Catalytic reduction of acetic acid, methyl acetate, and ethyl acetate over silica-supported copper

Microcalorimetric, infrared spectroscopic, and reaction kinetics measurements are combined with quantum-chemical calculations based on density-functional theory to investigate the selective reduction of acetic acid, methyl acetate, and ethyl acetate over silica-supported copper catalysts. Experimental values for initial heats of dissociative adsorption of methyl acetate, ethyl acetate, acetaldehyde, methanol, and ethanol on silica-supported copper are estimated to be 124, 130, 130, 128, and 140 kJ mol(-1), respectively. These values are in agreement with adsorption energies predicted from DFT calculations using Cu-13 clusters. Experimental values of activation energies for the dissociation of acetic acid, methyl acetate, ethyl acetate, and acetaldehyde on copper are estimated to be 83, 67, 62, and 75 kJ mol(-1), respectively. Results from DFT calculations also indicate that the activation energy for dissociation decreases from acetic acid to methyl acetate to ethyl acetate. The rate of reduction of n-alkyl acetates appears to be determined by the dissociative adsorption of these molecules and by the hydrogenation of surface acyl species. (C) 2000 Academic Press.