| NOx emissions from Diesel engine cause serious damage to human health and ecological environment,which should be strictly and effectively controlled.Recently,NOx Storage and Reduction?NSR?technology possesses huge application prospects in light-diesel vehicles for its advantages of low space utilization rate and without additionally adding reducing agent.NO is the main component of NOx emissions from Diesel engine.Compared with NO,NO2 is more easily stored on the surface of NSR catalyst.Thus,through Diesel Oxidation Catalyst?DOC?NO can be oxidized to NO2 so as to improve the rate of NO2/NOx at the entrance of NSR catalyst,which can effctively promote its NOx storage process.Therefore,the emphasis of this paper is to investigate the influence of DOC on NOx removal property of NSR catalyst.A series of homemade NSR catalysts Pt/xBa/Ce0.5Zr0.5O2?x=10,15,20?were prepared,in which x was mass fraction.Characterization methods were adopted to study its physical and chemical properties.At last,based on the simulated gas test platform,the performance of NSR catalysts were evaluated,and DOC catalyst?4Mn10Ce/?-Al2O3?as well as NSR catalyst(Pt/15Ba/Ce0.5Zr0.5O2)were selected to investigate the influence of DOC on NOx removal property of NSR catalyst.The main research contents and results are as follows:?1?The NSR catalysts Pt/xBa/Ce0.5Zr0.5O2?x=10,15,20?were prepared by the combination method of precipitation and impregnation.The catalysts were then characterized by using XRD?X-ray Diffraction?,BET?Brunauer-Emmett-Teller?and SEM/EDS?Scanning Electron Microscope/Energy Dispersive Spectrometer?.The results show that Ce-Zr oxides mainly exist as cubic fluorite structure,and its grain size increases first and then decreases with Ba loading increased.When Ba loading is 15 wt.%,its grain size reaches the manxium value of 7.1 nm.Mesoporous is the main structure of the NSR catalysts,of which the distribution range of the most probable aperture and pore size are 3-4 nm and 3-30 nm,seperately.The Pt/15Ba/Ce0.5Zr0.5O2 catalyst has the maximum specific surface area and the minimum pore size,which are 24.874m2g-1 and 3.374 nm,respectively.The storage components of catalysts exist as spherical and bulk structure,while the active components exist as spherical particles.The elemental compositions of NSR catalysts are C,O,Zr,Ce,Ba and Pt.?2?Based on the simulated gas test platform,a series of blank pipe tests were performed,and then the experiments were carried out to investigate NOx storage property,NOx complete storage and reduction property of NSR catalysts as well as storage species stability.The results show that the curves of NOx volume fraction changing with time basically respectively coincide in the process of blank pipe tests under different temperatures,O2 concentrations and airspeed,which illustrates that the influence of these parameters on test results errors are small that can be ignored.Pt/15Ba/Ce0.5Zr0.5O2 catalyst has the best NOx storage property,and its breakthrough time and storage saturation time seperatlely reach to 9 min and 90 min when the temperature is 350°C,and at the same time its NOx storage capacity and NOx conversion rate also achieve the maximum value in the NOx complete storage and reduction tests,which are674.14?mol/gcat and 32.40%,respectively.The position as well as quantity of NO and NO2desorption peaks are obviously different in the NO-TPD experiment results,which indicates that nitrates and nitrites are the main storage forms of NOx.?3?Simulated gas test method was adopted to perfom the property experiments of NOx storage and cycling NOx storage and reduction of NSR and DOC+NSR catalysts under 350°C,respectively,and the influence of DOC on NOx removal property of NSR catalyst was also analysised under different temperatures,O2 concentrations and airspeed.The results show that when the temperature is 350°C,the NOx storage efficiency of DOC+NSR catalyst is higher than that of NSR catalyst,which reaches to 43.01%.Its NOx storage efficiency attains above80%in the first 30 min,and the NOx conversion rate is improved by 10.21%,reaching to84.89%.However,when the temperature increases to 400°C and 450°C,its NOx conversion rate decreases by 5.37%and 7.62%,respectively,which indicates that the NOx removal property of DOC+NSR catalyst is inhibited by high temperatures.When the O2 concentration is constant,the NOx conversion rate of DOC+NSR catalyst is higher 5-10%than that of NSR catalyst,which reaches to the maximum value of 92.73%under the effect of 7.5%O2 concentration.Moreover,DOC can facilitate broadening the active window of O2 concentration of the NSR catalyst,and it shows favourable airspeed characteristics under the effect of DOC combined NSR catalyst.When the airspeed is 40000 h-1,it reaches the maximum NOx storage efficiency and NOx conversion rate,which are 93.59%and 87.04%,respectively. |
PDF Full Text Request