UBI-QEP study on purification of vehicle exhaust gas

Abstract

The Vehicle exhaust gas generally contains nitrogen oxides and the fossil fuel which do greatly harm to air environment. Although the use of catalytic converters for the vehicle gas has resulted in considerable progress in the past twenty years, a theoretical framework for explaining the experimental observations is still lacking. We use the UBI-QEP method to analyze the chemisorption species and calculate the energiti of elementary reactions on six metal single crystal surfaces, Pt(111), Pd(111), Rh(111), Ag(111) Cu(111) and Ni(111). It will help us to realize the reaction mechanism and choose the best suitable catalysts. The sequence of chemisorption heat for NOx is Ni > Rh > Cu > Pd > Pt > Ag. The dissociation of NOx decreases along the series Rh approximate to Ni > Cu > Pd > Pt > Ag. The decomposition of NO can easy happen via N2O intermediate. From calculations at low coverage, we can see two possible pathways of NOx reduction, the direct dissociation and CO-aided dissociation. At high coverage, however, CO-aided dissociation is main pathway. For complete oxidation of carbon monoxide, Pt, Pd, Ag and Cu are fine catalysts, but both Ni and Rh can not promote it. The Ni-Cu-based catalysts may replace the noble metal catalysts (Pt-Pd-Rh).