Basic Study On The Synergetic Removal Of Hydrocarbons From Vehicle Exhausts Using Non-thermal Plasma-catalysis

The air pollution situation in China is severe,and regional atmospheric environmental problems such as smog and photochemical pollution have become increasingly prominent.With the continuous increase in the number of motor vehicles in China,the contribution of automobile exhaust to air pollution has risen to the top in major developed regions.The hydrocarbon?HC?in the exhaust gas has a high proportion.It is not only a primary pollutant in the atmosphere,but also an important precursor of photochemical reaction.It is involved in the generation of secondary pollutants such as ozone and peroxyacetyl nitrate?PAN?.The result is an increase in the concentration of surface smog and ozone,which is a great hazard to the environment and the human body.Therefore,the vehicle exhaust HC must be strictly cleaned.At present,plasma synergistic catalysis has shown good potential in the treatment of volatile organic compounds,but there are few studies on the treatment of HC in automobile exhaust.In this paper,the influence of preparation conditions of supported Au/?-Al₂O₃ catalysts was first investigateded,and the effects of different loadings,calcination temperatures and calcination time on the physical properties of the catalyst surface were characterized and then analyzed in a tubular dielectric barrier discharge?DBD?reactor.The degradation performance of the catalyst to the typical HC-toluene was tested and the optimal catalyst preparation scheme was obtained.Secondly,the effects of different reaction conditions were tested on the basis of the optimal catalyst scheme,using mass spectrometry?MS?,scanning electromigration particle size spectrometer?SMPS+C?and gas chromatography-mass spectrometry?GC-MS?.The product of the reaction was analyzed,and the influence degree of reaction temperature,energy density and space velocity were evaluated by the reaction kinetic equation.Finally,a device for realizing DBD in an in-situ cell in situ diffuse reflectance Fourier transform infrared spectrometer?in situ DRIFTS?was designed.By analyzing the changes of surface groups in the adsorption and discharge of toluene and methane oxidation,it was speculated.The mechanism of degradation of toluene on the catalyst.The main findings are:?1?0.1 wt.%Au loading,calcination at 300°C for 5 h is the best preparation scheme.It has a small Au particle size?6.3 nm?,good dispersibility and reliable pore structure in surface physical properties.Toluene degradation performance is 100 ppmv?0.41 mg/m³?toluene at 20J/L energy density.There is 99.8%near 100%removal rate and 32%COx selectivity.With the increasing in the Au loading and calcination temperature,the size of the Au particles increased which reduced the catalytic performance on toluene.?2?Increasing the reaction temperature can effectively improve the discharge energy efficiency and reduce reaction by-products.The toluene removal rate of 10 J/L empty tube discharge increased from 40.3%to 48.8%at 25°C-250°C,increased to 65.9%at 25°C after loading catalyst,and increased to 92.2%at 250°C;CO₂ The selectivity also increases significantly with increasing temperature,reaching 66.9%at 250°C;the ozone outlet concentration decreases with increasing temperature,and the ozone concentration is generally below 17 ppmv after loading the catalyst;the system has high energy efficiency at 25°C was89.5 g/kWh,was improved to 125.0 g/kWh at 250°C;the by-products are benzaldehyde,phenol,benzoic acid,the formation of gas phase and solid phase by-products at a higher temperature is obviously reduced in comparision with those at room temperature;The amount of aerosol in the gas mixture from the DBD reactor loaded with a catalyst decreased by more than 99.99%compared with that from the DBD reactor without a catakyst(10^-610^-7/cm³);increasing the energy density can significantly increase toluene removal;when the space velocity increases,the toluene removal rate decreases significantly.From the reaction kinetic analysis,the influence order of three factors on the toluene removal is:T?reaction temperature?>ED?energy density??F?gas flow?.?3?Au/Al₂O₃ catalyst can adsorb more toluene than alumina at room temperature,but hardly adsorb at 250°C.In the infrared spectrum after the discharge of alumina at room temperature,the diffraction peaks of bicarbonate and alcohols,aldehydes and carboxylic acids appeared,while Au/Al₂O₃ was mainly aldehydes,and bicarbonate was significantly lower than alumina.It was speculated that the addition of Au might promote the transformation of toluene into benzaldehyde and the CO₂ gasification of bicarbonate.?4?A toluene degradation pathway on Au/Al₂O₃ was proposed.When toluene is adsorbed on Au and lattice O,it will be gradually oxidized to the bis-coordinate carbonate via two routes,then vaporized to CO₂ with the help of Au,and the catalyst activity can be maintained.