| Glycerol is a very important biomass-derived platform molecule.It can be converted to many value-added chemicals through several routes,among which catalytic oxidation of glycerol has attracted much attention.This process initially proceeds by means of not only the oxidation of the primary hydroxyl group,but also that of the secondary hydroxyl group.Therefore,it is of great importance to design effective catalysts to control the chemoselective orientation of glycerol oxidation.Herein,the thermodynamic analysis and the kinetic behavior over carbon supported Pt-based catalysts have been carried out.The main results are as follows:(1)For the possible reactions occurring during glycerol oxidation,the changes in Gibbs free energy and reaction enthalpy are less than zero,indicating that these reactions are thermodynamically favorable and exothermic.Moreover,these reactions can be considered as irreversible reactions as their equilibrium constants are large.(2)The reaction temperature,and glycerol/Pt molar ratio have been found to greatly influence the catalytic performance of Pt/CNTs,while the initial glycerol concentration and oxygen partial pressure have almost no impacts.(3)From the kinetic point of view,the carbon nanotubes supported Pt(Pt/CNTs)catalyst favors the oxidation of the primary hydroxyl group of glycerol(Route 1),while the Pt-Sb/CNTs catalyst favors that of the secondary hydroxyl group(Route 2).A kinetic model concerning Pt/CNTs catalyzed glycerol oxidation was further established,in which an oxidative dehydrogenation mechanism with the second dehydrogenation step being rate determining was assumed.The reaction order with respect to the oxygen partial pressure in Route 1 and Route 2 was estimated to be 0.52 and 0.3,respectively,and that with respect to the glycerol concentration was zero,respectively.The activation energy over Route 1(i.e.,33.27 kJ/mol)is a little lower than that over Route 2(i.e.,44.86 kJ/mol). |
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