Supported Cu catalysts on UiO-66 toward enhanced methanol selectivity by CO2 hydrogenation: Effect of Cu loading

Abstract

The xCu/MOF catalysts were synthesized by incipient-wetness impregnation of copper precursor on UiO-66 support, in which the Cu loadings were 5, 10, and 20% (wt.%). To gain insight into the properties of the materials, a range of techniques, including XRD, TEM, TGA, N2 physisorption, CO2-TPD, EDS, N2O chemisorption, XPS, IR, and NMR, were employed. The effectiveness of catalysts was evaluated for synthesizing methanol through CO2 hydrogenation under various Gas Hourly Space Velocities (GHSVs) and reaction conditions, including pressures of 10 and 30 bar, CO2/H2 ratios of 1:3, and CO2/H2/N2 ratios of 1:3:0.14 M, all conducted at a temperature of 250 °C. The active site in the Cu/UiO-66 catalyst is the interface between Cu+ nanoparticles (NPs) with Zr oxide SBU [Zr6O4(OH)4(−CO2) and the defects related to unsaturated Zr sites of the Zr-Oxo cluster due to the increase of Cu NPs occupying missing linker defects of the MOF structure. 20Cu/MOF catalyst, with the highest copper loading, showed the best methanol formation rate and CO2 conversion due to the strong metal-support interaction and the highest amount of the missing linker defects of the MOF structure.