DFT insights into doping and oxygen vacancy effects on CO and CO₂ adsorptions over CuAl2O4 spinel surfaces

Abstract

Introducing transition metals into CuAl2O4 spinel enhances catalyst stability and Cu sintering resistance in methanol steam reforming. Yet, the influence of doping on vacancy formation and the adsorption behaviors of CO2 (the primary product) and CO (the notorious byproduct) remains unclear. Herein, we employed DFT + U to investigate CO and CO2 adsorption on perfect, M-doped (Fe, Co, and Ni), and M-doped oxygen-deficient CuAl2O4 spinel (100) and (110) surfaces. We find that stronger CO adsorption on (100) than (110) surfaces across all M-doped surfaces, while CO2 adsorbs more stronger on (110) surfaces. The weakened CO adsorptions are observed on Fe and Ni-doped surfaces, demonstrating that doping plays a significant role in improving the resistance to CO poisoning. Co-doping promotes CO adsorption via a CO3-like structure on CuAl2O4(110) surface and boosts the CO oxidation. Furthermore, infrared spectroscopy simulation indicates that the vibrational frequencies for CO linear adsorption, formation of bent CO2- and CO3-like structures are within the ranges of 2042–2078, 1463–1566, and 1497–1816 cm−1, respectively. In addition, Ov on Ni-doped surfaces can significantly strengthen the CO2 adsorption by 0.6–1.3 eV, highlighting the doping and oxygen-defect engineering in enhancing the CO2 capture. This research uncovers the critical impact of metal doping and oxygen vacancies on CO and CO2 adsorptions over CuAl2O4 spinel catalyst, providing insights for developing catalysts with improved resistance to CO poisoning and enhanced CO oxidation which is vital for methanol steam reforming.