Preparation Of Supported Palladium Based Catalysts Via Biosynthesis And Their Performance In Benzene Oxidation

Volatile organic pollutants(VOCs)have the hazards of polluting the environment atmosphere and seriously influencing human health,which was the focus of environmental treatment.At present,the degradation methods of VOCs mainly include combustion method,biological degradation method and catalytic oxidation method,among which,catalytic oxidation method has the advantages of environment friendly,high efficiency and energy saving.Supported Pd catalyst show excellent activity on degradation of VOCs.However,there are still many problems need to be solved,such as how to prepare Pd catalyst in a green and efficient method,how to determine the valence effect of Pd,how to further improve catalytic performance and water-resistance.Therefore,this study based on benzene oxidation,and biosynthesis was used to prepare Pd/Co3O4 catalyst.Besides,Au was introduced to improve the catalytic performance of Au-Pd/Co3O4 catalysts,the effects of low-temperature reducibility,noble metal particle size and surface element valence on benzene oxidation were investigated by means of characterization methods,such as TEM,XPS,H2-TPR,etc,including the following works:Cacumen Platycladi(CP)extract was used to synthesis Pd/Co3O4 catalyst,and the effects of sol-immobilization method(SI),adsorption-reduction method(AR)and calcination treatment on Pd valence and catalytic activity were investigated.Results showed that the noble metal particles prepared by SI were spherical and possessed uniform size and distribution,which were superior for benzene oxidation than prepared by adsorption-reduction method.Different amount of Pd0 were obtained by calcinating with different temperatures,the more amount of Pd0 resulted in the better catalytic activity,which further proved that metallic Pd species were much more active.Besides,calcining resulted in better combination of palladium with support and better low-temperature reducibility.Test of benzene oxidation found that Pd/Co3O4 catalyst prepared by SI method with 0.5 wt.%of Pd loading,and without calcination were the optimum condition,benzene degradation rate of 90%when the temperature(T90%)was 205℃.The performance of the Pd/Co3O4 catalyst keep unchanged after continuous reaction for 150 h,which proved that the catalyst had good stability.Besides,to further improve the catalytic activity and water-resistance,Au was introduced and the Au-Pd/Co3O4 catalyst was prepared.Then the effects of CP extract concentration,reduction sequence of Au and Pd,molar ratios of Au and Pd were investigated.The optimized preparation were as follows:the concentration of CP extract was 5 g/L,first reduction of Pd and then Au,the molar ratios of Pd:Au was 1:1.Results of XPS showed that the first reduction of Pd and then Au could obtain a higher amount of Pd0;the addition of Au changed the molar ratio of Pd2+/Pdo on the surface of the catalyst.The catalytic activity was the best when the Pd0 amount was the highest and Pd:Au=1:1,and T90%was 178℃,which was 27℃ lower than Pd/Co3O4,and was better than the values reported in most literatures.Besides,the introduced of Au could improve the water-resistance of catalyst,therefore,the catalyst could maintain good activity under the condition of water vapor.The test of stability was carried out for 130 h and the performance of the Au-Pd/Co3O4 catalyst keep unchanged,which indicated the excellent catalytic stability of the catalyst.