Promoting effect of Silicotungstic acid on selective hydrogenolysis of glycerol to 1,3-propanediol over bifunctional Pt/STA/βzeolite catalysts

Selective conversion of glycerol to 1,3-propanediol (1,3-PDO) is challenging due to the differing reactivities of its hydroxyl groups, leading to low reaction rates and selectivity. This study identifies an optimal catalyst formulation and examines the role of its components. A novel Silicotungstic acid (STA)-promoted Pt-β-zeolite catalyst with a high Si/Al ratio (Si/Al = 300) was synthesized, varying the STA loading to evaluate its performance in glycerol hydrogenolysis using a slurry batch reactor. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), NH₃–TPD, H₂-TPR, CO chemisorption, FT-IR with pyridine as probe (Py-IR), thermogravimetric analysis (TGA) with pyridine/2,6-di-tert-butylpyridine as a probe (Py/dTBpy-TGA), HR-TEM, and XPS. XRD confirmed the presence of the tungsten bronze phase (H_0.53WO₃), which enhances glycerol conversion and 1,3-PDO selectivity. Increasing the STA-to-β-zeolite ratio up to 0.3 improved both conversion and selectivity, beyond which selectivity declined despite higher conversion. The Pt/0.3STA/β-zeolite catalyst exhibited the highest 1,3-PDO selectivity and productivity due to its strong Brønsted acidity, enhanced Pt-STA interaction, superior Pt dispersion, and hydrogen spillover. Compared to Pt/β-zeolite, this catalyst increased 1,3-PDO productivity tenfold and selectivity sixfold. After 5 h of reaction at 220 °C and 4 MPa, Pt/0.3STA/β-zeolite catalyst achieved 31.40 % selectivity at 25 % conversion. By contrast, unpromoted Pt/β-zeolite favoured 1,2-PDO formation due to its lower acidity and predominant Lewis acid sites. The effects of glycerol concentration, temperature, H₂ pressure, catalyst composition, Pt loading, and reaction time were also investigated to determine optimal conditions. Finally, a reaction mechanism for 1,3-PDO synthesis from glycerol is proposed based on reactant-product profiles.