Effect of excess palladium on the activity of perovskite catalysts for Oxidation of exhaust gas pollutants emitted from natural gas fueled vehicles (NGFVs)

LaMnO3 and LaMnPd0.05O3 (contains 2.15 wt% Pd) perovskite-type catalysts were prepared via solution combustion method, calcined at 700oC for 5 h and were characterized by X-ray diffraction method (XRD), BET specific surface area and H2 temperature programmed reduction (TPR). The catalysts activity for the abatement of pollutants (i.e. CO and CH4) emitted from natural-gas (NG) fuelled vehicles were investigated using a synthetic exhaust conditions. A gas mixture of 2 vol% CO and 2000 ppm CH4 in Ar together with proper flow of air (SN=1.1) was used as the synthetic exhaust gas of NG engines. Activity results show that T90% conversion for CO and CH4 oxidation reduces 130oC and 35oC respectively when small amount of excess Pd inserts into perovskite structure. The Pd content has a great influence on the activity below 500oC; however this effect would be moderated at temperatures above 500oC probably as a result of increasing temperature which favors the reduction of PdO to metallic Pd that appears to be less active than PdO. TPR results reveal that reduction temperature of Mn+4 to Mn+3 ions is reduced about 200oC for Pd containing perovskite; however, no discernable effect on the reduction temperature of Mn+3 to Mn+2 ions is observed.

کلیدواژه ها:

Perovskite-type catalysts ، Palladium ، Natural gas vehicles ، oxidation activity