Differentiating Intrinsic Reactivity of Copper, Copper-Zinc Alloy, and Copper/Zinc Oxide Interface for Methanol Steam Reforming by First-Principles Theory

Identifying the intrinsic activity of the distinct sites which coexist in oxide-supported metal particles is vital but challenging for rational design of catalysts. We treat the challenge here by density functional theory calculations to differentiate unbiasedly the intrinsic reactivity of a variety of sites observed under reaction conditions for methanol steam reforming on Cu/ZnO catalyst. Metallic Cu and CuZn alloy are found to be less active but highly selective toward formaldehyde because water dissociation is demanding, which limits the formation of hydroxyl and subsequent coupling necessary to yield CO2. Cu/ZnO interface is highly active and selective for H-2/CO2 because of its superior activity for water and methanol activation. Distinct hydrogen affinity at Cu/ZnO interface also leads to more favorable CO2 production via H2COO, in contrast to via HCOOH at (bi)metallic sites. The distinct reactivity of various structural motifs exposed and the importance of the metal/oxide for selectivity revealed is valuable for optimal design of catalysts.