Methanol Dehydrogenation to Methyl Formate Catalyzed by Cu/SiO2 Catalysts: Impact of Precipitation Procedure and Calcination Temperature

Considered three options for the synthesis of a catalyst by the precipitation method, the Cu/SiO2 catalysts prepared by varying the precipitation procedure and calcination temperature for the dehydrogenation of methanol was investigated. When the CuO/SiO2 catalyst precursors were prepared by the addition of a copper nitrate aqueous solution into an ammonia aqueous solution (reverse precipitation) and co-current flow addition of both aqueous solutions, after reduction with gaseous hydrogen, small-sized metallic copper nanocrystallites were formed in the reduced Cu/SiO2 catalysts as compared to those prepared by the addition of an ammonia aqueous solution into a copper nitrate aqueous solution (direct precipitation). The reduced Cu/SiO2 catalysts prepared by the reverse precipitation method with relatively lower acidity and basicity exhibited higher catalytic activity for the formation of methyl formate in methanol dehydrogenation. The reduced Cu/SiO2 catalysts prepared by the calcination at a lower temperature exhibited higher catalytic activity for the formation of methyl formate. The surface metallic Cu0 and Cu+ species catalyzed the methanol dehydrogenation to methyl formate, meanwhile the surface Cu+ cations enhanced the decomposition of the resultant methyl formate to CO and H2.