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

Cu 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 (similar to 99 %) and methanol formation rate (0.016 mol g(Cu)(-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/gamma-Al2O3 support, as shown by the DFT study. Additionally, the adsorption energy calculated using DFT showed preferential adsorption of CO2 and H-2 at the Cu/MgO(100) active site (-120.9 kJ/mol, -130.4 kJ/mol) compared to the Cu/gamma-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).

Automated summary

Cu nanoparticles supported on Mg-Al mixed oxide prepared by sol-gel method exhibited high methanol selectivity, with small copper particles showing strong interaction with the oxide support and higher methanol production rate.