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

Microcalorimetric, infrared spectroscopic, and reaction kinetics measuremen ts are combined with quantum-chemical calculations based on density-functio nal theory to investigate the selective reduction of acetic acid, methyl ac etate, and ethyl acetate over silica-supported copper catalysts. Experiment al values for initial heats of dissociative adsorption of methyl acetate, e thyl acetate, acetaldehyde, methanol, and ethanol on silica-supported coppe r 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 energi es 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), r espectively. Results from DFT calculations also indicate that the activatio n energy for dissociation decreases from acetic acid to methyl acetate to e thyl acetate. The rate of reduction of n-alkyl acetates appears to be deter mined by the dissociative adsorption of these molecules and by the hydrogen ation of surface acyl species. (C) 2000 Academic Press.