Enhanced Methanol Production over Non-promoted Cu-MgO-Al2O3Materials with Ex-solved 2 nm Cu Particles: Insights from anOperando Spectroscopic Study

Enhanced methanol production is obtained over a non-promotedCu-MgO-Al2O3mixed oxide catalyst derived from a Cu-Mg-Al hydrotalciteprecursor (HT) containing narrowly distributed small Cu NPs (2 nm).Conversions close to the equilibrium (similar to 20%) with a methanol selectivity of67% are achieved at 230 degrees C, 20 bar, and a space velocity of 571 mLmiddotgcat-1middoth-1.Based on operando spectroscopic studies, the striking activity of this Cu-basedcatalyst is ascribed to the stabilization of Cu+ions favored under reactionconditions due to lattice reorganization associated with the"HT-memory effect"promoted by water. Temperature-resolved infrared-mass spectrometry experi-ments have enabled the discernment of monodentate formate species, stabilized onCu+as the intermediate in methanol synthesis, in line with the results of density functional theory calculations. These monodentateformate species are much more reactive than bridge formate species, the latter ones behaving as intermediates in methane and COformation. Moreover, poisoning of the Cu0surface by strongly adsorbed species behaving as spectators is observed under reactionconditions. This work presents a detailed spectroscopic study highlighting the influence of the reaction pressure on the stabilizationof active surface sites, and the possibility of enhancing methanol production on usually less active non-promoted nano-sized coppercatalysts, provided that the proper support is selected, allowing the stabilization of doped Cu+. Thus, a methanol formation rate of2.6x10-3molMeOHmiddotgcat-1middoth-1at 230 degrees C, 20 bar, and WHSV = 28 500 mLmiddotgcat-1middoth-1is obtained on the Cu-MgO-Al2O3HT-derived catalyst with 71% methanol selectivity, compared to 2.2x10-4molMeOHmiddotgcat-1middoth-1with 54% methanol selectivity obtainedon a reference Cu/(Al2O3/MgO) catalyst not derived from a HT structure.