Direct synthesis of dimethyl ether from biomass-derived syngas over Cu–ZnO–Al2O3–ZrO2(x)/γ-Al2O3 bifunctional catalysts: Effect of Zr-loading

A series of Cu–ZnO–Al₂O₃–ZrO₂ catalysts with varying Zr contents was prepared as methanol synthesis catalyst by a co-precipitation method and characterized by inductively coupled plasma, N₂ physisorption, N₂O decomposition, H₂-temperature-programmed reduction, X-ray diffraction, and H₂/CO/CO₂-temperature-programmed desorption. Addition of a suitable amount of ZrO₂ to the Cu–ZnO–Al₂O₃ catalysts increased the Brunauer–Emmett–Teller surface areas and copper surface areas, and improved copper dispersion and reducibility of copper oxide. However, excessive addition of Zr resulted in larger Cu crystallite sizes after catalyst reduction. The Cu–ZnO–Al₂O₃–ZrO₂ catalysts were mixed physically with methanol dehydration γ-Al₂O₃ catalyst. The resulting catalysts were examined for the catalytic synthesis of dimethyl ether from biomass-derived syngas. Activity tests were conducted in a continuous flow-type fixed-bed reactor. The Cu–ZnO–Al₂O₃–ZrO₂/γ-Al₂O₃ bifunctional catalyst with 3 mol% Zr exhibited the best catalytic activity and stability. The well-dispersed copper particles with high reducibility and high Cu surface area in the bifunctional catalysts were responsible for the high catalytic performance.