Study On The Effect Of Support On The Catalytic Performance Of Supported PdCl₂-CuCl₂ Catalyst For Low Temperature CO Oxidation

Low-temperature CO oxidation has been widely used in reducing the damage caused by automobile exhaust,elimination of environmental pollution,fuel cell and carbon monoxide filter respirator,etc.And CO oxidation is often used as the probe reaction in the catalysis researches.Therefore,the studies on the catalysts with high performance for CO oxidation have certain practical significance and academic value.In this thesis,a series of supported Wacker catalysts(PdCl2-CuCl2/support)were prepared by the traditional impregnation method,NH3 coordination-impregnation method and two-step impregnation in the organic solvent method,and used to catalyze the low-temperature CO oxidation in the presence of high concentration moisture.Based on the characterizations for the physicochemical properties of the catalysts by FT-IR,XRD,ICP-OES,BET,TEM,H2-TPR,CO-TPD,XPS and so on,the influence of support on the catalytic performance and physicochemical properties of supported PdCl2-CuCl2 catalysts and the relationship between the structure and catalytic activity were investigated.The main results of the studies are listed as follows:1.Preparation of supported Pd-Cu-Clx/C-Al2O3 catalyst and its catalytic properties.C-Al2O3 aerogel as the catalyst support were prepared by the sol-gel progress and super critical drying technique.Wacker catalyst supported on C-Al2O3 aerogel with different contents of carbon and alumina was prepared by the traditional impregnation method,NH3 coordination-impregnation method and two-step impregnation method.And their catalytic activities for CO oxidation at low temperature were tested.The results show that,the Pd-Cu-Clx/C-Al2O3 catalyst prepared by two-step impregnation method exhibited a higher catalytic activity for CO oxidation than these prepared by other methods.The effect of support(C,C-Al2O3 and Al2O3 aerogel)on the catalytic activity was studied,which showed that the catalyst supported on the Al2O3 aerogel showed the best activity but least stability,and the Pd-Cu-Clx/C catalyst had relatively high stability in the presence of moisture.2.Preparation of supported Pd-Cu-Clx/CNT catalyst and its catalytic properties.The Pd-Cu-Clx/CNT catalyst was prepared by the two-step impregnation method.The effects of the Pd and Cu loadings,CO concentration and moisture content on the catalytic activity and stability of this catalyst were investigated.The results showed that,with the increase in the Pd and Cu loadings,the surface active Pd2+ and Cu2+ species increased.For the CO oxidation,the present of moderate water is necessary for sustaining the high activity of this catalyst,but the excessive water vapor in feed gas would injure the activity and stability of the catalyst.When the moisture was 3.1%in the reactant gas,the CO conversion still retained about 93%after 60 h of the reaction at 25 ? over the 3.3wt.%Pd-6.6wt.%Cu/CNT catalyst,indicating that this catalyst has very good stability and water-resistance.3.Effect of CNT support pretreatment on the catalytic activity of the Pd-Cu-Clx/CNT catalyst.The effect of CNT treatment with acid solutions on the catalytic activity of the Pd-Cu-Clx/CNT catalysts was investigated.The results shows that,the Pd-Cu-Clx/CNT catalyst after the CNT carrier treated by acid solution could significantly increase the surface active Cu2+ species,accelerating the oxidation of Pd0,and strengthen the interaction between Pd and Cu.The Pd-Cu-Clx catalyst supported on CNT pretreated with nitric acid or phosphoric acid by the two-step impregnation method,exhibits a higher activity:the CO was completely converted at 10 ? in the present of 3.1%moisture.