负载Pt-WOx催化剂上甘油选择氢解合成1, 3-丙二醇

甘油是重要的生物质基平台分子，可以从生物柴油生产过程中作为副产物大量获得。本文采用等容浸渍法，在氧化钛、三氧化二铝和氧化锆载体上制备一系列具有不同WO₃表面密度的负载Pt-WO_x催化剂，研究了它们在甘油选择氢解合成1, 3-丙二醇反应中的催化性能。实验结果表明，WO₃的表面密度显著影响这些催化剂的活性和1, 3-丙二醇选择性，它们均在1.5–2.0 W?nm^?2表面密度时表现出最优性能，表明分散的WO_x物种是影响Pt-WO_x催化剂性能的关键因素。通过原位红外CO吸附表征等方法发现Pt粒子与WO_x物种之间存在电荷转移和强相互作用，进而提高Pt-WO_x催化剂的甘油氢解转化为1, 3-丙二醇的活性。进一步比较甘油、1, 2-丙二醇和1, 3-丙二醇的氢解反应发现，1, 3-丙二醇的氢解速率常数低于甘油和1, 2-丙二醇，表明在Pt-WO_x催化剂上1, 3-丙二醇具有更高的反应稳定性，这跟Pt-WO_x催化剂具有较高的1, 3-丙二醇选择性相一致。结合氢气分压对甘油氢解活性表现出的火山型影响结果和在D₂/D₂O存在下，观察到的1, 3-丙二醇产物中仲碳与伯碳上的H原子数的比例(~1 : 2)，我们推测在甘油氢解合成1, 3-丙二醇反应中，甘油首先在Pt-WO_x催化剂上脱氢生成甘油醛中间体，然后甘油醛进一步脱水和加氢转化为1, 3-丙二醇。

Selective Hydrogenolysis of Glycerol to 1, 3-Propanediol over Supported Platinum-Tungsten Oxide Catalysts

Glycerol is a versatile platform compound that is formed in considerable amounts as a by-product of biodiesel production. The catalytic selective hydrogenolysis of glycerol to 1, 3-propanediol (1, 3-PDO) provides a sustainable route for the synthesis of this important diol. In this study, a series of platinum-tungsten oxide (Pt-WO_x) catalysts with different WO_x surface densities dispersed on titanium(Ⅳ) oxide, zirconium(Ⅳ) oxide, and aluminum oxide supports were prepared and evaluated for the glycerol hydrogenolysis to 1, 3-PDO. The highest reaction activity and 1, 3-PDO selectivity were achieved at a WO_x density of approximately 1.5–2.0 W·nm^?2, with all three support materials. Such a strong dependence on the surface density of WO_x revealed the critical role of the dispersed WO_x domains in the hydrogenolysis of glycerol to 1, 3-PDO. The infrared spectra for carbon monoxide adsorption confirmed the electron transfer and strong interaction between the Pt particles and WO_x domains. These phenomena were hypothesized to contribute to the superior selectivity to 1, 3-PDO over 1, 2-PDO of the supported Pt-WO_x catalysts when compared with the corresponding supported Pt catalysts. The realized superior 1, 3-PDO selectivity was consistent with its higher stability on the Pt-WO_x catalysts, as reflected by the lower reaction rate constant of 1, 3-PDO than those of 1, 2-PDO and glycerol obtained in their hydrogenolysis reactions. There existed a volcano-type dependence of the glycerol reaction activity on the hydrogen partial pressure. Such a dependence, together with the measured ratio (1 : 2) of the secondary to the primary C?H bonds in 1, 3-PDO in the presence of deuterium and deuterium oxide (replacing hydrogen and water, respectively), indicated that the glycerol hydrogenolysis proceeds by the kinetically relevant dehydrogenation of glycerol to the glyceraldehyde intermediate, followed by the dehydration and hydrogenation of glyceraldehyde to 1, 3-PDO over the Pt-WO_x catalysts.