Effect of calcination on Cu–Zn-loaded hydrotalcite catalysts for C–C bond formation derived from methanol

Abstract

In this study, Cu and Zn were loaded by co-impregnation on the hydrotalcite (HT) calcined at different conditions to determine how changes in the HT structure may influence the C–C bond formation from methanol feed. When partially decomposed HT573 (HT calcined at 573K) was used, the calcined catalyst contained clusters of octahedral CuO and ZnO, which most likely accumulate at the edge of the brucite-type main layer (BTML). After partial reduction of this catalyst at 573K (i.e., CuZn/HT573-C573-R573), approximately 24% of Cu2+ remained unreduced and had links to the BTML. The Cu0 balance indicated an interaction with tetrahedral ZnO. CuZn/HT573 catalyzes the conversion of methanol to produce higher oxygenates containing mainly linear alcohols, e.g., 1-hexanol. The morphology of Cu and Zn was different when HT673 (673K-calcined HT) was used to prepare the catalyst. Although HT phases were present after impregnation, tetrahedral CuO and ZnO were found in the mixed oxide after calcination. After partial reduction at 573K (CuZn/HT673-C673-R573), no bonding between Cu and substrate remained, although approximately 30% of Cu2+ remained. This catalyst stimulates the conversion of methanol to produce higher oxygenates such as ketones, ethers, and esters exhibiting branched carbon chains. Structural characterization was performed at different stages of catalyst preparation. The results obtained indicate that the methanol reaction activity and selectivity of Cu–Zn-loaded HT catalysts are strongly influenced by the morphology of Cu–Zn induced by differently calcined HT used in this study.