Abstract

The catalytic performance for Water Gas Shift Reaction and surface species at reaction conditions were studied by operando-DRIFTS of the bare Pr-promoted Ce oxide support, two supported monometallic Cu and Ni, and a bimetallic CuNi catalyst. All samples were thoroughly characterised by Operando-DRIFTS across a range of temperatures (150-375 degrees C) and two distinct reaction atmospheres: CO-H2O and CO-H2O-H-2. The results demonstrated that the nature of the surrounding atmosphere significantly influences the surface chemistry and product distribution. The reactivity was as follows: CePr < Cu/CePr < CuNi/CePr < Ni/CePr. However, the selectivity towards CO2 was CePr=Cu/CePr > CuNi/CePr > Ni/CePr due to the tendency to produce CH4 (on Ni-containing catalysts) when H-2 was present in the reaction feed. Hence, under oxidising conditions (absence of hydrogen), formate species were stabilised on CePr and Ni/CePr surfaces, indicating a predominant associative mechanism. In contrast, Cu-containing catalysts (Cu/CePr and CuNi/CePr) favoured carbonate formation and suppressed formate accumulation, promoting a redox-type pathway. Under reducing conditions (presence of H-2), Ni facilitated CH4 formation via methanation, particularly on Ni/CePr. The bimetallic CuNi/CePr catalyst behaved similarly to Cu/CePr under CO-H2O feed, showing no stable formates, but in the presence of H-2, methane formation and surface-stabilised formates were observed-mimicking the behaviour of Ni/CePr. These findings highlight the role of Cu in modulating the electronic and adsorptive properties of Ni, weakening formate adsorption and delaying methanation, thus enhancing CO2 selectivity. Overall, the CuNi/CePr system emerges as a complex multimetallic catalyst that adapts to both oxidising and reducing environments, improving WGS performance through a balanced interplay between redox and hydrogenation pathways.