Promoted stability of Cu/ZnO/Al₂O₃ catalysts for methanol production from CO₂ hydrogenation by La modification

Deactivation of Cu/ZnO/Al₂O₃ catalysts in CO₂ hydrogenation to methanol reaction is one of the main reasons limiting their application. We synthesized a series of La modified Cu/ZnO/Al₂O₃ catalysts by adding different contents of La to improve the stability. In the 100 h short-term stability test at 200 ℃ under 3 MPa with a GHSV of 12000 mL/(g·h) , the unmodified Cu/ZnO/Al₂O₃ catalysts degraded obviously over 100 h. In sharp contrast, the stability was significantly promoted by the addition of La. The best activity was achieved with 5% La added samples (4% CO₂ conversion and 85% methanol selectivity), which also showed impressive stability over 1000 h except about 17% deactivation during the initial 190−220 h. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results revealed that the addition of 5% La improved the dispersion of Cu and Zn, inhibited the sintering of Cu, stabilized the Cu^0/+ species and retarded oxidation of Cu in catalysts, which attributed to the high stability of the catalysts.