Display omitted •Ni–Cu alloy phase exhibits high activity and selectivity toward WGSR.•Ni–Cu alloy enhances CO adsorption at high temperature, preventing CO dissociation.•Carboxyl associative mechanism is found as a dominant reaction pathway.•Carboxyl species is the main intermediate with formate species as a spectator. The formation of methane as the undesired side product is one of the major issues in the water–gas shift (WGS) reaction, particularly for nickel-based catalysts. A detailed study of Ni–Cu bimetallic catalyst supported on nanopowder CeO2 is extensively investigated to suppress the methanation reaction as well as maintain high WGS reaction rate. XRD, EXAFS, H2-TPR and XPS reveal the formation of Ni–Cu alloy, while CO-TPR-MS, CO-TPD-MS and in situ DRIFTS show the enhancement of CO adsorption on Ni–Cu alloy at high temperature. The Ni–Cu/CeO2 catalyst with Ni/Cu ratio of 1 exhibits high reaction rate with the least methane formation due to the formation of Ni–Cu alloy phase. The Ni–Cu alloy phase is found to be the active site for WGS reaction with methane suppression as Ni–Cu alloy can enhance CO adsorption which prevents CO dissociation during high-temperature WGS reaction. Kinetic studies performed reveal that one-site carboxyl mechanism could be the main reaction pathway with formate as spectator. However, there could be other possibilities for the real reaction mechanism on Ni–Cu/CeO2 catalyst.