Comparison Of Pd-UiO-66 And Pd-UiO-66-NH₂ Catalysts Performance For Phenol Hydrogenation In Aqueous Medium

The rapid development of economy not only improves the people’s material life level,but also increases the burden of the natural environment and the demand for energy,especially for the non-renewable fossil fuels,such as petroleum,coal and natural gas.However,the standing stock of fossil fuels is quite limited,and with the use of fossil energy it will also produce a great deal of pollutants,which will have negative effect on the environment.Under the increasingly urgent situation,more and more scholars have focused their attention on the development of new types of alternative energy in recent decades.Therefore,Biomass energy with pollution-free,renewable,wide raw material sources and other advantages is outstanding in many alternative new energies for fossil fuels,and becomes the best ideal substitute for fossil fuels.But the obstacle for utilizing biomass energy are high oxygen content and low ratio of H/C,which is just attributed to the presence of aromatic compounds and its difficulty in degradation.However,the study of hydrogenation of oxygenated compounds of bio-oil not only can improve the H/C ratio but also reduce the oxygen content,which can effectively promote the quality of the bio-oil.Based on previous researches on hydrogenation of phenol,UiO-66 and UiO-66-NH2 modified with Pd,were synthesized by the simple wetness impregnation method in this work.The performance of Pd-UiO-66 was compared with Pd-UiO-66-NH2,in which the UiO-66 support had been modified through the introduction of-NH2 groups.Pd-UiO-66 and Pd-UiO-66-NH2 were characterized by BET,XRD,XPS and TEM.respectively.The characterization results indicated that the Pd particles are embedded in Pd-UiO-66 and fixed on Pd-UiO-66-NH2.With-NH2.UiO-66-NH2 is less crystalline and the crystalline structure of UiO-66-NH2 is somewhat damaged.Pd-UiO-66 has high activity for aqueous phenol hydrogenation,with 100%conversion of phenol being achieved within 2 h at 120 ℃,which is much higher than with the Pd-UiO-66-NH2 catalyst.Pd-UiO-66 has higher selectivity for cyclohexanol,and Pd-UiO-66-NH-2 has higher selectivity for cyclohexanone under the same reaction condition.In addition,the reaction kinetics model was also established in the base of the experimental data for phenol hydrogenation catalyzed by Pd-UiO-66 and Pd-UiO-66-NH2.The study of the chemical kinetics portion revealed that the hydrogenation reaction rates with the Pd-UiO-66 catalyst are over 10 times than those with Pd-UiO-66-NH2 under the same conditions.The phenol hydrogenation catalyzed by Pd-UiO-66 is more sensitive to the reaction temperature than Pd-UiO-66-NH2 catalyst.Thus,it has been shown that modifications of an MOF support for a catalyst can generate structural changes that result in different catalytic activities and selectivity in aqueous phenol hydrogenation.