| Volatile organic compounds (VOCs) are known as hazardous pollutants of airpollution because of the toxic, malodorous, mutagenic and carcinogenic properties.VOCs can lead to photochemical reactions and photochemical smog with nitrogenoxides under UV irradiation, meanwhile, VOCs are one of the culprits causing haze asthe precursor of PM2.5, and also threaten public health and the environment seriously.So control the pollution of VOCs is impending. Actually, VOCs gas emitted hasvarious components, it’s necessary to explore pollution control ways oftwo-component or multi-component VOCs. To the low concentrations of VOCs wastegas which has no value of recycling, catalytic oxidation is a simple, efficient andconvenient treatment technology. In addition, microwave heating is fast, high heatingefficiency, safety and environment friendly. Therefore, a new technology thatcombining microwave heating with catalytic oxidation will have broad applicationprospects and promising for control of VOCs emission.This paper selected TiO2and5A molecular sieve to prepare TiO2-5A compositecarrier in order to develop high stability, high active Cu-Mn-Ce/TiO2-5A catalyst atlow temperature. The catalyst and silicon carbide were combined to study the effect ofmicrowave-assisted catalytic oxidation of single, two-component toluene andchlorobenzene under aerobic conditions. On this basis, the experiment analyzed thereaction kinetics contrast to tube furnace heated catalytic oxidation. Based on theexperimental study and catalyst characterization tests, research results obtained are asfollows:(1) Silicon carbide was added to improve the Cu-Mn-Ce/TiO2-5A absorbingheat efficiency, and enhanced toluene, chlorobenzene catalytic oxidation effect. (2) Characteristics analysis of catalyst showed that active componentsuniformly distributed on the surface of catalyst and absorbed into the catalyst pore, sothat provided more active points. The active species of the catalyst were dispersed inthe form of multivalent oxides and higher catalytic activityCu1.5Mn1.5O4, CuMn2O4spinels; the mutual transformation of Cu2+/Cu+, Mn4+/Mn2+could promote the electrontransfer to enhance the catalytic activity; the mutual transformation ofCeO2/Ce2O3enhanced the capacity of oxygen storage and transfer which couldaccelerate the oxidation reaction rate.(3) Competitive adsorption between two-component toluene andchlorobenzene reduced their removal efficiencies of3%-12%than single component,the temperature of95%conversion(T95) for toluene in two-component was higher thansingle toluene about31oC, while the temperature of90%conversion(T90) forchlorobenzene in two-component was same to the T95of single chlorobenzene.It wasspeculated that toluene was oxidized to benzaldehyde and benzoic acid, andchlorobenzene was converted to phenol firstly, and mineralized to carbon dioxide andwater finally.(4) Contrast to tube furnace heating, microwave heating could maintain thegood stability of catalyst structure and the active component to enhance the oxidationof toluene and chlorobenzene heoxidation of toluene and chlorobenzene, and increasedconversion rate about31%-38%;‘Hot spot effect’ and ‘non-thermal effect’ undermicrowave irradiation enhanced conversion efficiencies of VOCs and reduced energyconsumption obviously, the low temperature of microwave oven cavity was beneficialto distribute reaction heat and keep bed temperature stable.(5) The analysis of reaction kinetics showed that microwave assisted and tubefurnace heated catalytic oxidation reaction of toluene and chlorobenzene are quasi onereaction. Comparing with tube furnace heating, microwave heating lessened activationenergy for toluene and chlorobenzene about2146J mol-1å'Œ1450J mol-1respectively,while enhancing the reaction rate constants of chlorobenzene and toluene about35times and6times. |
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