Copper-manganese catalysts with high activity for methanol synthesis

Abstract

Layered-double hydroxides (LDHs) based on copper, manganese, and aluminum were successfully prepared from sodium-free reactants, with x (Al3+/[Al3++Cu2++Mn2+]) values between 0.24 and 0.35, and y (Cu2+/Mn2+) values between 2.2 and 10.3. Catalysts obtained by calcination of the LDHs were characterized by EXAFS, XANES, XPS, ICP, XRD, TPR, N2O decomposition and BET, and were evaluated in the liquid-phase methanol synthesis reaction from synthesis gas. Characterization revealed that, in a commercial CuZnAl catalyst, the environment of copper is very similar to that prevailing in CuO. In the CuMnAl catalyst that presented the largest methanol synthesis activity, copper is more electron-deficient than in CuO and there is structural disorder beyond the first coordination sphere. TPR characterization suggests that manganese is in the 4+ oxidation state in the oxide precursor of this catalyst. The catalyst with the highest manganese content, y = 2.2, and prepared at higher pH, presented the highest methanol productivity and selectivity of all materials tested, including a commercial conventional CuZnAl catalyst, under our testing conditions. This was credited to the larger surface area of its oxide precursor, which resulted in smaller Cu crystallites and larger copper surface area than in the case of the remaining ones.