Inverse NiO_1–<i>x</i>/Cu Catalyst with High Activity toward Water–Gas Shift

Abstract

Ni additives into Cu catalyst can enhance the activity to the water–gas shift (WGS) reaction. However, an undesirable side reaction (methanation) would arise synchronously, consequently sharply degrading the selectivity to WGS. Herein, we propose an improved CuNi model system with potential excellent performance (both activity and selectivity) toward WGS, i.e., the inverse NiO_1–<i>x</i>/Cu­(111) (<i>x</i> < 1). The unsaturated Ni^δ+ species are expected to facilitate the rate-limiting step of WGS remarkably, H₂O dissociation, and subsequently, a rather smooth potential energy surface is found in the rest of the steps of WGS over the interface of NiO_1–<i>x</i>/Cu­(111), indicating a high reactivity. Meanwhile, a weak interaction between CO and NiO_1–<i>x</i> and a low activity of NiO_1–<i>x</i>/Cu­(111) toward CO dissociation imply that the oxidized Ni^δ+ species can effectively suppress the undesirable methanation found in CuNi catalysts, expecting to improve its selectivity toward WGS. The model system may be also applied to catalyze CO oxidation at proper conditions