Graphene-supported Pd Catalyst For Selective Hydrogenation Of Aromatic Compounds

The reaction products from selective hydrogenation of aromatic compounds always show high business value. However, the hydrogenation of benzene ring is more difficult than hydrogenation of alkene because the electron density of C=C in benzene ring is lower than that in alkene due to the electron delocalization of π-π bond in benzene ring. Moreover, after 1 mol H2 has been hydrogenated in benzene ring, the reactants are easily been excessively hydrogenated so that the targeted products can not be achieved. Recent years, the graphene has been extensively applied to prepare catalysts with high activity owing to its unique structure and properties. In addition, graphene can adsorb aromatic compounds by forming π-π conjugation between graphene and aromatic ring. In the thesis, we have prepared Pd/rGO catalyst and applied it into the hydrogenation of aromatic compounds, then studied the influence of π-π conjugation towards the hydrogenation by comparing the adsorption of graphene towards resorcinol and 1,3-cyclohexanedione.In this thesis, the Pd/rGO catalyst has been successfully prepared by modified Hummers method and co-reduction method, characterized by XRD, BET, TEM and Raman method. The results showed that the special surface area of Pd/rGO was lower than the theoretic special surface area of graphene, which was caused by the incompletely stripping and aggregation of graphene due to the Van der Waals force. In addition, the average diameter of Pd particle is 3.6 nm.In the hydrogenation of resorcinol, we have arranged the reaction in different catalytic supports, solvents, reaction condition. As shown in the results of hydrogenation catalyzed by Pd/rGO, Pd/AC, Pd/CNTs and Pd/SiO2, the Pd/rGO catalyst has exerted the highest activity:under certain conditions, the conversion of resorcinol and the selectivity of targeted products are 99.9% and 94.2%, respectively. In addition, the catalytic activity of Pd/rGO has been compared in different solvents. As a result, no hydrogenation occurred in polar solvents (acetonitrile and ethanol), high reactivity obtained in nonpolar solvents (dichloromethane and dichloroethane). Especially when taking dichloromethane as solvent, the highest conversion and selectivity have been achieved.Based on the results of hydrogenation of resorcinol and the research of π-π adsorption of graphene, we has applied graphene to adsorb resorcinol and 1,3-cyclohexanedione and analyzed the adsorption difference. In dichloromethane solvent, the equilibrium absorption capacity of graphene towards resorcinol was 5 times more than that towards 1,3-cyclohexanedione due to the strong π-π adsorption between resorcinol and graphene. The results helped to indicate that, in the hydrogenation,1,3-cyclohexanedione tended to desorbed from graphene and stopped the reaction after that the resorcinol has been hydrogenated by 1 mol H2, which could effectively prevent the excessively hydrogenation of resorcinol.In further, the catalytic activity of Pd/rGO in hydrogenation of phenol and other aromatic compounds has also been compared in various reaction conditions.