Regulation Of MnO₂ Catalysts And Study On The Performance Of Catalytic Oxidation Of Toluene

Low-temperature catalytic oxidation technology has great application potential in the treatment of volatile organic compounds（VOCs）,and manganese oxide has good catalytic performance.This article aims to make up for the shortcomings of cheap,efficient,and long-life non-noble metal catalysts in practical applications,and is dedicated to improving the catalytic oxidation performance of MnO₂.Three different modification methods were used to controllably synthesize MnO₂ catalysts with special microstructures,and the structure-activity relationship between catalyst structure and catalytic effect was clarified.In-situ DRIFTS technology was used to dynamically track the evolution of reactants,intermediate products and final products,revealing the reaction mechanism of toluene degradation catalyzed by different MnO₂ catalysts.This will provide theoretical guidance for the theoretical design of MnO₂ catalysts that effectively decompose toluene,and also provide theoretical support for low-temperature catalytic oxidation technology to decompose volatile organic compounds.In this paper,toluene is the target pollutant.Using a fixed bed continuous flow device to evaluate the performance of the catalyst.And using specific crystal plane exposure,vacuum reheat treatment to increase oxygen vacancies,and material reorganization to control MnO₂.The MnO₂ catalyst was synthesized by a hydrothermal method,and the effects of the exposure of specific crystal planes,oxygen vacancies and the core-shell structure of the MnO₂ catalyst on the catalytic degradation of toluene were preliminarily discussed.The detailed research results are as follows:（1）The effect of specific crystal plane exposure on the catalytic degradation of toluene by MnO₂.A series ofα-MnO₂ catalysts with specific exposed crystal faces of（1 1 0）,（2 1 0）and（3 1 0）were prepared by one-step hydrothermal method,respectively.Effects of different exposed crystal planes onα-MnO₂ catalytic oxidation of toluene were investigated.Through the combination of experimental characterization and DFT theoretical calculation,the properties and performance of the catalyst were analyzed and explained.Among of them,theα-MnO₂ catalyst with（2 1 0）as a specific exposed crystal plane shows the best catalytic performance,and the complete degradation of toluene can be achieved at 140^oC.The experimental and characterization results show that the unique atomic arrangement ofα-MnO₂-210catalysts enhances charge separation and conversion,promoted the formation of reactive oxygen species and the activation of toluene,which may be the reason whyα-MnO₂-210 showed excellent catalytic oxidation performance.（2）The effect of vacuum reheating treatment on the catalytic degradation of toluene byα-MnO₂ catalyst.Theα-MnO₂ catalyst was prepared by hydrothermal method.The catalyst calcined at 400^oC was reheated under vacuum,and the temperature of the vacuum reheat treatment was 140,180,and 200^oC,respectively.The catalytic performance of each sample prepared was studied.It can be concluded that theα-MnO₂ sample treated at 180^oC has the best catalytic performance,and the complete conversion of toluene is achieved at 275^oC,which is about 30^oC lower than the temperature at whichα-MnO₂ without heat treatment completely degrades toluene.The characterization result shows that the reheat treatment under vacuum condition is beneficial to increase the oxygen cavitation on the surface of theα-MnO₂ catalyst,thus effectively improving the catalytic performance of theα-MnO₂ catalyst.（3）The effect of core-shell structure La MnO₃@α-MnO₂ composite catalyst on toluene degradation performance.In the process of hydrothermal synthesis ofα-MnO₂,0.175,0.35 and 0.525g of La MnO₃ were added respectively,to synthesize the core-shell structure La MnO₃@α-MnO₂ composite catalytic material in situ.The La MnO₃@α-MnO₂ composite catalyst with complete core-shell structure is obtained when the amount of La MnO₃added is 15%;when 10%is added,a semi-closed core-shell structure La MnO₃@α-MnO₂ can be obtained.The La MnO₃@α-MnO₂-10 of the semi-enclosed core-shell structure showed the best catalytic activity,the complete conversion of toluene at 225^oC.The characterization result shows that a appropriate amount of La MnO₃ andα-MnO₂ composite material has a core-shell structure,which can increase the content of active oxygen on the surface of theα-MnO₂ catalyst,increase the contact interface,and improve its redox capacity,thereby increasing the performance of MnO₂ catalyst in the catalytic oxidation of toluene.