New insights on the Cu–Ce interaction in Cu/Ce catalysts based on ZSM-5 and Beta for the preferential oxidation of carbon monoxide in excess hydrogen

Abstract

Cu-Ce-modified zeolites are shown to be effective in preferential CO oxidation (CO-PROX) in H2-rich stream. Catalysts containing copper and cerium based on zeolites ZSM-5 (Si/Al = 15, 28 and 40) and Beta (Si/Al = 19) are synthesized by sequential incipient wetness impregnation and tested in total (CO-TOX) and preferential oxidation of CO. The influence of zeolite framework type, Si/Al ratio, metal loading and order of metal introduction on the formation of active sites and their activity and selectivity are studied. Based on XRD, TEM, XPS, adsorbed CO DRIFTS and H2-TPR studies it is shown that of the key importance is synergistic interaction of copper and cerium not only on the surface, but in the zeolite channels. Cu+ incorporated in CeO2 and mixed copper-cerium oxo/hydroxocations can both be active sites in CO oxidation. Wider channels of Beta framework favor the penetration of metal cations, but not formation of necessary active sites. The presence of CuO phase in the catalysts negatively affects the stability and selectivity in CO-PROX. ZSM-5-based catalyst containing largest amount of oxocations (2.6 wt% Cu, 10 wt% Ce, Si/Al = 15) makes it possible to completely remove CO from H2-rich mixture in CO-PROX at 150–190 °C.