W-doped Hierarchically Porous Silica Nanosphere Supported Platinum for Catalytic Glycerol Hydrogenolysis to 1,3-Propanediol

As a versatile platform molecule, glycerol has been widely studied for the production of high value-added chemicals. In particular, catalytic hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) is a highly desired route for glycerol valorization. Herein, hierarchically porous SiO2 nanospheres doped in situ with W (W-HPSN) were synthesized. The effect of the addition of short-chain alcohols (methanol, ethanol, and n-propanol) as co-solvents during the synthesis of W-HPSN on the catalytic performances of the Pt/W-HPSN catalysts in glycerol hydrogenolysis to 1,3-PDO was systematically investigated. The basic physicochemical properties, the chemical states of the active components, and the acidic properties of the catalysts were characterized by a variety of techniques. Compared with the Pt/W-HPSN-H2O catalyst prepared from W-HPSN synthesized only with water as the solvent, when the alcohols were added as the co-solvents, the specific surface area of the catalyst increased to different degrees. And aside from the micropores at 1.4 nm and the mesopores at >2 nm, new micropores appeared at 1.7 nm. In glycerol hydrogenolysis, the catalysts prepared from the W-HPSN synthesized with the addition of alcohols as the co-solvents also displayed improved glycerol conversion and 1,3-PDO selectivity, and the 1,3-PDO yields were in the order of Pt/W- HPSN- Me> Pt/ W-HPSN-Pr>Pt/W-HPSN- Et> Pt/ W-HPSN-H2O. On the best Pt/W-HPSN-Me catalyst synthesized with methanol as the co-solvent, the glycerol conversion and 1,3-PDO selectivity were 88.8% and 56.3%, respectively, in comparison to 64.1% and 40.7%, respectively, on the Pt/W-HPSN-H2O catalyst. Elemental analysis showed that the Pt and W loadings on the Pt/W-HPSN- H2O and Pt/W-HPSN-Me catalysts are identical. The X-ray photoelectron spectroscopy (XPS), Raman, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) characterizations revealed that the chemical states of the Pt and W species on the Pt/W-HPSN-H2O and Pt/W-HPSN-Me catalysts are similar. CO chemisorption and transmission electron microscopy (TEM) characterizations demonstrated that the Pt particle size on the Pt/W-HPSN-Me catalyst is smaller than that on the Pt/W-HPSN-H2O catalyst. And the cumene cracking reaction detected more in-situ generated Bronsted acid sites on the Pt/W-HPSN-Me catalyst than on the Pt/W-HPSN-H2O catalyst in H-2 atmosphere. On the basis of these characterization results, we propose that smaller Pt particle size and more in-situ generated Bronsted acid sites are conducive to a better catalytic performance of the Pt/W-HPSN catalyst. By further optimization of the composition of the W-HPSN-Me support, at the W/Si molar ratio of 1/320 and under the reaction conditions of 423 K, 4 MPa of H-2 pressure, and reaction time of only 12 h, the Pt/W-HPSN-Me catalyst afforded enhanced glycerol conversion and 1,3-PDO selectivity of 98.7% and 58.8%, respectively, thus giving rise to an outstanding 1,3-PDO yield of 58.0%. This work shows prospect for the HPSN material as an excellent catalyst support for the hydrogenolysis of glycerol to 1,3-PDO.