Study On The Performance Of Perovskite-Type Composite Oxides In VOCs Catalytic Combustion

Volatile organic compounds（VOCs）are widely derived from chemical production processes and are one of the main components of atmospheric pollutants,which seriously threaten human health and the ecological environment.Catalytic combustion technology has become an economical,practical and environmentally friendly treatment method for VOCs due to low energy consumption,high purification efficiency and low secondary pollutants.Catalyst is the core of catalytic combustion technology,and perovskite-type composite oxide catalyst has attracted much attention due to the advantages of low cost,high catalytic activity,good thermal stability and strong resistance to poisoning.In this paper,a series of perovskite-type LaMnO₃ catalysts have been prepared by the sol-gel method under different conditions and modified with adding urea during the preparation of the catalyst and supporting transition metal oxides to improve their catalytic combustion performance for toluene and chlorobenzene,thereby reducing the harm of VOCs to human health and ecological environment.First of all,a series of LaMnO₃ catalysts were prepared by sol-gel method and then they were applied to the catalytic combustion of toluene to investigate the effect of amount of citric acid,calcination temperature and calcination time on their catalytic activity,so as to screen out the better catalyst preparation conditions.Based on the results of single-factor experiments,the response surface method was applied to optimize the preparation condition of the LaMnO₃ catalyst and investigate the effect of three factors on the catalytic activity of the catalysts.The results showed that the optimized preparation conditions of the LaMnO₃catalyst was a mole ratio of citric acid to metal cations of 0.98:1,a calcination temperature of 616℃and a calcination time of 5.2 h.The order of effect of three factors on the catalytic activity of LaMnO₃ catalysts was as follows:calcination temperature>calcination time>amount of citric acid,and the interaction among these three factors had a significant effect on the catalytic activity of the LaMnO₃ catalysts.Secondly,a series of urea-added LaMnO₃ catalysts were prepared by sol-gel method,and their catalytic performance were tested by the catalytic combustion of toluene and chlorobenzene.It was found that the N-LMO-0.5 catalyst with a mole ratio of urea to citric acid of 0.5:1 had the best catalytic activity,which was mainly ascribed to a large specific surface area,a high surface Mn⁴⁺/Mn³⁺and O_ads/O_latt ratios,good low-temperature reduction performance and a relatively regular pore structure of the N-LMO-0.5 catalyst.In addition,the supported catalysts MO_x/LaMnO₃（M=Cr,Co,Cu）using LaMnO₃ with urea added as the support and different transition metal oxides as the active component were prepared by impregnation method,and then they were applied to the catalytic combustion reaction of chlorobenzene.The results indicated that the supported CoO_x/LaMnO₃ catalyst exhibited good catalytic activity and cycling stability.This result was mainly due to the fact that CoO_x/LaMnO₃ catalyst presented a good perovskite structure and a large specific surface area,while the interaction between the active component and the support enabled the Co oxide to disperse well on the surface of LaMnO₃ support without microcrystalline agglomeration,which was beneficial to promote the redox reaction between the CoO_x/LaMnO₃ catalyst and chlorobenzene.