Galvanic Deposition of Au on Paperlike Cu Fiber for High-Efficiency, Low-Temperature Gas-Phase Oxidation of Alcohols

The highly active and selective gold-on-copper fiber catalysts with excellent heat conductivity were successfully prepared for high-efficiency gas-phase selective oxidation of various alcohols. The Au/Cu-fiber catalysts were obtained by conducting galvanic deposition of Au onto a thin-sheet microfibrous structure that consisted of 5vol% Cu-fiber (8μm diameter), and 95vol% voidage. The best catalyst was Au-3/Cu-fiber-200 (Au loading: 3wt%; calcined at 200°C in air), which was effective for acyclic, benzylic, and polynary alcohols using a high weight hourly space velocity of 20h^-1. Benzyl alcohol conversion of 86% was obtained with 99% selectivity to benzaldehyde at 220°C. Cyclopropanemethanol could be transformed to cyclopropanecarboxaldehyde, with conversion of 91% and selectivity of 95% at 250°C. 1,2-Propanediol demonstrated a high conversion of 92%, with a medium selectivity of 74% at 340°C. An oxidation of volatile unsaturated alcohols, such as crotyl alcohol and 3-methyl-2-butenol, could also proceed highly selectively with good conversions at 280°C. A low ΔT of less than 10°C between the catalyst bed and the external wall of the reactor was observed in the selective oxidation of benzyl alcohol owing to the enhanced heat-transfer ability that permits rapid dissipation of large quantities of the reaction heat. Special AuCu(alloy)-Cu₂O active composites were formed during the reaction, and their cooperative effect contributed to increasing the low-temperature activity. By nature, the AuCu alloy can catalyze the oxidation of Cu₂O-H species with O₂ to release active Cu₂O sites.