SiO2改性的Cu-ZnO/HZSM-5催化剂及合成二甲醚性能

The silica modified Cu-ZnO/HZSM-5 catalysts were prepared via the co-precipitation sedimentation method using sodium silicate as silicon source, sodium carbonate as precipitant. These catalysts were characterized by means of XRD, SEM, H2-TPR, XPS techniques, and their catalytic performance in dimethyl ether (DME) synthesis from CO2 hydrogenation were evaluated in a fixed-bed reactor. It was found that the modification of SiO2 had a remarkable effect on the structures of the catalyst precursors, the diffraction peaks of aurichalcite (Zn3Cu2(OH)6(CO3)2) at 2θ=13.2° weakened and broadened with the SiO2 content, interestingly, those peaks disappeared when SiO2 content was beyond 3.5%. The XRD and SEM studies of the calcined catalysts showed that silica retarded the growth of CuO and ZnO crystals and inhibited the agglomeration of the calcined catalysts. The TPR profiles of silica modified Cu-ZnO/HZSM-5 catalysts revealed that the reduction peaks and the peak temperature were different from that of the Cu-ZnO/HZSM-5 catalyst without silica modification. The catalytic performance showed that the activity first increased and then decreases with the increase of the SiO2 content. The CO2 conversion of 28.53% and DME yield of 16.34% was obtained over 1.0% SiO2 modified Cu-ZnO/HZSM-5 catalyst, which was increased by 20% and 34%, respectively, than that of Cu-ZnO/HZSM-5 catalyst without silica modification. XPS and AES measurements of the 1.0% SiO2 modified Cu-ZnO/HZSM-5 catalyst revealed that, during the reduction of the catalyst by H2 at 250℃ or DME synthesis from CO2/H2 at 250℃, the chemical valance of copper and zinc was 0 and 2+, respectively. Cu0 was considered to be the surface active site for the synthesis of methanol from CO2 hydrogenation. The present method may offer opportunities to prepare the ultra-fine mono-component or multi-component catalysts via the coprecipitation method.