Catalytic Oxidation Of Glycerol Into DHA Over Pt-Sb Bimetallic Catalysts

Glycerol, a highly functionalized bioderived molecule, has been identified as an important building block for future biorefineries. Its conversion to value-added chemicals can be realized through several routes, among which chemoselective oxidation of glycerol into dihydroxyacetone (DHA) has attracted much attention for economic and environmental concerns. Bismuth or antimony modified Pt-based catalysts have been found to be very selective for glycerol oxidation into DHA. Compared with Pt-Bi, Pt-Sb bimetallic catalyst exhibited a higher selectivity to DHA and inhibited the cleavage of C-C bond. In this work, in order to explore highly efficient Pt-Sb bimetallic catalysts, size effects of Pt-Sb bimetallic catalyst for base-free oxidation of glycerol, structure and performance manipulation of Pt-Sb bimetallic catalysts and the role of Sb in glycerol oxidation have been investigated. The main results of this work are as follows:(1) A series of different sized carbon nanotubes (CNTs) supported Pt-Sb bimetallic catalysts were prepared by tuning the loadings, and then applied in the base-free oxidation of glycerol. Compared with Pt/CNTs, Pt-Sb/CNTs catalysts exhibit higher DHA selectivity and reactivity, suggesting that synergy between Pt and Sb facilitates the improvement of reactivity and DHA selectivity. A volcanic curve relationship between initial activity and particle size has been correlated, indicating the glycerol oxidation over Pt-Sb/CNTs catalysts being a typical structure-sensitive reaction. Moreover, larger sized Pt-Sb/CNTs catalysts is found to favor the formation of DHA and inhibits the cleavage of C-C bond, thus improving DHA yield and carbon use efficiency.(2) Pt-Sb/CNTs bimetallic catalysts with different PtSb alloy phases (Pt3Sb1 and Pt1Sb1) were further synthesized by changing atomic ratio of Pt to Sb. The base-free oxidation of glycerol over these catalysts with or without washing were comparatively studied. The results show that in the initial period of reaction, the PtSb alloy may be mainly responsible for the superior activity and DHA selectivity, and Pt3Sb1 alloy phase is proved to exhibit better performance than the corresponding Pt1Sb1 one. With time on stream, Sb leached into reaction solution and might undergo dynamic reconstruction on Pt surface, thus facilitating the further conversion of glycerol and the formation of DHA. Meanwhile, the acid products (like GLYA) were continuously accumulated and adsorbed on Pt surface, which might block part of Pt active sites for DHA formation and be disadvantageous for dynamic modification of Sb ion to Pt, resulting in reduced DHA selectivity.