Title of Invention

"A PROCESS FOR STABILIZATION OF TRANSITION ALUMINAS PREFERABLY GAMA ALUMINA"

Abstract

A iraew formulation for stabilisation of gamma-alumina and other transition alittimiinias is invented by using tin as stabilizer. A process four producing a high temperature resistant high surface area aliuimiiraa support, twhiclh comprises admixing tin in the form of an aqueous rosr iraon—aqueous solution or dispersion of the tin metal or salt, with active aluunina, drying the mixture and calcining it is described. The resulting catalyst support transition alumina stabilised iwiitlh) tin is useful for use in catalytic converter and other Ihtiglh) temperature catalytic processes, such as catalytic combustion. Hhiis may be deposited an a monolith honeycomb carrier. Siuitable catalysts may be deposited on this stabilized alumina support amd used for emission control applications.

Full Text

FIELD OF INVENTION This invention relates to a. process for stabilising of transition alumina support material and a process for preparing the stabilised support material. More specifically, it relates to a stabilized transition alumina support which shows better resistance to the reduction of high surface area even after it has been exposed for a long period of time to high temperatures (1100.degree C>. BACKGROUND OF INVENTION Typically, exhaust gas catalysts comprise a relatively low porosity ceramic support with a transition alumina coating having a high surface area. The underlying ceramic support is generally prepared by sintering a mold of clay or other ceramic material at a high temperature to impart density and strength. This, however, generally results in a support having a very low surface area. Consequently, the ceramic support must be coated with another material having a much higher surface area to contain the noblt metals. The procedure of depositing a high surface area "wash-coat", as such coating is generaly known, onto a low surface area ceramic support is disclosed in, for example, US Pat. Noc. 2742437 and 3824196. The ceramic supports may be provided in any shape, but typically they are in the for* of pellets or a honeycomb-type shape commonly known as a monolith. Transition aluminas which also include more extensively used gamma alumina typically having high surface area useful for supporting catalysts or active materials. During use such as in catalytic converter the transition aluminas loses its valuable surface area due to prolonged high temperature exposures or aging and finally transformed to the stable alpha (Of ) form of alumina. Some of the commonly known transition aluminas other than gamma are chi, kappa, eta, delta, theta etc. Gamma-alumina is often used as the Mashcoat in such exhaust gas catalysts. Although a gamma—alumina washcoat imparts a relatively high surface area to an exhaust gas catalyst, it results in number of undesirable effects. Gamma-alumina or other transition-alumina washcoats are thermodynamically unstable alumina phases. Eventually, this unstable phase transforms to a thermodynamically stable alpha-alumina ophase; however, in the process of transforming, the alumina loses surface area and traps noble metals, particularly rhodium, and may change their oxidation state, rendering the noble metals less effective or ineffective. US Pat. No.4294726 discloses a IMC catalyst composition containing platinuim amid rhodium obtained toy impregnating a gamma alumina carrier- material with am a cerium, zirconium and iron, and then calcining the material at o 500—700 C in air after which the material is impregnated with an aquteous solution of a salt of platinum and a salt of rhodium dried aintd suibsequently treated in a hydrogen—containing gas at a o temperature? of 25£H&5fB> C. The alumina may be thermally stabilized with calcium, strontium, magimesiuim or barium compouwids. The ceria—z-irconia— iron oxide treatment is followed by impregnating the treated carrier material twit In aqiuteouis salts of platinum) and rhodium and then calcining the impregnated material. US Pat. lto.443S2:lL9 discloses aim alumina supported catalyst for use on a substrate. The catalyst is stable at high temperatures. The stabilizing material is disclosed to be one of several compounds including those derived from barium* silicon, rare earth metals, alfcali and) alkaline earth metals, boron, thorium, hafnium and zirconium. Of the stabilizing materials, barium oscide, silicon dioxide and rare earth oxides which include lanthanum, cerium, prasetodynniufln, neodymduvm and others are indicated to be preferred. It is disclosed that contacting them with a calcined alumina film permits the calcined alumina film to retain a high surface area at higher temperatures. US Pat. MD..4504998 discloses a process for producing a high temperature resistant TIWC catalyst. The process includes forming an aqueous slurry of particles of gamma or other activated alumina and impregnating the alumina with soluble salts of selected metals including) cerium, zirconiuwn, at least one of iron and nickel and at least one of platinum, palladium* and rhodium and optionally, at least one of ncodyimituum,, lanthanum and praseody— o onitun. The impregnated alumina is calcined at &fftfff C and then dispersed in water to prepare a slurry which its coated on a honeycomb carrier ami dried to (obtain a finished catalyst. US Pat. No.4W»2W4)0s have been fouraJ inset mil for high temperature applications. The combiirnation of lanthanum and barium is found to provide a superior hydrothermal stabilization of alumina which supports the catalytic component, palladium. US Pat. No»49(&S243 discloses a otethod to improve thermal stability of a TMC catalyst contaiirningf preciotuis netals by incorporating a barium compound and a zimcontiiuun compound together with ceria and aliuunina. This is disclosed to for* a catalytic moiety to enhance stability of the alumina iwashcoat upon exposure to high teonperatuire. •701210032 (aimd /ftM—&15721 > discloses a catalytic composition comprising palladium, rhodium, active aluvmina, a cerium compound, a strontium compcnund amaS a ziLrcamiiuun) compound. These patents suggest the utility of alkaline earth metals in combination with ceria and zimocnraia to form) a thermtally stable alumina supported palladium containing iwasbcoat. It is known that transition alumina offers a very useful high surface area support. IHIowiiever, transition aluvnina is reifutired to be stabilized by impregnating or doping with other materials in order to withstand thermal aging. The use of tin for catalytic application? as an active material has been reported in the 1 itevrattuire, however the use of tin for stabilization of transition) altutotima is newer found. US Pat. NlQ.4l9ifl&l'7& discloses a high temperature stable catalyst supported on a support containing a composite oxide of aluminium and lanthanum. In this patent, lanthainmitim,, praseodymium* and neody— mium are said to promote the stabilization of the support, ie. alumina. Here the element, tin is referred as one of the cataly— tically active component and is used for the combustion reaction such as typically occurred during cleaniirag an eaehaust gas from an internal combustion engine or in a boiler or a gas turbine. In this patent, tiim is not employed to stabilize alumina. US Pat. No.S>0S337B also mentioned the use of tin for forming an active catalytic phase deposited on a particulate refractory oxide active support. The use of tin intended in this patent is exclusively for enhancing catalytic function and not intended for stabilizing refractory oxide $alunn£na$ support. US Pat. Jto.5326633 described coated substrates whereas a coating of electrically conductive tin ox idle? is employed for use in battery, catalysis, heating, shielding and field dependent fluid applications. This discloses process steps to form a tin oxide coating on aluuminat support material intended for effective catalysis without referring to any improvement of the alumina support characteristics or stabilization. It is further suggested to use tin oxide coated support to be further coated with high surface area materials such as alumina twasfhwcoat. It is also indicated to use this/oscide? coating on monolith advantageously for improving the thermal airnd electrical conductivity of the ceramic Monolith •for catalytic converter application. US Pat. No. 54139"J& discloses an exhaust gas purifying catalyst wherein tin is referred as one of the active Material. In this patent also, tin is suggested as one of the catalytic Material for deposition on a silicate carrier. US Pat. No.5494701 describes a process for producing continuous tin oxide coating on monolithic su.tibstrates- Tin oxide precursor powder is applied on the substrate preferably as charged flui — dized powder mrfhtereas electrostatic fltuiidized beds, spray systems and other means of applying potwders are required. Typical powder tin oxide precursors mentioned are stannous chloride, IOM molecular weight organic salts or (complexes of tin, particularly IOM molecular weight organic salts and complexes such as stannous 9 acetate and acetylacetonate completes of tin. 6 R Meiima et al in their paper "Preparation and characterization of Thermostable Silver on alpha—alumina Catalysts" published in Applied catalysis, 44 C1.98OJ) 133—152 described the enhance thei— snostability o-ff alpha—alumina brought about by 'anchoring" the silver particles with tin oxide previously applied to the support. In this iMratrlk, tin is applied to the stable alpha—alumina particles and not to any of transition alumina, (moreover, the objective (here twists to obtain a highly thermostable silver catalyst. OBJECTS OF THE INVENTION It is therefore an object of this invention to propose a formulation for stabilizing transition) alumina support material for the preparation of a stuipport system which is stable. Yet another object of this invention is to propose a formulation for stabilizing transition alumina support Material to obtain a support material »dhich is inexpensive. A still fuirtheir object of this invention* is to propose a formulation) containimi tin for tfhe stabilization) of transition alumina support material (which improves the thermal and electrical conductivity of gammar-alumina. DESCRIPTION OF THE INVENTION According to this invention* is provided a process for stabilization torff gamma—alumina and other trasrositiorn aluminas Mhich comprises by treatment-, with tin, tin oxide powder or any of its precursor and thereby providing the tiiro cation to the surface of the transition aluimtiima. In accordance with this invention, tiiro cam be very (conveniently used •for stabilization of gamma amid other transition alumina. Precursors, of tim suwch as staurmouts s*iilfat«f» stannomis chloride ancH/or fine tin oxitdte powndler may be taken for impregnation with ganrma and otttner traimsi tion alumina, ffiany other compound of tin can also be talken so as to incorporate tin in transition alumina. Incorporation of tin from fraction of a percent to preferably 10% calculated as finale percent in transition alumina, very effectively stabilises the transition* altumiima. This stabilisation of transition altumima helps in retaining their swrface area whereby their thermal durability and performance against thermal aging improves. The present invention suggests that tint can toe used moire advantageously over some of the other elements conventionally being used for stabilisation) of alumina. This is to overcome both technical and comnnercial limitations of other stabilizing element depending oupomt the circumstances. Impregnation with tiirn may also improve the thermal and electrical conductivity of gamma—alumina coating) ram ceramic stuitostrate„ wfrnich is very much beneficial for advanced catalytic converter applications. Commercially available transition aliutmina can be very easily impregnated »*ith tin. Transition! alumina powder preferably gamma— alumina is suspended in Mtater or nora—aqueous medium like metha-nol „ ethanol, isopropamiol „ toltutene and others* Tin in the form of tin metal or salts are dispersed in the same medium Mhere alumina is dispersed. The dispersed tiira or tin preouirsor is then added slowly to the gamiBa-alumiinia suspension and thoroughly mixed for sufficient period of time to achieve very good homogeneous mining. The impregnated so I tut ti rant thus prepared is evaporated preferably in a rotary drier. The resulting pounder is dried and calcined at 4490— o o £>00 C preferably at 500 C for considerable time to convert the precursor of tin to stannotus oxide. The transition aluvnina is thus impregnated Mith tin or tin com— pouurnd in such a manner to (maintain the addition of tin as Al'JfF ;sStraff molar ratio in the range of 0.2 to 20%, preferably 1 23 2 to 10X and more preferably between .2 to SX. The tin—stabilized gamma—alumina or transition alumina powder thuts prepared cairn be used as altutmina Mashcoat and other applications withere active alumina iwith high surface area is needed. For sotich applications, tlhie stabilized alumina powder is suspended iim aafueoiuis or morn—aqjtuteouis medium and generally applied on a substrate. The substrate could be metallic, ceramic or composite and haviiroji physical structure of honeycomb, palleted, S owder na/can be appropriately coated on the substrate or can be used as prepared with or without the physical structure of honeycomb, palleted, fibrous or tubular shape. Gamma airad otheir transition alumina having a high specific surface area has been used frequently as a carrier or coating material. o o However, at a temperature of above 800 C, particularly above 900 C, the loss of specific surface area is started due to the phase transition into alpha—alumina and increase of the crystal particle diameter and, consequently the particles of the noble metal or base /metal used as the catalytically active component are coagulated to deteriorate the catalytic activity. This can be avoided by suitably stabilizing the transition alumina. The high teflmpeiratiutire stabilized alumina support according to the present invention) /may comprise the part for supporting the active coMponent or catalyst and/or a substrate for carrying the support and/or a catalyst or active component itself. The high temperature stabilized aliuuniima according to the invention can also have the shape of a (honeycomb structure. The present invention is preferably applied to an automobile which is driven by a gasoline engine or a diesel engine. The invention will now be explained in greater detail with the help of the following nan—limiting examples and iIllustrated with the help of tlhte accompanying drawings. Fig.l — DTA plots of gamma—alumina pure and impregnated with various mole percentage of tin added as staminous suilfate. Pure gamma—alumina is designated as "g—alumina" and 1,2,3,4,5 and 10 mole percent tint «molar ratio, Al:JBU/SfrwBL = 98/2, 97/3, 96/4, 95/5, 90/10 respectively) as "1","2","3","4",*5" and "Iff' respectively. Fig.2 — BET surface area of neat treated gamma—alumina pure and impregnated with other additives are plotted. Heat treatment is o performed at 1:8.00 C for various fixed duration of time. The loss of surface area is represented by respective plots for each type of gamma—alumina formulation. Pure gamma—alumina and gamma— alutrmina impregnated twith 10 mole $» bariuunr added as barium nitrate, 10 mole % of lanthanum added as lanthanum nitrate, 10 mole X cerium added as cerium nitrate, 10 mole X zirconium added as zirconium) nitrate and 10 mole % of tin added as stannous sul — fate are designated as g—alumina* 10 BW, 5LW, 10 CM, 10 ZN and 10 TS respectively iiro this figure. Fig.3 — OTA plots of gamma—alumina pure and impregnated with various mole percentage of tin added as stannous chloride. Pure gamma—alumlma Is designated as *g—alumina'and "3. and 4 mole % tin (molar ratios, A.lJR,y&nflL - 9O/2 and 96/4 respectively* as'ZPC' and £ J £ '"4TC* respect I velly Im tnls figure. Fig.4 — BET surface area of tin—modlfled and lantfrnajntttmt—modified gamnta—alumina plotted against soaking time at 1100 C heat treatment. (E2La—ethairaol processed 2. (mole % La, W2La—Mater processed "2. mole % La, E5La—ethanol processed 5 mole percent La, E3tin—ethanol processed 3 mole % tin, W3tin-twater processed 3 mole % tin}. EXAMPLE 1 Gamma-alumina powder- of type AIKPO015 manufactured by Sumitomo Chemical Co., Japan is tafeen for stabilization. This transition 2 alumina wiitlh W.995 wrlkX ptuirity had a surface area of 140 • /g and therefore suitable for waslhcoatiraji application particularly for making catalytic converter tusedl in automobile pollution control. However, Mnis transition alumina alone is not suitable for long tenni high temperature application since it transforms into its (most stable phase alpha—alunoiima and its high surface area reduces at elevated! temperature. Therefore, this alumina requires stabilization for it Its lutse at elevated temperature. 10.00g of AKPeftlS gaawna-aluniima is added in 200ml of distilled * water and thoroughly mixed using a magnetic stirrer and ultrasonic dispersion,. 0.21Z7g of sfcannous sulfate (SnSfM) is added in 100fml of distilled Mater and thoroughly mixed using a magnetic stirrer. The stairmous sulfate suspension is slowly added to the gamma—alumim>a suspension and mixed together thoroughly using a magnetic: stirrer. Thiuts, the said) gamma—alumina is impregnated with 1 mole X of tin €molar ratio, fSL' 'W '/SnOC = 99/1). 23 2 In a similar fashion as described above, the said gamma—alumina is impregnated! twtiith 2,3,4,5 and 10 mole X tin ttmolar ratio, A! -fe:/9n»V - 9B/2,i 97/3, 96/4, 95/5, 90/10 respectively* using 23 2 required quantity of stannous sulfate as precursor. The impregnated! atcgiuieotus suspension is then evaporated in a rotary 1 0 vacuum dryer. Tlhe resulting powder is dried at 110 C for 15 hrs. o in an electric dryer -followed by heat treatment at 500 C for 2 hrs. iim air. The tin impregnated gamma—alumina powder is then characterised usiimg differential thermal airnalysis fDTAJ. The resulting DTA plots o>f gamma—alumtina Mith vairiouis mole X of tin impregnation is shown iim Fig.l. The phase transformation from transition alumina to its stable phase alpha—aliuvmina is resulted in the exothermic o peak beyomd 1200 C. A clear shift of this DTA peak can be observed iim Fig.:1 when tin is impregnated with pure gamma-aluianina. As it can be seen that the tint—impregnated transition alumina transform to its stable alpha—alumina unless it is heated o at least 7$$ C more than the temperature required for pure gamma— alumina to transform to alpha—alumina. This conversion to alpha— alumina is associated with sintering of the active transition aluimina potMdeir airnd ewentmially loss of surface area. Therefore, impregnation of tin caused the stabilisation of the transition alumina beyond its normal transformation temperature. The stabilizing effect on its surface area is more clear in Fig.2 where BET swrface area of transition alumina is plotted in comparison (with tiira— impregnated transition alumina after subjecting them a thermal treatment for various fixed duration of time. The effect of tin—impregnation is again clearly seen. Even after 50 hrs. of soaking at 1100 Cv the swrface area retained by tin- 2 impregnated aiumiima is nearly 50 m /g, whereas the pure gamma- 2 aluunina losses its stuirface area to less than 10 m / hrs. of soaking at the same temperature. Figj™.2 also shows the superiority of tin stabilization over conventional ceriuavn atmd zirconium staJbilizatian of gamma—alumina and si mi lair if not better performance over widely used lanthanum stabilization. However, the stabilization by barium is only found to retain more surface area than tin. A further (comparison between surf acre area retained by gamma— aluvmina with 5 mole $» lanthanum impregnation and with 3 mole % tin impregnation is presented in Table 1 CaJ and ICbJ for both as prepared and after 100 hrs. of accelerated aging at 1100 C. Table l BET surface airea (measurement rsults for lanthanum (La) and Tin (Table Removed) Table l*b) BET suirface area (measurement results for lanthanum (Table Removed) It can be observed from Tables 1 and l$b) that gamma—alumina impregnation (with 3%. Tim is (giving swore surface area and pore voltuune which shows superior thermal stabilization over 5X lanthanum. EXAIWPLE 2 10.00g of gamma—alumina potwder of type AKPB015 manufactured by Sumitomo Chemical Co., Japan its added in 200ml of distilled water and! thoroughly minced using a magnetic stirrer and ultrasonic dispersion. ^,37f5g of stannous chloride CSnCl ) is added in 100ml 2 of distilled water and thoroughly aniseed using a magnetic stirrer. The stannrauis chloride suspension is slowly added to the gamma— aluvmina suspensiatn) and mixed together thoroughly using a magnetic stirrer. Tthtius the said gamma—alumina is impregnated with 2 mole % of tin *molar ratio, Al O /SnO = 98/2). 23 2 In a similar fashion as described above, the said gamma—alumina is impregnated iwith 4 mole % tiin {molar ratio, Al O /SnO = 96/4) 23 2 usiirag required quaimtity of startnous chloride as precursor. The impregnated aqueous suspension is then evaporated in a rotary o vaciiuum dryer. The resulting powder is dried at .110 C for IS hrs o in an electric dryer followed by heat treatment at 500 C for 2 hrs. iira air. The tiin impregnated gamma—alumina powder is then characterised usiirag tdiflfereiratial thermal sum a lysis (DTA). The resulting DTA plots of gamma—altuumina with various mole X of tin impregnation is shown imt Fig.3- The pihiase transformation from transition alumina to its stable phase alpha—altwiBina is resulted in the exothermico peah: beyomd l.2!00> C. A clear shift of this DTA peak can be observed iint Fig.3 iwthen tin is impregnated with pure gamma— alumina;. (8s it cairn be seen that the tin—impregnated transition aluvmina transform to its stable alpha—alumina unless it is heated o at least 7(0f C more than the temperature required for pure gamma— aluuniina to trarrnsfoTrm to alpha—alumina. This conversion to alpha— aluumina is associated) with sintering of the active transition aluumina potwder airad) eventually loss of surface area. Therefore, impregnation of tin caused the stabilization of the transition aluumina beyond its iraoirmal transformation temperature. EXAMPLE 3 10.00g of gamma—alumina powder of type AKPG015 manufactured by Sumitomo Qhemitcal Co., Japan is added in 280ml of ethanol and thoroughly mixed using a magnetic stirrer and ultrasonic dispersion. [email protected] of starmnious sulphate ISnSO ) is added in 100ml of 4 ethanol and) thorouighly mixed using a magnetic stirrer. The start— nous siulphate stutspension is slowly added to the gamma—alumina suspension and mixed together thoroughly using a magnetic stirrer. Thus, the said gamma—alumina is impregnated with 3 mole % of tiim imal-xtr ratio, Al O /Snd = 97/31. 23 2 The impregnated mion—aqueous suspension is then evaporated in a o rotary vacuum dryer. The resulting powder is dried at 110 C for o 15 hrs. in an electric dryer followed by heat treatment at 500 C for "2. hrs. in air. The effect of tin (can thermal stability of alumina when processed through ethanol fntedium is fwrther studied by high temperature heat—treatment of tinHbsased! airad 1 an thanum—based transition alumina fonmulatioms. Tin—modified and lanthanum—modified gamma- aluminas aire simultaneously heated to 1100 C and soaked for fixed period of time. Tttnus,, heat—treated samples are tested for BET surface area airad flhe results are plotted in Fig.4. The improvement o.-ff tlhienmal resistance of tin—modified gamma—alumina by incorporating etlhiaimol processing {medium is seen in Fig.4, which performs as good as widely used lanthanum—Modified gamma—alumina. This lomtg period off high temperature treatment is almost equivalent ten accelerated aging test and provides confidence on durability of the tin—toased transition) alumina Mashcoat formulation for the entire lifespan of the automobile Mhere this formulation could h WE CLAIM! 1. A process for stabilization of transition aluminas preferably gamma altMina by treating maid Material with tin, tin OKid* powder or any of itm precursors and thereby providing the tin cation to the *urfac« of the transition alumina, which comprises a step of impregnating the aluMina surface with a tin compound such a« herein described in a suspending medium or solvent followed by calcination for the decomposition of the tin compound, the Al Q, SnO2 Molar ratio being Maintained in the range of 0.2 to 20K. 2. A procema mm claiMed in claiM 1 wherein the transition alumina i» stabilized by impregnating with tin or tin compound in such a manner to maintain the addition of tin as Al2. molar ratio preferably in the range of 1 to 10X and More preferably between 2 to 5X. 3. A process as claimed in claim 1 wherein the suspending medium or solvent is such as acetone, ethanol, Methanol, toluene, isopropyl alcohol, methylethylketone, butylacetate, dimethyl- formide or other non-aqueous medium or solvent. 4. A process as claiMed in claiM 1, wherein tin is used optionally with one or MOTE of any other stabilizing Materials such as cerium, zirconium, lanthanum, bariuM, etc. 5. The stabilised aluMina produced by the process as claiMed in claim 1, used in coating a metallic, ceramic or composite substrate having physical structure of honeycomb, palleted, fibrous or tubular shape. 6. The stabilived alueiina pottder produced by the process as claimed in claia) 1 u*ed as prepared in the shape of honeycoob, pallet, rod or tube.

Documents:

1532-del-1999-abstract.pdf

1532-del-1999-claims.pdf

1532-del-1999-correspondence-others.pdf

1532-del-1999-correspondence-po.pdf

1532-del-1999-description (complete).pdf

1532-del-1999-drawings.pdf

1532-del-1999-form-1.pdf

1532-del-1999-form-19.pdf

1532-del-1999-form-2.pdf

1532-del-1999-form-3.pdf

1532-del-1999-gpa.pdf