Study of NOx selective catalytic reduction by ethanol over Ag/Al2O3 catalyst on a HD diesel engine

摘要

The selective catalytic reduction(SCR)of NOx by ethanol over Ag/Al2O3 catalyst has been proven to significantly reduce NOx emission in a simulated engine exhaust gas environment in our previous research.However,the exhaust gas from real engines is too complicated to be simulated.Therefore,the Ag/Al2O3 catalyst is needed to be evaluated for its application on real diesel engines.In this paper,firstly the catalyst performance was evaluated on an engine test bench and the effect of the catalyst on PM emission was investigated.Then,an integrated aftertreatment system composed of Ag/Al2O3 catalyst+Cu/TiO2 catalyst+Pt/TiO2 catalyst and ethanol dosing based on open loop control was designed and established.Finally the diesel engine emissions with the aftertreatment system were tested on the ESC test cycle.The result showed that under the condition of fresh catalyst and space velocity(SV)= 30,000 h~(-1),a high NOx conversion(up to 90%)can be obtained in the range of temperature 350-450 °C.The NOx conversion efficiency will go up with the increase of the ethanol dosage,but cause the great increase of the CO emission and THC emission at the same time.Under the condition of inlet temperature = 400 °C and ethanol to NOx mole ratio(n_E:n_(NOX))= 1.5,the NOx conversion can maintain above 70% when the space velocity is less than 50,000h~(-1).The aging test showed that sulfur absorbed on catalyst surface is the main reason for the deterioration of the catalyst activation.Additionally,the Ag/Al2O3 catalyst can effectively reduce the soluble organic fraction(SOF)in particulate matter(PM),but have no effect on dry soot(DS).The Ag/Al2O3 catalyst can decrease the sulfate slightly when the inlet temperature is below 410 °C,but dramatically increase the sulfate when the inlet temperature is above 470 °C.Totally,the PM emission can be decreased more than half of the original engine-out emission under the condition of inlet temperature 336 °C,but increased a little when inlet temperature is above 470 °C.The engine emissions based on the ESC test showed that the engine with the aftertreatment system can completely meet EURO III regulations.