Regarding the spent Ir-Mo/SiO2 catalyst, all remaining Mo(VI) species are converted yielding an increased amount of both Mo(IV) and Mo(0) according to the Mo K-edge XANES (Figure ) and LCF analysis (Figure ). Notably, the respective EXAFS spectrum can be fitted with two scattering paths corresponding to Mo-O and Mo-Ir (Figure , Table From the perspective of Ir L3-edge EXAFS, no respective Ir-Mo path can be fitted for both the fresh and spent Ir-Mo/SiO2 catalyst, and only an Ir-Ir path consistent with metallic Ir is found. This is likely due to the low concentration of Mo with respect to Ir (1:8). The monometallic Mo material, MoO3/SiO2, in the absence of Ir, is also reduced under HDO conditions (with 1-nonanol), but only from Mo(VI) to Mo(IV), while no metallic Mo(0) is observed, corroborating the strong interaction between Ir and Mo in Ir-Mo/SiO2 and the necessity of a second metal to achieve a reduction to Mo(0). Overall, these combined results confirm the reduction of Mo by Ir and the alloying of Mo into catalyst. In contrast to the other metals, while Mo(0) is present in the fresh Ni-Mo/SiO2 material, presumably in an alloyed state or the interface, it does not withstand the HDO conditions. This absence of an alloy phase parallels the absence of (or very low) HDO reactivity. In summary, it can be concluded that across all the investigated bimetallic catalysts based on the motif M-Mo/SiO2, for which HDO activity is observed (M = Ir, Rh, Pt, and Pd for tertiary alcohols), Mo is reduced to a metallic state in significant extent and incorporated in the nanoparticles of M, forming an alloy. In sharp contrast, no significant alloying is observed for Ni exposed to HDO conditions, likely inhibiting synergies between the two elements and the loss of HDO activity. This indicates that the presence of reduced Mo and alloying is most probably key and enables the activation of C-O bonds in oxygenates like alcohols (Figure ). In light of the high Mo-O bond strength and the need of having reduced Mo sites, one can propose that Mo sites in M-Mo alloys help to activate the C-O bond by strongly binding oxygen functionalities, while the late transition metal activates H2 and helps to (re-)reduce both Mo and the hydrocarbyl part. This parallels what is observed with bimetallic reverse-water-gas-shift (RWGS) catalysts. We hypothesise that the re-reduction step is challenging for Ni, leading to the observed dealloying and the low activity. Regarding Pd, the negligible variation in Mo(0) content before and after the reaction with 1-nonanol suggests that Pd-Mo phases are not able to promote bond cleavage of strong primary C-O bonds, while it is possible for more polarizable tertiary alcohol bonds.