The water gas shift reaction has been studied with density functional theory on Pt(111)/M(111) pseudomorphic monolayer catalysts (where M is the host metal). Both redox and carboxyl intermediate mechanisms were explored. It was found that the barriers for dissociation reactions (H2O, OH, OH disproportionation) are lower on systems with an expanded lattice parameter of Pt (when compared to pure Pt) and that the barriers for formation reactions (CO oxidation, carboxyl formation) are higher compared to Pt(111). Similarly, this situation is reversed for the alloys with a compressed lattice parameter. In all cases, the carboxyl reaction path is favored and water dissociation was found to have the highest barrier along the reaction path. Using results from our previous studies for NO oxidation for NOx storage reduction (NSR) on the same systems, we were able to construct volcano plots for both the oxidation mode and the reduction mode of NSR (if H2 produced from WGS is conceived to be kinetically critical).