Develop High-Performance Cu-Based RWGS Catalysts by Controlling Oxide–Oxide Interface

Abstract

The high-temperature reverse water–gas shift (RWGS) is an industrially relevant reaction. Cu-based catalysts easily sinter and deactivate under these conditions. We demonstrate that it is possible to obtain high-performance and stable catalysts by modifying the mechanism of action. Cu/CeO_x-MgO (denoted as Cu/Ce_xMg_y) catalysts were developed in which Cu nanoparticles mostly generate spillover H that migrates to support sites where CO₂ is selectively reduced, with the rate controlled by the oxide–oxide CeO_x-MgO interface. An optimal Cu/Ce_0.05Mg_0.95 catalyst (in terms of performance at the lowest possible Ce amount) exhibits a near-equilibrium CO₂ conversion with a reaction rate of 516.0 μmol·g_cat^–1·s^–1, near-total selectivity to CO at 600 °C, and a high space-velocity of 300,000 mL·g_cat^–1·h^–1. These are among the top performances in the RWGS reaction. Extensive characterization data have proven that the surface-abundant Ce-[O_v]-Mg sites play a critical role in CO₂ adsorption/activation as well as the carrier for the spillover of hydrogen species. The mechanism is substantially different from those indicated for Cu-based catalysts for CO₂ hydrogenation. By decoupling H and CO₂ activation sites and realizing efficient surface mobility of H-spillover species via an enhanced oxide–oxide interface, it is possible to maintain the overall stability and activity of the catalyst when the Cu nanoparticles sinter at a high temperature (i.e., ≥600 °C).