A first principles study of the adsorption and hydrogenation of formic acid on a Cu3Zn material: Implication for bulk alloying effect on CO2 hydrogenation reactivity of Cu/ZnO-based catalysts

Abstract

HCOOH hydrogenation to H2COOH were, until recently, assumed to be the rate controlling step in methanol synthesis from CO2/H2 mixtures over Cu-based catalysts. Using the density functional method and periodic supercell slab models, we have studied the critical elementary reaction, along with the molecular adsorption of HCOOH, on the clean, H, CH3O, and H + CH3O-precovered Cu3Zn(114), Cu3Zn(214) and, as a reference, Cu(111) substrates, which are intimately related to the surface chemical composition of real CO2 hydrogenation catalysts. Among the three metal and alloyed surfaces with and without coadsorbates, the stepped alloy surface is always the optimum site for HCOOH binding, thereby serving as a reservoir for the reactive HCOOH species. And the atomically flat alloy surface shows more favorable kinetics and thermochemistry than the pure copper substrate for H2COOH formation. The synergetic interaction between the alloyed surfaces in promoting the slow reaction reveals that a binary bulk alloy, while present in reduced Cu/ZnO catalyst, demonstrates promising catalytic performance in terms of activity towards the overall methanol synthesis process. This paper stresses that there is a requirement for further experimental validation studies.