高性能汽車尾氣凈化催化劑的制備_英文_

1、Article I D :025329837(2004022*Communication :8586R eceived d ate :2003210221.First author :ZHAN G Huaihong ,male ,born in 1973,MS student.Corresponding author :CHEN Y aoqiang.Tel :(02889001472;E 2mail :nic7501.Found ation item :Supported by the National Natural Science Foundation of China (20273043

2、and the National Natural Science K ey Founda 2tion of China (20333030.Preparation of an Advanced Automotive Exhaust C atalystZHANG Huaihong ,GONG Maochu ,GUO J iaxiu ,ZHAO Bin ,CHEN Y aoqiang(College of Chemist ry ,S ichuan U niversity ,Chengdu 610064,S ichuan ,China K ey w ords :platinum ,alumina ,

3、rhodium ,ceria ,zirconia ,yttria ,three 2way catalystC LC number :O643/X7Document code :AThe catalytic converter was developed for the control of vehicle emission.Much work has been de 2voted to the study of the catalytic materials and their application in the catalytic converter.For improving the a

4、ctivity and durability of the catalyst ,the possible approaches are increasing the platinum group metal (P GM loading and increasing the catalyst amount.Currently ,the Critical Standard (Europe for automotive emission control has been adopted in many cities.The present commercial catalysts cannot ac

5、hieve the high performance required for automotive exhaust gas control.To meet the requirements of the standard ,the of an advanced automotive exhaust catalyst is desired.The significant improvements in three 2way cata 2lyst (TWC have been achieved by incorporating rare earth metal promoters ,such a

6、s CeO 2,into TWC.The contribution of CeO 2to the improvement of TWC activity has been studied by many re 2searchers 13.The behavior of Rh/CeO 2catalyst is of interest owing to its excellent performance as a fresh TWC.This has been discussed in terms of the P GM 2Ce interaction 4as well as the oxygen

7、 storage capacity (OSC .However ,the catalyst can be deac 2tivated at high temperature because of being sintered.It has been reported that adding ZrO 2into CeO 2can increase OSC 1,5,and stabilize CeO 2particles against thermal sintering 5,6.A recent study showed that the introduction of a small amou

8、nt of yttria into CeO 22ZrO 2solid solution can give good thermal stabil 2ity and increase oxygen ion mobility ,and thus en 2hance the catalyst redox property 7.An advanced catalyst with high low 2temperature activity and high 2temperature durability has been pre 2pared in our laboratory.The Rh/CeO

9、22ZrO 22Y 2O 3is used in TWC systems ,as it is important to maintain the advantage of the Rh 2CeO 2interaction.To confirm the high performance of the catalyst ,TWC was de 2posited on cordierite and metal substrate (supplied by Emitec Co Ltd respectively.A Rh chlorate solution was deposited on CeO 22

10、ZrO 22Y 2O 3powder by incipient wetness method.The resulting powder was dried at 110for 2h and cal 2cined at 500for 2h ,thereby forming Rh/CeO 22ZrO 22Y 2O 3powder (A with w (Rh =011%.A Pt chlorate solution was deposited on activated alumina (La stabilized powder by incipient wetness method.The resu

11、lting powder was dried at 110for 2h and calcined at 500for 2h ,thereby forming Pt/2Al 2O 3powder (B with w (Pt =110%.The powders (A and (B were blended in pre 2scribed ratios ,and H 2O was added to make a wash 2coat.This washcoat was coated on cordierite sub 2strate and metal substrate respectively

12、,then dried at 120for 2h and calcined at 500for 3h.The noble metal content on all catalysts was 110g/L (n (Pt /n (Rh =10.On the other hand ,the current catalyst was prepared as follows :a Rh chlorate and Pt chlorate solution was used to co 2impregnate a mixture of 2Al 2O 3and CeO 22ZrO 2.The other s

13、teps were the same as the advanced catalyst coat method.The above obtained catalysts were aged with steam at 900for 5h.The catalysts were evaluated under the following conditions ;0108%NO 20106%C 3H 82016%CO 210%H 2O 2N 2balance ,SV =313×104h -1,=100400.The reaction gas composition was maintain

14、ed ex 2cept for changing the oxygen between rich and lean第25卷第2期催化學報2004年2月Vol.25No.2Chi nese Journal of CatalysisFebruary 2004with an amplitude of±011air/fuel(A/Fratio.The light2off temperature was measured at the stoichio2 metric A/F ratio.Before measuring the light2off tem2 perature,the cata

15、lysts were heated up to550and kept at this temperature for2h in the simulated gas and then cooled down to100.The light2off temperatures of different catalysts are listed in Table1.For the fresh current and ad2 vanced Pt/Rh catalysts deposited on cordierite sub2 strate,the latter shows lower light2of

16、f temperature than the former,especially with respect to CO and NO x.The light2off temperature of the aged current and advanced Pt/Rh catalysts can be explained by the high rate of water2gas2shift reaction8contributed from the strong Rh2CeO2interaction9.This result indicates that the advanced cataly

17、st maintains the strong Rh2CeO2interaction even after severe aging.T able1Light2off temperatures of different catalystsSubstrate Catalyst50%/HC CO NO xCordierite current fresh260218231aged310251269advanced fresh240183194aged286221228 Metal current fresh280225237aged341258279advanced fresh263217223ag

18、ed32524526550%the temperature at which the reactant conversion is50%For the Pt/Rh catalysts deposited on metal sub2 strate,the fresh advanced catalyst shows lower light2 off temperature than the fresh current catalyst,espe2 cially with respect to CO and NO x.The light2off temperatures of the aged cu

19、rrent and advanced cata2 lysts indicate that the advanced catalyst maintains the strong Rh2CeO2interaction after severe aging.This suggests that the advanced catalyst contains the Pt/2Al2O3and Rh/CeO22ZrO22Y2O3in its structure.It maintains simultaneously high surface area and Rh2 CeO2interaction.Als

20、o,there are certain synergistic actions between Pt/2Al2O3and Rh/CeO22ZrO22 Y2O3.On the other hand,the current catalyst does not show the Rh2CeO2interaction.The above results show that the advanced cata2 lyst has lower light2off temperature and durability than the current catalyst.However,compared wi

21、th the catalyst deposited on cordierite substrate,the cat2 alyst deposited on metal substrate shows higher light2 off temperature.This is because the surface area for contact of exhaust gas and the catalyst decreased. This suggests that the catalyst performance is related to the cell density of the

22、substrate.R eferences1Fornasiero P,Di Monte R,Ranga Rao G,K aspar J,Meri2 ani S,Trovarelli A,Graziani M.J Catal,1995,151(1: 1682Vlaic G,Fornasiero P,G eremia S,K as par J,Graziani M.J Catal,1997,168(2:3863Y ang Zh B,Lin P Y,Wang W D,Yu Sh M.Cuihua X uebao(Chin J Catal,2001,22(4:3654Bera P,Patil K C,Jayaram V,Subbanna G N,Hegde M S.J Catal,2000,196(2:2935Hori