| Volatile organic compounds(VOCs)pollution is one of the environmental problems which are badly in need of control.For VOCs treatment,non thermal plasma(NTP)combined catalysis technology had gotten great attentions recently for its high removal efficiency,rapid reaction and high selectivity for VOCs removal,moreover,it can treat VOCs at room temperature and atmospheric pressure.In the technology,catalyst is the key factor to ensure high removal efficiency and minerization of VOCs oxidation.It is necessary to develop novel catalysts and study the action mechanism of catalysts.In this work,the performances of toluene oxidation by NTP with silica and alumina based materials were evaluated.And the effect mechanisms of catalysts were investigated in the view of the features of support and the active components of catalysts.The ordered mesoporous aluminas with large specific surface area and uniform pore-size distribution were synthesized by the method of evaporation-induced self-assembly(EISA)in ethanolic solution of a triblock copolymer(P123).And then ordered materials including ordered alumina,MCM-41 and zeolite 13 X were packed in the NTP reactor to study the performance of toluene oxidation,respectively.Results showed that compared with NTP alone reaction,these support materials in NTP could enhance toluene oxidation,among which zeolite 13 X exhibited the best activity.Moreover,the discharge effect of zeolite 13 X in NTP was the strongest,suggesting the effect of different support materials on toluene oxidation was related to discharge effect in NTP.In order to reveal the effect of adsorption ability and pore structure of one category of support material on toluene degradation,different types of zeolites(5A,HZSM-5,H? and HY)were selected to remove toluene in the NTP reaction.The results showed that all the zeolites,whether with toluene adsorption ability or not,significantly enhanced the toluene removal efficiency.Moreover,the carbon balance and CO2 selectivity showed the same tendency of HY > H?(HZSM-5)>5A,which was basically consistent with toluene adsorption ability,while opposed with the ozone emission.These results meant that in the NTP reaction with different zeolites,toluene removal efficiency was relevant to discharge effect and toluene adsorption ability of the zeolites,while carbon balance and CO2 selectivity of toluene oxidation mainly depended on toluene adsorption ability of the zeolites.The organic byproducts were analyzed and the components with the largest abundance were benzaldehyde and benzene.Compared to other zeolites,organic byproducts on the surface of zeolite 5A was the fewwest.Since the toluene removal efficiency was not high enough with alumina in the NTP,metal(Ag,Mn and Ni)doped-ordered aluminas(MA)were prepared and evaluated furtherly.The toluene removal efficiency followed the order of Ag/MA>Mn/MA>Ni/MA,and the toluene removal efficiency of Ag/MA system reached 93.0%.Among all of the Mn/MA catalysts with different Mn/Al ratio,10%Mn/MA catalyst exhibited the best activity in NTP-catalytic oxidation of toluene.When Mn/Al ratio increased to 30% and 40%,the specific surface area decreased,pore size distribution became wide and Mn Ox crystal occurred.The toluene removal efficiencies with zeolite in the NTP were nearly 100%,but the highest carbon balance was only 83%.In order to further improve carbon balance,Ag/HY and Ag/H? catalysts were prepared by impregnation.With silver loaded on the zeolites,both the toluene adsorption ability and the performance of toluene oxidation increased.Moreover,Ag/HY exhibited higher carbon balance,less organic byproducts,lower ozone concentration than Ag/H?.The carbon balance and CO2 selectivity of Ag/HY system arrived to 98.1% and 93.3%,respectively.The advantageous performance of Ag/HY contributed to the smaller nanoparticles and higher dispersion of silver species on the surface of Ag/HY.Furthermore,the state of silver on the surface of Ag/HY was Ag0 which further improved the mineralization of toluene oxidation.In addition,based on the results including toluene adsorption,ozone adsorption,intermediates and ozone concentration,the pathways and mechanisms of toluene oxidation by NTP –catalysis system were proposed.The effect of Si/Al ratio of zeolite HZSM-5 on plasma-catalytic oxidation toluene was studied.Among the zeolites HZSM-5 with different Si/Al ratio(Si/Al=25,100 and 160),Ag/HZ160 owned the best toluene adsorption ability and the largest number of lattice oxygen,resulting in highest carbon balance and CO2 selectivity of toluene oxidation.Moreover,Ag/HZ100 had the best oxidation-reduction performance and obtained the highest toluene removal efficiency... |
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