Studies on the active species and on dispersion of Cu in Cu/SiO_2 and Cu/Zn/SiO_2 for hydrogen production via methanol partial oxidation

摘要

The partial oxidation of methanol to hydrogen (CH_3OH + 1/2O_2→2H_2 + CO_2) was investigated over Cu/SiO_2 and Cu/Zn/SiO_2 catalysts prepared by deposition-precipitation method. The effects of Cu loadings in Cu/SiO_2 and different Cu/Zn ratios in Cu/Zn/SiO_2 catalysts on activities have been investigated in detail. The kinetic results show that the catalyst with 10% Cu loading (Cu/Zn 7:3) exhibits the highest CH_3OH conversion and H_2 selectivity than other catalysts. The results of XRD and XPS characterizations indicate that Cu~0 species in catalysts is an active species for high activity, but Cu~+ species inhibits the partial oxidation of methanol to hydrogen. The appropriate introduction of Zn results in higher dispersion of Cu~0, which leads to high activity of the catalysts for hydrogen generation. However, overloading of Zn results in the formation of bigger crystallites of Cu_2O in the catalyst which decreases the activity of the catalyst.