Dimethyl ether synthesis from CO2 hydrogenation on La-modified CuO-ZnO-Al2O3/HZSM-5 bifunctional catalysts

A series of CuO-ZnO-Al2O3-La2O3/HZSM-5 bifunctional catalysts with various La loadings for dimethyl ether (DME) directly synthesized from CO2 hydrogenation were prepared. The catalysts were characterized with N-2 adsorption-desorption, X-ray diffraction (XRD), H-2 temperature-programmed reduction (H-2-TPR), NH3 temperature-programmed desorption (NH3-TPD) and N2O titration techniques, and tested for the synthesis of DME directly from CO2 hydrogenation in a fixed-bed reactor. The results showed that the reducibility, dispersion of bifunctional catalysts were strongly dependent on the addition of La. With the addition of appropriate amount of La, the crystallite size of CuO was decreased and the dispersion of Cu on the surface was enhanced, which resulted in the increased conversion of CO2. It was also found that the selectivity to DME was related to the intensity and amount of strong acid site on the catalyst surface. The presence of La favored the production of DME, and the optimum catalytic activity was obtained when the amount of La was 2.0 wt.%.