CO hydrogenation over Pd/HZSM-5 catalysts: Temperature-programmed desorption, (CO)-C-13/(CO)-O-18 isotope analysis, and in-situ infrared spectroscopy

Abstract

Temperature-programmed desorption(TPD) and (CO)-C-13/O-18 isotope analysis were employed to study the selectivity changes with metal dispersion in CO hydrogenation over Pd/HZSM-5 catalysts. It was confirmed that the major products were methanol and dimethylether on the catalysts with higher Pd dispersion while the selectivity shifted to hydrocarbons on the catalysts with lower Pd dispersion. For the catalysts with large Pd particles, the TPD and isotope analysis showed that the CO adsorption was stronger and that the CO dissociation into surface carbon and CO2 occurred more rapidly. The changes in selectivity of CO hydrogenation with metal dispersion were attributed to the differences in the adsorption strength and dissociation rate. The in-situ FT-IR study suggested that the formates should be the surface intermediates for the formation of methanol.