CA1069874A - Metal oxyhalide catalysts - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Metal oxyhalides of the general formula ABO3-fXf having perovskite-type crystal structures in which A and B are each cations of at least one metal and a portion of the type B cations are catalytically active; X is fluoride or cloride; and f is about from 0.01 to 1.0; useful for the promotion of oxidation and reduction reactions, including those involved in the cleanup of exhaust gases of internal combustion engines and their use in oxidation and reduction reactions.

Description

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BACK~OUN~ O~ Tll~, IN~ TIO~
Many metal oxide,s and other metal-based composi-tions are kno~n as hetero~eneous catal~sts for gas and liquid phase oxidation and reduction reactions ln the chemi-cal process and petroleum refinlng lndustrles. However, these catalyst composltlons often deterlorate in u~e, losing their crystallo~raphic identity or active components through volatilization, poisoning or crystallite growth.
For example, catalytic r~orming reau~res catalysts that provide active acidic sites such as halogen. These ac-id sites in conventional re~orming and hydrocracking cata-lysts are continuously lost durin~ operation~ with concomi-tant loss in catalyst utility.
Moreover, current envlronmental concerns require catalysts capable o~ converting the ob~ectionable components o~ industrial and automotive exhaust streams to innocuous sub-stances. I~own catalysts have ~enerally been unable to ~rith-stand the reducing atmospheres, hig~ temperatures, and anti~
knock additive residues cor~monly ~ound in such applications.
S~RY OF TII~ ~JVh~TION
The present invention provides catalysts which are useful in catalytic oxidation-rcduction reactions, includlng those found in chemical processes, petroleum refining applica-tions, and exhaus-t stream conversions, and exhibit high the~nal stability and enhanced resistance to reducin~ environments and chemical poisoning,.
~pccifically, the prcscnt lnventlorl ~rovldes cataly-tic compounds of the general forlllula A~O3 ~r and have a perovsl;ite crystal structure ~hereln ~ and B are each cations of at least one metal and at least, a~out 1~ o~ the Type B

catlons are derived rrOm at least one catalytic metal selected ~rom those transltion metals }laving atomlc numbers Or from 24 to 30 and the platinum metals; 0 is oxide; X ls rluoride or chloride; and f is about from 0.01 to 1Ø
The invention further provides a process of bringing lnto contact at least one oxidiæable reactant and at least one reducible reactant in the presence o~ a catalyst and under such conditions a~ to e~fect a change ln oxidation state of at least one reactant, characterized in that the reac~ants are brought lnto contact ln the presence Or at least one catalytlc compound of the general ~ormula AB03 fX~
and having the perovskite crystal structure wherein A and B are each cations Or at least one metal and at least about 1% of the Type B catlons are dérived rrom at least one catalyticaliy active metal selected from metals of Groups VB, VIB, VIIB, VIII and IB of the Periodic Table;
0 is oxide, X is fluoride or chloride; and ~ is about from 0.01 to 2.5.
Preferably, the A and B cation sites are occupied by ions which contribute to the catalytic activity or - stability Or the compounds.
DETAILED DRSCRIPTION O~ THE INVENTI()N
The metal oxyhalides of this lnvention have a perovskite crystalllne confie;uration.
Ideal perovskite structures contain cations of appropriate relative sizes and coordination properties and -~ have cubic crystalline forms in whlch the corners of the unit cubes are occupied by the lar~,er l'ype A cations (each coordlnated with twelve oxide ions), the centers of the cube~
3 are occupled b!y the smaller Type B cations (each coordinated . . ~

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with six oxide lons), an~ the races Or the cubes are occu-~ied by oxide ions. Variations and di~tortions of thls fundamen~al cubic cr~stal structure are known among materi-als commonly considered to he perovskltes or perovskite-like.
Distortions Or the cubic crystal structure o~ perovskite ànd perovskite-like metal oxides include rhombohedral, orthorhom-blc, pseudocubic, tetragonal, and pseudotetragonal modifica-tions. In all tllese crystal structures, it is requlred that the total number of A site cations should substantially equal the total number of B si'~e cations, also that the combined charge of the cations substantially equals the charge on the ~ -oxy~en atoms~
The particular B site metals and A site metals ' present depend to some degree u~on the radii of the metal cations. The lmportance of ionic radli in perovskite cry~
stal structures has been discussed by many authors, e.g., ~' by Krebs in ~Fundamentals o~ Inorganic Crystal Chernistry,~
McGraw Hill, London (1968). ~he Type A catlons o~ the pres-ent composlti.ons generally exhibit ionic radii o~ from about o.8 to 1.65 Angstroms, while the Type B cations generall~
have lonic radii of from about 0.4 to 1.4 Angstroms. The ionic radii referred to herein are those tabulated by Shannon and Prewitt, Acta Cryst. B25 925 tl969) and B26 1046 (1970).
In the oxyhalides of thiæ invention, the same compositional ion size, and steric relationships pertain except that a ~ction of the divalent oxygen ions Or the ~BO3 type perovskite crystal lattice haæ been repla¢ed by monovalent halogen æelected from f'luoride and chlorlde ln `' 3 amounts correspondln~ to an "f" value .in the ~ormula o~ about ~rom O.Ol to .~.O, ancl usllally O.O5 to O.5 T~le perovskite type metal oxyhalides o~ this in-ventlon thus have the ~eneral emplrical formula AB03 rX~, in which the total number o~ A cations substantially equals the total number o~ B cations an~ the combined charge of the A and B cations substantially eauals the combined charges o~
the oxide and halide lons.
In general, the stoichiometric requisites for the metals, oxygen and halogen in the compounds of the pr~sent invention are met. However, the pr~sent compounds can con-tain de~ect structures with an excess or a deflciency of metal ions of up to about 25 atomic percent o~ the re~uisite for the ideal ABO3 fXf perovskite crystal structure without seriously detractin~ from their desirable characteristics.
Since the halide valence Or one is less than the oxide valence of two~ the electrical neutrality of the composi-tion can be achieved~ if needed, by one or both of the ~ollowing techniques. Two or more cations havin~ dlfferent valences can be selected for incorporatlon into the A or B sites, or one or more cations capable o~ assumlng di~ferent valence states can be selected for use in the compounds.
The particular cations of Type A used in the present compositions are not critical provided they exhibit suitable ionic radii and are o~herwise capable of entering into perovslcite formation alon~ wlth the other components making up the cr~stal lattlce. Included are mono-, di-, tri- and tetravalent cations. Thus, the metals of Type A can be selected from metals of the Periodic Table Groups IA, IB, IIA, II~,IIIB, A~ IVA, and ~A, rrom the lanthanide rare ~arth metals (atomlc number.~ 58 through 71) _5_ and from the actinide rare e~,rth meta,l~, tatomic numbers 90 through 104).
Preferably they are cations Or metals whose ~irst ionization potential is not ~,reater than about 6.9~, i.e., metals of Groups IA, IIA, IIIB, the rare earth series and the actini~e series, in particular ~a, K, Ca, Sr, Ba, La or a mixture of cations of lanthanide rare earth metals. One ~uch mixture of lanthanide rare earth metals con~alns about , one-half cerlum, one-third lanthanum one-slxth neodymlum, ;;~, 10 and smaller amounts of the remainin~ metals o~ atomlc numbers '`~
58 through 71. The~e metals provide stlll ~reater stabillty to the present compoun~s.
The cat:ions of T~pe B also can be selected ~rom any cations havin~, suitable ionic radii and ~re otherwise capable o~ enterin~ into the perovskite crystal-line structure. At least about 1~ Or these cations should be selected from catalytic metals having atomlc numbers 24 to 30, that is, Cr, rln, Fe, Co, N~, Zn and Cu, and the plati~
num metals Ru, Rh, Pd, Os, Pt and Ir. The polyvalent metals of atomic num~ers 2ll to 29 and the ~latinum metals platinum and ruthenium provide increased catalytic e~fect, and are therefore preferred. When a platinum metal is used, catalytic metals other than the platimum group metals are pre~erably present in amounts corresponding to at least about 10% Or the B sltes. When the catalytlc metal ions lnclude one or more platlnum group metal ions, either as the sole catalytic material or as a component of a mix-'~ ture of catalytic material, the platinum ~,roup metal wlll normally comprlse from ahout 1 to 20~ o~ the ~ t~pe metals.
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Ruthenlum, osmium, rhodillrn anrl Ir:LdLum are capa-ble of occu~,vin~ all of the rrype B catlon site5 in perov~kite crystal structures, but little additional benefit is achieved when more than about 20% of th~ sites are occupied by these metals. Palladium an~1 platinum ions are lar~er than ruthenium, osmium, rhodlum and irldium ions and general-ly not more than about 10% of the Type B sites of cr,ystal-line oxides of the ~B~3_fXf tvpe carl be occupled by the lons o~ these metals wlth retention o~ a perovskite structure.
Palladium is ty~ically divalent; rhodium ls typically tri-valent; ruthenium~ iridium and platinum are typlcally tetra-valent; and osrnium can have a valence o~ four, ~ive, six or seven in these compounds. Mixtures of the platinum métals obtained by the partlal refinlng of their ores can also be used in these com~ounds.
Many of these catal~tic metals can exhibit two or more valences differing in lncrements of l or 2 valence units. Com~ounds containin~ these metals are generally more actlve catalysts, ~03slbly because these metals are capable o~ existing in perovskite crystal structures in two or three valences differing by one valence unit increments. Cata-lysts of the present invention wherein a Type B metal is present in two valences often exhibits increased catalytic activity over similar compounds in which the metal ls pres-ent in only a single valence, nossibly because of the en-hanced electron mobility through their crystal structures resulting from tl1e presence of a variable-valence metal.
For this reason too it may o~ten be advanta~eous ko employ such variable-valent catalytic components alon~ with nlatinum metal cata]~tlc components in the compositions Or . :.. - - - ' ' ' ~06987~

this invention. In such em~od~ments, at least about 5~ of the B sites will be occupled by a variable-valent metal in a first valence and at least about 5% b~ the same metal in a second valence; the valences dlfferlnF, preferably by one -unit.
An~ B tvpe sites not occuPied bv the catalytic metals can be occupled bv other cat,ions of metals from ~7roups IA~ IIA, IIB, IIIA, III~, IVA, IVB, VA, VB, VIB~ and VIIB o~ the Periodic Table havin~ the proper ion size and valence for the particu]ar com~osition contem~latcd. For maximum contribution to crystal lattice stability, it is preferred to emplo~ filler catlons of metals whose first ionization potential is not greater than 7.10 (i.e., metals of Groups IA, IIA, IIIA, IIIB, the rare earth series, the actinide series, IVB, VB AND VIB), preferably not greater than 6.90. Aluminum imparts to perovskite crystal struc-tures a high degree Or thermal stability, resistance to lattice reduction in a reducing atmosphere and durability in ~ -catalytic applications, and is accordingly particularly pre~
ferred as a dlluent material.
The Periodic T~ble to which reference is made herein i~ that given at pages 448-449, "Handbook of Chemistry and Physlcs," 40th Edition, Chemlcal Rubber Publishing Company (1958-59).
It ls ~enerall,y prererred t;~at; the sever~] compon-ents of thc present compositions be selected a~ to their nature and proportions such that the l,attice Stabillty Index (LSI) value of the composition 1.5 minimized and i8 not greater than about ].3.2 electron volts, and preferably, not greater than 12Ø In general, lower LSI values lndicate .
. ,; .

-~06"3~37~

more stable catalytic compositions~
The LSI value~ are the sum o~ the product~ o~ (a) the atomic fraction of each A site cation and each B site catlon times (b) t~e ~irst ionization potential of each such metal. Accordingly, the I.5I value is calculated by the following equation:

LSI = fl.Il + f2.I2 __ ~ fi Ii + ~l.Il ~ f2 I2 a a a a a a b b b b b b where fa~ f2~ fa~ fbl~ fb2, ri are the atomic fractions o~
cations Al, A2, -- Al, Bl, B2, -- Bi~ respectively~ Ia~ 12 -- Ia are the first ionization potentials of the metals corresponding to the A site cations and Ib, Ib ~~ Ib are the ~irst ioni.zation potentials Or the metals correspondlng to the B site cations involved. When a variable-valence metal is present in a composition, an atomic ~ractlon is assigned to the amount of the metal in each valence consistent with ; the requirements Or electrical neutrality o~ the present compositions.
By ionization potential is meant the gas phase ~irst ionizatlon potentlal of the element as given by Vedeneyev et al, "~ond Energies, Ionization Potentials and Electron Affinities," St. Martin's Press (1966).
The compositions of this invention can be pre-pared by heatin~ mixtures of metal oxides and/or precursors thereo~ with metal halides that are thermally stable below 9~0C. and relatively involatile under substantiall~ anhy-drous conditions ror suf~icient times an(1 tem~eratures which permit spontaneous formatlon of the compositions.
The metal compounds will provide the desired metal oxy~en and halide moieties and ~referablv will be used in the stoichiometric proportions correspondin~ to the composltion _9_ ~LO~'3137~

desired. The oxlde providin~ s~artln~ m~teri,als in¢lude not only ~he oxi~le~ t~lemselves hut such precur~ors as the carbonates, carboxylates (acetates, oxalates, tartrakes), nitrites and nitrates which are converted to oxides by pro-longed heating ln oxidizlng atmospheres at the temperatures at which these com~ositlons are formed.
A metal chloride or fluoride Or one or more of the metals involved, which may be of the A type and/or the B type, in an amount providing the desired proportion o~
halogen in the flnal composi~ion, can be admixed wlth the rest o~ the perovsklte-forming components, preferably in the form of the metallic carbonates co~recipitated from aqueous solution, the metal moieties of said material being Or the A and~or B tynes as needed and in the desired proportions to complete the perovskite formulation.
The present compounds are in many instances formed by atomic diffusion, without melting o~ any of the starting or potential intermediate materials, and are suhJect to coating of unreacted particles by reaction products.
Accordingly, the mixture of materials which are heated should ~
generally be finely subdivided and intimately mixed before ' heating, and thoroughly ground and mixed by any conventlonal technlques several tim~s durln~ the heating period. The heating times and temperatures required for the formation o~
; significant amounts of these catalytic compounds depend upon the particular compositions being formed, the times required usually being shorter at higher temperatures. Temperatures above about 900C. are usually sui,table for the formati,on of these compounds, using flrin~. times of hours to days with occasional intermediate grindin~, and mixln~ but tempera-tures of from 500 to 1500C. can also he used.

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The co~te-l ~erovsl~lte composLtlons Or the inven~
tion can be used as catalysts in the form o~ ~ree-flowing po~rders, for example, in fluld-bed reactlon systems, or in the form of shaped structures providing efficient contact bet~een the catalyst and reactant ~.ases. The catal~st composltions can contain minor or ma,~or amounts o~ catalyti-cally inert materlals, with the catalytic compositions primarlly on thc surfaces of the inert material or dispersed throughout. For example, the powdered compounds can be rormed into porous catalyst pellets in which they are dis-persed throughout by conventional techniques employing pel-let presses, rolling mixers or extruders. Dlspersants, lubricants, and binders are often used in conJunction with the preparation of such pellets.
Cataly`tic compositions of this invention are preferably used in the form of coatings on suitable refractory supports. The compositions of the present lnvention can be applied to supports elther before or after the completion of the catalytic compositions. For example, the perovskite -substrates Or the present catal~tic com~ositions can be formed on supports whlch are sufficiently high melting and non-reactive to withstand the subsequent processing steps ln-volved in the application of the catalytic metal oxide com-positions to the perovskite substrate. Alternatively, the cat~l~tic com~ositlon Or the lnvention can be preformed and a~plied to the su~port structure in a slurr~
Thc metal oxyhalide~, of this invention can be used in catalytic oxidation and reduction xeac~ions in which the oxidation s-tate of at least one reactant is chan~ed. They : ' .

~L069874 are especially use~ul as ca-t~lysts :~or the oxldatlon o~ o~i-dizable carbon components to compoun~s oI hiFJher oxidation states, tlle reductioll of car~on monoxide and of nltrogen oxides to compounds of lo~er oxidation states and the reduction of hydrocarbyl mercaptans and sul~ides to substantially sulfur-~ree hydrocarbon composi-tions.
Incorporation of` the hali~e cornponent o~ the inven-tion in~o the perovskite structure as de~ined pro~ides active (~cidic) metal-halide ~roups in the crystal lattice, wllich groups constitute the kind Or reac~ion sites considered import-ant in re~o~ning and hydrocrackln~ petroleum chemical operations.
They can also be used as a valuable tneans of providin~ cataly-tically active me~als in more than one valance state (di~ering by a cllarge of one) in the sam~ crystal lattice, ~hich split-ting of tlle valellce states can be beneficial in promot~.tg those re- .
actions which depend on t~e presence in the catalyst of a metal in tlro or more valence states for higher catalytic activity.
Among the oxidation processes for which the present catalysts can be used is the oxidation o.~ carbon monoxide to ~-, .
carbon dloxide and o~ hydrocarbons to carbon dioxide.
Hydrocarbons which can he used include those having 1-20 carbon atoms, including those that are normally gaseous and those that can be entrained in a gaseous stream such as the liquefied petroleum gases and the volatile aromatic, ole~ln-ic and parar~inic hydrocarbons which are commonly in industrial solvents and i.n fuels ~or lnternal combustion en-glne~. The oxidant for these processes can be oxy~en,nitrogen oxides, such as N0 and ~l02~ which components are normally present ln the exhaust gase~ of internal combustion ; 30 engines.

~ -12-.

~Lo~ 4 Thc compounds of this invention can also be used to catal~ze the re~uctlon of such oxides of nitro~,en as nitric oxide, nitrogen dioxide, dinitrogen trioxlde, dinitrogen tetroxide and the hi~,her oxides of nitrogen such a~ may be present in waste ~ases from the production and use of nitric acid as well as in the exhaust gases o~ internal combustion engines. The reductant ror these processes can be hydrogen, carbon monoxide and suc~l hydrocarbons as descrlbed above and as present in said exhaust gases.
10The metal oxyhalides of thls invention contalning ruthenium are particularly useful as catalysts for the re-duction of nitrogen oxides. They generally catalyze the reduction of these oxides to innocuous compounds (e.g., nitrogen) instead of to ammonia. Metal oxyhalides contain--ing platinum and palladium are particularly useful as catalysts for the complete oxidation of carbon compounds to carbon dioxide.
Thus the compositions Or this invention are useful for the slmultaneous oxidation and reduction inrolved in -~
the cleanup Or the exhaust gases of automotive and other internal combustion engines.
Still another hydrocarbon oxidation process that can be catalyzed by metal oxyhalides of this invention is the steam reforming of hydrocarbons. ~his process known also as hydrocarbon rerorming involves reaction of methane or a homolog thereor such as those ~ound in volatile naphthas wlth steam in the presence of a catal~st o~ the invention. Those containin~ Ni or Co or a platlnum metal selected rrom Pd, Pt, Ir, Ru and Rh supported on alumina, magnesia, or a baslc oxide composition are particularl,y well suited for th:lr, , ~LO~i~8~7~

application. The resulting product stream contains CO and H2~ normally accom~anied hy C~2 rormed by reaction of C0 with excess steam in the well-known water gas shift. Reac-tion temperatures are normally in the range 450 to 1000C., usually not above 900C., at pressures up to about 700 psi and usually at least about 100 to 200 psi for methane re-forming at reactant ratios of from about 1.5 to 6 moles o~
steam per carbon in the hydrocarbon feed stock.
The metal oxyhalides Or this invention can also be used in the water gas shift reactlon which involves reaction o~ CO with H20 (steam) at moderatel~ elevated temperatures.
Particularly suitable are those catalysts containing catlon~
Or the first transition metal series, such as Fe, Co, Ni or Cu, preferably Fe or Cu. The resulting product-stream is depleted in C0 ànd contains C02 and H2. Tempera~ures in general are in the 20~ to 500C. range, with hi~her conver-sions favored at the lower temperatures, higher reaction rates at the higher temperatures. The process appears to be largely independent of pressure.
Still another hydrocarbon oxidation process that can be catalyzed by metal oxyhalides as described herein is the dehydrogenation o~ aliphatic, cycloaliphatic and alkylaro-; matic hydrocarbons having 4 to 12 carbon atoms and at least two saturated (i.e., nonolefinic and nonaromatic) -CH-groups which are ad~acent or in 1,6-positions relative to one another (corresponding to sald first oxidation state) to hydrocarbons, usually Or the ~.ame carbon content, formed by removal of the hydrogens ~ro~ one or more pairs Or sa~d -CH-groups (correspondin~ to said seconcl oxidatlon state).
The presence Or halogen in the catalysts Or this inventlon ' ~065'~374 in such reactions substantially reduce8 or eliminate~ the need rOr the addition Or halogen-containing compounds to the feed stream to be dehydrogenated.
In the catalytic reforming process Or the petroleum refining industr~, a relativel,y low octane value feed stream cont~ining dehydrocyclizable and aromatlzable hydrocarbons is converted into a relatively high octane value exit stream containing aromatic hydrocarbons of the gasoline boilin~ ran~e as the essential components resulting primarily from dehydroc~clization of open-chain compcnents to cyclohexanes and aromatization o~ cyclohexanes. Accom-panying reactions include hydrocrackin~ to lower carbon con-tent components and isomerization of stralght-chain to high~
er octane value branched-chain components. The process i8 generally carried in the presence of hydrogen to suppress side reactlons leading to carbonization and to produce a composition which is largel~ satur~ted except for the aro-matic hydrocarbon content.
Still further processes that can be catalyzed in accordance with this invention are those ~ischer-Tropsch re-actlons involving the reduction of carbon monoxide with ' hydrogen ln the presence of a metal oxyhalide catalyst as defined, particularly those containing ~e, Co, Ni, or Ru at elevated tem~eratures (usuall~ 150 to 600C.) and pressures (up to 15000 psi) effective to Pro(luce one or more products containing chemically bound C and ~I with or without chemi cally bound O such as methane or one or more gaseous, liquid or solid higher hydrocarbons~ with or wlthout alcohols~
aldehydes, ketones and ~atty acids.

' .. ' ' "' ~36~S7~

Another reduction ~,~roce~s catalv~ed b~ ox~halide~ de-~ined herein ls the catalytlc desulfurization Or hydrogenaly-sis of or~anic divalent sulfur compounds, such as those naturally occurring in feed stocks used in the petroleum chemical industry, ~or example~ those used for the productlon of synthesis gas (C~ an~ ~12) bv steam reformln~. as described earlier, which stocks include mercaptans, linear sulfides, cycllc sulfides and the aromatic cycllc sulfide thiophene.
The invention is further illustrated by the following speciric examples, in which parts and nercentages are by weight unless otherwise indicated.

The catalytic compositlons of Examples 1-7 were pre-pared by heating mixtures of ~recursor compounds containing anpropriate stoichiometric amounts of the metals and halogens involved. The mixed precursor compounds were obtained by one of two procedures, as indicated in Table I:
Procedure A: An aaueous ~otassium carbonate solutlon _ was added to ~n aqueous solution of metal nitrates and the resulting insoluble materials were separated, washed, dried, and ground and a powdered low-volatility halogen compound (e.g., aluminum Pluoride, lanthanum chloride, or thorium fluoride) was added.
Procedure B: ~n a~ueous ~.~otassium carbonate solutlon was added to a slurry of a powdered water-insoluble low-volatility compound (e.~., aluminum fluoride, molybdenum oxide, or platinum oxide) in an aa~ueous solutlon o~ metal nltrates and the resulting ln-soluble rnaterials were separated, washed, dried, 30 and ground :''' - . :
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The mixed precur~or compound~ were heQted in cruci-bles in air at 900 or 1000C. f`or ~everal da~s with occa-~ional coolin~ rindln~s~ and mixing. The re~ultin~5 me~l oxide compo~itlons were finely ground. ~he e~p~cted pero~skite structure~ of the product~ w~r~ con~lrmed by their æ-ray di~raction patterns .
TABLE I
etal O?~yhalide~

Preparation 10Example Metal Ox~halide Procedure ~] ~FeO 0 8A10 0 ~1 2 . 8FO . 2 A

2 [L~ CrO.8A1~ O2 9C10 1 B

3 [~;aO 2BaO ~ [CU0.5A10.1MO ~I2~7~Q.3 B

4 ~aO 9 rh0~ eO.5CrO~O2 6F~-4 A
CaO 5$rO ~1CA1O.9P~O.~IO2.6 0.4 B
[~ 0, 5sro. ~1 ~A~O . gP~ 0~;;l o2 6Clo 1.~. g 7 [~aO 75Sr~ ~ CAlo.~PtO.lC o.5~ 2.6 O~ ~ A
me catalyst~ were applled to ~u~p~rts ~or ca~al~-tic per~ormance testing~ O~e part o~ '~lsp~ *M alumina disper ant aIld binder ~obtained ~rom the Contine~al Oil Compa~ urf'ace ~rea about 164 squ~re meter~ per gra~, de-termiIled with ~itrogen by the Brunauer-~mmett-Teller methD~) was mi;~ed wlth ~7 parts o~ water containing a ~ew drop8 0~
commerc~ oncentrated hydrochlorlc acid. To ~is mixture was added 7.5 ;parts of the catalytic compo~iti~n to s~btain a ~:
~tabl~ thixotr~pic ~l~ry. A c~llnder o~ "T~rve;5s:"~' alumina caramic honeycomb w~h ~traight-throu~h cell~ (obtai}~ed from E.I. du Pont d~ Nemours & Company) wa~ ~oaked ln ~ater.

* denotes trade mark , .. . . .

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This cylinder weig~red about 6 to 7 grams, was about 2.5 centimeters in diameter and thickness and nominally had a cell size Or l/16 inch, wall thickness Or 0.018 inch, open area of 50%, 253 hexagonal holes per square lnch, and a nominal geometric surface area of 462 square feet per cubic root. The water-soaked cylinder was dipped into the slurry o~ the catalytic composition, the gross eY.CeSS Or slurry was removed by blowing the cylinder with air, the cylinder was dried, and the cyllnder coated with the catalytlc composltion and binder was heated for about 30 minutes in air in a murfle furnace at about 700C. The cyllnder was again soaked in water, dlp~ed int~ the slurry, blown free of excess slurry, and dried and then heated in air at about 700C. for two hours. The percenta~e increase in weiF,ht o~ the cylinder due to the adherent`catalytic composltion and binder was about 15-25~.
The catalytic activity of these compositions in the reduction Or nitric oxide by carbon monoxide was determined.
The "Torvex" ceramic honeycomb c,ylinder coated with the catalytic composition and blnder was installed in a stain-less steel chamber with a nominal internal diameter of 2.5 centimeters, hei~ht of 2.5 centimeters, and volume o~ 12.3 cubic centimeters. Nitrogen containing about 2000 parts per million of nitric oxide and about 10,000 parts per million carbon monoxide was passed throu~,h the chamber at a - nominal ~ourl,y sp<lce velocity Or abou~ 40,000 hr. l and pressure of one pound per s~uare lnch gauge while the feed gas and the catalyst charnber were heated so that the temper-ature of the gas entering the catalyst chamber increased from about 60C. to about 600C. over about 90 minutes.

w18-Samples of the inlet and exit ga~e~ were obtained periodi-cally. The nltric oxide in ~hese s~mple~ was oxldized to nitrogen dioxide. r~he resulting gas mixture was anal~zed and the percent reduction in ~he nitric oxide concentration of the gas upon passine through the catalyst chamber was calculated. A smooth plot was made o~ the degree o~ conver-~ion of nitric oxide at di~erent catalyst chamber inlet temperatures for each c~talytic compo~it~on. From a ~mooth curve through ~ach plot, te~peratures were estim~ted ~or "light-of~" (the lnt0rcept with the tempe~ature axis o~ ~n extrapolation of the portion of the curve at which the de-gree of conversion changed rapidly with temperature) and ~or nitric ox~de con~ersiong of 25%~ 50%~ and 90~. me cataly~t temperature was higher th~n the catalyst bed inlet tempera-~ure with all the catalytic composition~ at nitric oxide conversion3 greater than about 25~ Table II gives the e~-timated temperatures ~or l'light-o~" and ~or 25~, 50~0~ and 90~ conversion o~ nitric oxide be~ore and a~ter heating the catalyst-coated honeycomb cylinder~ ~or 100 hours at about 900C~
me catalytic act~vity o~ the "Tor~ex" cylinder coated with the catalytic composition and blnder in the oxi-dation o~ c~rbon monoxide wa~ determined in a similar apparatus and by a similar procedure. Nltrogen containing about 10 000 parts per million of carbon monoxide and 10 000 parts per mlllion o~ oxygen wa~ pas~ed through khe catalyst chamber and the entering and exiting gas mixtures were a~alyzed chromatoOE aphically using a column containing gran-ules of "L~nde"* 13X molecular ~ieveO The estimated tempera-tures ~or '71ight-o~t' and ~or 25~, 50%, and 90~ converg~ n : * denote~ trade mark ,c..~,~' '~

..

o~ carbon mono~lde bef`ore a~d a~-ter heating the c~tal~t-coated honeycomb cylind~r~ for 100 hour~ ~t about 900C. are glven in Table II.
The catalyatic activlt~ of the ~Torve~ cylinder~
coated with the catalytic compoPition in ~he oxldation o~
propane Nere de~ermined in a simllar apparatu~ and by a similar procedure. ~itrogen containing about 1300 part~
per million o~ propane was determine~ in a ~imilar appara~u3 and by a slmil~r procedure. Nl~rogen containi~ about 1300 part~ per million o~ propane and 8800 part~ per million o~
oxygen was passed through the cat~ly~t chamber and th~ en-tering and exiting g~æes were ~nalyzad chromatographicall~
uslng a column containing 80-100 mesh "Poropak"* QO The temperatures for ~ ht-of~ and ~or ~5~J ~0%, and 90% con-v~r~ion o~ propane before a~d a~ter heating ~he ca~alyst-coated honeycomb cylinder~ ~or 100 hour~ at about 900G are ~iven in T~ble II.

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, 9~374 Small samplcs (about 60 to 80 milligram~) Or each of the metal oxyha~ es of Examples l, 2, 5, 6 and 7 were heated in a Du Pont ~odel 950 Thermogravimetric Analyæer in an atmosphere contalning 1% hydrogen, 4% carbon monoxlde, and g5% nitrogen (by volume, flowlng at a rate of 30 milli-llters per minute), with the temperature lncreasing in a programmed manner at a rate o~ 10C. per mlnute to a rinal temperature of 1000C. The changes in weight given in Table III indicate the stability of the crystal structures of the Example metal oxyhalldes under the experimental con- -ditions. Wlth the oxyrluorides:
(a) The metal oxyfluoride [La]~Feo.8Aloo2]o2.6Fo.4 (Example l) d~d not change significantly in weight.
(b) The Example 5 and 7 metal oxyfluorides decreased in weight by 5.9% and 2.6% and did not significantly in-crease in weight in any temperature region up to 1000C.
The metal oxychlorides showed larger changes ln weight than the metal oxyfluorides.
The x-ray diffraction patterns o~ all these metal oxyhalides contained the same strong lines after heatlng in the reducing atmosphere to 1000C. as before heating.

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Claims (24)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A catalytic composition of the general formula ABO3-fXf and having a perovskite crystal structure, wherein the Type A cations are cations of at least one metal selected from Groups IA, IB, IIA, IIB, IIIB, IVA, VA, the lanthanide rare earth metals and the actinide rare earth metals, said cations having ionic radii between about 0.8 to 1.65 Angstroms;
at least 1% of the Type B cations are cations of at least one catalytic metal selected from metals having atomic numbers 24 to 30 and the platinum metals, and the remain-der of the Type B cations are cations of at least one metal selected from Groups IA, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIB and VIIB, said cations having ionic radii between about 0.4 to 1.4 Angstroms, 0 is oxide;
X is fluoride or chloride; and f is about 0.01 to 1Ø

2. A catalytic composition of Claim 1 wherein f is about from 0.05 to 0.5.

3. A catalytic composition of Claim 1 wherein Type B
cations comprise metals of atomic number 24 to 30 and platinum metals, the metals of atomic number 24 to 30 occupying at least about 10% of the Type B cation sites and the platinum metals occupying at least about 1% of the Type B cation sites.

4. A catalytic composition of Claim 3 wherein at least about 5% of the Type B cation sites occupied by cations of metals having atomic numbers 24-29 axe occupied by metals ions in a first valence and at least a further 5% of the Type B cation sites are occupied by ions of the same metal in a second valence.

5. A catalytic composition of Claim 1 which comprises cations of at least one platinum metal, and the platinum metal cations occupy about from 1 to 20% of the Type B
sites.

6. A catalytic composition of Claim 3 wherein the Type B cation sites not occupied by catalytic metal cations are occupied by cations of metals having a first ionization potential not greater than 7.10.

7. A catalytic composition of Claim 1 wherein the Type A cations and the Type B cations and their proportions are chosen such that the sum of the product of the atomic fractions of all the cations and the first ionization potentials of all the corresponding metals is not greater than 13.2 electron-volts.

8. A catalytic composition of Claim 1 on a shaped support.

9. A catalytic composition of Claim 5 further com-prising cations of at least one metal having an atomic number of from 24-29, occupying at least about 10% of the Type B cation sites.

10. A catalytic composition of Claim 1 wherein sub-stantially all of the Type A cation sites are occupied by cations of metals having a first ionization potential not greater than 6.9.

11. The catalytic composition of Claim 1 having the formula [La] [Fe0.8Al0.2]O2.8F0.2.

12. The catalytic composition of Claim 1 having the formula [La] [Cr0.8Al0.2]O2.9Cl0.1.

13. The catalytic composition of Claim 1 having the formula [La0.2a0.8][Cu0.5Al0.1Mo0.4]02.7F0.3.

14. The catalytic composition of Claim 1 having the formula [La0.4Th0.1][Fe0.5Cr0.5]O2.6F0.4.

15. The catalytic composition of Claim 1 having the formula [La0.5Sr0.5] [Al0.9Pt0.1] O2.6F0.4.

16. The catalytic composition of Claim 1 having the formula [La0.5Sr0.5] [Al0.9Pt0.1] O2.6Cl0.4.

17. The catalytic composition of Claim 1 having the formula [La0.75Sr0.25] [Al0.4Pt0.1Co0.5] O2.6F0.4.

18. A catalytic composition of Claim 1 wherein the Type A cations are selected from Na, K, Ca, Ba, La or a mixture of the lanthanide rare earth metals.

19. A catalytic composition of Claim 1 wherein the Type A cations consist essentially of a lanthanide rare earth metal.

20. A catalytic composition of Claim 1 wherein the Type A cations consist essentially of a lanthanide rare earth metal and a metal of Group IIA of the Periodic Table.

21. A catalytic composition of Claim 1 wherein the Type B cations comprise aluminum.

22. In the process of bringing into contact a gaseous stream comprising at least one oxidizable and at least one reducible reactant selected from oxygen, hydrogen, carbon monoxide, hydrocarbons and nitrogen oxides in the pres-ence of a catalyst and under such conditions as to effect a change in the oxidation state of at least one reactant, the improvement which comprises bringing the reactants into contact in the presence of at least one catalytic composition of Claim 1

23. A process of Claim 22 wherein a stoichiometric excess of reducible reactants is present in the gaseous stream and the cations of catalytically active metal comprise platinum cations.

24. A process of Claim 22 wherein a stoichiometric excess of oxidizable reactants is present in the gaseous stream and the cations of catalytically active metal comprise ruthenium cations.