Transition metal promoters in CuO/CeO2 catalysts for CO removal from hydrogen streams

Either cobalt or molybdenum was added to CuO/CeO2 support by incipient wetness impregnation, with Cu/Me (Me = Co, Mo) atom ratio of 3. The as-prepared catalysts were characterized and tested in CO-PROX, WGS and OWGS reactions. Both compounds are mainly as Co3O4 and MoO3, although part of molybdenum was detected as Mo+5. Addition of molybdenum modified the lattice of ceria and as well as the textural properties, as a fraction of molybdenum was inserted in ceria lattice. In addition, molybdena assisted the sintering of ceria. Addition of cobalt did not modify substantially the structure and texture of ceria. The concentration of surface oxygen vacancies decreased after addition of Co or Mo, as found by Raman spectroscopy. It was found that CuCe sample has the highest concentration of small, well-dispersed copper species among all the samples.There was found a variety of copper species in different interaction degree with the surroundings. The less reducible sample was a molybdenum-containing sample, while below 125 °C the highest CO uptake to H2 uptake ratio corresponds to CoCuCe sample, which correlated with its highest selectivity in CO-PROX. CO conversion of CuCe and CoCuCe catalysts in CO-PROX, WGS and OWGS reactions were similar, but cobalt-containing catalysts was more selective towards CO2 in CO-PROX, suggesting that the active copper species for both reactions should be different. Activity of MoCuCe sample is suppressed in CO-PROX, WGS and OWGS reactions. Cobalt was found to suppress H2 oxidation in CO-PROX reaction. CoCuCe catalyst is highly selective and active catalyst for CO-PROX, but its activity in WGS and OWGS does not overcome the activity of CuCe catalyst.

► Promoters decrease the concentration of surface oxygen vacancies. ► Easily reducible copper species concentration decrease with promoters. ► Co greatly enhances selectivity in CO-PROX. ► Mo addition suppresses catalyst activity.