The Characteristics And Modification Of Layered Perovskites In Catalytic VOC Oxidation

Volatile organic compounds(VOCs)are the precursors of haze and ozone pollutants,the elimination of which is one of the focuses in current air pollution control.In China,the industrial source VOCs flue gases usually comprise multiple air pollutants.The presence of chlorinated organics in the medical manufacturing industry,the high humidity in steal sintering and the high temperature due to fluctuated operation conditions all incline to cause deactivation of some commercial catalysts in the catalytic combustion technology.Accordingly,improving the resistance of the industrial catalysts to chlorine poisoning and high temperature and humidity is a hot topic in current research.In this dissertation,based on the characteristics and modification of Ruddlesden-Popper layered perovskite with good thermal stability in VOC oxidation(i.e.benzene series,alkanes,chlorinated alkanes),the catalytic activity and the resistance to chlorine and water of the catalysts are investigated.The structural characteristics and oxygen species of layered perovskites were investigated on the basis of nickel-based RP layered perovskites.The LaNiO3(n=?)had enriched chemisorbed oxygen and good low-temperature redox property whilst the La2NiO4(n=1)only possessed a large amount of interstitial oxygen with high mobility;the multi-layered perovskite La4Ni3O10(n=3)was with moderate chemisorbed oxygen and good superficial oxygen mobility.On the basis of these characteristics,the reactive oxygen species for surface/interface catalytic oxidation were then analyzed using toluene and methane oxidation as the respective probe reaction.The results showed that LaNiO3 was favoured for surface reaction and La4Ni3O10 could facilitate the interfacial reaction whilst La2NiO4 was not active for both reactions.It was indicated that the chemical adsorbed oxygen and the superficial oxygen were active to catalyze the reaction of toluene and methane,respectively,but the interstitial ones were inert.For DCM oxidation,the effect of acidity and superficial oxygen mobility on catalytic performance was clarified.With the use of manganese based RP layered perovskite,the phosphoric acid treatment increased the surface area and acidic sites and promoted low-temperature redox property of the modified catalyst,thereby improving the DCM adsorption and deep oxidation.The dechlorination behaviours and water-resistance of the catalysts were then explored.The results showed that the enriched hydroxyl and excellent lattice oxygen mobility as induced by the acid treatment could effectively improve the dechlorination capacity and the stability of manganese-based layered perovskites even under the anhydrous condition.With additive water,the chlorine poisoning was inhibited and the catalytic activity was improved over the modified catalyst La3Mn2O7-P for DCM oxidation.In particular,no obvious deactivation was observed even increasing the water content from 5 vol%to 10 vol%,showing a good water resistance of La3Mn2O7-P.In this dissertation,the main active oxygen species involved in the catalytic oxidation reaction in the perovskite-like catalyst were identified,and a composite catalyst of phosphate-pseudo-perovskite was constructed for CVOC oxidation.In the high humidity environment,the reaction temperature of DCM oxidation over the modified perovskite-like catalyst was reduced effectively and the resistance to chlorine and water was enhanced.It provides the experimental and theoretical basis for the optimization design and catalytic application of perovskite-type catalytic materials.