Study On Four-ways Catalysts For Diesel Engine Exhaust

With the widely applications of diesel engines, the influence caused by the exhaust pollutants(carbon particles, NOX, CO and HCs) on the atmosphere environment should be taken seriously. The irregular emission of exhaust pollutants is one of the leading causes of urban haze, which threaten people’s daily travel and physical health. Simultaneous removal of carbon particles, NOX, CO and HCs is one of the most ideal means to reduce the emissions of pollutants in diesel exhaust.This paper mainly studies the activity of Ru-Ir bimetallic precious metal catalysts and the trimetallic catalysts. On this basis the exploration of four-ways catalyst was carried.The single precious metal catalysts and bimetallic catalysts were prepared by anatase-type Ti O2 as the carrier, Ru and Ir as the main active ingredients. The effects of Ru-Ir load ratio and thermostatic temperature on the catalytic activity under oxygen-rich conditions were determined. The results show that: Ru-Ir/Ti O2 is effective for the simultaneous removal of soot and NOX under the oxygen-rich condition. Ihe removal efficiency decreases first and then rises with the increasing load ration of Ir. When the ratio of Ru:Ir is 9:1, Ru-Ir/Ti O2 catalyst shows the highest activity(Tpeak = 437 ℃, ηNOx = 42.65%). In the constant temperature experiments, the catalyst shows a steady soot oxidation rate and the highest removal efficiency of NOX at 322 ℃, the highest removal efficiency can reach 71.20%.Furthermore, the bimetallic precious metal catalysts were modified by precious metals(Ag, Au, Pd, Pt and Rh). The effects of precious metals species, load ratio and total load were concerned. The results show that: under oxygen-rich conditions, only after Ag added the simultaneous removal efficiency of carbon particles and NOX can inprove. With the load ratio of Ag increasing, the catalytic activity of carbon particulates decreases at first, and then increases, and then decreases again. The catalytic activity of NOX decreases all along. When the load ratio of Ag: Ru: Ir is 10: 81: 9, and the total load is 1 wt.%, the catalytic activity reaches the best(Tpeak= 417 ℃, ηNOx= 46.35%). In the constant temperature experiments, the catalyst shows a higher oxidation rate of carbon particles and the highest removal efficiency of NOX at 322 ℃, the highest removal efficiency can reach 72.56%.The activity of four-ways catalyst with Ag-Ru-Ir/Ti O2 is studied, and its path of four-ways catalytic reactions is explored by the control experiments. The results show that: in the process of four-ways catalytic reactions, the catalyst can remove carbon particles, CO and C3H6 with the removal efficiency of 99.9%, while the NOX removal efficiency is just 13.57%. In the constant temperature experiment, the removal efficiency of NOX is 46.23%, and both of C3H6 and CO can be removed completely. In the control experiments under these two conditions(oxygen-rich conditions and anaerobic conditions), the reaction path of the four-ways catalysts under oxygen-rich conditions can be obtained.