Production of hexane from sorbitol in aqueous medium over Pt/NbOPO4 catalyst
Liquid bio-fuels derived from renewable biomass are of great importance on the potential substitution for the diminishing fossil fuels. Aqueous-phase process of sugar and sugar-derived molecules can be used to produce a range of alkanes and oxygenates. In this work, Pt/NbOPO 4 multifunctional catalyst was used in the alkane production by the hydrodeoxygenation of sorbitol in aqueous solution. The results indicated that Pt/NbOPO 4 catalyst showed the highest activity with 60% yield of C6 and C5 alkanes at 250 °C and 4 MPa H 2 among a series of catalysts. The reaction pathway showed that this process included dehydration, hydrogenolysis and CC bond cleavage. Isosorbide is the product of dehydration reaction and also an important intermediate in this process, which undergoes ring opening and following hydrogenolysis to form C6 hexane. The activation energy of sorbitol dehydration and isosorbide hydrogenolysis was calculated, that is 72.7 kJ/mol and 147.6 kJ/mol, respectively, over Pt/NbOPO 4 catalyst, much lower than those over Pt/ZrP and Pt/H-Beta catalysts, which would be attributed to the strong and high acid amount of NbOPO 4 as well as the promotion effect of NbO x for CO bond cleavage. The above results also showed that isosorbide hydrogenolysis is the rate-determine step. More importantly, Pt/NbOPO 4 catalyst was very stable, there was nearly no decrease of sorbitol conversion and no change of products distribution after working in a fixed bed reactor for 100 h. Therefore, Pt/NbOPO 4 is an efficient and stable catalyst for hexane production from sorbitol in aqueous media.
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