Improved stability of Pd/HZSM-5 bifunctional catalysts by the addition of promoters (CeO2, CaO) for the One-step synthesis of dimethyl ether from Sulfur-containing CO2 hydrogenation

Pd/HZSM-5 bifunctional catalysts modified with CeO2 and Ca) promotors were prepared by impregnation. The combined promotor effects on the activity and stability of Pd/HZSM-5 bifunctional catalysts for one-step-synthesis of dimethyl ether (DME) from the sulfur-containing CO2 hydrogenation at 250 degrees C and GHSV of 1600 h(-1) under three megapascals were investigated. The physical and chemical characteristics, activity, sulfur resistance stability and carbon deposition of the bifunctional catalysts Were analyzed by XRD, N-2 adsorption, FT-IR, CO2-TPD, NH3-TPD, H-2-TPR and TPO-TG. Correlations were identified between the quantity of the combined promotors and the moderate acidity level of the surface and active Pd dispersion of the bifunctional catalyst. The optimum stability of Pd/HZSM-5 bifunctional catalyst occurred with the addition of 3 wt% CeO2 and 1 wt% CaO, and the CO2 conversion and DME selectivity remained higher than 19% and 67% after a 20 h reaction. The rates of carbon-deposition, the moderate-acidity-loss and the Pd-site-loss were reduced by 61.1%, 38.79% and 22.17%, respectively, compared with promotor-free Pd/HZSM-5. (C) 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.