Steam reforming of methanol over Cu/CeO2 catalysts studied in comparison with Cu/ZnO and Cu/Zn(Al)O catalysts

A series of Ce1-xCuxO2-delta mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce1-xCuxO2-delta mixed oxides indicated that Cu2+ ions were dissolved in CeO2 lattices to form a solid solution by calcination at 773 K when x < 0.2. A TPR (temperature- programmed reduction) investigation showed that the CeO2 promotes the reduction of the Cu2+ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu2+ species in the Ce1-xCuxO2-delta mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu2+ species which dissolved into the CeO2 lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO2. The Ce1-xCuxO2-delta mixed oxides were reduced to form Cu/CeO2 catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/Al2O3 catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO2 (over 97%) and H-2: A 3.8 wt% Cu/CeO2 catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513 K (W/F = 4.9 g h mol(-1)), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al) O (32.3%) and Cu/Al2O3 (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO2 catalysts may be due to the highly dispersed Cu metal particles and the strong metal-support interaction between the Cu metal and CeO2 support. Slow deactivations were observed over the 3.8 wt% Cu/CeO2 catalyst at 493 and 513 K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773 K followed by reduction in H-2 at 673 K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature- programmed oxidation) method, the amounts of coke on the 3.8 wt% Cu/CeO2 catalyst were 0.8 wt% at 493 K and 1.7wt% at 513 K after 24 h on stream.