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-FeOx/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-FeOx/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-FeOx/rutile). Irc-r-FeOx/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-FeOx/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 FeOx species were constructed on the active catalyst. The active sites should be the interface between the Ir–Fe surface alloy and the FeOx species.