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The water–gas shift (WGS) reaction (CO + H₂O ↔ CO₂ + H₂) plays an important role in the hydrogen economy because it is an effective way to reduce the carbon release to net-zero CO₂ emissions. The general goal of this research is to develop nanosized oxo-rhenium catalyst formulations promoted by K and Co components for the WGS process. Rhenium, as a low-cost catalyst component, is a good choice compared to platinum group metals. A surface density of 2 Re atoms/nm² on a γ-Al₂O₃ support as well as cobalt (3 wt.% CoO) and potassium (5 wt.% K₂O) amounts were chosen to match the composition of our own active sour WGS KCoRe catalyst developed some years ago. An initial evaluation of the impact of replacing half of the rhenium with molybdenum, which is more affordable, was also studied. The purpose of this study is to explore the catalytic ability of CoRe, K-CoRe, CoReMo, and K-CoReMo formulations in the WGS reaction and elucidate the effect of a CO/Ar reaction mixture used in an activation–reduction pretreatment to form active catalyst structures. Oxo-K-Co-Re(Mo) entities formed in synthesized samples and their reducibility were analyzed via several physicochemical methods, such as N₂ physisorption, PXRD, UV-vis DRS, and H₂-TPR. In summary, the selected potassium- and cobalt-promoted Re-containing formulations have potential as catalysts for the classical WGS reaction. The selection of an appropriate procedure for activation–reduction, involving the reducing gas (CO or H₂), temperature, and duration, was needed for tuning the K-CoRe catalyst’s high activity for the WGS reaction with structural stability and longevity. Full article