Dynamic transformation of active components in Cu-ZnO-Al2O3 catalyst for methanol synthesis at high temperature

The dynamic transformation of active components in the Cu-ZnO-Al2O3 catalys t for methanol synthesis during the calcination, reduction and reaction was investigated by XRD and XPS methods. The results showed that, when the cat alyst was calcined in air, the particle size of the components increases wi th increasing calcination temperature, ZnO crystal grain grows faster than CuO crystal grain and aggregates on the surface of the catalyst, resulting in a decrease of the surface Cu/Zn ratio. During the reduction and reaction , the decrease in surface free energy of Cu crystal grain due to the intera ction between hydrogen and CU particle is more than that of ZnO crystal gra in, which is favorable for growth of the Cu crystal grain. The lower meltin g point of Cu makes the Cu particles own a lower activation energy of surfa ce migration and a higher surface diffusion coefficient, therefore the grow th of the Cu crystal grain controlled by surface diffusion is faster. But t he ZnO crystal grain grows slower in the reducing atmosphere because of its higher melting point. In comparison with the calcined catalyst, the surfac e Cu/Zn ratio of the catalyst after reduction and reaction increases obviou sly.