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°C in a one-pot process. The procedure starts with methanol dehydrogenation to hydrogen and formaldehyde at the interface of the Cu₂O⋅SiO₂–Cu⁰ particle mixture, and subsequently, the formaldehyde intermediate condenses with substantial methanol to form DMM in the liquid phase. The Cu⁰, CuO, and chrysocolla species are inactive for hydrogen generation from methanol, and the intrinsic active species for methanol decomposition is the Cu₂O⋅SiO₂–Cu⁰ 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 Cu⁰ was not active, but the combined Cu⁰ and Cu⁺ sites with interfaces on SiO₂ with an optimal Cu⁺/Cu⁰ 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.