Selective C–O Hydrogenolysis of Terminal C–OH Bond in 1,2-Diols over Rutile-Titania-Supported Iridium-Iron Catalysts

Catalysts with high selectivity to cleave terminal OH groups of 1,2-alkanediol are vital to extending the scope of value-added products from biomass instead of fossil fuels but have not yet been reported so far. In this study, 1,2-butanediol (1,2-BuD) hydrogenolysis was selected as a model reaction to develop such a regioselective catalyst. The selectivity to 2-butanol (2-BuOH) over Ir/rutile TiO2 (Ir = 5 wt %) was moderate (53%) initially but rapidly decreased (39%) at a longer reaction time (72 h). Addition of Fe to Ir/rutile enhanced both activity and selectivity. Ir-FeO x /rutile (Ir = 5 wt %, Fe/Ir = 0.25) was an effective catalyst, while other oxide supports including anatase TiO2 gave lower selectivity to 2-BuOH. A severe deactivation phenomenon was observed during the reuse experiment over the Ir-FeO x /rutile (Ir = 5 wt %, Fe/Ir = 0.25) catalyst. Interestingly, the reusability of the catalyst was reinforced by optimizing the preparation method (involving the calcination followed by reduction and subsequent loading of Fe; Irc‑r-FeO x /rutile). Irc‑r-FeO x /rutile (Ir = 5 wt %, Fe/Ir = 0.25) was reusable at least 4 times and gave a high 2-BuOH yield (64%) from 1,2-BuD. Such regioselectivity given by Irc‑r-FeO x /rutile (Ir = 5 wt %, Fe/Ir = 0.25) was also demonstrated in the hydrogenolysis of related alcohols: 1,2-propanediol to 2-propanol (yield: 53%), glycerol to 1,2-propanediol (yield: 62%), glycerol to 2-propanol (yield: 30%), 1,3-butanediol to 2-BuOH (yield: 83%), and erythritol to 2,3-butanediol (yield: 30%). Characterization with X-ray diffraction (XRD), temperature-programmed reduction with H2 (H2-TPR), transmission electron microscope-energy-dispersive X-ray (TEM-EDX), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), CO adsorption, and DRIFT of adsorbed CO suggested that Ir particles with the Ir–Fe alloy on the surface (3 nm) modified with FeO x species were constructed on the active catalyst. The active sites should be the interface between the Ir–Fe surface alloy and the FeO x species.