Effects Of Si/Al Ratio And NiO On The Interaction Of Non-thermal Plasma And ZSM-5 Catalysts

Non-thermal plasma technique has unique advantage of rapid oxidation of VOCs at room temperature and atmospheric pressure.It is a promising solution to treat VOCs pollution.Nowadays,its two challenges are as follows: one is its low energy efficiency,and the other is that the performance of the plasma catalysis system would be decreased in the presence of water vapor in the gas stream.The key to solve these problems is to develop catalysts with high activity and durability to water vapor.Our study concentrated on the effect of different silica and alumina ratio(Si/Al)on ZSM-5 and Ni/ZSM-5 catalysts,and then analyzed their contribution to the toluene degradation under plasma activation.ZSM-5 doped with nickel oxide was synthesized by impregnation method,and then characterized by N2 adsorption(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),H2-temperature program reduction(H2-TPR),NH3-temperature programmed desorption(NH3-TPD),Toluene-temperature programmed desorption(TolueneTPD)and so on.First of all,the influences of Si/Al on ZSM-5 and Ni/ZSM-5 were investigated for the toluene adsorption capacity at room temperature and atmosphere pressure.Meanwhile,the toluene removal efficiency,carbon balance,carbon dioxide selectivity and stability(after 5 discharge times)were evaluated under NiO and different Si/Al in non-thermal plasma system by three discharge voltage(8 kV,10 kV,12 kV).Moreover,organic products over the catalyst surface were analyzed by GC-MS.The results clearly demonstrated that the Si/Al is an essential parameter which could modify the physicochemical characteristics of zeolite itself and also influence the loading form of Ni.Higher Si/Al and the presence of NiO could promote the toluene oxidation,carbon dioxide selectivity,carbon balance and catalyst stability,and decrease the formation of by-products in the process of plasma-catalysis.Then,a special plasma reactor was designed to study the adsorption species and intermediate products on 6 different catalysts surface during the toluene degradation in continuous discharge plasma system under 10 kV.At the same time,combined the TOF-MS results,the rate-determining step of toluene degradation pathway and key intermediate products were discussed.The result shows that benzoic acid was the main by-product both on catalyst surface and in gaseous phase,which would impede the further reaction steps because of its special stability.