Effect of W Content on Structure and Catalytic Performance of Pt/GaWZrOx Catalysts in Glycerol Selective Hydrogenolysis

The Pt-WOx catalyst system has received much attention for its high activity and selectivity in glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO). In this work, the Ga-doped GaWZrOx solid acid supports (GaWZ) with different W contents were prepared, and then Pt/GaWZ catalysts were prepared by the wetness impregnation method. The effects of the W contents on the physicochemical properties and catalytic performance of the Pt/GaWZ catalysts were systematically investigated. CO chemisorption and X-ray photoelectron spectroscopy (XPS) characterizations revealed that the dispersion of Pt on the GaWZ supports first increasesd with the increase in the W content, reached a maximum of 86% on the Pt/GaWZ(10) catalyst with 10% (w) of W, and then decreased at 15% (w) of W. UV-Vis diffuse reflectance (UV-Vis DRS), Fourier transform infrared (FTIR), and XPS characterization showed that the W in the Pt/GaWZ catalysts interacted with the Zr-OH functional groups on the tetragonal phase ZrO2, thus forming mono-dispersed WOx species. When the W content was greater than 7.5% (w), the second layer of the WOx species began to emerge. The mono-dispersed WOx species may be conducive to the high dispersion of Pt. The results of the temperature-programmed desorption of NH3 (NH3-TPD) and pyridine adsorption infrared (Py-IR) characterizations showed that the higher the W content, the higher the amount of the acid on the catalyst, with the simultaneous increase in the amounts of both the Bronsted acids and Lewis acids. In glycerol hydrogenolysis over the Pt/GaWZ catalysts, with the increase in the W content, the glycerol conversion evolved in a volcano-shaped trend, while the selectivity to the target product 1,3-PDO increased monotonically. The highest yield of 1,3-PDO of 47.5% was achieved over the Pt/GaWZ(10) catalyst, and the catalyst also displayed excellent recycling stability. On the basis of the characterization results, we propose that the Pt dispersion and the synergistic interaction between Pt and WOx species determine the activity of the Pt/GaWZ catalysts in glycerol hydrogenolysis, and the Bronsted acid site pertaining to the WOx species is the key to determine the selectivity to 1,3-PDO over the Pt/GaWZ catalysts, as evidenced by the good linear relationship between the 1,3-PDO selectivity and the amount of the Bronsted acid sites.