Au/SiO2-Based Catalysts for Propanol/Propanal Synthesis from CO2, C2H4, and H2 in a Dual-reactor System

CO2 hydrogenation to value-added products is a promising approach for controlling CO2 emissions into the atmosphere. In this work, we introduce and validate a dual-reactor approach for improving the oxo-selectivity (propanol plus propanal) in the direct production of these oxygenates from C2H4, CO2, and H2 over SiO2-supported Au-containing catalysts. The reverse water gas shift reaction was performed at high temperatures in the upstream-located reactor, while the hydroformylation reaction of ethylene was carried out at lower temperatures in the downstream-located reactor without the need for expensive preseparation of the product mixture from the first reactor. Both reactors operated at the same pressure. The effects of temperature, total pressure, and the ratio of CO/H2 adjusted through temperature in the upstream-located reactor, as well as the Au loading content and the Cs doping content on the catalytic activity and oxo-selectivity were investigated. The highest oxo-selectivity of 60% at ethylene conversion of 15% was achieved. The size of Au crystallites was established to be an important selectivity-governing factor. This catalyst characteristic depends on Au loading and Cs presence.