Coproduction of methanol and dimethyl ether from biomass-derived syngas on a Cu-ZnO-Al2O3/γ-Al2O3 hybrid catalyst

The coproduction of methanol (MeOH) and dimethyl ether (DME) from biomass-derived synthesis gas on the coprecipitated Cu-ZnO-Al2O3/gamma-Al2O3 hybrid catalysts has been investigated to overcome the equilibrium conversion of CO on the MeOH only synthetic reaction at the H-2-decificient condition. Two different types of gamma-Al2O3 were employed as the solid-acid component of hybrid catalyst: one prepared by a precipitation method and the other prepared by a sol-gel method. Several hybrid catalysts were prepared by the coprecipitation method in the slurry of gamma-Al2O3 with the variation in the weight ratio of MeOH synthesis catalyst (Cu-ZnO-Al2O3) to solid-acid catalyst (gamma-Al2O3) as well as by changing aging time during synthesis. The catalytic activity results revealed that the best yield of MeOH and DME with concomitant decrease in the CO2 formation was obtained on the hybrid catalyst containing gamma-Al2O3 prepared by the sol-gel method with an aging time of 6 h. The hybrid catalysts were characterized by using the BET surface area measurements, NH3 temperature programmed desorption (NH3-TPD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), and X-ray diffraction (XRD) methods. The observed catalytic properties were related to the surface area of Cu metal, dispersion of Cu-ZnO-Al2O3 particles, and reducibility and acidity of hybrid catalysts. The enhanced catalytic activity with low selectivity to CO2 is attributed to the facile reducibility of well-dispersed copper oxides at low temperatures and also to the benign acid strength of the hybrid catalysts.