Direct Synthesis of Hydrogen and Dimethoxylmethane from Methanol on Copper/Silica Catalysts with Optimal Cu+/Cu0 Sites

Hydrogen is an important sustainable resource, and here we report a catalytic route for the direct production of hydrogen (with a purity of 95%) and dimethoxylmethane (DMM) from supercritical methanol over a Cu/SiO2 catalyst prepared by deposition-precipitation with ammonia (DPA) at 240 degrees C in a one-pot process. The procedure starts with methanol dehydrogenation to hydrogen and formaldehyde at the interface of the Cu2OSiO2-Cu-0 particle mixture, and subsequently, the formaldehyde intermediate condenses with substantial methanol to form DMM in the liquid phase. The Cu-0, CuO, and chrysocolla species are inactive for hydrogen generation from methanol, and the intrinsic active species for methanol decomposition is the Cu2OSiO2-Cu-0 nanoparticle interface, which is produced from the hydrogen reduction of Cu2Si2O5(OH)(2) or from the methanol reduction of Cu-O-Si moieties. A correlation between the structure and activity on reduced Cu/SiO2 (DPA) suggested that only Cu-0 was not active, but the combined Cu-0 and Cu+ sites with interfaces on SiO2 with an optimal Cu+/Cu-0 ratio of 1.56 were highly active for methanol dehydrogenation and subsequent condensation steps. The developed new catalytic system offers a facile and atom-economical way to generate pure hydrogen (almost CO free) from liquid methanol that can be used in fuel cell and hydrogen-involved biomass reactions.