Effect of WO x on Bifunctional Pd–WO x /Al2O3 Catalysts for the Selective Hydrogenolysis of Glucose to 1,2-Propanediol

• Published in: ACS catalysis Vol. 5; pp. 4612 - 4623
• Main Authors: Liu, Chengwei, Zhang, Chenghua, Sun, Sikai, Liu, Kangkai, Hao, Shunli, Xu, Jian, Zhu, Yulei, Li, Yongwang
• Format: Journal Article
• Language: English
• Published: American Chemical Society 2015
• Subjects: 1,2-propanediol; biomass; glucose; isomerization; WO x; fructose; hydrogenolysis; Pd−WO x /Al2O3
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.5b00800

A series of Pd–WO x /Al2O3 catalysts with different contents of WO x were prepared by stepwise incipient wetness impregnations. The influence of WO x on the physicochemical properties of Pd–WO x /Al2O3 catalysts, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propanediol (1,2-PDO), was investigated. At low surface W density (0.3–2.1 W nm–2), distorted isolated WO x and oligomeric WO x are present on the Pd–WO x /Al2O3 catalysts. Furthermore, isolated WO4 are the dominating species on the Pd–WO x (5%)/Al2O3 catalyst. When the W density increased to 3.1 W nm–2, polymeric WO x species are dominant on the Pd–WO x (30%)/Al2O3 catalyst. The Pd surface area decreased while the acid amount increased with increasing W density. Furthermore, increased Lewis acid sites are provided by isolated WO4 and oligomeric WO x species whereas increased Brønsted acid sites exist on polymeric WO x species. Lewis acid sites promote glucose isomerization to fructose, which is an intermediate in glucose hydrogenolysis to 1,2-PDO. Metal sites catalyze CO hydrogenation and C–C hydrogenolysis, which avoid the coke formation on catalysts. 1,2-PDO selectivity is dependent on the synergy of Lewis acid and metal sites; however, Brønsted acid sites have no contribution to the 1,2-PDO production. Typically, the Pd–WO x (5%)/Al2O3 catalyst possessing the optimal balance of Lewis acid and the metal site shows a 1,2-PDO selectivity of 60.8% at a glucose conversion of 92.2% and has a lifetime of over 200 h.