UC Davis

Though much of the reaction mechanism of the oxidative conversion of methanol to formaldehyde on silver is well understood, recent discovery of acetaldehyde as a product of methanol oxidation over a silver catalyst has led to questions about the potential for carbon-carbon coupling reactions. This has created an opportunity for theoretical research to identify the mechanism for the formation of acetaldehyde and other two-carbon products. Analysis of density functional theory (DFT) data from available literature largely supports previously proposed network of elementary steps, which include pathways for formaldehyde, carbon monoxide and carbon dioxide production. DFT calculations in this work and microkinetic modeling study provide theoretical explanations of reaction mechanisms that form acetaldehyde, methyl formate, and dimethyl ether. Free energy calculations show that the activation energy of intermediate coupling reactions could play a central role in controlling selectivities of two-carbon species, favoring the synthesis of methyl formate. Microkinetic modeling reveals that direct formation of acetaldehyde and methyl formate, as well as the synthesis of dimethyl ether, are coverage-limited by CHO* and CH3*, respectively. This work introduces a set of reaction mechanisms which likely explain experimental observations of two-carbon products in the partial oxidation of methanol over silver.