Highly efficient Zr-substituted catalysts CuZnAl1−xZrxO used for hydrogen production via dimethyl ether steam reforming

Abstract

A series of CuZnAl1−xZrxO catalysts with different weight ratios of ZrO2/(Al2O3 + ZrO2) were prepared by co-precipitation and used for catalytic production of hydrogen via the route of dimethyl ether steam reforming (DME SR). Multiple techniques such as N2 physisorption, X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H2-TPR), N2O chemisorption and X-ray absorption fine structure (XAFS, including XANES and EXAFS) were employed for catalyst characterization. It is found that the relative contents of Al and Zr greatly influence the catalytic performance of the catalysts including DME conversion, H2 yield and CO/CO2 selectivity. The catalyst CuZnAl0.8Zr0.2O shows not only the highest DME conversion but also the highest H2 yield in the whole reaction temperature region of 300–425 °C. Poorly crystallized CuO and ZnO phases were identified by XRD for CuZnAl1−xZrxO catalysts. The crystallinity of them increases with the decrease of Al content. The partial substitution of Al by Zr improves both the reducibility and the dispersion of copper species as revealed by H2-TPR results. The N2O chemisorption and Cu K-edge XAFS results conformably indicate that the Cu species in CuZnAl0.8Zr0.2O possesses the highest dispersion. In addition, after used in DME SR reaction, the catalyst CuZnAl0.8Zr0.2O possesses the highest Cu+/Cu0 ratio, as calculated by Cu K-edge XANES fitting. The lowest CO selectivity during DME SR over this catalyst is highly related to the highest Cu+/Cu0 ratio.