Effect of rare-earth element modification on the performance of Cu/ZnAl catalysts derived from hydrotalcite precursor in methanol steam reforming

Zn-Al layered double hydroxides (ZnAl-LDHs) were prepared on γ-Al₂O₃ by an in-situ synthesis method; with ZnAl-LDHs as the supports, a series of rare-earth element M (M=Y, La, Ce, Sm and Gd) doped M/Cu/ZnAl catalysts were then obtained through sequential wet impregnation method and used in the methanol steam reforming to produce hydrogen. The M/Cu/ZnAl catalysts were characterized by XRD, SEM-EDS, N₂ sorption, H₂-TPR, XPS and N₂O titration and the effect of rare-earth metal doping on their catalytic performance in the methanol steam reforming was then investigated. The results showed that the activity of Cu/ZnAl catalyst is closely related to the copper surface area and the reducibility; larger copper surface area and lower reduction temperature lead to a higher catalytic activity in methanol steam reforming. The addition of rare-earth elements including Ce, Sm and Gd can improve the copper dispersion, surface copper area and the catalyst reducibility, which is helpful to enhance the activity of M/Cu/ZnAl catalysts. Especially, the Ce/Cu/ZnAl catalyst exhibits the highest activity; over it, the methanol conversion is 100% (about 40% higher than that over the Cu/ZnAl catalyst) and the CO concentration in the product is only 0.39%, for the methanol steam reforming at 250℃.