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.