Selective Hydrogenolysis of Erythritol over Ir−ReO_x/Rutile-TiO₂ Catalyst

Partial hydrogenolysis of erythritol, which can be produced at large scale by fermentation, to 1,4-butanediol (1,4-BuD) is investigated with Ir−ReO_x/SiO₂ and Ir−ReO_x/rutile-TiO₂ catalysts. In addition to the higher conversion rate over Ir−ReO_x/TiO₂ than over Ir−ReO_x/SiO₂, which has been also reported for glycerol hydrogenolysis, Ir−ReO_x/TiO₂ showed higher selectivity to 1,4-BuD than Ir−ReO_x/SiO₂, especially at low conversion levels, leading to high 1,4-BuD productivity of 20 mmol_1,4-BuD g_Ir⁻¹ h⁻¹ at 373 K (36 % conversion, 33 % selectivity). The productivity based on the noble metal amount is higher than those reported previously, although the maximum yield of 1,4-BuD (23 %) is not higher than the highest reported values. The reactions of various triols, diols and mono-ols are tested and the selectivity and the reaction rates are compared between catalysts and between substrates. The Ir−ReO_x/TiO₂ catalyst showed about twofold higher activity than Ir−ReO_x/SiO₂ in hydrogenolysis of the C−OH bond at the 2- or 3-positions in 1,2- and 1,3-diols, respectively, whereas the hydrogenolysis of C−OH at the 1-position is less promoted by the TiO₂ support. Lowering the loading amount of Ir on TiO₂ (from 4 wt % to 2 or 1 wt %) decreases the Ir-based activity and 1,4-BuD selectivity. Similarly, increasing the loading amount on SiO₂ from 4 wt % to 20 wt % increases the Ir-based activity and 1,4-BuD selectivity, although they remain lower than those for TiO₂-supported catalyst with 4 wt % Ir. High metal loadings on the support seem to be important.