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

فاقد چكيده

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.