Study On Oxidation Of VOCs Based On Palladium Catalysts Supported On Different Supports

With the continuous increase of volatile organic compounds(VOCs)and their harmful effects on human health and the ecological environment,it is of great significance and urgency to develop effective VOCs elimination technology.Among all of the technologies,catalytic combustion technology is the most economical and effective treatment technologies.It has the advantages of low energy consumption,low light-off temperature,wide application range,high efficiency and no secondary pollution.It is known that the key of this technology is developing a high efficient catalyst with low cost.In this thesis,an oxygenated VOCs isopropanol and aromatic VOCs toluene were selected as probe contaminants.A series of Pd-based catalysts were prepared by using mesoporous Al2O3 and TiO2 nanosheets as supports.The effects of Pd-based catalysts on the combustion properties of isopropanol or toluene were investigated by using different preparation methods,changing pretreatment atmosphere,doping different acid or alkaline elements and introducing non-noble metal elements with Pd.Combined with characterization techniques such as N2 adsorption and desorption,transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy,CO adsorption in situ infrared spectroscopy,H2 temperature programmed reduction,the relationship between catalyst structure and properties was studied.The conclusions are as follows:(1)Pd/MA,Co/MA and Pd/Co/MA catalysts were prepared by impregnation method using mesoporous alumina as supports.The effects of different pretreatment atmospheres on the performance of the catalyst were studied.At the same time,the effect of mutual relationship between Co and Pd on the catalytic combustion activity of isopropanol was studied.The results show that the pretreatment atmosphere has a great influence on the catalytic activity of the catalyst,and the catalytst treated by H2 displayed the best catalytic activity toword the oxidation of isopropanol.In addition,after the H2 reduction treatment,there is a synergistic effect between Co and Pd,and Co has a stabilizing effect on Pd.Furtherly,we doped different acid(Ti,W),alkaline(Ba,Mg)elements in the mesoporous alumina support during the preparation process,and then loaded Pd.The effect of one-step doping of different acid-alkaline elements on the catalytic combustion activity of toluene was investigated.It was found that the doping of alkaline elements not only lowers the light-off temperature of the catalyst,but also the temperature at which the complete conversion of toluene is significantly lower than that of the acid-doped catalyst.This is because the modification of alkaline elements promotes the dispersion of Pd species,changes the density of Pd outer electron clouds,and enhances the redox capacity of Pd species.(2)The single metal Pd/TiO2 catalysts were synthesized by different methods(impregnation method,precipitation deposition method,photodeposition method,NaBH4 reduction method)with titanium dioxide nanosheets as supports.We investigate the effects of different synthetic methods on the catalytic activity of the catalyst for the oxidation of toluene and also the difference in the activity of the catalyst with the commercial P25 as the support.The results show that the catalyst supported on TiO2 nanosheets displayed higher catalytic activity than that on P25.The Pd/TiO2(NS)catalyst with better catalytic activity is because that the {001}crystal plane is mainly the exposed crystal plane.The one synthesized by the impregnation method has the best activity,which is probably related to the elimination of the water washing step in the synthesis process.On this basis,we synthesized Pd-M(M=Cu,Co)bimetallic catalysts by impregnation method and precipitation deposition method.It was found that under different preparation methods,the co-doping of the elements had a significant difference in the activity of the catalyst for the catalytic oxidation of toluene.In the impregnation method,the co-doping of Cu and Pd significantly improved the catalytic activity of toluene,while the Pd-Co/TiO2 catalyst significantly inhibited the catalytic combustion of toluene.In the precipitation deposition method,the effect of co-doping elements is not obvious,and the activity of Pd-Cu/TiO2 catalyst with the best activity is slightly higher than that of Pd-Co/TiO2 catalyst.It indicates that the different state of existence of Co on the surface of TiO2 will have different effects on the activity of Pd/TiO2.