catalysts (Li/RhY). As the amount of added Li increased, the main product transformed from methane to CO. Simultaneously, we observed promotion of ethanol production, as well as methanol production. Moreover, when 1.8% of CO was 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 ion-exchanged zeolite catalyst (RhY). We studied the mechanism of the promotion effect of Li by means of in situ FT-IR observations. IR spectra of CO/CO2 adsorption and those for subsequent TPR were observed. On RhY, CO2 molecules were adsorbed as terminal CO species which were the same as those found 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/Rh=10). The results indicate that the Li additives created a new reaction path on the catalyst surface, where CO2 adsorption enhancement as well as stabilization of adsorbed CO species occurred.