La, V, and Fe promotion of Rh/SiO_2 for CO hydrogenation: Effect on adsorption and reaction

摘要

This study is a continuation of the research reported recently that showed La and V doubly promoted Rh/SiO_2 catalysts to be active and selective for the synthesis of ethanol from syngas. In this work, the effect of Fe on Rh-La-V/SiO_2 was examined and the role of each individual promoter was further scrutinized. Several series of promoted Rh/SiO_2 catalysts were prepared by incipient wetness and characterized by BET, XRD, TEM, FTIR, TPR, and H_2-TPD. The catalytic activity was tested using a fixed-bed differential reactor at 230 °C and 1.8 atm. It was found that the addition of 0.8 wt% Fe, 2.6 wt% La, and 1.5 wt% V to 1.5 wt% Rh/SiO_2 resulted in the highest selectivity to ethanol (34.6%) and a moderate activity compared to other promoted catalysts. The investigation based on the catalytic performance and other characterizations of Rh/SiO_2 promoted by different promoters suggests that the primary promoting effects of La, V, and Fe are different. The main effects of the addition of different promoters in this study appear to be increasing CO adsorption and insertion for La, decreasing CO adsorption but enhancing CO dissociation and chain growth for V, and decreasing CO adsorption but enhancing hydrogenation for Fe. The synergistic effects of the multiple promoters indicate that the key in catalyst design for ethanol synthesis from syngas is to optimize CO dissociation, hydrogenation, and CO insertion in a balanced way.