| The process and the thermodynamics of NO reduction by H2 are studied. It isindicated that H2 can reduce NO under lean-burn conditions at low temperatures,and the resultants are N2O and NH3 in addition to N2.In this paper, the process of NO reduction by H2 over Pd/Al2O3 isinvestigated. With the increasing temperature, the NO conversion increases first,and then decreases. The change of N2 and NH3 selectivity has the same trend,while N2O decreases first, and then increases. With the increase of NO or O2concentration, the NO conversion is inhibited. The increase of H2 concentrationprompts the activity. It is reverse that the occurrence of H2O decreases the activityat low temperatures, and has no effect at high temperatures. Besides, theoccurrence of H2O has no effect to the resultants. It is indicated that the NOconversion and the distribution of resultants correlate with the concentration ofreactants NO, H2 and O2, in other word, the competitive adsorption among NO,H2 and O2 results in the change of the catalyst.To study the reaction mechanism, Dumesic et al have proposed microkineticanalysis, which combines observed experimental results to elementary reactions.It has been used and proved effective. In this paper, a microkinetic model isdeveloped to quantitatively describe the mechanism of NO reduction in thepresence of excess H2 or O2 by Chemical Kinetics Simulator (CKS) package. It isindicated that there is competing adsorption, and the sequence is following: NO >O2 > H2. The reaction mechanism and the distribution of resultants are influencedby conditions. To verify the mechanism, in-situ diffuse reflectance IRspectroscopy (DRIFTS) is used to observe species in the reaction. Transientexperiments show the competitive adsorption among NO, O2 and H2. Simulateddata are in accord with experimental data. In a word, the mechanism can describethe NO conversion and the distribution of resultants as a function of temperatureand the component of exhaust gas.
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