Tuning CO2 Hydrogenation Selectivity through Reaction-Driven Restructuring on Cu-Ni Bimetal Catalysts

Abstract

Tuning the selectivity of CO₂ hydrogenation is of significant scientific interest, especially using nickel-based catalysts. Fundamental insights into CO₂ hydrogenation on Ni-based catalysts demonstrate that CO is a primary intermediate, and product selectivity is strongly dependent on the oxidation state of Ni. Therefore, modifying the electronic structure of the nickel surface is a compelling strategy for tuning product selectivity. Herein, we synthesized well dispersed Cu-Ni bimetallic nanoparticles (NPs) using a simple hydrothermal method for CO selective CO₂ hydrogenation. A detailed study on the monometallic (Ni and Cu) and bimetallic (Cu_xNi_1-x) catalysts supported on γ-Al₂O₃ was performed to increase CO selectivity while maintaining the high reaction rate. The Cu_0.5Ni_0.5/γ-Al₂O₃ catalyst shows a high CO₂ conversion and more CO product selectivity than its monometallic counterparts. The surface electronic and geometric structure of Cu_0.5Ni_0.5 bimetallic NPs was studied using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ diffuse reflectance infrared Fourier-transform spectroscopy under reaction conditions. The Cu core atoms migrate toward the surface, resulting in the restructuring of the Cu@Ni core-shell structure to a Cu-Ni alloy during the reaction and functioning as the active site by enhancing CO desorption. A systematic correlation is obtained between catalytic activity from a continuous fixed-bed flow reactor and the surface electronic structural details derived from AP-XPS results, establishing the structure-activity relationship. This investigation contributes to providing a strategy for controlling CO₂ hydrogenation selectivity by modifying the surface structure of bimetallic NP catalysts.

Keywords: CO2 hydrogenation; Cu−Ni alloy; ambient pressure X-ray photoelectron spectroscopy; in situ DRIFT; surface restructuring.