The influence of Cr, Zn and Co additives on the performance of skeletal copper catalysts for methanol synthesis and related reactions

The effects of chromium, zinc and cobalt additives on the properties of skeletal copper catalysts for the reactions of methanol synthesis (MS), water gas shift (WGS) and methanol steam reforming (MSR) have been studied. Catalysts were prepared by doping Cr, Zn and Co additives on the surfaces of fully leached skeletal copper. Small amounts of Cr2O3 were found to significantly enhance the activity for the water gas shift reaction. Improvements were also observed for methanol steam reforming and methanol synthesis reactions. The presence of ZnO on the surface of skeletal copper was shown to greatly enhance methanol synthesis, suggesting that very active Cu-ZnO sites were created. ZnO also enhanced the activity for both the water gas shift and methanol steam reforming reactions. On the other hand, addition of Co had no effect on methanol synthesis activity and gave poor selectivity for methanol steam reforming. More significantly, the Co additive reduced the activity of skeletal Cu to the extent that more than 1.1 wt.% Co additive on the surface resulted in negligible activity for the WGS reaction. The reason for the different performance with the Co additive is thought to be the reduction of surface CoO to metallic cobalt under the reducing conditions of catalyst pretreatment and reaction. Temperature programmed reduction (TPR), fitration with N2O, and CO chemisorption measurements support this reasoning. This investigation of the role of additives in methanol steam reforming and the water gas shift reactions provides support for a recently proposed pathway for methanol steam reforming reaction over Cu catalysts via a formaldehyde or methyl formate intermediate. (C) 2003 Published by Elsevier B.V.