Nitrogen-doped carbon nanotubes as bifunctional catalysts with enhanced catalytic performance for selective oxidation of ethanol

The gas-phase selective oxidation of ethanol to acetaldehyde is a promising alternative to current Wacker process in which ethylene is catalyzed to acetaldehyde by palladium and copper chlorides in strong acidic solutions. The supported gold catalyst has been reported and showed excellent catalytic performance in gas-phase oxidation of ethanol. But its high price stimulates the studies to focus on non-noble-metal catalysts, or non-metal catalysts. Here, we report that nitrogen-doped carbon nanotubes as a bifunctional catalyst exhibits robust performance in the selective oxidation of ethanol to acetaldehyde. A stable catalytic performance with ethanol conversion of 72% and acetaldehyde selectivity of 90% at 270 °C was obtained. The substantial enhancement of acetaldehyde yield was ascribed to the synergistic effect of synchronously promoting the dissociative adsorption of O2 and ethanol adsorption when incorporating graphite-like and pyridine-like nitrogen species. The kinetic analysis indicates that the introduction of nitrogen species can significantly decrease the activation energy of the reaction. The study of this bifunctional carbocatalyst may also provide guidance for the design of new carbon-based catalytic systems for the selective oxidation of alcohols via regulating the adsorption and activation ability of catalyst to reactants.

The acetaldehyde selectivity and ethanol conversion are both distinctly enhanced due to the strong synergistic effect of promoting the dissociative adsorption of oxygen and the adsorption to ethanol after incorporating nitrogen into carbon nanotubes.223