CN102744064B - Catalyst and its preparation for nitrogen oxide in automobile exhaust processing - Google Patents

Abstract

The present invention is provided to the catalyst of nitrogen oxide in automobile exhaust processing and its preparation.For the catalyst using aluminium cerium zirconium as carrier, a small amount of noble metal is active metal, by the doping of rare earth element, improves the NO of catalyst_xConversion ratio and heat endurance.After the h of aging 100, its NO of described catalyst_xPurifying rate is held essentially constant, and undoped with catalyst its NO_xPurifying rate reduces by more than 20%.

Description

Catalyst and its preparation for nitrogen oxide in automobile exhaust processing

Technical field

The invention belongs to nano-catalytic application, and in particular to a kind of rare earth doped aluminium-cerium-zirconium carrier application The NO in vehicle exhaust_xPurification.

Background technology

In recent years, sharply increasing with automobile quantity, the tail gas of motor vehicle emission have become the main dirt of atmosphere pollution One of dye source, the NO in its composition_xSeriously endanger environment and the health of the public.China is at present to NO_xPurification generally uses three First catalyst, very big due to being influenceed by engine air-fuel ratio, traditional three-way catalyst is to NO_xClean-up effect and bad.Cause Under this lean-burn condition（Air-fuel ratio>1) NO_xPurification is one of current challenging problem.Exhaust of lean-burn automotive at present The research of purification is concentrated mainly on NO_xDirectly decompose, selective catalysis reduces and NO_xStorage-reduction etc., wherein NO_xStorage- Reduction technique is increasingly subject to pay attention to due to the plurality of advantages such as purification efficiency is high, temperature window is wide, operating cost is low.

NO_xThe general principle of storage-reduction method is by NO under lean-burn condition_xAdsorption storage gets up, then in rich condition Under discharge, N is changed into by reducing agent₂.Wherein Pt/Ba/Al₂O₃It is typical NO_xStorage-reduction catalyzer, exist at present Japanese industrialized production.But the sulfur content in fuel on Japanese market is low, and some domestic sulfur contents in fuel are higher, easily It is that catalyst is poisoned, therefore Pt/Ba/Al₂O₃Catalyst is restricted in practical application at home.In addition, NO_xStorage Deposit-heat endurance of reducing catalyst is also a pressing issues for being badly in need of solving, composition BaO and carrier are stored at high temperature Al₂O₃Or CeO₂With reference to generation BaAlO₄Or BaCeO₃So as to inactivate.We have found that by the difference of rare earth element ion radius, enter Enter in aluminium-cerium-zirconium support crystal lattice, produce more oxygen vacancies, can effectively suppress BaAlO₄Or BaCeO₃Generation, so as to carry The heat endurance of high catalyst.There is presently no pertinent literature and patent to be reported this.

The content of the invention

High, the strong NO of stability the invention provides a kind of catalytic activity_xCleaning catalyst.

The catalyst includes precious metals pt, Pd and the one kind or more in Rh of aluminium-cerium-zirconium carrier and load on this carrier Kind active component, alkali metal or alkaline-earth metal storage component, the aluminium-cerium-zirconium carrier are by Modified by Rare Earth Elements.

It is described to be used for NO_xThe catalyst of purification, the carrier components include Al₂O₃、CeO₂And ZrO₂。

It is described to be used for NO_xThe catalyst of purification, aluminium-cerium that the catalyst uses-doping of zirconium carrier La, Y, Sm, Nd and Pr Deng rare earth element.Rare earth element accounts for the 1-10 % of aluminium-cerium-zirconium carrier quality（Calculated with La or Nd）.It is preferred that 5%.

It is described to be used for NO_xThe catalyst of purification, the noble metal of dipping is one or more in Pt, Pd and Rh.It is preferred that Pt.

Described NO_xCleaning catalyst, active metal weight account for the 0.5-1 % of total catalyst weight.

Described NO_xCleaning catalyst, the catalyst is using the alkaline earths such as Li, Na, K, Rb alkali metal or Mg, Ca, Ba, Sr gold One or more in category are auxiliary agent.It is preferred that Ba, K, wherein Ba, K mass fraction account for 16 % of carrier（Calculated with Ba）.

The preparation method of described catalyst, include the synthesis of fresh sample, then be calcined by 500 °C -700 °C.

Its sintering temperature is preferably 550 °C.

By La, Y, Nd or Pr doping, NO is improved_xThe heat endurance of cleaning catalyst, in 350 °C of agings 100 Its activity keeps stable after h.

Brief description of the drawings

Fig. 1 is：Rare earth doped element La, Y, Nd and undoped with Pt/Ba/ACZ catalyst ns O change into NO₂Activity.

Fig. 2 is：Rare earth doped element La, Y, Nd and undoped with Pt/Ba/ACZ catalyst ns O_xConversion rate curve.

Fig. 3 is：Rare earth doped element La, Y, Nd and undoped with Pt/Ba/ACZ catalyst thermostabilization.

Embodiment

The present invention is used for NO_xIt the catalyst of purification, can in granular form use, coating load can also be used as in entirety Integral catalyzer is formed on formula porous matrix.Monolithic porous matrix can be the ceramics such as cellular cordierite, mullite Matrix or other alloy substrates.

The NO of the present invention_xCleaning catalyst can be individually carried on a matrix, can also be with current three-element catalytic Agent mixing one multicomponent catalyst of composition.

More specifically the catalyst of the present invention is illustrated with reference to embodiment, but these embodiments are to the present invention's Scope is without any restrictions.

Embodiment 1

（1）The preparation of control sample：By Al (NO₃)₃ ^.6H₂O, Ce (NO₃)₃ ^.6H₂O and Zr (NO₃)₄ ^.5H₂O wiring solution-formings, its Middle Al₂O₃：CeO₂：ZrO₂Mass percent be 67：22：11.Then 30 % H are added₂O₂As oxidant, NH is used₃ ^.H₂O It is 10 as precipitating reagent to pH, is washed by centrifugation, by H₂PtCl₆ ^.6H₂O is distributed in above-mentioned slurries, aging, drying, 550 ° After C is calcined 4 h, by Ba (NO₃)₂It is impregnated into using incipient impregnation mode after being calcined on the carrier of gained, drying.Through 500 ° CH₂/N₂Gained catalyst is Pt/Ba/ Al after reduction₂O₃-Ce_0.67Zr_0.33O₂Catalyst, it is designated as catalyst 1.

（2）Adulterate the preparation of lanthanum catalyst：By Al (NO₃)₃ ^.6H₂O, Ce (NO₃)₃ ^.6H₂O, Zr (NO₃)₄ ^.5H₂O and La (NO₃)₃ ^.6H₂O wiring solution-formings, wherein Al₂O₃：CeO₂：ZrO₂=67：22：11, add 30 % H₂O₂, La₂O₃For carrier quality 5%, with 30 % H₂O₂As oxidant, NH₃ ^.H₂O is precipitating reagent, and it is 10 to be precipitated to pH, is washed by centrifugation, will H₂PtCl₆ ^.6H₂O is distributed in above-mentioned slurries, aging, drying, after 550 °C of 4 h of roasting, by Ba (NO₃)₂Using incipient impregnation Mode be impregnated into roasting after gained carrier on, drying.Through 500 °C of H₂/N₂Gained catalyst is Pt/Ba/ after reduction La₂O₃-Al₂O₃-Ce_0.67Zr_0.33O₂Catalyst.It is designated as catalyst 2.

Embodiment 2

(1) preparation of control sample：By Al (NO₃)₃ ^.6H₂O, Ce (NO₃)₃ ^.6H₂O and Zr (NO₃)₄ ^.5H₂O wiring solution-formings, its Middle Al₂O₃：CeO₂：ZrO₂Mass percent be 67：22：11.Then 30 % H are added₂O₂As oxidant, NH is used₃ ^.H₂O It is 10 as precipitating reagent to pH, is washed by centrifugation, by H₂PtCl₆ ^.6H₂O is distributed in above-mentioned slurries, aging, drying, 550 ° After C is calcined 4 h, by Ba (NO₃)₂It is impregnated into using incipient impregnation mode after being calcined on the carrier of gained, drying.Through 500 ° CH₂/N₂Gained catalyst is Pt/Ba/ Al after reduction₂O₃-Ce_0.67Zr_0.33O₂Catalyst, it is designated as catalyst 1.

(2) preparation of neodymium catalyst is adulterated：By Al (NO₃)₃ ^.6H₂O, Ce (NO₃)₃ ^.6H₂O, Zr (NO₃)₄ ^.5H₂O and Nd (NO₃)₃ ^.6H₂O wiring solution-formings, wherein Al₂O₃：CeO₂：ZrO₂Mass percent be 67：22：11, then add 30 % H₂O₂As oxidant, with NH₃ ^.H₂O is precipitating reagent, and it is 10 to be precipitated to pH, is washed by centrifugation, by H₂PtCl₆ ^.6H₂O is distributed to In above-mentioned slurries, aging, drying, after 550 °C are calcined 4 h, by Ba (NO₃)₂After roasting being impregnated into using incipient impregnation mode On the carrier of gained.Drying.Through 500 °C of H₂/N₂Gained catalyst is Pt/Ba/Nd after reduction₂O₃-Al₂O₃- Ce_0.67Zr_0.33O₂Catalyst.It is designated as catalyst 3.

The performance of embodiment catalyst is evaluated below

Catalyst is to NO under the different temperatures of test case 1_x Conversion ratio

Embodiment 1-2 catalyst each 0.5 mL, the h of air speed 72 000 is respectively adopted^-1, in continuous stream actuating miniature fixed bed Upper carry out NO_xStorage and determination by reduction, NO in tail gas_x Change in concentration passes through chemiluminescence NO-NO₂-NO_xAnalyzer detects (Thermo, 42i-HL).Reacting gas forms：500 ppm NO, 8Vol%O₂, 8Vol%CO₂, N₂For Balance Air.Exist respectively Catalyst is determined under 200 °C, 250 °C, 300 °C, 350 °C, 400 °C to NO_x Changing effect, test result is shown in Fig. 1, by taking 5 % rare earth elements (La or Nd) doped catalyst as an example, test result of the present invention is not limited to 5 % rare earth elements and mixed Miscellaneous catalyst.

It will be seen from figure 1 that described catalyst 2 and 3 has for the catalyst 1 undoped with rare earth element Higher NO-to-NO₂Conversion ratio.At 350 °C, the NO-to-NO of catalyst 1,2 and 3₂Conversion ratio is respectively 33 %, 64 % With 43 %.

Figure it is seen that described catalyst 2 and 3 has for the catalyst 1 undoped with rare earth element Preferable NO_xConversion ratio.T=350 °C, the NO of catalyst 2_x It is converted into N₂Conversion ratio be 98 %, the NO of catalyst 3_x Conversion Rate is 94 %, and the NO of catalyst 1_xConversion ratio is 83 %.In NO of 200 °C and 300 °C its catalyst 2 than catalyst 1_xTurn Rate improves 20 more than %.

The catalyst 1-3 of test case 2 cycle life test

Reacting gas forms：500 ppm NO, 8 Vol%O₂, 8 Vol%CO₂, N₂For Balance Air.Air speed is 72 000 h^-1, continuously NO is being determined after the h of aging 100 in flowing fixed bed under 350 °C_xThe stability ability of conversion ratio.Its result is shown in figure 3。

Fig. 3 catalyst 1 is in N₂After 100 h are stabilized under atmosphere, NO_x Conversion ratio reduces by 20 more than %, deactivation phenomenom occurs.

Fig. 3 catalyst 2 is in N₂After 100 h are stabilized under atmosphere, NO_x Conversion ratio is held essentially constant, and is not inactivated Phenomenon.

Fig. 3 catalyst 3 is in N₂After 100 h are stabilized under atmosphere, NO_x Conversion ratio also keeps not becoming substantially.

The representative embodiment of the present invention is the foregoing is only, it is every according to the modification done in scope of the present invention patent With change, it should all belong to covering scope of the invention.

Claims (8)

1. one kind is used for NO_xThe catalyst of purification, it is characterized in that：The catalyst is by aluminium-cerium-zirconium carrier and loads on this carrier Precious metals pt and alkaline-earth metal storage component composition；Aluminium-cerium-zirconium the carrier is Al₂O₃、CeO₂And ZrO₂, it passes through rare earth Element is modified, one or more of the rare earth element in La, Y, Sm, Nd or Pr；The alkaline-earth metal be selected from Mg, Ca, One or more in Ba or Sr.

2. catalyst according to claim 1, it is characterised in that：The doping of the rare earth element accounts for aluminium-cerium-zirconium carrier The 1-10% of mass fraction.

3. catalyst as claimed in claim 1 or 2, it is characterised in that：Described alkaline-earth metal accounts for the 10- of total catalyst weight 16%.

4. catalyst according to claim 1 or 2, it is characterised in that：The Pt accounts for the 0.5-1% of total catalyst weight.

5. catalyst according to claim 1, it is characterised in that：The catalyst is Pt/Ba/La₂O₃-Al₂O₃- Ce_0.67Zr_0.33O₂Or Pt/Ba/Nd₂O₃-Al₂O₃-Ce_0.67Zr_0.33O₂。

6. the preparation method of any one of the claim 1-5 catalyst, including：The synthesis of fresh sample, then by 500-700 DEG C Roasting.

7. the preparation method of catalyst according to claim 6, it is characterised in that：The sintering temperature is 550 DEG C.

8. the NO that any one of the claim 1-5 catalyst is used in vehicle exhaust_xPurification.