Do Ni/Cu and Cu/Ni Alloys have Different Catalytic Performances towards Water‐Gas Shift? A Density Functional Theory Investigation

Abstract

Density functional calculations were preformed to investigate whether adding Ni into a Cu surface (denoted as Cu/Ni) or adding Cu into a Ni surface (Ni/Cu) is more efficient for catalyzing the water-gas shift (WGS)? The reactions of water dissociation and monoxide dissociation were selected to assess the activity and selectivity towards WGS, respectively. Our results show that Ni-atom modification of surfaces is thermodynamically favorable for both reactions. Kinetically, compared with pure Cu, water dissociation is greatly facilitated on Ni-modified surfaces, and the activity is insensitive to the Ni concentration; however, monoxide dissociation is not well-promoted on one Ni-atom-modified surfaces, but two Ni-atom modification can notably decrease the dissociation barriers. Overall, on the basis of these results, we conclude that 1) the catalytic performance of bimetallic metals is superior to monometallic ones; 2) at the same Ni concentration on the surface, Cu/Ni and Ni/Cu alloys have almost the same performance towards WGS; and 3) to acquire high WGS performance, the surface Ni atoms should either be low in concentration or highly dispersed.

General concepts, assumptions, drawbacks, and misuses in kinetic Monte Carlo and microkinetic modeling simulations applied to computational heterogeneous catalysis

“…Both diagrams should be used to unravel the underlying molecular mechanism although with the necessary caution when aiming to make predictions regarding the performance of a given catalyst for a given complex gas‐surface reaction. Establishing a ranking of plausible reaction mechanisms and the most efficient catalysts based only on the values of energy barriers of some forward processes [e.g., the rate‐determining steps (RDSs)] is not always fully justified although this is often the choice in many studies . Very low energy barriers for reverse processes can greatly hinder reactivity, even if the forward energy barrier is affordable.…”

Ni-based bimetallic heterogeneous catalysts for energy and environmental applications

“…In the last few years, the WSG reaction has been extensively studied over a bimetallic Ni-Cu system where the main concern was to suppress the methanation reaction by increasing the CO adsorption. [216][217][218][219][220][221][222][223] In a recent study, experimental analyses such as CO-TPR-MS, CO-TPD-MS and in situ DRIFTS have proved that the CO adsorption can be enhanced on a Ni-Cu alloy at a high temperature. 220 The Ni-Cu/CeO 2 catalyst with a Ni/Cu ratio of one exhibited a high reaction rate with the least methane formation due to the formation of a Ni-Cu alloy phase.…”

Nickel‐based Catalysts for High‐temperature Water Gas Shift Reaction‐Methane Suppression

“…who also found that barrier for C−O bond scission is strongly dependent on surface concentration of Ni on Cu. Low concentration of Ni or highly dispersed Ni on Cu can result in lower water dissociation barrier and attain higher selectivity towards WGS instead of CO methanation by increasing CO dissociation barrier as lower CO dissociation barrier favors methane formation These studies certainly provided important insights into bimetallic systems for WGS reaction but wider range of bimetallic combination of Ni‐based bimetallic catalyst are still not well explored.…”