The Study Of No_x Storage And Reduction Technology At Low Temperature And Interaction Between Noble Metals With Metal Oxides

NOxstorage and reduction is a very efficient NOxremoval technology, which isapplied in lean-burn engine and diesel engine. The components include noble metals,storage materials and supports. The low temperature NOxstorage and reductionperformance was focused. The NOxstorage capacity was investigated using the ceriabased materials as storage components. And NOxreduction performance wasinvestigated based on Pt based catalysts. The influence of the interaction mechanismbetween noble metals, storage materials and supports on the NSR performance wasinvestigated, which could provide guide for the application of NOxreduction andreduction.The method for static and transient NOxstorage capacity was established. Basedon the LNT catalysts of Pt/Al2O3mixed with different CeO2supports, the relationshipbetween the physical structure, surface Ce3+contents, the redox character and NOxstorage properties were systematically explored. It indicates that high contents ofsurface Ce3+benefit NOxstorage process and the interaction with Pt/Al2O3can improvethe activity of active oxygen, formation more nitrates. Besides, there was impeditiveadsorption between CO2and NOx, which lead to the decrease of NOxstorage capacityof CeO2.The Pt/Al2O3+CeO2+Ba/Al2O3(Ba/CeO2) catalysts was utilized to simulate thelow temperature cold-start process, which focus on the NOxstorage capacity withtemperature from100oC to400oC. It was found that NOxstorage conversion decreasedas temperature increasing, and there was lowest NOxconversion at around150oC.Single components were analyzed as to the NOxconversion. And it indicates that CeO2present large amount of NOxadsorption at100oC, however, the bidentate nitrites wereless stable and decomposed, which lead to the decrease of the NOxconversion. TheCeZr solid solutions and the BaO/La2O3loaded on CeO2were investigated as NOxstorage materials. It was found that CeZr can improve the stability of the NOxadsorbedspecies and the nitrates formation. BaO loaded on CeO2supports can utilize the synergyof the strong basicity and the redox properties, and form stable NOxadsorbed speciesto inhibit NO release at low temperature, while the less interaction between La2O3andCeO2can not improve the stability of bidentate nitrites on CeO2supports.The NOxreduction performance was systematically investigated over Pt/Al2O3 +Ba/Al2O3at low temperature in rich period. It was found that NO was not reducedcompletely at200oC, leading to NO release and decrease of NO reduction conversion.Different reductants (CO, H2) were studied as to the reduction characters. It was foundthat CO present strong adsorption on Pt sites at low temperature, which inhibit NOadsorption, thus CO presents low NO reduction conversion. While Pd based catalystspresent weak CO adsorption at low temperature, which present high NO conversionwhen CO and H2coexist, and inhibit NO release at low temperature.By use of H2-TPR, Pt/Al2O3+CeO2mixture were systematically treated at differentconditions to investigate the influence on the redox properties of CeO2. It was foundthat there was strong interaction between Pt and CeO2. The conditions at450oC in inertgas could oxidize Pt and migrate to the CeO2surface. The oxidized Pt can be reducedby H2during H2-TPR, then facilitated the H2dissociation and improve the surface activeoxygen reduction.