Methyl Formate Pathway in Methanol Steam Reforming on Copper: Density Functional Calculations

Abstract

Methyl formate has been proposed to be an intermediate in methanol steam reforming (MSR) on copper catalysts. We show here using plane-wave density functional theory that methyl formate can indeed be formed by reaction between formaldehyde and methoxyl. However, this reaction competes unfavorable with that between formaldehyde and hydroxyl, which explains why methyl formate is only observed in the absence of water. Methyl formate can be further hydrolyzed by a surface OH species to produce formic acid, which can dehydrogenate to produce CO2. This process has a lower overall barrier than MSR, thus consistent with the experimental observation that the steam reforming of methyl formate is faster than MSR. However, this hydrolysis process might have difficulties competing with desorption of methyl formate, which has a small adsorption energy. Our theoretical model, which is consistent with all experimental observations related to methyl formate in MSR, thus assigns a minor role for the methyl formate pathway.