Effects of Reduction Pretreatment on Ni─Cu Bimetallic Catalysts and Their Catalytic Performance on CO2 Hydrogenation

Abstract

The performance of bimetallic catalysts is closely related to their surface structure, and the surface reconstruction process can affect the distribution of active sites, electronic structure, and reactant adsorption behavior. Traditional research has mostly focused on optimizing synthesis processes, such as controlling the size and distribution of metal particles, whereas there is relatively little research on the effect of pretreatment conditions on the dynamic structure of catalysts. In this study, a 10Ni─1Cu catalyst was synthesized using the deposition–precipitation method, and the effects of different pretreatment conditions on its performance were investigated. The catalyst was first pretreated at 500°C in a 60%H₂/40%N₂ atmosphere, followed by reduction under different pretreatment atmospheres (10%H₂/90%N₂ or 15%CO₂/60%H₂/25%N₂) at the same temperature. At 400°C and a space velocity of 30 L h⁻¹ g⁻¹, the methane production rate of the catalyst treated in the reaction atmosphere significantly increased from 12.4 to 15.8 µmol g⁻¹ s⁻¹ compared to the catalyst treated with hydrogen alone. Characterization techniques, such as TEM, x-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), were employed to study the structural properties of the catalysts, focusing on the surface properties after reduction and the surface species during the reaction. This study demonstrates that catalysts pretreated in the reaction atmosphere enhance methane production rates by regulating the surface structure and forming Ni─Cu alloy structures with a lower Ni/Cu ratio, thereby optimizing the selectivity of hydrogenation products.