Catalytic C-O bond hydrogenolysis of tetrahydrofuran-dimethanol over metal supported WOx/TiO2 catalysts

[Display omitted] •Pt- & Rh-WOx/TiO2 have 2 orders of magnitude higher activity than Ru- & Pd-WOx/TiO2.•Pt- & Rh-WOx/TiO2 have less overcoats of WOx and more reduction of W6+ to W5+.•THFDM reaction rate passes through a maximum with H2 pressure.•A higher H2 pressure makes H2 coverage higher and further reduces the W.•Catalyst deactivation is likely due to tungsten leaching. M-WOx/TiO2 (M = Pt-, Rh-, Pd-, and Ru) catalysts were prepared and studied for tetrahydrofuran-dimethanol (THFDM) hydrogenolysis. All catalysts have a small metal particle size (< 2 nm) but show catalytic activities that differ by two orders of magnitude. From a combination of CO chemisorption and STEM, we conclude that this wide gap in activity is primarily due to overgrowth of WOx/TiO2 covering the metal particle of the less-active catalysts. This overgrowth decreases the number of exposed hydrogenation sites in these catalysts, lowering the overall reaction rate. The catalyst with the highest activity (Pt-WOx/TiO2) was studied at various pressures of H2, with catalytic activity passing through a maximum with increasing pressure. This is likely due to changes in the oxidation state of Wδ+ on the catalyst surface, which changes from W6+ to W5+ and W4+ with increasing hydrogen pressure. Moreover, H2 can strongly adsorb on the catalyst surface and inhibit the activity at high hydrogen pressure. The apparent activation energy of THFDM conversion over Pt-WOx/TiO2 is 47 kJ·mol−1. Pt-WOx/TiO2 showed a decrease in conversion from 45% to 23% over 46 h on stream in a continuous flow reactor. Catalyst deactivation is likely due to leaching of W. THFDM can be efficiently converted to 1,2,6-hexanetriol (HTO) in the presence of Pt/TiO2 and homogeneous W salts.