Facile Ester Synthesis on Ag-Modified Nanoporous Au: Oxidative Coupling of Ethanol and 1-Butanol Under UHV Conditions

A dilute Ag alloy of nanoporous Au (npAu) has been shown to self-couple methanol with 100 % selectivity and high conversion under catalytic flow conditions. However, because prior studies in flow reactors showed difficulty in self-coupling ethanol and 1-butanol over npAu in flow reactors, the inherent capability on npAu for self-coupling of ethanol and 1-butanol was examined under ultrahigh vacuum conditions on identical npAu catalysts. This study shows that the oxygen-covered Ag-modified npAu does efficiently effect the self-coupling of ethanol and 1-butanol under UHV conditions. The coupling is initiated by adsorbed atomic oxygen formed from O-2 dissociation via a chemisorbed molecular state. The amount of ester formed increases with the degree of oxygen precoverage at the expense of aldehyde production. Repeated annealing of the catalyst above 550 K for temperature programmed reaction changes the ligament and pore sizes, affecting the product distribution, but high reactivity is sustained over many heating cycles. [GRAPHICS] .