Inducing synergy in bimetallic RhNi catalysts for CO2 methanation by galvanic replacement

CO2 utilisation as a chemical feedstock could transform fuels production and help mitigate climate change. Direct CO2 reduction for energy production requires the development of active, stable, and low-cost catalysts selective for methane. A bimetallic Ni@Rh core-shell catalyst prepared by galvanic replacement (GR) exhibits a 3.5-fold rate enhancement for CO2 methanation relative to an analogue prepared by chemical reduction (CR) and is twice as active as monometallic Rh/Al2O3. Superior performance of RhNi/Al2O3 (GR) is attributed to Rh dispersion as an atomically thin RhOx shell encapsulating Ni nanoparticles, stabilised by a strong Rh-Ni interaction. Operando IR spectroscopy identifies reactively-formed CO from the dissociative chemisorption of CO2 over Rh as the key intermediate for methane production. Surface formate from the dissociative chemisorption of CO2 and subsequent hydrogenation (via spillover from Rh sites) over alumina is a catalytic spectator. This mechanistic insight paves the way to high activity nanostructured catalysts for CO2 methanation.