Response to Comment on "Active sites for CO₂ hydrogenation to methanol on Cu/ZnO catalysts".

Abstract

In their Comment on the our recent Report, Nakamura <i>et al</i> argue that our x-ray photoelectron spectroscopy (XPS) analysis was affected by the presence of formate species on the catalyst surface. This argument is not valid because the reactant gases were evacuated at temperatures from 525 to 575 kelvin, conditions under which formate is not stable on the catalyst surface. An analysis of the XPS results obtained after exposing zinc oxide/copper (111) [ZnO/Cu(111)] surfaces to hydrogen (H₂) and mixtures of carbon dioxide (CO₂)/H₂ show an absence of carbon (C) 1s signal, no asymmetries in the oxygen (O) 1s peak, and a Zn:O intensity close to 1:1. Thus, the most active phase of these catalysts contained a ZnO-Cu interface.