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

Introducing transition metals into CuAl2O4 2 O 4 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 2 (the primary product) and CO (the notorious byproduct) remains unclear. Herein, we employed DFT + U to investigate CO and CO2 2 adsorption on perfect, M-doped (Fe, Co, and Ni), and M-doped oxygen-deficient CuAl2O4 2 O 4 spinel (100) and (1 10) surfaces. We find that stronger CO adsorption on (100) than (1 10) surfaces across all Mdoped surfaces, while CO2 2 adsorbs more stronger on (1 10) 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 3-like structure on CuAl2O4(1 2 O 4 (1 1 0) surface and boosts the CO oxidation. Furthermore, infrared spectroscopy simulation indicates that the vibrational frequencies for CO linear adsorption, formation of bent CO2- 2- and CO3-like 3-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 2 adsorption by 0.6-1.3 eV, highlighting the doping and oxygen-defect engineering in enhancing the CO2 2 capture. This research uncovers the critical impact of metal doping and oxygen vacancies on CO and CO2 2 adsorptions over CuAl2O4 2 O 4 spinel catalyst, providing insights for developing catalysts with improved resistance to CO poisoning and enhanced CO oxidation which is vital for methanol steam reforming.