Aqueous-phase hydrodeoxygenation of sorbitol: A comparative study of Pt/Zr phosphate and Ptsingle bondReOx/C

In this paper, we have studied the aqueous-phase hydrodeoxygenation of sorbitol over two fundamentally different types of bifunctional catalysts: Pt/Zr-P and Ptsingle bondReOx/C in a continuous flow reactor. During the reaction, the Pt/Zr-P catalyst undergoes phase transformations of amorphous into crystalline Zr-P having a rhombohedral framework along with a 97% loss of surface area, 86% loss of Pt surface sites, and 95% loss of surface acid sites. Ptsingle bondReOx/C has a higher hydrothermal stability than that of Pt/Zr-P and only lost 17% of its surface area during the reaction. The number of Pt surface sites increased by a factor of 3.5 for the Ptsingle bondReOx/C catalyst after reaction. Products were classified into three major categories: (1) light gases, (2) gasoline-range products, and (3) aqueous-phase products. The light gases included CO2 and C1single bondC4 alkanes. The gasoline-range products included C5single bondC6 alkanes, C2single bondC6 alcohols, tetrahydrofurans, tetrahydropyrans, and small amounts of C2single bondC6 aldehydes, ketones, and organic acids. The aqueous-phase products included isosorbide, mannitol, sorbitan, hexanetriol, C2single bondC6 diols, glycerol, and methanol. The gasoline-range yield of each catalyst was 66.8% and 44.4% for the Pt/Zr-P and Ptsingle bondReOx/C catalysts, respectively. The Ptsingle bondReOx/C catalyst had a 34 times higher reaction rates than Pt/Zr-P on a Pt mass basis. However, the turnover frequency of both catalysts was similar based on the number of surface Pt sites measured after reaction. The acid sites on the Ptsingle bondReOx catalyst are able to isomerize sorbitol into mannitol, whereas no mannitol was observed with the Pt/Zr-P catalyst. Mannitol had a lower rate of coke formation than sorbitol for APHDO on the Pt/Zr-P catalyst. The Ptsingle bondReOx/C had a higher selectivity toward secondary alcohols than Pt/Zr-P which produced all primary alcohols. The Ptsingle bondReOx/C had a higher CO2 selectivity than Pt/Zr-P, suggesting the Ptsingle bondReOx/C has a higher rate of decarbonylation than Pt/Zr-P. Pt/Zr-P had a higher rate of Csingle bondO bond cleavage than Ptsingle bondReOx/C, leading to higher C6 product selectivity (35.8% vs. 11.6%).