In this study, we have systematically investigated the effect of Mo on alcohol deoxygenation for bimetallic materials based on M-Mo/SiO2 (M = Ni, Pd, Pt, Rh, and Ir). The SOMC preparation protocol, combined with an air-free approach for characterization before and after catalysis, allows for a direct comparison of activity and structure between the five investigated metals. The promotional effect of Mo was particularly strong in combination with Ir, but also significant with Rh and Pt. For PdMo, efficient HDO activity is observed only with tertiary alcohols, while almost no conversion to product was seen for the secondary and primary alcohols, opening the possibility to explore the selective deoxygenation of diols with Pd-Mo alloys. For Nibased catalysts, no significant deoxygenation activity is observed, which parallels the lack of formation of a stable alloy with Mo under the investigated reaction conditions. Coming to the role of Mo, while Brønsted (and/or Lewis) acidity is often inferred to be an important factor for HDO activity, our data indicates that Mo, in the low amounts used here (0.3 wt.%), has little impact on the acidity of the explored catalysts, yet strongly enhances the catalytic performance. In contrast, CO-adsorbed IR spectroscopy and XAS clearly indicate the presence of reduced Mo, in particular Mo(0), and suggest that alloying is key to obtain HDO activity. Presumably, Mo activates the C-O bond by coordination to oxygen followed by a redox process, while the other transition metals (Pd, Pt, Rh, and Ir) help to activate H2, which is used to keep Mo in a reduced state and enable catalytic turnover.