Synthesis of ethanol from syngas over Rh/Ce1−xZrxO2 catalysts

Rh/Ce1−xZrxO2 (x = 0–1) samples (with 2 wt% Rh loading) were prepared by a coprecipitation method using NH3·H2O as a precipitant. The resultant samples were used as catalysts for the synthesis of ethanol from syngas in a high-pressure fixed-bed flow reactor under typical reaction conditions of T = 548 K, P = 2.4 MPa, H2/CO = 2/1, and W/F = 10 g h mol−1. XRD results indicated that Zr4+ ions entered in the CeO2 lattices when x was less than 0.2 in Rh/Ce1−xZrxO2. TPR results indicated that the reducibility of CeO2 increased by inducing Zr4+ ions into the CeO2 lattices in Rh/Ce0.8Zr0.2O2. NH3-TPD and CO2-TPD results indicated that Rh/Ce0.8Zr0.2O2 contained both acid sites and base sites on the surface. Rh/CeO2 showed a CO conversion of 23.7%, which was higher than those over Rh/SiO2 (10.1%), Rh/MgO (10.8%), and Rh/ZrO2 (18.2%) at 548 K because a strong interaction between support and metal (SISM) existed in Rh/CeO2. Moreover, the CO conversion over Rh/Ce0.8Zr0.2O2 (27.3%) was higher than that over Rh/CeO2 (23.7%) due to the smaller Rh particle size and the stronger reducibility in Rh/Ce0.8Zr0.2O2. The main oxygenated products were acetaldehyde and ethanol over neutral or acidic supports supported Rh catalysts (Rh/SiO2, Rh/ZrO2), and were methanol and ethanol over basic supports supported Rh catalysts (Rh/MgO, Rh/CeO2, Rh/Ce0.8Zr0.2O2). Rh/Ce0.8Zr0.2O2 showed the highest selectivity for ethanol among various catalysts because the Ce0.8Zr0.2O2 support simultaneously possesses reducibility, acidity and basicity.