The Investigation Of Performance Of V-Ti And Mn-Ti Based Catalysts For The Catalytic Degradation Of PCDD/Fs

Polychlorinated dibenzo-p-dioxins and dibenzofurans（PCDD/Fs） are a series of persistent organic pollutants with acute toxicity that trigger a great number of negative effects on the ecological environment and human physical health which aroused widely attention of international community. in order to reduce the emissions of PCDD/Fs in the environmental that produced by waste incineration and industrial processes, catalytic combustion method has been applied in industries widely because of its advantages of low energy consumption, high efficiency of degradation, no secondary pollutions, a wide range of applications, simple operations and that has became the hot topic of catalytic degradation of gas phase PCDD/Fs researches.In this paper, a series of V-Ti, Mn-Ti and corresponding doped or modified catalysts were prepared by dry powder mixing method, then utilize the chlorobenzene as the model compounds of the PCDD/Fs for the catalytic degradation tests, discussed the effects that the content of active component, calcination temperature, doped with transition metal oxides or lanthanum metal oxides and sulfate modification on the activity of the catalysts; moreover x-ray diffraction（XRD）,specific surface area analysis（BET）,scanning electron microscopy（SEM）,temperature programmed reduction（H₂-TPR） and x-ray photoelectron spectroscopy（XPS） were used to characterize the catalysts, the results indicate that:（1）V₂O₅ content has a great influence on the low temperature catalytic performance of V-Ti catalysts, the low content of V₂O₅ will lead to the lack of active sites on the V-Ti catalysts and poor in low temperature catalytic performance, while the high content of V₂O₅ will lead to the agglomeration of active components result in the reduction of low temperature catalytic efficiency, therefore the V-Ti catalysts with 6wt% V₂O₅ content owned the best low temperature catalytic activity, the catalytic degradation efficiency of 60% can be achieved at 200℃, the catalytic degradation efficiency reached 95% at 300℃. the well distributed active sites of Mn oxidation species on the Mn-Ti catalysts surface has a very important effect on its low temperature catalytic activity; when the Mn content is 3.2wt%, the catalytic activity of Mn-Ti has reached the best state with the catalytic degradation efficiency of 36% at 200℃, the catalytic degradation efficiency reached 72% at 300℃; however when the Mn content is further increased to 5.8wt%, the low temperature catalytic activity is not improved; it is concluded that when the Mn content is 3.2wt%, the active sites of Mn oxidation species has been fully loaded on the TiO₂ support.（2）The calcination temperature has also an important influence on the catalysis activity of V-Ti and Mn-Ti catalysts. they have the tendency that the catalytic activity gradually decreased with the calcination temperature increased, namely η（400℃） > η（500℃） > η（600℃） > η（700℃）, the reason is that with the calcination temperature increased, it can arouse the anatase TiO₂ support transformed into the rutile TiO₂ and TiO₂ grain coarsening, the specific surface area, pore volume and active sites also reduced, these factors could result in the decrease of low temperature catalytic activity.（3）The transition metal oxides, lanthanum metal oxides doping and ammonium sulfate modification have different effects on the low temperature catalytic activity of V-Ti and Mn-Ti catalysts. in the case of transition metal oxides, CoO_x can improve the low temperature catalytic efficiency of V-Ti and Mn-Ti catalysts, NbO_x can enhance the medium and high temperature catalytic efficiency of V-Ti catalysts, YO_x can increase the medium and high temperature catalytic efficiency of Mn-Ti catalysts. in the case of lanthanum metal oxides, CeO_x can greatly improve the low temperature catalytic efficiency of V-Ti and Mn-Ti catalysts, NdO_x can enhance the medium and high temperature catalytic efficiency of V-Ti catalysts, PrO_x can increase the medium and high catalytic efficiency of Mn-Ti catalysts, among them, the catalysts with the best low temperature catalytic efficiency is the CeO_x doped catalysts, the catalytic degradation efficiency of 75% and 53% can be achieved by the best V-Ce-Ti and Mn-Ce-Ti at 200℃ respectively. for the ammonium sulfate modified V-Ti catalysts, with the content of the sulfate increased, the catalytic degradation efficiency increased at small range, the V-Ti-SO₄^2- catalysts with the sulfate radical content of 1wt%、3wt% and 5wt% for the chlorobenzene degradation efficiency are 61%、63% and 66% at 200℃ respectively, the reason is that the specific surface area and pore volume increased significantly with the content of the sulfate increased, meanwhile the refinement of the anatase TiO₂ crystal is beneficial to the active components well loaded on the support, all of these factors are beneficial to the catalytic combustion of chlorobenzene molecules, thereby the catalytic degradation efficiency has been improved to some extent.