CA2131795C - Preparation of stabilized alumina having enhanced resistance to loss of surface area at high temperatures - Google Patents
Preparation of stabilized alumina having enhanced resistance to loss of surface area at high temperatures Download PDFInfo
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- CA2131795C CA2131795C CA002131795A CA2131795A CA2131795C CA 2131795 C CA2131795 C CA 2131795C CA 002131795 A CA002131795 A CA 002131795A CA 2131795 A CA2131795 A CA 2131795A CA 2131795 C CA2131795 C CA 2131795C
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- alumina
- boehmite alumina
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/021—After-treatment of oxides or hydroxides
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
- C01P2006/13—Surface area thermal stability thereof at high temperatures
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/14—Pore volume
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/16—Pore diameter
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/16—Pore diameter
- C01P2006/17—Pore diameter distribution
Abstract
A process for preparing stabilized alumina having increased surface area retention at high temperature in which a gel of a boehmite alumina which has been obtained by hydrothermally treating an aqueous mixture of a precursor beohmite alumina having a pH of from about 5 to about 9 for a period of time sufficient to convert the greater portion of the precursor boehmite alumina to a colloidal sol is subjected to working as, for example, by using a sufficient shearing force for a sufficient period of time to produce a worked boehmite alumina which has an increase in pore volume of at least about 30 percent and an increase of median pore radius of at least about 20 percent, a stabilizer being added to the boehmite alumina, the stabilizer being an oxide of a metal such as barium or a metal included in the lanthanide series of metals or a compound of such metals which converts to an oxide at elevated temperatures.
Description
PCI'I LJS93/02104 WO 93/1?968 FREPARATiON OF STABILIZED ALUNiiNA ~IAVINO EN~iANCEI~
RESISTANCE TO LOSS OF SURFACE AREA AT HI(~HI TEMPERATtI'RES
BACI~GRO~ OF TIIE INVENTION
1 Field of the Invention S The present invention relates to a process for producing alumina which can be converted to catalyst supports exhibiting enhanced resistance to loss of surface area when subjected to high teanperatures.
RESISTANCE TO LOSS OF SURFACE AREA AT HI(~HI TEMPERATtI'RES
BACI~GRO~ OF TIIE INVENTION
1 Field of the Invention S The present invention relates to a process for producing alumina which can be converted to catalyst supports exhibiting enhanced resistance to loss of surface area when subjected to high teanperatures.
2. I~~c~°it~ti~n of the Bhckg_round One ~f the key requirements of a catalyst support or substrate such as alumina (A10,) is high suxface area. Increased surface area allows for deposition of the catalytically active species, enhances reactivity between the catalydcally active species and the reactants and; in general, makes for a mare efficient catalyst support. In the case o~ catalyst supports'of alumina used in catalytic c~OVerters for automobiles, i.e.
auto~atalyst supports, high surface area is particularly desirable because of short residence times betweed reactants and catalytic species, the desire xo minimize the size ~f the catalytic con~rerter and hence the need for a high efficiency catalyst.
A particular problem with autocatalyst sup~rts involves the high temperatures to which the supports are subjected. Nigh temperatures deleteriously effect the structut'al integrity of the catalyst support , resulting in a loss ~f surface area. In effect; the elevated temperatures cause the catalyst to c~llapse on itself.
It is known that stabiloizers such as oxides of barium and the lan~anide series of elegnents can stabilize aut~catalysts an the sense that the loss of structural integrity of the - support is retarded. In' particulaf, oxides \of barium, lanthanum or other lanthanide elements have bin used in alumina based auto~talyst supports as heat stabilizers: .
CVO 93t1796~ PCT/iJS93/02104 SZJ1V~IAI~Y ~F ThIE INDENTION
It is therefore an object of the present invention to provide a process for producing stabilized alumina which can be used in catalyst supports and other structural substrates requiring high surface area.
Still another object of the present invention is to provide a catalyst support exhibiting enhanced resistance to structural degradation at high temperatures.
The above and other objects of the present invention will become apparent from the description given herein and the appended claims.
According to the process of the present invention, a stabilized alumina of enhanced resistance tci high temperature surface area loss is prepared by forming a gel of a boehmite alumina, the boehnnite alumina being obtained by hydrothermally ~ treating an aqueous mixture of a precursor boehmite alumina having a pl~i of from about 5 to about 9 for a period of time sufficient to convert the greater portion of the precursor boehmite alumana to a colloidal s~l. 'The gel is subjected to working, i.e.
by using ' ~ suf~cien2 shearing force for a sufficient period of time to produce a w~rkerl boehnnite alumin~ and increase the pore volume by at least 30 percent and the median p~re radius by at least 2U percent. A stabilizer is added to the boehrnite alurrsina, the stabilizer being an oxide of a metal such as buriurn or a metal included in the lanthazaide aeries of metals ~r a compound of such metals which converts to an 2~ oxide at elevated temperatures. Mixtures ~f such stabilizers can be employed if desired; the arnount of the stabilizer used being sufficient to decrease loss of porosity of a e~lcined ahamina pr~duced frown the worked alumin~.
In an optimal embodiment of the inven~a~n, the stabilizer can be added to a calcin~! product obtained by calcining the worked (sheared) boehanite alumina.
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.i DETAILED DESCRIP'I'I~N OF TI-IF I'Rh.FERRED EMBODIMENT
T'he aluminas which can be treated according to the process of the present invention are boehmite aluwinas which leave L~~oru hydrotherlnally treated under conditions to convent tile gru~att:r portion crf tHc 1»~olornito alumina to a colloidal see, the thus hydrothermall}' treated aluminas loaning tl~e starting material boehmite alumina for use in the process of the prcaent invention. 'l'he boehmite alumina which is hydrothermally treated, hr,reinafter referred to as precursor boehmite alumina, is preferably, although nc:~t n~~essarilv, cabtc~ioecll by thG° Hydrolysis of an aluminum alkoxide in the well known tGrshiorr. 'The aluminum alkoxide (trialkoxide) can be produced, in the well known manner, by reacting a low molecular weight alcohol, a linear or branched chain, with an all.rminuln-bearily material. Such alunainum-bearing materials include pure ali.utninua~a and rloixecl allu~y scrap.
Typical methods for preparing stlCl7 altrrllrnum alkoxides arc: shown, Fox example, in U.S. Patent No.
4,242,271. 'The aluminum alkoxide can be 11y<lrolyzed the well known manner, such as by the process tau~,lat in tJ.;~. 1'atwt No, 4,202.,b7(). Especially preferred are aluminas obtained from the hydrolysis of aluminum alkoxides derived from Ziegler Chemistry in the well known manner. \Whilc: the prei~rred feedstoclc used as the precursor alumina is an alumina slurry, particulurl~ a slurry produced by the hydrolysis of aluminum alkoxides, it will Oe rocc°~gni:red that aluminas from other sources can be formed into slurries and hydrotHermally treated to produce the precursor alumina.
The starting material bochlnite alumina used in the process of the present invention can be obtained tl~,corclin~ tc.a the process disclosed and claimed in U.S.
Patent No. 4,676,928. Basically, the process clisclosccl in U.S. Patent I\To.
4,676,928 involves taking a precursor boehmite altlmina, forming the precursor ?lamina into an aqueous slurry or mixture, tire pl-I bt~in~ in the range ol' f"rom about 5 to about 9, and there hating the aqueous slushy of the prc~:trrs<>r illunkiva at elevated temperatures, generally about 70°C or grearter, For a sufficient period oI" time to convert the greater portion of the precursor hoehrnlte alucnina to a c:.olloidal see.
In using the process cliselo''ecl in lJ.'~. 1'tvton~ 110. 4,Ei7Ci,92'8 to form the .,° ,.nQ '~ . ..m . . ... .. wy .l~r , ~,' ~ . . ...n.. . ... f. .
..,_....~ . .. ,.,~ , y ~~.. .
~i . ., f.., .
~Y~ 93/1796 PCTIL1~931~21t14 '1~ ~. 3 ~'~ ~ ~
starting material boehmite alumina used in the present process, a colloidal sol can be employed. Alternately, a colloidal sol which has been dried to form a dried powder can be formed into an aqueous dispersion and used. In either event, the alumina content will range from about 15 to about 55 percent-by-weight calculated as Ah~,, depending on whether or not a gelling agent is employed. In cases where a gelling agent is empl~yed, the gel will normally contain from about 15 to about 25 percent-by-weight AIZ~,. In the absence of a gelling agent, the gel will generally contain from about 35 to about 55 percent-by-weight A120,.
Generally the process is conducted by forming an aqueous slurry or dispersion; either as the sol as described above, or by dispersing a dried sol in an aqueous medium. Once the slurry of the starting material boehmite alumina has been formed, it must be gelled or thickened to increase the viscosity prior to being worked.
The term "gel" ~s used herein refers to a suspension, colloidal in nature, in which shearing stresses below a certain mite value fail to produce permanent deformation.
~;~Iling of the aluanina slurry can be carried out simply by concentrating the slurry by the removal of water to firm a viscous gel of increased alumina content.
Additic~n~ily, or ~Itematively; the gelling ~f the dispersion can be carved out by the addition of gelling,age~ts. Such gelling agents are generally water-soluble compounds which are well known by those skilled in the art to be compounds which will de-stabilize aqueous colloidal ystems. Ton-limiting examples of such gelling agents include minerr~ll acids such ~s nitric acid, hydrochloric acid, etc., organic acids such as formic acid, acetic acid; etc. ~ polyvalent metat salts, etc. For example, water-soluble salts of certain polyvalent metals such ~s the nitrates, chlorides, acetates, sulfates, etc:, of metals such as aluminum, iron, magnesium, manganese, etc.
can be used. i~'hen employed, such gelling agents will be added in an amount sufficient to increase the viscosity to the desired degree, i.e. until a gel is formed, amounts of fr~rrc~ about 0. I t~ about 50 percent-by-weight based on the weight of alumina in the gel being generally used.
It is generally necessary, when viseosifying the alumina dispersion, whether such be accomplished by concentrating the dispersion and/or the addition of gelling agents, to add sufficient acid to maintain the gelled alumina in a flowable condition.
Generally speaking; monobasic acids such as nitric acid, hydrochloric acid, formic WO 93/1796 ~ ~ ~ ~ ~ ~ PGT/US93/021~~
S
acid, acetic acid, and so forth can be employed. The amount of acid added should be kept to a minimum; consistent with achieving desired gelling, as increased acid decreases porosity.
Worlting or shearing of the gel to the desired extent can be accomplished in S a variety of equipment and under widely varying conditions. In general, any apparatus which is capable of imparting high shear to viscous systems can be employed. Ikon-limiting examples of apparatus which can be used to carry out the working or shearing step include plastic melt viscometers, mullers commonly used for mixing paste-like materials, Briers fot preparing high viscosity pastes and gels and the like. Parameters such ' as shear rate, shear time, temperature, etc. will vary depending upon the concentration of alumina in the gel, the type of gelling agent employed; the type of precursor boehmite employed and-the type of hydrothermal treatment applied to the precursor alumina to obtain the staring material boehmite used in the process of the present invention. In general; conditions of high shearing, 1S high concentration of alun~ina in the gel and minimu~in acid concentration are preferred. 'Femperatuee can vary. widely as from arnmbient to about 100C. In general, the gel will be subjected to a sufficient shearing force;
for a sufficient period of time to increase the pore volume by at least 30 ~ and the median ,pore radius by at least 20% over' that of the alumina in the unworked gel: Such increase in porosity parameters can be determined by techniques well kmown to these skilled in the art.
It can be shown by transmission electron microscopy (TEIIrL) that 'ordinary boehmite which. has not been treated according to the process o~
U:S. Patent No.
4,676,928; exists in floe form of extensive aggregates of individual crystallites of relatively small size, i.e. less than about 50~ in thickness (020 plane): Such aluminas exhibit extensive'aggregation of the crystallites, i.e. microgels' Aluminas which have been"preparing according to the process of tLS. Patent rlo. 4,6T6,928, as seen by 'i'El~, also exist -as aggregates but unlike ordinary boehrriite the microgels are made up ~f stacks of plate-like crystallites which are generally highly oriented: iWhen the latter type of alumina starting material is treated according o the process of the print inrrention, and again as can be observed by TEM microscopy;
the orientted, stacks of crystallites become much more randomly oriented or de~aggldmerated resulting in a more open structure of the aggregates; i.e: increased porosity. Thus, ... ....._.... . ._ ,.,......~ ,.. _,~.,",.~,, . -~-.. _....f. ~_F. ,..... ..
...,..... .. , :...r,. .......... ~.. .,~".~ ...f.:;..
WO 93/ 179b8 PCT/1JS93/021 U4 ~~ ;~"~ ~~J
to achieve the unexpected increase in porosity using the process of the present invention, it is necessary to employ a starting material alumina which has been prepared . in accordance with the process of U.S. Fatent No.
4, 676,928 or an equivalent wherein the alumina exists essentially as microgels comprising stacks of plate-like crystallites. Such staring material aluminas can be characterized as being comprised of microgels which are comprised of numerous, associated stacked crystallites on the order of from about 50 to about 150 nm in diameter, the individual crystallite size being on the order of from about 50 to about 150~e in thickness (020 plane).
'The process of the present invention includes the addition of a stabilizer to a boehanite alumina r~rhich has been worked, i.e: sheared; as described above. The w term "stabilizer" or "stabilization", as used herein- and with reference to the alumina obtained by tlve process described above, refers to a compound or process which acts to decrease or retard Ioss of surface area when the alumina, calcined to AI=03, is subjected to elevated temperatures; i.e: I000C or greater, generally 1200C or .
greater. The stabilir.er can be an oxide of barium; an oxide of a lanthanide metal such as lanthanum; cerium, etc:; a compound of barium which is converted to an oxide upon heating at an elevated temperature or a; compound of a lanthanide metal which is converted to an oxide at an elevated temperate~re.
Especially preferred stabilisers aa~e oxides or barium or lanthanum; or x compound of barium or lanthanum which is converted to an oxide upon heating at an elevated temperature.
In the more preferred method; a compound of barium or a lanthanide metal which can be converted to the oxide 'is used rather than the oxide thereof.
This permits the stabilizer to be incorpdrated in the form of an aqueous solution or dispersion ensuring more' unit;~rm distribution of the stabilizer thrbnghbut the alumina.
The stabilizer may be added at various points in the process.
For examgle, the stabiliser can,be added to the boehmite alumina prior to gelling, during the gelling or after the boehmite alurnina is sheared. Thus; the stabilizer can be added to the >aoehanite aluanina. prior to the boehmite alumina being worked or after the boehmite alumina i5 worked: For example; the worked boehmite alumina can be dried and the stabilizer added to the dried; worked beohmite alumina. In an alternative embodiment ~f the present invention; the worked boehmite alumina can be dried and calcined to ~Vf,~ 93/17968 ~ ~ ~ ~ "~ ~ C~ PCl'/US93/02104 produce a calcined product, i.e. Al=O,, and the stabilizer added to the calcined product. The stabilizer will be added in an amount sufficient to decrease loss of porosity of a calcined alumina which is subjected to elevated temperatures. In general, the amount of the stabilizer added will be such as to provide a stabilizer content of from about 0.5 to about 20 weight percent based on AlzO, whether in the boehmite alumina or in the calcined product.
It is believed that the unexpected stability of alumina prepared according to the process of the present invention results from the fact that the starting material boehmite is comprised of aggregations of individual pseudoboehmite crystallites, the crystallites being of a generally larger size, i.e. from about 50 to about 150 A in thickness (020 plan); than the conventional boehmite aluminas wherein the individual crystallites are generally about 50 r~ and smaller in thickness (020 plan).
Further, in the staring material baehmite used in the process of the present invention the individual crystallites are plate-like structures which are generally arranged in an ~rdered, stacked configuration as can be seen by transmission electron microscopy (;~~). den such an aluanina is subjected to working as by shearing, the individual drystallites become more randomly distributed; i.e. the stacks of crystallites are disoriented leaving voids or pores, i.e. greater porcssity and highdr surface area. This porosity provides for a reactive; accessible surface yielding higher catalytic activity.
'fhe incorporation of a stabilizer enhances the structural integrity of the alumina in the sense that when subjected td high temperature; the surface area remains, i.e. the alui~nirta does not collapse upon itself: Thus, to achieve the unexpected, stabilized surface area retention using the process ~f the present inventian, it is necessary to employ, as a starting material alumina; a boehmite alumina which has been prepared in accordance with the precess of U.S: Patent h3o. 4;6'7,325 or an equivalent wherein the alumina exists essentially as microgels comprising stacks of plate-like crystallites. Such starting material aluminas can be characterized as being comprised ' ~f mierogels vrhich are comprised of numerous, associated stacked crystallites on the order of from about 50 t~ about 150 nm in diameter; the individual crystallite size being, ~s not~i; ~n the order of from about 50 to about 150 in thickness (020 plan).
~e press of the present invention can be used t~ make catalyst supports which retain a high surface area, i.e. about 50 mZ/g or greater upon ealcination at 1~V(~ 93117968 P(.'C/US93/02104 1200°C for three hours.
To more fully illustrate the present invention, the following non-limiting examples are presented. The DISP~L~ aluminas used in the following examples are boehmite aluminas marketed by Vista Chemical Company and made in accordance with the teachings of tl.S. Patent No. 4,676,928. In all cases surface area was obtained by the mufti-point SET method.
Exarra Ire 1 A series of samples were prepared by adding a predetermined amount of a 62.8 percent-by-weight lanthanum nitrate hexahydrate solution to a predetermined amount of DISP~L~ 120 alumina sol or DISPA.L~ 180 alumina powder. The addition of th$ lhnthanuan solution resulted in gelation of the alumina sol.
'The aluminallanthanum mixture was then worked on a Haake Torque Itlaeometer. The material was then removed from the rheometer/mixer, dried over night at 70°C, and then fired at 1200°C for three hours. The firing temperature and time were selected to mimic the conditions- that cause loss of surface area azid porosity collapse, i.e.
conditions a catalyst would experience during use at elevated temperatures such as in a catalytic c~nverter. High surface areas, i.e: about 50 m2lg or greater, following such treatment at 1200°G are indicative of a highly stable catalyst which would retain high' surface area and provide improved catalytic activity for longer lifetimes under high temperature extremes. The results are shown in Table 1 below. Sample 1 is a contrtsl sample ~rhich was not work~l best contained stabilizer.
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~.'~;.'.:., .~_..,....~y.~ ..:,~.... .... -... v.~.~... .....,.....".-., .
..,....'~ ..w~~ .' .:.
'W~ 9311?968 ~ ~~ ~ PCT/US93/02~04 v Q
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As can be seen from the data in Table l, samples prepared in accordance with the process of the present invention wherein the alumina is worked, i.e.
sheared, and contains a stabilizer; exhibit high surface area retention, i.e. generally greater than about 50 m~/g even after being subjected to a temperature of 1200°C for three hours.
S This is to be contrasted with Sample i in which an unworked alumina containing stabilizer showed a surface area markedly less than 50 mZlg after being heated to 1200 ° C for three hours:
Examples 2-4 which follow demonstrate that retention of high surface area of calcined products is not achieved with conventional boehmite aluminas. In the 10 examples, the CATAPAL~ aluminas used are conventional aluminas marketed by Vista Chemical Company which have not been prepared in accordance with the process of U:S: Patent No. 4,676;928.
~~ple Z
IS 100 g of CATAPAL A~ alumina and 452_ g deionized water were placed in a Balcex-Perkins Muller and sheared for 20 pninutes: The resulting material was dried at 6fi°C and calcined three h~urs as 1200°C. The surface area on the ealcined product was determined' to be 5.8 m~lg.
ample 3 g of CATAPAL A~ alumina; 32 g deionized water and 2.42 g lanthanum nitrate solution (6I .1 wt: % lanthanum nitrate) were mixed f4r 10 minutes and dried at 66°C. 'The resulting powder was calcined three hours at 120Q°C. The resulting caleined product was found to have a surface area of 26:1 m2/g.
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~~3~ 795 WO 93/ l 7968 PCT/US93/02t Q4 Example 4 700 g CATAPAL A~ alumina, 452 g deionized water and 69.79 lanthanum nitrate solution (61.1 wt. % Lanthanum nitrate) were placed in a Baker-Perkins MuIIer and sheared for 20 minutes. The resulting material was dried at 66°C
and calcined three hours at 1200°C. The calcined product was found to have a surface area of 42.5 mZ/g.
As can be seen from a comphrrison of the surface area of the calcined products ~btained in Examples 2-4, although both working and stabilizing result in a calcined product which retains surface area as contrasted with a CATAPAL Am alurnina which has not been worked and/or stabilized, the surface area remains below about 50 mz/g.
~ In this regard, a CATAPAL A~ alumina which has not been worked (sheared) or stabilized has a surface area of 4.7 mZ/g after calcining for three hours at 1200°C.
IS The following examples (5-8) demonstrate that when an alumina such as that prepared according to U:S. Patent No. 4;6'76;928 is employed; the combination of working and stabilizing 'results in an end product which retains a surface area of greater than about 50 m2/g even when calcined at 1200°C for three hours.
Example 5 A sample of DISPAL~ I8N4-80 alumina p~wcter was calcined three hours at 12Q0°C and found to have a surface area of 4.7 m=Ig.
700 g I?ISPAL~ I8N4-80 alumina and 452 ~ deionized watex were placed in a Baker-Perkins Muller and sheared for 2d minutes. The resulting material was dried at 66°C and calcined three hours at 1200°C. The calcined material was found to have a surface area of 9.1 m=/g:
~0 ~Z
I00 g DISPAL~' 18N4-80 alumina, 100 g deioniaed water and 2.69 g Ianthanum nitrate solutit~n (61.1 wt: % lanthanum nitrate) were mixed for 10 minutes i~VO 93/17968 PCTI~l1S93/~2104 and dried at 66°C. The resulting powder was calcined three hours as 1200°C. The calcined material was found to hare a surface area of 35.4 m~/g.
Exapn~fe 8 S ?00 g DISPAL~ 18114-80 alumina452 g deionized water and ?5.24 lanthanum nitrate solution (61.1 wt. % lanthanum nitrate) were placed in a Faker-Perkin MuIIer and shred for 20 minutes. The resulting material was dried at 66°C
and calcined three hours at 1200°C. The resulting calcined material was found to have a surface area of 52:9 m2lg.
,~s ~ be seen from a comparison of Examples 5-8, the combination of working and stabilizing (Example 8) DISPILI,,~ alumina, i.e. aluminas prepared in accordance with the teaching of U.S. Patent Ido. 4,6?6,928, results in a dramatic increase in retained surface area of the final, t<xalcined product, i.e. a surface area of 15 greater khan 50 m~/g is obtained even after the material has bin subjected to a ~mpera~re ~f 1200 ° C for three hours:
~ I
IOO g of DI~PAI:~ 18N4-20 alumina and 4.54 g barium acetate powder were 20 mixed for 10 minutes and dr~ect at 66°C. ~'he resulting powder was calcined three h~urs at 1200°C: The c~lcined material was found to have a surface area of 63 m2/g.
~~~~~0 ?00 ~ of DISPEI.h,~' l8IvT4-80 alumina, 602 g deionized water, and 103.64 g 25 barium acetate pov~rder v~ere placedk in a ~aker~Perkins lVluller arid sheaared for 20 minutes. The rcsultir~g gel was dried at 66°C and calcined three hours at 1200°C.
The calcined material was f~und t~ have a surface area of ?2.1 mZ/g.
.Ass can be seen from E~mples 9 end 1~the combination ~f stabilization with 30 a barium containing mat~ri~I and 'working pmvades a marked iracrea~ in retained surface area (compare the surface -area of the calcined material from Examples 9 and with the surface area of the calcined materials in Examples 5-?). Although, as can r::
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.a.r,1 . :",.
e't ,. '. w .~. ,.a.
.Y S.. :~. ..t. .n.
,. A 'l i . ,. . ...
.-r.4.. . ,.. ,.. . . -._ n.:l.r,m's.,l.n..;;"., .. . . ........r . , ,.s.;..,.. . ,.... . ... .. ..
,... .. ...r, "... ,., . .. .... . .. ..
PCI'/US93/021 i~~
be seen from Example 9, the presence of barium stabilization alone gives a surface area of greater than 50 Mm'/g, barium presents certain toxicity problems not presented by the use of lanthanum. However, it can be seen that the use of both barium stabilization and working gives sharply increased retained surface area (note Example 10).
Examule 11 100 g CATAPAL A~ alumina, 500 g deionized water, and 12.59 g barium acetate powder was mixed for 15 minutes and dried at 66°C. The resulting powder was calGined three hours as 1200°C: The calcined material had a surface area of 43:4 m=/g.
Exa~n~nle 12_ 7pp g C,~'TAPAL~ A alumina, 452 g deionized water, and 88.13 g barium acetate powder were placed' in a Baker-Perkins Muller and sheared for 20 minutes.
,hhe resulting gel was dried ar 66°C and calcin~d three hours at 1200°C. The calcined material was found to have a surface area of 45.8 m~/g.
As can be seen from the data in Examples 11 and 12, while the addition of stabilizer and working on a cmnventional boehmite alumina, i.e. an alurnina not made in accordance with the teaching of U.S. Patent No. 4;676;928, results in increased, retained surface area, the retained surface area is substantially less than ~0 m~lg.
600 g ~I~PAL~ 18N4-25 alumina sot and 24.90 g aluminum nitrate solution (50 wt. % aluminum nitrate; 50 wt. l deion~zed water) were minced to form an alumina gel. The gel was sheared on a Haa% Torque Rheameter for 10 minutes at 60°C, 110 rpm. The AIZU, content of the sheared gel was 26.8 perront.
53.0 g of ih~ sheared gel, 2.6 g barium acotate powder, and $0:0 g deionized water were mixed for 10 miinutes and dried at ~°C. The resulting powder was calcined three hours at 1200°C. The calcined material was found to:have a surface area of 67.8 hi /g:
.~x~~tr~?,i;d k x...~' ;l 1 at~;.:~ ~ Y i.f.l. 5i ~ ". ~ ._ ,')~ a .. ., .. .
.~ ~' . ,. . .. ,'., w,~4 ..
W~ 93117968 ~CT/US93/~2104 ~~~~.r~ t.~'~
Exam~nle 14 55.7 g of the sheared gel of Example 13 were dried at 66°C. The resulting dried gel (18 g), 2.77 g barium acetate powder and 80.0 g deionized water were mixed for 10 minutes and dried at 66°C. The resulting powder was calcined three hours at 1200°C. The calcined material.viias found to have a surface area of 68.7 malg: -lExhrnole 15 52.24 g of the sheared gel of Example l3 were dried at 66°C. The dried gel was calcined two hours at 250°C followed by 24 hours at 600°C.
The resulting material ~rhs mixed for 10 minutes with 2.59 g barium acetate powder and 20.0 g deionized water. The slurry vvas dried at 66°C and the resulting powder calcined thr~ hours at 120Q°C. The calcined material was found to have a surface area of 70.6 m2/g.
Exam~le ~b 53.0 g of the sheared gel of Example 13, 1.84 g lanthanum nitrate solution (61.1 wt: % lanthanum nitrate), ~d 80.0 g dei~nized water were mixed for 10 minutes and dried at 66°C: The resulting powder has calcined three hours at 1200°C. The calcined material was found to have a surface area 6f 50.2 m2/g.
Dle l7 55.75 g of the sheared gel of Example 13 were dried at 66°C. The resulting dried gel ( 18 g), 1.94 g lanthanum nitrate soluti6n, and 80.0 g deionized water were ~ mixes fir 10 minutes and dried at 66°C. The resulting powder was calcined three hours at 1200°C. 'The cca~llcined material was found to nave a surface area of 47.7 m2/g, 52.24 g of the shred gel of Example 13 were dried at °C. The resulting d~~ gel w~: ~eia~ ,~,~ hours at 25Q°C, followed by 24 hours at 600°C. The resulting material was rnix~d for 10 minutes with 1:82 g lanthanum nitrate solution W~ 93/17968 ~ ~ ~ ~ '~ ~ ~ PCT/US93/a2104 (61.1 wt. % lanthanum nitrate) and 20.0 g deionized water. The slurry was dried at 66°C and the resulting powder calcined three hours at 1200°C.
The calcined material was found to have a surface area of 52.2 m'Ig.
5 As can be seen from a comparison of Examples 13-18, the combination of working (shearing) and the use of a stabilizer results in an alumina which, after calcining at 1200°C for three hours, in general, retains a surface area of greater than about SO m2lg. As can be seen from these examples, best results are obtained in terms ~f retained surface area when the worked or sheared gel is first dried and 10 calcined and the stabilizer then added to the calcined material. Compare, for exaanple, the retained surface area obtained by the procedure of Examples IS
and 18.
In general, however, the data in Examples I3-18, as well as the other examples, demanstrate that the stabilizer can be added after the gel has been worked, after the gel has been worked and dried, after the gel has been worked, dried and calcined, 15 and the ieetained surface area still remains above about 50 ma/g.
~~ foregoing c~iscl~sure and description of the invention is illustrative and explanatory thereof, and various changes in the method steps may be made within the scope of the appended claims without departing from the spirit of the invention.
auto~atalyst supports, high surface area is particularly desirable because of short residence times betweed reactants and catalytic species, the desire xo minimize the size ~f the catalytic con~rerter and hence the need for a high efficiency catalyst.
A particular problem with autocatalyst sup~rts involves the high temperatures to which the supports are subjected. Nigh temperatures deleteriously effect the structut'al integrity of the catalyst support , resulting in a loss ~f surface area. In effect; the elevated temperatures cause the catalyst to c~llapse on itself.
It is known that stabiloizers such as oxides of barium and the lan~anide series of elegnents can stabilize aut~catalysts an the sense that the loss of structural integrity of the - support is retarded. In' particulaf, oxides \of barium, lanthanum or other lanthanide elements have bin used in alumina based auto~talyst supports as heat stabilizers: .
CVO 93t1796~ PCT/iJS93/02104 SZJ1V~IAI~Y ~F ThIE INDENTION
It is therefore an object of the present invention to provide a process for producing stabilized alumina which can be used in catalyst supports and other structural substrates requiring high surface area.
Still another object of the present invention is to provide a catalyst support exhibiting enhanced resistance to structural degradation at high temperatures.
The above and other objects of the present invention will become apparent from the description given herein and the appended claims.
According to the process of the present invention, a stabilized alumina of enhanced resistance tci high temperature surface area loss is prepared by forming a gel of a boehmite alumina, the boehnnite alumina being obtained by hydrothermally ~ treating an aqueous mixture of a precursor boehmite alumina having a pl~i of from about 5 to about 9 for a period of time sufficient to convert the greater portion of the precursor boehmite alumana to a colloidal s~l. 'The gel is subjected to working, i.e.
by using ' ~ suf~cien2 shearing force for a sufficient period of time to produce a w~rkerl boehnnite alumin~ and increase the pore volume by at least 30 percent and the median p~re radius by at least 2U percent. A stabilizer is added to the boehrnite alurrsina, the stabilizer being an oxide of a metal such as buriurn or a metal included in the lanthazaide aeries of metals ~r a compound of such metals which converts to an 2~ oxide at elevated temperatures. Mixtures ~f such stabilizers can be employed if desired; the arnount of the stabilizer used being sufficient to decrease loss of porosity of a e~lcined ahamina pr~duced frown the worked alumin~.
In an optimal embodiment of the inven~a~n, the stabilizer can be added to a calcin~! product obtained by calcining the worked (sheared) boehanite alumina.
_ .._ . .... .. _.._ .... . ~. . : _, ..... . .,. ... :. ~F ... : . . ..~....
. ,.. , .
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.i DETAILED DESCRIP'I'I~N OF TI-IF I'Rh.FERRED EMBODIMENT
T'he aluminas which can be treated according to the process of the present invention are boehmite aluwinas which leave L~~oru hydrotherlnally treated under conditions to convent tile gru~att:r portion crf tHc 1»~olornito alumina to a colloidal see, the thus hydrothermall}' treated aluminas loaning tl~e starting material boehmite alumina for use in the process of the prcaent invention. 'l'he boehmite alumina which is hydrothermally treated, hr,reinafter referred to as precursor boehmite alumina, is preferably, although nc:~t n~~essarilv, cabtc~ioecll by thG° Hydrolysis of an aluminum alkoxide in the well known tGrshiorr. 'The aluminum alkoxide (trialkoxide) can be produced, in the well known manner, by reacting a low molecular weight alcohol, a linear or branched chain, with an all.rminuln-bearily material. Such alunainum-bearing materials include pure ali.utninua~a and rloixecl allu~y scrap.
Typical methods for preparing stlCl7 altrrllrnum alkoxides arc: shown, Fox example, in U.S. Patent No.
4,242,271. 'The aluminum alkoxide can be 11y<lrolyzed the well known manner, such as by the process tau~,lat in tJ.;~. 1'atwt No, 4,202.,b7(). Especially preferred are aluminas obtained from the hydrolysis of aluminum alkoxides derived from Ziegler Chemistry in the well known manner. \Whilc: the prei~rred feedstoclc used as the precursor alumina is an alumina slurry, particulurl~ a slurry produced by the hydrolysis of aluminum alkoxides, it will Oe rocc°~gni:red that aluminas from other sources can be formed into slurries and hydrotHermally treated to produce the precursor alumina.
The starting material bochlnite alumina used in the process of the present invention can be obtained tl~,corclin~ tc.a the process disclosed and claimed in U.S.
Patent No. 4,676,928. Basically, the process clisclosccl in U.S. Patent I\To.
4,676,928 involves taking a precursor boehmite altlmina, forming the precursor ?lamina into an aqueous slurry or mixture, tire pl-I bt~in~ in the range ol' f"rom about 5 to about 9, and there hating the aqueous slushy of the prc~:trrs<>r illunkiva at elevated temperatures, generally about 70°C or grearter, For a sufficient period oI" time to convert the greater portion of the precursor hoehrnlte alucnina to a c:.olloidal see.
In using the process cliselo''ecl in lJ.'~. 1'tvton~ 110. 4,Ei7Ci,92'8 to form the .,° ,.nQ '~ . ..m . . ... .. wy .l~r , ~,' ~ . . ...n.. . ... f. .
..,_....~ . .. ,.,~ , y ~~.. .
~i . ., f.., .
~Y~ 93/1796 PCTIL1~931~21t14 '1~ ~. 3 ~'~ ~ ~
starting material boehmite alumina used in the present process, a colloidal sol can be employed. Alternately, a colloidal sol which has been dried to form a dried powder can be formed into an aqueous dispersion and used. In either event, the alumina content will range from about 15 to about 55 percent-by-weight calculated as Ah~,, depending on whether or not a gelling agent is employed. In cases where a gelling agent is empl~yed, the gel will normally contain from about 15 to about 25 percent-by-weight AIZ~,. In the absence of a gelling agent, the gel will generally contain from about 35 to about 55 percent-by-weight A120,.
Generally the process is conducted by forming an aqueous slurry or dispersion; either as the sol as described above, or by dispersing a dried sol in an aqueous medium. Once the slurry of the starting material boehmite alumina has been formed, it must be gelled or thickened to increase the viscosity prior to being worked.
The term "gel" ~s used herein refers to a suspension, colloidal in nature, in which shearing stresses below a certain mite value fail to produce permanent deformation.
~;~Iling of the aluanina slurry can be carried out simply by concentrating the slurry by the removal of water to firm a viscous gel of increased alumina content.
Additic~n~ily, or ~Itematively; the gelling ~f the dispersion can be carved out by the addition of gelling,age~ts. Such gelling agents are generally water-soluble compounds which are well known by those skilled in the art to be compounds which will de-stabilize aqueous colloidal ystems. Ton-limiting examples of such gelling agents include minerr~ll acids such ~s nitric acid, hydrochloric acid, etc., organic acids such as formic acid, acetic acid; etc. ~ polyvalent metat salts, etc. For example, water-soluble salts of certain polyvalent metals such ~s the nitrates, chlorides, acetates, sulfates, etc:, of metals such as aluminum, iron, magnesium, manganese, etc.
can be used. i~'hen employed, such gelling agents will be added in an amount sufficient to increase the viscosity to the desired degree, i.e. until a gel is formed, amounts of fr~rrc~ about 0. I t~ about 50 percent-by-weight based on the weight of alumina in the gel being generally used.
It is generally necessary, when viseosifying the alumina dispersion, whether such be accomplished by concentrating the dispersion and/or the addition of gelling agents, to add sufficient acid to maintain the gelled alumina in a flowable condition.
Generally speaking; monobasic acids such as nitric acid, hydrochloric acid, formic WO 93/1796 ~ ~ ~ ~ ~ ~ PGT/US93/021~~
S
acid, acetic acid, and so forth can be employed. The amount of acid added should be kept to a minimum; consistent with achieving desired gelling, as increased acid decreases porosity.
Worlting or shearing of the gel to the desired extent can be accomplished in S a variety of equipment and under widely varying conditions. In general, any apparatus which is capable of imparting high shear to viscous systems can be employed. Ikon-limiting examples of apparatus which can be used to carry out the working or shearing step include plastic melt viscometers, mullers commonly used for mixing paste-like materials, Briers fot preparing high viscosity pastes and gels and the like. Parameters such ' as shear rate, shear time, temperature, etc. will vary depending upon the concentration of alumina in the gel, the type of gelling agent employed; the type of precursor boehmite employed and-the type of hydrothermal treatment applied to the precursor alumina to obtain the staring material boehmite used in the process of the present invention. In general; conditions of high shearing, 1S high concentration of alun~ina in the gel and minimu~in acid concentration are preferred. 'Femperatuee can vary. widely as from arnmbient to about 100C. In general, the gel will be subjected to a sufficient shearing force;
for a sufficient period of time to increase the pore volume by at least 30 ~ and the median ,pore radius by at least 20% over' that of the alumina in the unworked gel: Such increase in porosity parameters can be determined by techniques well kmown to these skilled in the art.
It can be shown by transmission electron microscopy (TEIIrL) that 'ordinary boehmite which. has not been treated according to the process o~
U:S. Patent No.
4,676,928; exists in floe form of extensive aggregates of individual crystallites of relatively small size, i.e. less than about 50~ in thickness (020 plane): Such aluminas exhibit extensive'aggregation of the crystallites, i.e. microgels' Aluminas which have been"preparing according to the process of tLS. Patent rlo. 4,6T6,928, as seen by 'i'El~, also exist -as aggregates but unlike ordinary boehrriite the microgels are made up ~f stacks of plate-like crystallites which are generally highly oriented: iWhen the latter type of alumina starting material is treated according o the process of the print inrrention, and again as can be observed by TEM microscopy;
the orientted, stacks of crystallites become much more randomly oriented or de~aggldmerated resulting in a more open structure of the aggregates; i.e: increased porosity. Thus, ... ....._.... . ._ ,.,......~ ,.. _,~.,",.~,, . -~-.. _....f. ~_F. ,..... ..
...,..... .. , :...r,. .......... ~.. .,~".~ ...f.:;..
WO 93/ 179b8 PCT/1JS93/021 U4 ~~ ;~"~ ~~J
to achieve the unexpected increase in porosity using the process of the present invention, it is necessary to employ a starting material alumina which has been prepared . in accordance with the process of U.S. Fatent No.
4, 676,928 or an equivalent wherein the alumina exists essentially as microgels comprising stacks of plate-like crystallites. Such staring material aluminas can be characterized as being comprised of microgels which are comprised of numerous, associated stacked crystallites on the order of from about 50 to about 150 nm in diameter, the individual crystallite size being on the order of from about 50 to about 150~e in thickness (020 plane).
'The process of the present invention includes the addition of a stabilizer to a boehanite alumina r~rhich has been worked, i.e: sheared; as described above. The w term "stabilizer" or "stabilization", as used herein- and with reference to the alumina obtained by tlve process described above, refers to a compound or process which acts to decrease or retard Ioss of surface area when the alumina, calcined to AI=03, is subjected to elevated temperatures; i.e: I000C or greater, generally 1200C or .
greater. The stabilir.er can be an oxide of barium; an oxide of a lanthanide metal such as lanthanum; cerium, etc:; a compound of barium which is converted to an oxide upon heating at an elevated temperature or a; compound of a lanthanide metal which is converted to an oxide at an elevated temperate~re.
Especially preferred stabilisers aa~e oxides or barium or lanthanum; or x compound of barium or lanthanum which is converted to an oxide upon heating at an elevated temperature.
In the more preferred method; a compound of barium or a lanthanide metal which can be converted to the oxide 'is used rather than the oxide thereof.
This permits the stabilizer to be incorpdrated in the form of an aqueous solution or dispersion ensuring more' unit;~rm distribution of the stabilizer thrbnghbut the alumina.
The stabilizer may be added at various points in the process.
For examgle, the stabiliser can,be added to the boehmite alumina prior to gelling, during the gelling or after the boehmite alurnina is sheared. Thus; the stabilizer can be added to the >aoehanite aluanina. prior to the boehmite alumina being worked or after the boehmite alumina i5 worked: For example; the worked boehmite alumina can be dried and the stabilizer added to the dried; worked beohmite alumina. In an alternative embodiment ~f the present invention; the worked boehmite alumina can be dried and calcined to ~Vf,~ 93/17968 ~ ~ ~ ~ "~ ~ C~ PCl'/US93/02104 produce a calcined product, i.e. Al=O,, and the stabilizer added to the calcined product. The stabilizer will be added in an amount sufficient to decrease loss of porosity of a calcined alumina which is subjected to elevated temperatures. In general, the amount of the stabilizer added will be such as to provide a stabilizer content of from about 0.5 to about 20 weight percent based on AlzO, whether in the boehmite alumina or in the calcined product.
It is believed that the unexpected stability of alumina prepared according to the process of the present invention results from the fact that the starting material boehmite is comprised of aggregations of individual pseudoboehmite crystallites, the crystallites being of a generally larger size, i.e. from about 50 to about 150 A in thickness (020 plan); than the conventional boehmite aluminas wherein the individual crystallites are generally about 50 r~ and smaller in thickness (020 plan).
Further, in the staring material baehmite used in the process of the present invention the individual crystallites are plate-like structures which are generally arranged in an ~rdered, stacked configuration as can be seen by transmission electron microscopy (;~~). den such an aluanina is subjected to working as by shearing, the individual drystallites become more randomly distributed; i.e. the stacks of crystallites are disoriented leaving voids or pores, i.e. greater porcssity and highdr surface area. This porosity provides for a reactive; accessible surface yielding higher catalytic activity.
'fhe incorporation of a stabilizer enhances the structural integrity of the alumina in the sense that when subjected td high temperature; the surface area remains, i.e. the alui~nirta does not collapse upon itself: Thus, to achieve the unexpected, stabilized surface area retention using the process ~f the present inventian, it is necessary to employ, as a starting material alumina; a boehmite alumina which has been prepared in accordance with the precess of U.S: Patent h3o. 4;6'7,325 or an equivalent wherein the alumina exists essentially as microgels comprising stacks of plate-like crystallites. Such starting material aluminas can be characterized as being comprised ' ~f mierogels vrhich are comprised of numerous, associated stacked crystallites on the order of from about 50 t~ about 150 nm in diameter; the individual crystallite size being, ~s not~i; ~n the order of from about 50 to about 150 in thickness (020 plan).
~e press of the present invention can be used t~ make catalyst supports which retain a high surface area, i.e. about 50 mZ/g or greater upon ealcination at 1~V(~ 93117968 P(.'C/US93/02104 1200°C for three hours.
To more fully illustrate the present invention, the following non-limiting examples are presented. The DISP~L~ aluminas used in the following examples are boehmite aluminas marketed by Vista Chemical Company and made in accordance with the teachings of tl.S. Patent No. 4,676,928. In all cases surface area was obtained by the mufti-point SET method.
Exarra Ire 1 A series of samples were prepared by adding a predetermined amount of a 62.8 percent-by-weight lanthanum nitrate hexahydrate solution to a predetermined amount of DISP~L~ 120 alumina sol or DISPA.L~ 180 alumina powder. The addition of th$ lhnthanuan solution resulted in gelation of the alumina sol.
'The aluminallanthanum mixture was then worked on a Haake Torque Itlaeometer. The material was then removed from the rheometer/mixer, dried over night at 70°C, and then fired at 1200°C for three hours. The firing temperature and time were selected to mimic the conditions- that cause loss of surface area azid porosity collapse, i.e.
conditions a catalyst would experience during use at elevated temperatures such as in a catalytic c~nverter. High surface areas, i.e: about 50 m2lg or greater, following such treatment at 1200°G are indicative of a highly stable catalyst which would retain high' surface area and provide improved catalytic activity for longer lifetimes under high temperature extremes. The results are shown in Table 1 below. Sample 1 is a contrtsl sample ~rhich was not work~l best contained stabilizer.
:1 ~.;;y>:, . '. ,..; . ,... r ~ ... . . , ~ri'.'...,~,.,. ,.'W:':. ..' ...... ,', , ...'.'.'... ":.. :...n. ;F.;. :
~.'~;.'.:., .~_..,....~y.~ ..:,~.... .... -... v.~.~... .....,.....".-., .
..,....'~ ..w~~ .' .:.
'W~ 9311?968 ~ ~~ ~ PCT/US93/02~04 v Q
v co co w o r v~ m a N titu1 ~i'tf1 t1!lf1 ~~.1 ea v-J
N
ye O O O O O O
oat 1 O N N rt O O
ri N N rt rt rt co o a o 0 0 0 ~ o--t~ ,-ara co m ~. ' O- 0. ~.
N N N
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~ ~ ~ ~ ~ .-~to N N, N N N I~ N
~ v ' v ' o o a O ' a s ~ t~ (n ~ (~ ~
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a v~o N N N N N
r1 N fag <J'In W tv W~ 93/17968 PCT/US93/02104 _ ~ ~. 3 ~.'~ '~
As can be seen from the data in Table l, samples prepared in accordance with the process of the present invention wherein the alumina is worked, i.e.
sheared, and contains a stabilizer; exhibit high surface area retention, i.e. generally greater than about 50 m~/g even after being subjected to a temperature of 1200°C for three hours.
S This is to be contrasted with Sample i in which an unworked alumina containing stabilizer showed a surface area markedly less than 50 mZlg after being heated to 1200 ° C for three hours:
Examples 2-4 which follow demonstrate that retention of high surface area of calcined products is not achieved with conventional boehmite aluminas. In the 10 examples, the CATAPAL~ aluminas used are conventional aluminas marketed by Vista Chemical Company which have not been prepared in accordance with the process of U:S: Patent No. 4,676;928.
~~ple Z
IS 100 g of CATAPAL A~ alumina and 452_ g deionized water were placed in a Balcex-Perkins Muller and sheared for 20 pninutes: The resulting material was dried at 6fi°C and calcined three h~urs as 1200°C. The surface area on the ealcined product was determined' to be 5.8 m~lg.
ample 3 g of CATAPAL A~ alumina; 32 g deionized water and 2.42 g lanthanum nitrate solution (6I .1 wt: % lanthanum nitrate) were mixed f4r 10 minutes and dried at 66°C. 'The resulting powder was calcined three hours at 120Q°C. The resulting caleined product was found to have a surface area of 26:1 m2/g.
.-..r ..;..r 7~ ...., ..,r... . .
S I .
. .:1.,, t >< ~~.:., i.r.:i~.:
F' aF ... . . . , . . r . .
u.. I. . x . . . . . . . ... . .. , . .
°STA:..,..::f. .h....'~.,.,. ....,..,........... .._,.. .....4 ~.,..u.
. ....a... n... .. .. . ,. .....~. ..... ~ r r. ~ ....... ...t, . . , o. , . .
..
~~3~ 795 WO 93/ l 7968 PCT/US93/02t Q4 Example 4 700 g CATAPAL A~ alumina, 452 g deionized water and 69.79 lanthanum nitrate solution (61.1 wt. % Lanthanum nitrate) were placed in a Baker-Perkins MuIIer and sheared for 20 minutes. The resulting material was dried at 66°C
and calcined three hours at 1200°C. The calcined product was found to have a surface area of 42.5 mZ/g.
As can be seen from a comphrrison of the surface area of the calcined products ~btained in Examples 2-4, although both working and stabilizing result in a calcined product which retains surface area as contrasted with a CATAPAL Am alurnina which has not been worked and/or stabilized, the surface area remains below about 50 mz/g.
~ In this regard, a CATAPAL A~ alumina which has not been worked (sheared) or stabilized has a surface area of 4.7 mZ/g after calcining for three hours at 1200°C.
IS The following examples (5-8) demonstrate that when an alumina such as that prepared according to U:S. Patent No. 4;6'76;928 is employed; the combination of working and stabilizing 'results in an end product which retains a surface area of greater than about 50 m2/g even when calcined at 1200°C for three hours.
Example 5 A sample of DISPAL~ I8N4-80 alumina p~wcter was calcined three hours at 12Q0°C and found to have a surface area of 4.7 m=Ig.
700 g I?ISPAL~ I8N4-80 alumina and 452 ~ deionized watex were placed in a Baker-Perkins Muller and sheared for 2d minutes. The resulting material was dried at 66°C and calcined three hours at 1200°C. The calcined material was found to have a surface area of 9.1 m=/g:
~0 ~Z
I00 g DISPAL~' 18N4-80 alumina, 100 g deioniaed water and 2.69 g Ianthanum nitrate solutit~n (61.1 wt: % lanthanum nitrate) were mixed for 10 minutes i~VO 93/17968 PCTI~l1S93/~2104 and dried at 66°C. The resulting powder was calcined three hours as 1200°C. The calcined material was found to hare a surface area of 35.4 m~/g.
Exapn~fe 8 S ?00 g DISPAL~ 18114-80 alumina452 g deionized water and ?5.24 lanthanum nitrate solution (61.1 wt. % lanthanum nitrate) were placed in a Faker-Perkin MuIIer and shred for 20 minutes. The resulting material was dried at 66°C
and calcined three hours at 1200°C. The resulting calcined material was found to have a surface area of 52:9 m2lg.
,~s ~ be seen from a comparison of Examples 5-8, the combination of working and stabilizing (Example 8) DISPILI,,~ alumina, i.e. aluminas prepared in accordance with the teaching of U.S. Patent Ido. 4,6?6,928, results in a dramatic increase in retained surface area of the final, t<xalcined product, i.e. a surface area of 15 greater khan 50 m~/g is obtained even after the material has bin subjected to a ~mpera~re ~f 1200 ° C for three hours:
~ I
IOO g of DI~PAI:~ 18N4-20 alumina and 4.54 g barium acetate powder were 20 mixed for 10 minutes and dr~ect at 66°C. ~'he resulting powder was calcined three h~urs at 1200°C: The c~lcined material was found to have a surface area of 63 m2/g.
~~~~~0 ?00 ~ of DISPEI.h,~' l8IvT4-80 alumina, 602 g deionized water, and 103.64 g 25 barium acetate pov~rder v~ere placedk in a ~aker~Perkins lVluller arid sheaared for 20 minutes. The rcsultir~g gel was dried at 66°C and calcined three hours at 1200°C.
The calcined material was f~und t~ have a surface area of ?2.1 mZ/g.
.Ass can be seen from E~mples 9 end 1~the combination ~f stabilization with 30 a barium containing mat~ri~I and 'working pmvades a marked iracrea~ in retained surface area (compare the surface -area of the calcined material from Examples 9 and with the surface area of the calcined materials in Examples 5-?). Although, as can r::
. t 3: °:
~':n : v ...5: ,r.t..;
Y . ..L':S. : ..5. .
. .5 ~.
a ) ' ~~tF
..,x~~
J,A. h A
.:: , , -"
.a.r,1 . :",.
e't ,. '. w .~. ,.a.
.Y S.. :~. ..t. .n.
,. A 'l i . ,. . ...
.-r.4.. . ,.. ,.. . . -._ n.:l.r,m's.,l.n..;;"., .. . . ........r . , ,.s.;..,.. . ,.... . ... .. ..
,... .. ...r, "... ,., . .. .... . .. ..
PCI'/US93/021 i~~
be seen from Example 9, the presence of barium stabilization alone gives a surface area of greater than 50 Mm'/g, barium presents certain toxicity problems not presented by the use of lanthanum. However, it can be seen that the use of both barium stabilization and working gives sharply increased retained surface area (note Example 10).
Examule 11 100 g CATAPAL A~ alumina, 500 g deionized water, and 12.59 g barium acetate powder was mixed for 15 minutes and dried at 66°C. The resulting powder was calGined three hours as 1200°C: The calcined material had a surface area of 43:4 m=/g.
Exa~n~nle 12_ 7pp g C,~'TAPAL~ A alumina, 452 g deionized water, and 88.13 g barium acetate powder were placed' in a Baker-Perkins Muller and sheared for 20 minutes.
,hhe resulting gel was dried ar 66°C and calcin~d three hours at 1200°C. The calcined material was found to have a surface area of 45.8 m~/g.
As can be seen from the data in Examples 11 and 12, while the addition of stabilizer and working on a cmnventional boehmite alumina, i.e. an alurnina not made in accordance with the teaching of U.S. Patent No. 4;676;928, results in increased, retained surface area, the retained surface area is substantially less than ~0 m~lg.
600 g ~I~PAL~ 18N4-25 alumina sot and 24.90 g aluminum nitrate solution (50 wt. % aluminum nitrate; 50 wt. l deion~zed water) were minced to form an alumina gel. The gel was sheared on a Haa% Torque Rheameter for 10 minutes at 60°C, 110 rpm. The AIZU, content of the sheared gel was 26.8 perront.
53.0 g of ih~ sheared gel, 2.6 g barium acotate powder, and $0:0 g deionized water were mixed for 10 miinutes and dried at ~°C. The resulting powder was calcined three hours at 1200°C. The calcined material was found to:have a surface area of 67.8 hi /g:
.~x~~tr~?,i;d k x...~' ;l 1 at~;.:~ ~ Y i.f.l. 5i ~ ". ~ ._ ,')~ a .. ., .. .
.~ ~' . ,. . .. ,'., w,~4 ..
W~ 93117968 ~CT/US93/~2104 ~~~~.r~ t.~'~
Exam~nle 14 55.7 g of the sheared gel of Example 13 were dried at 66°C. The resulting dried gel (18 g), 2.77 g barium acetate powder and 80.0 g deionized water were mixed for 10 minutes and dried at 66°C. The resulting powder was calcined three hours at 1200°C. The calcined material.viias found to have a surface area of 68.7 malg: -lExhrnole 15 52.24 g of the sheared gel of Example l3 were dried at 66°C. The dried gel was calcined two hours at 250°C followed by 24 hours at 600°C.
The resulting material ~rhs mixed for 10 minutes with 2.59 g barium acetate powder and 20.0 g deionized water. The slurry vvas dried at 66°C and the resulting powder calcined thr~ hours at 120Q°C. The calcined material was found to have a surface area of 70.6 m2/g.
Exam~le ~b 53.0 g of the sheared gel of Example 13, 1.84 g lanthanum nitrate solution (61.1 wt: % lanthanum nitrate), ~d 80.0 g dei~nized water were mixed for 10 minutes and dried at 66°C: The resulting powder has calcined three hours at 1200°C. The calcined material was found to have a surface area 6f 50.2 m2/g.
Dle l7 55.75 g of the sheared gel of Example 13 were dried at 66°C. The resulting dried gel ( 18 g), 1.94 g lanthanum nitrate soluti6n, and 80.0 g deionized water were ~ mixes fir 10 minutes and dried at 66°C. The resulting powder was calcined three hours at 1200°C. 'The cca~llcined material was found to nave a surface area of 47.7 m2/g, 52.24 g of the shred gel of Example 13 were dried at °C. The resulting d~~ gel w~: ~eia~ ,~,~ hours at 25Q°C, followed by 24 hours at 600°C. The resulting material was rnix~d for 10 minutes with 1:82 g lanthanum nitrate solution W~ 93/17968 ~ ~ ~ ~ '~ ~ ~ PCT/US93/a2104 (61.1 wt. % lanthanum nitrate) and 20.0 g deionized water. The slurry was dried at 66°C and the resulting powder calcined three hours at 1200°C.
The calcined material was found to have a surface area of 52.2 m'Ig.
5 As can be seen from a comparison of Examples 13-18, the combination of working (shearing) and the use of a stabilizer results in an alumina which, after calcining at 1200°C for three hours, in general, retains a surface area of greater than about SO m2lg. As can be seen from these examples, best results are obtained in terms ~f retained surface area when the worked or sheared gel is first dried and 10 calcined and the stabilizer then added to the calcined material. Compare, for exaanple, the retained surface area obtained by the procedure of Examples IS
and 18.
In general, however, the data in Examples I3-18, as well as the other examples, demanstrate that the stabilizer can be added after the gel has been worked, after the gel has been worked and dried, after the gel has been worked, dried and calcined, 15 and the ieetained surface area still remains above about 50 ma/g.
~~ foregoing c~iscl~sure and description of the invention is illustrative and explanatory thereof, and various changes in the method steps may be made within the scope of the appended claims without departing from the spirit of the invention.
Claims (11)
1. A process for preparing stabilized alumina comprising:
forming a gel of a treated boehmite alumina, said gel containing from about 15 to about 55 percent-by-weight Al2O3, said treated boehmite alumina being obtained by hydrothermally treating an aqueous mixture of precursor boehmite alumina and acid for a period of time sufficient to convert the greater portion of said precursor boehmite alumina to a colloidal sol of treated boehmite alumina having a pH of above about 4;
subjecting said gel to a sufficient shearing force at a temperature of from ambient to about 100°C for a sufficient period of time to increase the pore volume of said treated boehmite alumina in said gel by at least 30% and the median pore radius of said treated boehmite alumina in said gel by at least 20% over that of said boehmite alumina in said gel prior to shearing and produce a worked boehmite alumina;
and adding a stabilizer to said boehmite alumina, said stabilizer being selected from the group consisting of an oxide of barium, an oxide of a lanthanide metal, a compound of barium that is converted to an oxide upon heating at an elevated temperature, a compound of a lanthanide metal that is converted to an oxide upon heating at an elevated temperature, and mixtures thereof, said stabilizer being added in an amount sufficient to enhance resistance to loss of surface area of a calcined alumina produced from said worked boehmite alumina.
forming a gel of a treated boehmite alumina, said gel containing from about 15 to about 55 percent-by-weight Al2O3, said treated boehmite alumina being obtained by hydrothermally treating an aqueous mixture of precursor boehmite alumina and acid for a period of time sufficient to convert the greater portion of said precursor boehmite alumina to a colloidal sol of treated boehmite alumina having a pH of above about 4;
subjecting said gel to a sufficient shearing force at a temperature of from ambient to about 100°C for a sufficient period of time to increase the pore volume of said treated boehmite alumina in said gel by at least 30% and the median pore radius of said treated boehmite alumina in said gel by at least 20% over that of said boehmite alumina in said gel prior to shearing and produce a worked boehmite alumina;
and adding a stabilizer to said boehmite alumina, said stabilizer being selected from the group consisting of an oxide of barium, an oxide of a lanthanide metal, a compound of barium that is converted to an oxide upon heating at an elevated temperature, a compound of a lanthanide metal that is converted to an oxide upon heating at an elevated temperature, and mixtures thereof, said stabilizer being added in an amount sufficient to enhance resistance to loss of surface area of a calcined alumina produced from said worked boehmite alumina.
2. The process of claim 1 wherein an aqueous dispersion of said treated boehmite alumina is formed.
3. The process of claim 1 wherein said stabilizer is added in an amount of from about 0.5 to about 20 percent-by-weight calculated as oxide based on Al2O3 content of said boehmite alumina.
4. The process of claim 1 wherein said stabilizer is a compound of lanthanum.
5. The process of claim 1 wherein said stabilizer is a compound of barium.
6. The process of claim 1 wherein said stabiliser is added to said boehmite alumina prior to said shearing.
7. The process of claim 1 wherein said stabiliser is added to said boehmite alumina after said shearing.
8. A process for preparing a stabilized calcined alumina comprising:
forming a gel of a treated boehmite alumina, said gel containing from about 15 to about 55 percent-by-weight Al2O3, said treated boehmite alumina being obtained by hydrothermally treating an aqueous mixture of precursor boehmite alumina for a period of time sufficient to convert the greater portion of said precursor boehmite alumina to a colloidal sol of said treated alumina having a pH of above about 4;
subjecting; said gel to al sufficient shearing force at a temperature of from ambient to about 100°C for 4 sufficient period of time to increase the pore volume of said treated boehmite alumina in said gel by at least 30% and the median pore radius of said treated alumina in said gel by at least 20% over that of slid boehmite alumina in said gel prior to sharing and produce a worked boehmite alumina;
calcining said worked boehmite alumina to produce a calcined product; and adding a stabilizer to said calcined product said stabilizer being selected from the group consisting of oxides of barium and lanthanide metals, compounds of barium and lanthanide metals that are converted to oxides upon heating at an elevated temperature, and mixtures thereof, slid stabiliser being added in an amount sufficient to enhance resistance to loss of surface area of said calcined product.
forming a gel of a treated boehmite alumina, said gel containing from about 15 to about 55 percent-by-weight Al2O3, said treated boehmite alumina being obtained by hydrothermally treating an aqueous mixture of precursor boehmite alumina for a period of time sufficient to convert the greater portion of said precursor boehmite alumina to a colloidal sol of said treated alumina having a pH of above about 4;
subjecting; said gel to al sufficient shearing force at a temperature of from ambient to about 100°C for 4 sufficient period of time to increase the pore volume of said treated boehmite alumina in said gel by at least 30% and the median pore radius of said treated alumina in said gel by at least 20% over that of slid boehmite alumina in said gel prior to sharing and produce a worked boehmite alumina;
calcining said worked boehmite alumina to produce a calcined product; and adding a stabilizer to said calcined product said stabilizer being selected from the group consisting of oxides of barium and lanthanide metals, compounds of barium and lanthanide metals that are converted to oxides upon heating at an elevated temperature, and mixtures thereof, slid stabiliser being added in an amount sufficient to enhance resistance to loss of surface area of said calcined product.
9. The process of claim 8 wherein said stabilizer is added in an amount of from about 0.5 to about 20 percent-by-weight calculated as oxide based on Al2O3 content of said calcined product.
10. The process of claim 8 wherein said stabilizer is a compound of lanthanum.
11. The process of claim 8 wherein said stabilizer is a compound of barium.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84988292A | 1992-03-12 | 1992-03-12 | |
| US84974792A | 1992-03-12 | 1992-03-12 | |
| US849,747 | 1992-03-12 | ||
| US849,882 | 1992-03-12 | ||
| PCT/US1993/002104 WO1993017968A1 (en) | 1992-03-12 | 1993-03-10 | Preparation of stabilized alumina having enhanced resistance to loss of surface area at high temperatures |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2131795A1 CA2131795A1 (en) | 1993-09-16 |
| CA2131795C true CA2131795C (en) | 2004-02-03 |
Family
ID=27126871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002131795A Expired - Fee Related CA2131795C (en) | 1992-03-12 | 1993-03-10 | Preparation of stabilized alumina having enhanced resistance to loss of surface area at high temperatures |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0630356A4 (en) |
| CA (1) | CA2131795C (en) |
| WO (1) | WO1993017968A1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5389589A (en) * | 1992-12-22 | 1995-02-14 | Allied-Signal Inc. | Barium-containing alumina |
| DE19634855C2 (en) * | 1996-08-28 | 1998-07-02 | Haldenwanger Tech Keramik Gmbh | Process for the production of an oxidation protection for porous ceramics based on SiC and Si¶3¶N¶4¶ |
| US6129904A (en) * | 1996-09-19 | 2000-10-10 | Sud-Chemie A.G. | Aluminum oxide masses with very narrow pore radius distribution |
| WO2010137657A1 (en) * | 2009-05-27 | 2010-12-02 | 株式会社 キャタラー | Catalyst for purification of exhaust gas |
| GB201220912D0 (en) | 2012-11-21 | 2013-01-02 | Johnson Matthey Plc | Oxidation catalyst for treating the exhaust gas of a compression ignition engine |
| EP3915675A1 (en) * | 2020-05-26 | 2021-12-01 | SASOL Germany GmbH | Stable shaped alumina carriers and method for producing same |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4220559A (en) * | 1978-02-14 | 1980-09-02 | Engelhard Minerals & Chemicals Corporation | High temperature-stable catalyst composition |
| JPS5527830A (en) * | 1978-08-15 | 1980-02-28 | Chiyoda Chem Eng & Constr Co Ltd | Production of alumina carrier |
| JPS6034733A (en) * | 1983-08-04 | 1985-02-22 | Nikki Universal Co Ltd | Preparation of carrier of alumina catalyst |
| US4861410A (en) * | 1985-02-25 | 1989-08-29 | University Of Florida | Method of joining metal oxide containing ceramic bodies |
| JPS61245844A (en) * | 1985-04-25 | 1986-11-01 | Babcock Hitachi Kk | Combustion catalyst and its preparation |
| US4676928A (en) * | 1986-01-30 | 1987-06-30 | Vista Chemical Company | Process for producing water dispersible alumina |
| JPS62180751A (en) * | 1986-02-03 | 1987-08-08 | Toyota Central Res & Dev Lab Inc | Heat resistant alumina carrier |
| DE3823895C1 (en) * | 1988-07-14 | 1989-12-21 | Condea Chemie Gmbh, 2212 Brunsbuettel, De |
-
1993
- 1993-03-10 WO PCT/US1993/002104 patent/WO1993017968A1/en not_active Application Discontinuation
- 1993-03-10 EP EP93907334A patent/EP0630356A4/en not_active Ceased
- 1993-03-10 CA CA002131795A patent/CA2131795C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0630356A4 (en) | 1995-06-14 |
| CA2131795A1 (en) | 1993-09-16 |
| WO1993017968A1 (en) | 1993-09-16 |
| EP0630356A1 (en) | 1994-12-28 |
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