Promotional effects of Cr and Fe on Rh/SiO2 catalyst for the preparation of ethanol from CO hydrogenation

Abstract

A series of Cr and Fe promoted Rh-based silica supported catalysts were prepared by an incipient co-impregnation method. The performance of the catalysts was investigated by the hydrogenation of carbon monoxide to ethanol. The catalysts were characterized by N₂ adsorption–desorption, X-ray diffraction, transmission electron microscopy, H₂ temperature-programmed reduction, temperature programmed surface reaction, and Fourier transform infrared spectroscopy. The results revealed that addition of 0.2–0.4 wt% Cr to Rh/SiO₂ increased its activity significantly. However, further addition of 0.1–0.2 wt% Fe lowered CO conversion slightly, while the selectivity towards ethanol was enhanced significantly. Therefore, high catalytic activity and selectivity toward ethanol were achieved by simultaneous introduction of 0.4 wt% Cr and 0.2 wt% Fe to Rh/SiO₂. This may be due to improved dispersion of Rh particles, moderate ability to dissociate CO molecules, and high ratio of Rh⁺ sites to Rh⁰ sites.