CuZnAl hydrotalcites as suitable precursors for chromium-free ester hydrogenolysis catalysts

Ester hydrogenolysis is industrially performed over Adkins catalysts. Their use is being restricted as they contain environmentally unfriendly Cr2O3. As a potential replacement, five co-precipitated CuZnAl catalysts with various Cu/Zn and Al/(Cu+Zn) atomic ratios were studied. The structure transformation during the whole catalyst lifecycle was determined. The catalyst precursors consisted of CuZnAl-hydrotalcite (HTC). Although the Cu/Zn ratio did not affect the HTC structure, an increase in Al content resulted in smaller Cu nanoparticles with a larger surface area. In the reduced catalysts, both Cu+ and Cu0 species were identified using FTIR-CO. XPS revealed catalyst surface reconstruction after catalyst reduction and catalytic reaction. The evaluation of the catalysts in dimethyl adipate hydrogenolysis indicated that the catalyst having the lowest Cu loading possessed the highest activity, due to its high SCu and Cu/Zn = 1. Generally, higher activity was achieved by reducing the Cu/Zn and increasing the Al/(Cu+Zn) ratios.