Synthesis and Characterization. All bimetallic materials are prepared in two steps. The first step involves the dispersion of 0.3 wt.% Mo on SiO2 (Degussa-Evonik, Aerosil-200), which corresponds to ca. 0.1 Mo/nm 2 via incipient-wetness impregnation of ammonium heptamolybdate ((NH4)6Mo7O24), followed by calcination (500 °C under a flow of dry synthetic air). The second metal (ca. 1 M atom/nm 2 ) is introduced using SOMC (Figure ). We select amidinate-based precursors, because they provide a structurally unified platform for all five investigated metals M (Ni, Pd, Pt, Rh, and Ir) and afford supported nanoparticles with relatively narrow size distribution upon treatment under H2. In short, after grafting the amidinate-based precursors on isolated surface OH groups, as evidenced by IR spectroscopy (Figure , middle spectrum), the obtained materials are treated under a flow of H2 at 500 °C. The resulting IR spectrum (Figure , top spectrum) confirms the removal of all organic ligand fragments while the isolated OH groups are restored. The respective monometallic materials are prepared from the same precursors, using SiO2-700 (SiO2 subjected to a temperature treatment at 700 °C at 10 -6 mbar) in place of the Mo-doped support. HAADF-STEM micrographs of all as-prepared materials are recorded and analysed without prior exposure to air (Table , Figure and). All materials contain narrowly dispersed nanoparticles of 2-3 nm. With the exception of PtMo, all bimetallic materials exhibit smaller and more narrowly dispersed nanoparticles compared to their monometallic counterparts. For NiMo, the sub-nanometre particles are not resolved. For PdMo, the particles are considerably better dispersed, than in the monometallic case; this effect had been previously observed for alloyed bimetallic Pd-Ga/SiO2 derived from the same precursor. Both IrMo and RhMo also display nanoparticles that are ca. 1 nm smaller than the respective monometallic materials. The strong influence of Mo is particularly remarkable considering that the M:Mo ratio is ca. 8:1, suggesting a strong interaction between the two metals. HDO Activity. Next, the synthesized materials are evaluated for the HDO of primary, secondary, and tertiary alcohols. For 1nonanol (at a catalyst loading of 0.75 mol% M, 130 °C, 20 bar of H2 and decalin as a solvent) the corresponding alkane, n-nonane, is formed in good to high yield within 24 h for the bimetallic materials containing Rh, Ir, and Pt. On the other hand, none of the monometallic materials, including MoO3/SiO2, enable efficient HDO under the same conditions. Notably, n-octane (ca. 7%) and traces of n-heptane besides n-nonane are observed with Rh-Mo/SiO2, indicating that C-C cleavage also occurs as a side reaction with Rh. In sharp contrast, bimetallic Ni-Mo/SiO2 and Pd-Mo/SiO2 do not catalyse the HDO reaction of primary alcohols under the investigated conditions. In the case of 2-nonanol, Rh, Pt, and Ir, in combination with Mo, are again highly active materials affording the deoxygenated products in good yield. Pd-Mo/SiO2 enables low conversion, yielding only ca. 6% nnonane. Only traces of product (~1%) are observed for Ni-Mo/SiO2. In the case of 2-nonanol, no C-C cracking-derived side products are observed even for Rh-Mo/SiO2. In contrast to 1-nonanol, some of the monometallic materials display minor productivity in HDO of 2-nonanol: ca. 2% yield with Rh/SiO2 and ca. 6% yield for Ir/SiO2 and Pt/SiO2. Note that the conversion could not be determined due to the overlap of the 2-nonanol GC signal with one isomer of decalin. Finally, the materials are also evaluated for the deoxygenation of a tertiary alcohol, namely 2,6-dimethylheptan-2-ol. All of the monometallic materials display deoxygenation activity, in particular Rh/SiO2 and Ir/SiO2 afford the product, 2,6-dimethylheptane, in 18% and 44% yield, respectively. The monometallic materials based on Ni, Pd, and Pt show lower yields of 1%, 3%, and 5%, respectively. Yet, addition of Mo again increases the HDO activity, resulting in high yields of HDO product (~80%) for RhMo, IrMo, PtMo, and PdMo. In contrast to primary and secondary alcohols, the PdMo material gives good yield of deoxygenated product with the alcohol. However, NiMo remains poorly active with a HDO product yield of ca. 5%. Considering that Pd-Mo/SiO2 is inactive for 1-nonanol and 2nonanol, we highlight the possibility of selectively deoxygenating tertiary alcohols over primary and secondary alcohols. Subjecting a mixture of 1-nonanol and 2,6-dimethylheptan-2-ol to HDO conditions with Pd-Mo/SiO2 leads to the selective formation of 2,6-dimethylheptane in 64% yield (76% conversion), while no n-nonane is observed. The activity of the Pd-Mo/SiO2 catalyst seems to be partially inhibited by the presence of 1nonanol, however, the deoxygenation is highly selective. Since Ir-Mo/SiO2 displays the most promising properties as a general deoxygenation catalyst for aliphatic alcohols, we further investigate the reactivity of this catalyst. First, the reaction profile is examined by monitoring the reaction products at various reaction times (1, 3, and 8 h), which confirms that 24 h reaction time is necessary for achieving full conversion (Figure ). We also check the possibility of recycling the catalyst, which reveals a constant decrease of activity, giving 86%, 60%, and 15% yields after the 1 st , 2 nd , and 5 th cycle, respectively (Figure ). The treatment of the spent material with H₂ or calcination followed by H₂ cannot fully restore the high activity observed in the first cycle. Elemental analysis after five cycles reveals a partial loss of metals, with approximately 35% reduction in Mo content and 15% reduction in Ir. While this loss likely contributes to some of the observed decline in activity, it does not account for the entirety of the decrease, suggesting that irreversible structural changes may have occurred under reaction conditions. Investigation of Structure-Activity Relationship. The significant difference in reactivity between monometallic and bimetallic materials suggests a key influence of Mo, leading to a synergistic enhancement of catalytic performance. Surface Acidity. One possible effect leading to enhanced HDO activity is a marked increase in Brønsted acidity upon adding Mo on the silica surface, which could help activating the alcohol by protonation, thereby facilitating C-O activation and formation of water as a by-product. Similarly, Mo(VI) can act as a Lewis acid and weaken C-O bonds by coordinating oxygen lone pairs. To probe the possibility of enhanced Brønsted and/or Lewis acidity induced by Mo, we next turn to N-pyridine adsorption on the most active catalyst (Ir-Mo/SiO2) and analyse the pyridine-exposed material by N magic angle spinning solid-state (MAS-SS) NMR spectroscopy. Notably, only H-bonded pyridine interacting with surface silanol groups is observed, with no evidence of pyridinium formation or pyridine bound to Lewis acidic surface sites, indicating no enhanced Brønsted or Lewis acidity in bimetallic materials. This observation suggests that the promoting role of Mo is of a different nature. Probing Electronic Effects of Mo with CO-IR Spectroscopy. To investigate whether Mo can affect the electronic structure of late transition metal nanoparticles, we turn to IR spectroscopy of adsorbed CO as a probe molecule, without exposing the as-prepared materials to air. Looking first at the Ir-based systems, the IR stretching frequency of adsorbed terminal CO is observed at 2079 cm -1 for Ir/SiO2 vs. 2072 cm -1 in the bimetallic material, Ir-Mo/SiO2. Besides the red-shift, this band decreases in intensity (Figure ), suggesting a significant influence of Mo on the electronic structure of metallic nanoparticles. The observed red shift suggests more electron-rich Ir centres, consistent with alloying (vide infra). Notably, a significant difference of CO signatures in mono-vs. bimetallic materials is also observed for Rh, Pt, and Pd, where Mo increases activity, likely indicating alloy formation (Figures ).