Tuning CO<sub>2</sub> Hydrogenation Selectivity through Reaction-Driven Restructuring on Cu–Ni Bimetal Catalysts
Kasala Prabhakar Reddy, Daeho Kim, Seunghwa Hong, Ki-Jeong Kim, Ryong Ryoo, Jeong Young Park
Abstract
Tuning the selectivity of CO 2 hydrogenation is of significant scientific interest, especially using nickel-based catalysts. Fundamental insights into CO 2 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 CO 2 hydrogenation. A detailed study on the monometallic (Ni and Cu) and bimetallic (Cu x Ni 1– x ) catalysts supported on γ-Al 2 O 3 was performed to increase CO selectivity while maintaining the high reaction rate. The Cu 0.5 Ni 0.5 /γ-Al 2 O 3 catalyst shows a high CO 2 conversion and more CO product selectivity than its monometallic counterparts. The surface electronic and geometric structure of Cu 0.5 Ni 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 CO 2 hydrogenation selectivity by modifying the surface structure of bimetallic NP catalysts.