Understanding the Origin of Structure Sensitivity in Nano Crystalline Mixed Cu/Mg−Al Oxides Catalyst for Low‐Pressure Methanol Synthesis

Abstract

AbstractCu nanoparticles of size 5–10 nm supported on Mg−Al mixed oxide were prepared by the sol‐gel method. Cu loading was varied from 2.5 to 10 wt % on the support to investigate the effect on particle size and activity/selectivity of the catalyst. The Cu/Mg−Al catalysts containing small copper nanoparticles favor high selectivity of methanol, while the rate of CO formation was higher for larger copper particles. The high methanol selectivity (∼99 %) and methanol formation rate (0.016 mol gCu−1 h−1) over the 4.8Cu/Mg−Al catalyst was due to the combined effect of the presence of high Cu dispersion, Cu surface area, and strong interaction between small Cu particles with Mg−Al support. The high stability of the catalyst was attributed to the strong binding of the Cu cluster (−179.7 kJ/mol) to the MgO/γ‐Al2O3 support, as shown by the DFT study. Additionally, the adsorption energy calculated using DFT showed preferential adsorption of CO2 and H2 at the Cu/MgO(100) active site (−120.9 kJ/mol, −130.4 kJ/mol) compared to the Cu/γ‐Al2O3(100) (−64.2 kJ/mol, −85.7 kJ/mol)active site. The high selectivity of the catalyst towards methanol can be attributed to the higher stability of the formate (HCOO) intermediate (−257.2 kJ/mol) compared to the carboxylate (COOH) intermediate (−131.0 kJ/mol).