Oxidic catalyst compositions containing a platinum group metal

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SWEDEN (12) PUBLICATION PAPER. IBltan 7415423-8 (19) SE (51) International class⁴BUILDING 23/54 B01D 53/36. - (44) The application laid out and the application document published (41) The application is generally available • (22) The patent application was submitted

87-02-16

5- 0 6- 1 1

74-12-10 (11) Publication number 448 348 (24) Running day 12/12/10

PATENT AUTHORITY (62) SUman's application number (86); International filing day (86) Filing date for European patent application (30) Priority information

73-12-10 US 423093

73-12-10 US 423096

Application received as:

E Swedish patent application □ Completed international patent application with number □ converted European patent application with number

73-12-10 US 423095

73-12-10 US 423114 (71) (72) (74) (54)

Applicant Engelhard Corporation, Iselin NJ US

Inventor S G. Hindin, G R. Pond, J C. Dettling, Mendham, Elizabeth, Jackson, NJ

Representative Grahn Patent Office

Description Oxidation catalyst, method of preparation thereof and use of the catalyst for combustion of carbonaceous fuel (56) Published publications: SE 6253/72), SE 7506286-9

Rfrnrna mnm narentes anaer international identification code, INID code. Letters in clamps indicate international document code

448 348

The invention relates to an oxidation catalyst for carrying out catalytically maintained thermal combustion of carbonaceous fuel, in particular a catalyst which is characterized by its high stability and retains good activity at high temperatures. The invention also relates to a method of preparing the catalyst and its use.

Catalyst compositions exhibit relatively large surface area per unit weight to allow the greatest possible amount of reaction components to come into contact with the catalyst. Dess10. besides, large surface area is important when catalyst composition one contains a precious metal, for example platinum, because of the high metal costs and because high degree of dispersion is required to prevent excessive growth of metal crystallites. It is desirable to maintain this large surface area under prolonged use and under severe conditions, i.a. reaction temperatures of 1200 ° C or higher. Aluminum oxide is an excellent and relatively economical carrier for many catalysts. Many crystal forms of alumina, for example the chi, kappa, gamma, delta, eta and theta forms exhibit very large surface area in relation to weight. One serious disadvantage of alumina as a catalyst support, however, is that at about 1000 to 1200^OC is converted to the alpha form, substantially reducing the surface area.

Thus, it is highly desirable to stabilize alumina-containing catalyst compositions based on alumina with large surface area in order to substantially prevent the conversion to the alpha alpha form with small surface area and consequent loss of activity.

Accordingly, an object of the present invention is the use of high temperature stability catalyst compositions. These objects and advantages are set forth in the following description.

More particularly, the invention relates to an oxidation cat * 2 lysator, which is characterized by a surface area of ​​at least 20 m / g after calcination for two hours at 1200 ° C and consisting essentially of

448 348 (a) a catalytically active, calcined mixture of 50-95% by weight alumina, 2-25% by weight of a rare earth metal oxide, in which the metal has atomic numbers 57-71, and 2-25% by weight of a metal oxide selected from the following, namely, chromium oxide, tungsten oxide, a metal of group IVB metal in the periodic table and mixtures of two or more of these metal oxides; and (b) a catalytically effective amount, i.e. 0.1-20% by weight of a platinum metal added after the calcination of the mixture.

In preparing this catalyst mixture, the mixture is first calcined at a temperature of at least 850 ° C, after which the mixture is added with a catalytically effective amount of a platinum metal. Such a catalyst composition is stable even at high temperature and maintains its activity at a large number of reactions carried out at high temperature, especially at those combustion reactions conducted at high temperature.

The mixture is prepared by calcining an intimate mixture of an aluminum compound, a rare earth metal compound and at least one metal compound in which the metal is selected from a group consisting of chromium, tungsten, a metal of the group IVB in the periodic table and mixtures thereof. Preferably, for some manufacturing processes, the aluminum compound is alumina. The stated compounds, if not already in oxide form, must be able to give rise to the formation of respective oxides by calcination in air (oxygen) at a temperature of at least 850 ° C or 500 ° C. The combination of rare earth oxide and oxides or oxides of other metals can be considered as high temperature stabilizing component for the alumina.

The amount ratio of the alumina to the stabilizing metal oxide component, i.e., the rare earth metal oxide and oxides of Group IVB metals in the Periodic Table and chromium and tungsten and / or mixtures of these compounds, is largely determined by empirical criteria. Although the invention is not to be limited to the following theory, a brief mention may be helpful in illustrating the invention. It is believed that the addition of the sta

448 The 348 mobilizing component to the alumina or precursor to alumina and calcining the mixture at a temperature of at least 850 ° C optionally converts the present non-oxide components into oxides and allows the stabilizing oxides to enter the alumina lattice and prevent or substantially reduce subsequent alumina conversion to alfa.

All surface areas mentioned in the present context have been determined by the BET method or by equivalent method.

The terminology used above for the metals, ie. rare earth or lanthanum series and metals belonging to the group IVB, is the terminology used in connection with the usual, long form of the periodic system. Thus, metals of the group IVB are meant titanium, zirconium, hafnium and thorium, and rare earth or lanthanide metals refer to the metals with atomic numbers 57-71.

The catalytic composition may also contain a minor amount of other constituents, namely up to about 5% by weight based on the mixture. may serve as promoters or activators for oxidation and reduction reactions. Such constituents may be, for example, manganese, vanadium, copper, iron, cobalt and nickel, usually as metal oxide or sulfide.

The calcined mixture can be prepared in any desired form, for example in the form of a powder, in the form of beads or in the form of tablets. The one required for this purpose. the forming or machining is carried out prior to calcination to promote the adhesion of the particles. After calcination, a platinum metal is added to the mixture. In addition, the mixture can be applied or deposited on a carrier or substrate which is relatively inert, whereupon the platinum metal is added or the catalyst composition can be applied or deposited on the inert carrier.

For compositions used in the present invention, the blend preferably contains from 5 to 15% by weight of rare earth metal oxide based on the total weight of the blend. Oxide of metal from group IVB in the periodic table exists! an amount of preferably 5-15% by weight of the total weight of the mixture. Chromium or tungsten oxide may be included with 2-25, preferably 5-15% by weight of the total weight of the mixture. Mixtures of metal oxides

448 348 from the group IVB of the periodic table and chromium and / or tungsten oxides may be included in 5-30, preferably 5-15% by weight of the total weight of the mixture. If the amount of alumina is too low, the resulting mixture does not provide a sufficient surface area for catalytic activity. However, if more alumina than stated above is included in the mixture, it may not be sufficiently stabilized but will lose surface area during conversion to the alpha form.

In order to achieve the advantages of the invention, it is generally necessary that the stabilizing component be in intimate admixture with the alumina during preclination. For example, an intimate mixture can be obtained by preparing a slurry of alumina and water-soluble or water-dispersible compounds of the stabilizing components. If desired, hydrated alumina, for example aluminum trihydrate, is mixed with aqueous solutions of a salt of a rare earth metal and at least one salt of the other metals, so that the stabilizing components are sorbed by the alumina. The solid components are then recovered from the slurry and calcined to obtain the oxide mixture . The alumina is preferably present in finely divided or colloidal form, thereby achieving maximum sorption area. As an example, it is possible to use a finely divided, newly precipitated aluminum trihydrate of particle size such that 70-90% thereof passes through a screen with mesh opening 0.044 mm. When the large particle size alumina is used, the sorption of the stabilizing components results from the solution, and the subsequent calcination at least a stabilized, outer casing of alumina on particle X13.

Another way to prepare intimate blend of alumina and stabilizing components is to assemble all the components, including the alumina, out of aqueous solutions. Various methods of coagulation are suitable. Such methods include, for example, surface adsorption, wherein one or more components in ionic form are sorbed on the surface by one precipitate, solid, and inclusion, wherein the compound (s) have such dimensions and chemical composition as to fit into the crystal structure of a precipitate. solid, without causing significant distortion.

In co-precipitation, a suitable precipitating agent, usually a base, is added to an aqueous solution of the compounds. The co-precipitation can also be achieved by simultaneously adding the precipitant and the solution of the compound into a vessel containing water. Företrädes5

448 348, such a precipitant is selected so that unsuitable or unnecessary contaminants are volatilized and decomposed during calcination at 8-50 ° C or higher temperature, or can be removed by washing or extraction. The precipitating blacksmith can initiate and complete essentially 5 simultaneous collapse of the components. suitable precipitating agents are ammonium compounds such as ammonium hydroxide or am. monium carbonate, as well as other hydroxides and carbonates of the alkali metals.

The precipitating agent may be used in the form of a diluted or concentrated 10. The rate at which the precipitate is added and the rate of agitation applied depends on the desired precipitation. Thus, dilute precipitate solutions favor, slow addition of the precipitate and vigorous stirring generally coarse, grainy precipitation. The temperature maintained during the addition of the precipitant may be between about 0 and about 90 ° 0.

Higher temperatures generally give coarser precipitation. The precipitant is added until a pH of about 5-9.0 is reached. Vid. -this time, the combined mixture is recovered from the slurry, whereupon it is optionally washed, digested or recrystallized.

The intimate mixture of alumina and stabilizing components is calcined at a temperature of at least about 850 ° C (or 500 ° C, compare above), preferably at about 900-1200 ° C, though not at such a high temperature or for such a long time. that the mixture undergoes excessive sintering. The calcination conditions are chosen so as to obtain a catalytically active mixture having a relatively large surface area, namely at least about 25, preferably at least about 75 m / g. .

Calcination. is preferably carried out prior to mixing, applied to a carrier and in a freely flowable state. This is preferred for economic reasons and for preventing excessive sintering.

Calcination in air to prepare the mixture and prior to the addition of a platinum metal is of importance to the invention. It has been found that an intimate mixture of the stabilizing components and the alumina is stable after calcination at such temperatures, before any further preparative steps are carried out. Since both the alumina and the stabilizing components are intimately admixed, the simultaneous heating of the intimately admixed components substantially reduces unwanted alumina conversion. Moreover. promotes calcination prior to deposition on an inert carrier adherence of the calcined mixture to the substrate, which allows the application of higher throughput ghas · '. with the final catalyst composition under less risk

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448 348 ^β for erosion. In addition, the calcination significantly reduces the possibility of reaction between the stabilizing component and the alumina on the one hand and the other substrate on the one hand. Such reactions between the alumina and the substrate favor the formation of inactive forms of S alumina, thereby reducing the surface area and activity of the alumina. If the stabilizing component reacted with the support, skull thereby, the effective amount of said component available for stabilization is reduced. A further advantage of such calcination is an economic advantage, for calcining the resulting powder mixture before it is applied to an inert carrier requires m-interior. amount of heat: in a smaller oven. In addition, it is essential that the calcination is performed before you. adds the platinum metal, this to avoid loss of this metal by occlusion.

Suitable aluminum-containing compounds are alumina, gamma, et5-eta, kappa, delta and theta forms of alumina and for co-precipitation water-soluble aluminum compounds, for example salts such as aluminum halides, aluminum nitrate, aluminum acetate and aluminum sulfate.

driving the preparation of the catalytic mixture useful compounds of the rare earth metals are, for example, compounds of cerium, lanthanum, neodymium, samarium, praseodymium and the like, as well as the commercially available mixtures of rare earth metals. The most commonly used rare earth metal is cerium. If a mixture of rare earth metals is used, it is preferably a mixture in which cerium is the predominant component. suitable water-soluble, rare earth metal compounds are i.a. acetate, halides, nitrates, sulphates and the like, (SO₄)₃, Hd (C₂hrs₃O₂)₃,.

Sm (KO₃)₃ and TmBrj.

The oxides of metals from the group IVB in the periodic table, ie. titanium, thorium, zirconia and hafnium oxide, are added to the alumina in the form of their water-soluble precursors. Thus, for example, water-soluble salts of group IVB metals such as nitrate, acetate, halides, sulfate and the like can be used. suitable water-soluble compounds are Zr (K0₃)₄, ZrCl 2, Zr (S0₄)₂, ZrOCl₂, Ti₂(C₂0₄)₃and HfOCl₂.

Examples of useful water-soluble compounds of chromium and tungsten may be mentioned chromium acetate, chromium nitrate, chromium halides, chromium oxide (chromic acid), chromium oxalate and complex compounds of chromium, such as chlorine pentamine, ammonium chloride, tungsten halide, tungsten oxide salts, such as tungsten dioxide, such as tungsten dioxide.

A platinum metal is added to the calcined mixture, such as Ce (C₂EI₃0₂)₃, CeBr₃, CeQlOjK, 0e₂

448 348 to obtain the catalyst compositions used according to the invention, as shown, to be effective for long time reactions at. high temperature. Such metals were added, or generally mixed, in. Sufficient amounts to produce substantially. activity. The useful platinum metals are platinum, ruthenium, palladium, iridium and rhodium. The metals, metal combinations or alloys selected depend largely on activity, specificity, volatility, deactivation by specific components, such as.

are included among the reaction components, and furthermore, said choice depends. on economic factors.

The amount of platinum metal added to the calcined mixture depends primarily on such requirements as activity and life expectancy, and secondly on economic factors. Theoretically is the maximum. the amount required to substantially coat the available surface without causing excessive metal crystallite growth and loss of activity during use. Two main phenomena competing with each other must be taken into account in this surface treatment. Thus, it is advisable to completely coat the substrate surface in order to obtain the largest possible surface of platinum metal and thus maximum activity, but if the surface is fully coated, crystallite growth between adjacent crystallites, which reduces the surface area and greatly reduces the activity. Consequently, a suitable balance must be achieved between maximum coating and proper dispersion. In the alternative, one must take into account the permissible size of the catalyst dry casing when determining the amount of platinum metal. If the casing must be small, the amount of platinum metal is preferably increased within the above limits. For example, for the treatment of car exhaust, the catalyst casing is relatively small, especially if uniform honeycomb carriers are used, and a higher content may then be desirable. For economic reasons, one must of course use the least amount of platinum metal to achieve the main purpose, which is to promote the reaction. Generally, the platinum metal constitutes a minor part of the catalyst mixture and typically does not exceed about 20% by weight of the calcined mixture. The amount may be between about 0.1 and about 20%, preferably between about 0.2 and about 10%, thereby combining good economy and high activity with long-term usability. These percentages are calculated based on the amount of calcined mixture. For example, if the mixture is used on an inert carrier, it may comprise about 10% of the weight of the carrier and the percentage of the platinum metal calculated on the substrate and the mixture is correspondingly smaller.

During the preparation of the catalyst mixture one can be used

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448 348 different compounds and / or complexes as well as dispersions of any of the elemental platinum metals to obtain deposition of the metal on the mixture. Water soluble platinum metal compounds or complexes can be used. The platinum metal can be precipitated out of solution, for example as a sulfide, by contact with hydrogen sulfide. The only limitation for the carrier fluids is that they do not react with. platinum metal and can be removed by evaporation or decomposition at. subsequent heating and / or vacuum treatment, which may be carried out as part of the preparation or in use -ax the final catalyst composition. suitable platinum metal compounds are, for example, chloroplatinic (1V) acid, potassium platinum chloride, ammonium platinum thiocyanate. Platinum platinum tetrahydroxide, platinum metal chlorides, oxides, sulfides and nitrates, platinum tetramine chloride, palladium tetramine chloride, sodium palladium chloride, hexamminrodium chloride and hexammini rium chloride can be used if a mixture of platinum and p. palladium can be used in water-soluble forms, for example as amine hydroxides, or chloroplatinic acid (IV) acid and palladium nitrate can be used in the preparation of the catalyst used according to the invention. The platinum metal may be included in the catalyst mixture in elemental or base form, for example as an oxide or a sulfide. During the subsequent treatment, for example the calcination or use, substantially all of the platinum metal is converted into elemental form.

Although these catalyst mixtures are useful for many reactions, they are. are not necessarily equivalent in all processes, nor are those useful in the same process necessarily necessarily equivalent to each other. ...........

Although not necessary, the catalysts according to the invention suitably have a relatively catalytically inert carrier. Scim carriers are preferably used with a uniform skeleton of relatively large dimensions, for example a honeycomb material, but smaller particles can be used, for example tablets or beads. The size of these tablets may vary according to the system, its design and timing parameters, in which the tablets are intended to be used, but the diameter of the tablets is between about 0.4 and about 15, preferably between about 0.8 and about 6 mm, and the length of the tablets is about 0.4-25), preferably about 0.8-6 mm.

When using a carrier, the calcined mixture is generally included with a small amount of the total catalyst mixture, namely usually between about 2 and about 50, preferably between about 5 and about 20% by weight, based on the total weight of the mixture and the carrier. The amount used depends on economic factors,

448 348 space as well. configuration. These carriers, whether in the form of contiguous skeletons or tablets, suitably consist of a substantially inert, rigid material which can. maintain outer shape and strength at high temperatures, for example at temperatures up to about 1800 ° 0. The carrier typically has only a small coefficient of thermal expansion, good resistance to heat shock and low thermal conductivity. Although a carrier with porous, surface is preferred, the surface may. may be relatively unorthodox, but in the latter case it is desirable that the surface be roughened, so that the adhesion of the deposited mixtures is improved.

The support may be metallic and / or ceramic. Preferred carriers, either in skeletal or other form, are mainly composed of refractory metal oxides, i.a. combined oxides, for example aluminosilicate. suitable carrier materials include cordierite, cordierite alpha alumina, silicon nitride ,. silicon carbide, zircon mullite, spodumene, alumina-silica-magnesium oxide, and zirconium silicate. Examples of other suitable refractory ceramic materials are sillimanite, magnesium silicate, zirconium, petalite, alpha alumina and aluminosilicate.

Although the carrier may be made of glazed ceramics, it is preferred to be glazed, and it may be substantially fully crystalline and characterized by the absence, of any substantial amount of vitreous or amorphous matrix. In addition, it may have a substantially available porosity and. preferably having a watertight pore volume of at least about 10%. Such carriers are described in U.S. Patent No. 5,565,830, the entire contents of which are incorporated herein by reference.

The geometric or apparent surface area of ​​the skeleton or honeycomb material, including the walls of the gas flow channels, is generally about 0.5-6, preferably 1-5 m 2 per liter of carrier. This surface area is sufficient for depositing a satisfactory amount of the mixture or final catalyst composition. The channels.

o which in number is 15-400, preferably 25-75 per cm of cross-sectional area, may be distributed over the entire surface of the wearer and form an open surface of more than 60% of the total surface area of ​​the wearer. The walls must be thick enough to give the wearer rigidity and cohesion, but at the same time the surface area must be large. The wall thickness is thus between about 0.05 and about 0.6 mm. The flow channels can be of any shape and size consistent with the desired surface area and should be large enough to allow relatively free passage of the gaseous reaction mixture. Preferably, the length of the channels is at least about 0.25 cm, in order to be added

448 348 ensure-adequate contact or residence time, and achieve it; desired reaction. Although the channels are generally parallel, they can go in several different directions and a channel can communicate with one or more adjacent channels.

In a method of preparing catalysts provided with the catalytic mixtures used in the invention, a carrier is contacted with a water slurry of the substantially water-insoluble, calcined alumina and stabilizing component mixture. The solids content of the slurry forms an adhesive deposit on the support and is dried or calcined a second time at a temperature to obtain a relatively catalytically active product. The second drying or calcination takes place at a temperature so low that no excessive sintering occurs in the mixture. suitable calcination temperatures are generally between about 300 and about 7θ0 ° 0, at which temperatures assure catalytic activity without excessive sintering. Preferably, the calcination is carried out at about 400-600 ° C. After this second calcination, the coating on the support has a surface area of ​​at least about 75 m / g. lower temperature can be applied to dry the mixture if the second calcination is not carried out.

After the coated surface was dried or calcined, a platinum metal component was added to increase the catalytic activity of the mixture. The platinum metal can be added in the above manner, preferably from an aqueous solution or a solution in another solvent, and for impregnating or depositing the platinum metal component one on the coated surface. /

After the platinum metal is added, the whole is dried and can be calcined a third time under such conditions as to obtain a mixture of such properties as to favor selected reactions.

This last calcination stabilizes the finished catalyst composition so that the activity of the catalyst during the first stages of use does not change significantly. The temperature of this last calcination step must be so low that no significant sintering occurs in the underlying coating, since such sintering would cause substantial occlusion of the platinum metal component. Thus, the calcination can be carried out at a temperature between about 300 and about 700 ° C, preferably at about 400-600 ° C.

An alternative method of preparing the catalyst compositions used in the present invention, if a relatively inert carrier is used, involves adding the platinum metal component to the calcined mixture before depositing it on the support. Thus, for example, one can prepare, for example, a water slurry of the calcined mixture and. add the platinum metal component to the slurry and mix it intimately into the slurry. The platinum metal component may be in the form given above and may be precipitated in the manner given above. The final mixture containing the platinum metal can then be dried or calcined so as to. obtains a catalytically active composition in a form suitable for deposition on a substrate or for use without such deposition as a final catalyst either finely divided or coarse-grained. Subsequent calcinations or drying can be carried out in the above manner. The calcined material generally has a surface area. of at least about 25, preferably at least about 75 m²/ G. .

The following examples describe the general manufacturing process. for some representative, stabilized catalytic mixtures and compositions used in the present invention. By percentage, parts and proportions in this context are meant weight percent, parts by weight and weight proportions, unless otherwise expressly stated.

Example 1; . For making a stabilized b country licks off.

CeOg, CrOg and AlgOO were dissolved 17.82 g of cerium nitrate and 14.41 g of zirconyl nitrate in .628 ml of HgO to a total volume of 632.5 ml. 275 g of activated AlgO₂ powder was stirred into the solution at a constant rate of i.

minutes. The entire solution was then evaporated to dryness under heating and. stirring, whereupon the residue was introduced into a drying oven at a temperature of 120 ° C, where it was allowed to dry overnight. The dried product was ground to a particle size such that it passed through a 0.84 mm mesh screen and was calcined at 970 ° C for 1 hour.

g of the mixture having a density of 0.476 g / cm 2 and containing 3.3% CoOg, 3.3% ZrOg and 93.4% AlgOO were then tested for its ability to maintain surface area during calcination at 1200 ° C for hours. It turned out that the surface area after such calcination was

36.6 m²/ G. :

Example 2; 186 grams of the calcined powder prepared according to Example 1 were mixed with 286 ml of HgO and 13.9 ml of concentrated HHO 3 and ground in a ball mill for 19 hours at 68 rpm (US Stoneware 3.79 liter malt drum). 330 ml of the thus obtained slurry having a density of 1.4 g / cm 2 and a pH of 4.45 were diluted with 30 ml of water to a viscosity of about 68 cP. 330 cm 2 cord honeycomb material

2erit with about 40 parallel gas flow channels per cm across 40 incision areas were dipped in this diluted slicker, then drained and blown with air, then dried at 120 ° C for 2.5 hours and

448 348 was calcined at 500 ° C for 2 hours. The resulting adhesive surface coating of the mixture constituted about 17% by weight of the coated honeycomb material.

Example 5: A honeycomb material coated with CeO 2, ZrOg and ÄlgO it theoretically contained 0.9 wt% Pt and 0.3 wt% PcL.

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After the honeycomb material was allowed to stand for 10 minutes during intermittent take-up and immersion in the solution, it was taken out of the solution, allowed to drain and excess solution was blown off. The honeycomb material was then treated with gaseous hydrogen sulfide for 15 minutes and washed free with chloride. deionized water. The thus obtained impregnated honeycomb material was dried all night at 110'0 and then calcined in flowing air for 2 hours at. 500 ° C. The final catalyst contained about 0.4 wt.% Pt and 0.1 wt.% Pd.

Example 4: A zircon mullite honeycomb material was coated with a blend.

lick containing Cr₂O₂, CeO₂ and A₂O₂ and then impregnated with Pt using amine hydroxide as a platinum source. 1200 g of activated aluminum powder with a particle size such that it passed through a 0.42 mm mesh aperture, was slurried in a mixer in a solution prepared by dissolving 1263 g Cr (ITO 2) and 691 g

Ce (110) 6.6 H 2 O in 156 ml of 110 ° at 75 ° G. An additional 240 ml of HgO was added slowly and the whole stirred for 0.5 hours. After this stirring, the mass had uniform appearance and dark green color. The pulp was dried at.

110 ° C. The resulting large chunks were crushed and the material dried for 16 hours at 110 ° C. After drying, the solid was crushed and sieved through a 0.42 mm mesh opening and the powder calcined for 4 hours at 1000 ° C. 35θ g of the powder was charged into a ball mill (2 liter drum) and 350 ml of HgO, 7 ml of concentrated HNO₂ and ceramic balls were added. The drum was rotated for 16 hours at 99 rpm. The pH of the assay was 3.7. 3θθ ml of the slurry was diluted with. 100 ml of H₂O containing 1 ml of concentrated ΗΝΌ-. A zircon honeycomb material 3.

mullite from American J_ava Corporation with approximately 15.5 flow-through island channels per cm of cross-sectional area was dipped in the diluted lick and kept submerged therein for 1 minute, after which it was taken up and blown. air for removing slick your excess. The honeycomb material was dried for 16 minutes at 110 ° C and then calcined for 2 hours at 1000 ° C. After the material cooled, it turned out that it was absorbed

16.7% by weight lick, which had a composition of about 70% by weight Al 2 O-, 14% by weight C 2 O and 16% by weight CeOg.

448 348

The coated honeycomb material was then dipped in an aqueous solution of platinum tetramine hydroxide containing 0.435 g of platinum in 184 ml of solution, and. was kept immersed therein for 1 minute, then excess was blown off and the catalyst dried at 110 ° C. After drying, the honeycomb material was calcined for 2 hours at 400 ° C. The final honeycomb material nominally contained 0.5 weight percent Pt.

/ Example 5^; A zircon mullite honeycomb material was coated with one mixture containing CrgOO, CeOg and A₂O- and impregnated with Pd using amine hydroxide. \ .10. This catalyst was prepared in exactly the manner indicated for preparing the catalyst in Example 4 with the only change that instead of dipping the liner coated honeycomb material in a platinum tetramine hydroxide solution, it was dipped in a palladium tetramine hydroxide solution, final honeycomb material containing nominally 0.5 weight percent Pd.

Example 6-: An α-aluminum honeycomb material was coated with a mixture prepared by milling in the ball mill of a powder of CeOg, and A1 ~ O, with a nalladium nitrate solution.

A CeO 2 -CrgOyA 2 O ball mill of the powder with a solution of PdCNO ^g in distilled water for 17 hours at a rotational speed of 114 rpm. Subsequently, diluted with an equal volume of 1% (concentrated) HNO 3 in water, this diluted lick was used for dipping a honeycomb material of α-alumina with 6.7 corrugations per cm. After blowing off the licking excess, the honeycomb material was dried at 110 ° C and finally calcined for 2 hours at 500 ° C. This was obtained in this way

JO a slicker uptake of 7.4% by weight. The surface coated. the block of honeycomb material was once again dipped in a newly prepared slurry of a mixture prepared in the above manner. After drying and calcining, the block was weighed and it was found that the uptake was. • 12.0% by weight licks and the Pd content was 0.21% by weight.

Example 7: -A mixture of CeO £, θ^Γ2θ5 ZrOg and AlpO4 were prepared by dissolving 22.95 g of cerium nitrate, 18.56 g of zirconyl nitrate and 47.92 g of chromium nitrate in 587.5 ml Ή 2 ο to a final volume of 632.5 ml.

275 g of activated alumina powder was added to the solution with constant stirring for 10 minutes. The slurry was then evaporated to dryness under heating and stirring and set in a drying oven at a temperature of 120 ° C, whereupon it was allowed to dry overnight. The^-

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448 348 dried solid residue was reduced to such a particle size that it passed through one. screen with mesh opening 0.84 mm and. was calcined at 97 ° C for one hour. 5 g of the mixture with a density of 0.958 g / cm 2 and. containing 4% GeOg, .4% Cr₂O₂, 4% ZrOg, and 88% then for 2 hours at 1200 ° C. It was found that the surface area after this calcination was 29.9 m / g.

Example 8:

191 S of a mixture of GeO 3 was prepared in the manner set forth in Example 7 and charged in a 0.95 µl

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ters of malting barrels containing 665 g. Then Ί9Ί cm-5 H₂O plus 14.4 cm² concentrated HHOy was added. The whole was then ground in the ball mill for 19 hours at a rotation of 66 rpm. The slurry was poured, diluted with 40 ml of water to a viscosity of 15 cP and For example, surface coating of a honeycomb material of the kind mentioned above is used in Example 4 and in the manner described in the same example. The catalyst so prepared, after calcination at 500 ° C, contained Ί5% by weight of the mixture based on the total amount of weight of coated honeycomb material.

Example 9. A mixture was prepared from a technical mixture of. rare earth metals, and Al 2 Cy 14.87 g of a mixture of rare earth metal nitrate was used. After conversion, the theoretical oxide levels were as follows: ΟθΟ £ 48%,^ΐ3· £ θ5 24%, ^ 2θ5 17% »^^Γ6θ11 ^Y2 ° and other oxides 0.8%.

The mixture of rare earth metals and 3.95 g CrO 2 was dissolved x water and the solution was diluted to 80.3 ml. 51 g Al ^ Oj^{me &lt;}^ ^one TA³¹®²¹of 300 m 2 / g after grinding was added to the solution with stirring for 5 minutes. The slurry was poured into an evaporation dish, dried under stirring for 1 hour under an IB lamp, set in one. oven and dried at 110 ° C all night. The dried mixture weighed 65.1 g and contained 40% by weight of rare earth metal oxides, 5% by weight TegO 2 and 85% by weight A 2 O 2. The mixture was crushed to a powder and 5 g thereof were calcined at 1200 ° C for 4 hours. The surface area of ​​the calcined powder was 43.7 m / g ·.

Example 10O^; A zircon mullite honeycomb with dimensions of 25x76 mm and 4.7 corrugations per cm was coated with a mixture prepared in the manner set forth in Example 9 with the change that a

2-kilo batch was prepared and chromium nitrate was used instead of CrO After the dried powder was ground, it was calcined at 1000 ° C for 4 hours. 240 g of the mixture thus obtained was loaded into a 4.7 liter mill drum together with 4.5 kg of coal balls. 432 ml of wetted and 18 ml of concentrated nitric acid were added and the slurry was ground for 17 hours, then cooled to 25 ° C. The slurry had a density

448 348 of 1.4-9 g / cm 2 and a viscosity of 12 cP. 1% nitric acid was added to one density of 1.38 g / cm 2. The slurry was then loaded into a container and stirred continuously. A honeycomb material was immersed in the slurry, blown dry and dried at 110 ° C all night. The honeycomb material so coated was calcined for 2 hours at 500 ° C and. weighed. It was found that it absorbed 15.3% mixture based on the total weight of coated honeycomb material. This was then immersed in a solution of 18 g of HajPdCl 2 in 51®1 water and kept immersed in this solution for half an hour. Then the honeycomb material was taken up, excess: palladium solution was blown off and the deposited material was hydrolyzed in a hot sodium bicarbonate solution. It treated honeycombs in this way. the material was then washed, chloride-free and dried at 110 ° G all night. The final weight gain of the honeycomb material was 1.05% PdO. Example 11; A mixture of the same composition son of Example 10, i.e. 10% rare earth metal oxides, 5%^Cr2°5 ^{ocil 8}2% 3 was prepared by co-precipitation. 187.7 g of aluminum nitrate, 7.4 g of the rare earth metal nitrate mixture used in Example 9, and 7.9 g of chromium nitrate were dissolved in series in one liter of water and the solution was poured into a drip funnel. A second solution was prepared from 400 µl of ammonium hydroxide (28.3% and 1600 ml of water and poured into another dropping funnel.

In a 6 liter beaker, 2000 ml of water was charged and placed under heavy mechanical stirring. The nitrate solution was then added to the water in the beaker at room temperature over the course of 30 minutes. The ammonia solution was added simultaneously with the nitrate solution at such a rate that the pH of the slurry in the beaker was maintained at 9.0. After the addition of the nitrate solution was completed, it was found that 580 ml of the ammonia solution was also added. Stirring was continued for 15 minutes after the collapse was completed. The slurry was then allowed to stand throughout nature, then filtered and resuspended in 2 liters of water. The second slurry was filtered, excess water was removed and. drying was carried out for 4 days at room temperature. The filter cake was hand-ground to a powder, dried in a dough at room temperature and the entire following night at 110 ° C. There were thus obtained 4-2 g of mixture, the surface area of ​​which was good after calcination at 1200 ° C for 4 hours. Representative mixtures prepared according to the above example and results obtained after calcination at 1200 ° C are summarized in Table I.

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448 348

In practice, the catalysts of the invention are particularly useful for the oxidation of carbonaceous fuels at high temperatures. For example, the catalysts can advantageously be used for catalytically maintained thermal combustion of carbonaceous fuels in a manner more fully described in the Swedish patent application.

7406105-2, the contents of which are included in the present description.

This process involves substantially adiabatic combustion of at least a portion of a carbonaceous fuel in admixture with air and in the presence of a catalyst composition at an operating temperature substantially above the instantaneous ignition of the fuel-air mixture, but at such a low temperature that no substantial formation of nitrogen oxides, happens.

Flammable mixtures of most fuels and air normally have such properties that they are combusted at relatively high temperatures, ie. at temperatures of about 1800 ° C and higher, whereby substantial amounts of nitrogen oxides (Ν0_χ) is formed. In contrast, little or no NO is formed in a system in which fuel is catalytically combusted at relatively low temperatures.

For a real catalytic oxidation reaction, the reaction rate can be graphed as a function of temperature. For a given catalyst and a given combination of reaction conditions, the reaction rate is also increased as the temperature initially rises. The rate increase is an exponential function of temperature.

As the temperature rises further, the reaction rate 25 passes through a transition zone, where the limiting parameters which determine the reaction rate change from being determined by the catalyst to. to be determined by the material transport. When the catalytic reaction becomes; so fast that the reaction components do not reach the catalyst surface as quickly as they react there with one another, the reaction changes and gets a rate regulated by the material transport, and the catalytic reaction rate changes much less with further temperature rise. The reaction can, so to speak, be controlled by the material transport. In catalytic reactions, the rates of which are determined by the rate at which the reaction components reach.

the catalyst surface, one cannot: distinguish between a more active and a less active catalyst, because the actual catalyst activity is then not a determinant of the reaction rate. Whether the catalyst activity increases above the activity required for the rate at which the reaction components reach catalyst 40, no faster catalytic reaction can be achieved under the given conditions. '

448 348

It has been found that it is possible to achieve substantially adiabatic combustion in the presence of a catalyst at a reaction rate many times greater than the limited rate. whereby the reaction components reach the catalyst. With. the second CRD exceeds the catalytically supported thermal combustion rate at which the reaction components reach the catalyst surfaces. If the catalyst operating temperature is significantly increased in the region where the transport determines the reaction rate, the reaction rate again begins to increase exponentially with the temperature.

This is in clear contradiction to catalytic technology and the modes of kinetics of material transport. The phenomenon can be explained by the fact that the catalyst surface and the gas layer adjacent to it have a temperature above that at which the thermal combustion occurs at a rate higher than the catalytic, and the temperature of the catalytic surface is above the instantaneous combustion temperature of the fuel-air mixture (as below should be defined). The fuel molecules entering this layer burn spontaneously without penetrating to the catalyst surface. It is believed that this layer will become deeper as the combustion proceeds. Finally, the entire gas mass has been heated to a temperature at which thermal reactions occur throughout the gas stream and not only adjacent the catalyst surface. At this point, the thermal reactions even continue without further contact between the gas and the catalyst as the gases pass through the combustion zone.

By the instantaneous self-ignition temperature for a fuel air mixture is meant, in the present context, the temperature at which the ignition delay of the fuel-air mixture entering the catalyst is negligible in comparison with the residence time of the mixture in the combustion zone.

In this process, one can use a fuel quantity equivalent to a heating value of about 5-Ίθ kg of propane per hour and liter of catalyst. It is not necessary to maintain a quantity ratio of fuel: air falling within the flame interval, and consequently extinguishing due to variations in the ratio of fuel: air is not as serious a problem as in conventional combustion devices.

The adiabatic flame temperature of the fuel-air mixture at a given combination of conditions (e.g., initial temperature and to some extent original pressure) is determined by the fuel: air ratio. The. The blends stated generally have a composition within the flammability range or they also have a composition which is outside the flammability range on the fuel-poor side thereof, but there may be fuel-air mixtures without. clearly defined flammability intervals which nevertheless have a theoretical adiabatic flame temperature within the operating conditions of the invention. Typically, the mixtures fed into the combustion zone have a fuel ratio: air, which is such that there is an excess of oxygen; in relation to the stoichiometric amount required for complete conversion of the fuel to carbon dioxide and water. Preferably, the free oxygen content is at least about 1.5 times the stoichiometric amount required for complete combustion of the fuel. Although the process is described using air as a non-fuel component. it is obvious that it is oxygen, which. are the elements required to maintain proper combustion. If desired, the oxygen content of the non-fuel component can be varied and by air, in the present context, always refers to the non-fuel component of the mixture. The fuel-air mixture fed into the combustion zone can contain as little free oxygen as 10% by volume or less, which may be the case, for example, when using an exhaust gas as a source of oxygen, in which a portion of the oxygen reacts. In turbine operation, the weight ratio of air fuel in the mixture fed into the combustion system is often above about 30: 1 and some turbines are intended for air: fuel ratios of up to 200: 1 or even for higher ratios.

The carbonaceous fuels map to be gaseous or liquid at normal temperature and normal pressure. suitable hydrocarbon fuels may be, for example, low molecular weight aliphatic hydrocarbons such as methane, ethane, propane, butane, pentane; petrol; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene; naphtha; diesel fuel; kerosene; other average distillate fuels; hydro-treated heavier fuels and the like.

Other useful carbonaceous fuels include alcohols such as methanol, ethanol, isopropanol; ethers such as diethyl ether and aromatic ethers such as ethyl phenyl ether; and carbon monoxide. In combustion of diluted fuels containing inert constituents, for example. low gas value urban gas, fuel-air mixtures with adiabatic flame temperatures within the specified range can be either fuel-rich or low-fuel. When fuel-rich mixtures are used, additional air or fuel-air mixtures can be introduced into the effluent from the catalyst zone to obtain a total excess air for complete combustion of the fuel components to 40 carbon dioxide and water. As noted above, the thermal reactions on the downstream side of the catalyst zone continue, provided the effluent ·

448 The temperature is substantially above the temperature for instantaneous self-ignition.

The fuel-air mixture is generally passed to the catalyst in the combustion zone at a gas flow rate before or at the inlet to the catalyst, which is above the maximum velocity, whereby the flame propagates in the gas mixture. This can be achieved by increasing the air flow or by appropriately shaping the inlet «to the combustion chamber, for example by throttling the nozzle here. This avoids baking oil, which causes the formation of NO ... Prior to &lt;0, said gas flow rate is maintained adjacent the catalyst inlet. suitable linear gas velocities are usually above one meter per second, but substantially higher velocities may of course be required depending on such factors as temperature, pressure and gas composition. At least a significant portion of the combustion takes place in the catalytic zone and the combustion can be substantially flame-free.

The carbonaceous fuel, which usually has an adiabatic flare temperature of at least 1800 ° C, when combusted with a stoichiometric amount of air (atmospheric composition) at the temperature prevailing at the inlet, is burned substantially adiabatically in the catalyst zone.

Although the instantaneous self-ignition temperature for a typical fuel may be below about 1100 ° C, it is extremely difficult to achieve stable, adiabatic combustion of the fuel below about 1800 ° C in primary combustion systems. It is for this reason that gas25 turbines limited to operating temperatures of 1100 ° C typically have primary combustion at temperatures above 2200 ° C. As pointed out above, combustion individual use of the catalyst according to the present invention is characterized. invention of using a fuel-air mixture having adiabatic flame temperature substantially above the temperature of instantaneous self-ignition of the mixture but below a temperature at which substantial NO formation occurs. This adiabatic flame temperature is largely determined by the residence time and pressure.

Generally, the adiabatic flame temperatures of the mixtures are between about 900 and about 1800, preferably between about 1100 and about 1650 ° C. If you work at a temperature well above

1800 ° C, substantial NO formation is obtained even at short contact times. This reduces the advantages of the invention over conventional thermal systems. A higher temperature within the defini-&gt;

however, the range is desirable, since the system requires less catalyst and thermal reactions are of an order of magnitude faster, but the adiabatic flame temperature used may be due to

448 348 such factors as the desired effluent composition and the overall design of the system. It is thus to be noted that a fuel which would normally burn at such a high temperature that it formed ΝΟ_χ,. successfully combusted within the defined temperature range 5 without, notably, NO_x~ Yield.

The catalyst used in this process generally operates at a temperature close to the theoretical adiabatic flame temperature of the fuel-air mixture which is fed into the combustion zone. The entire catalyst does not need to have this temperature, but preferably the majority or substantially all of the catalyst surface has this temperature, which is usually between about 925 and 1760.^QC, preferably between about 1100 and about 1650 ° C. The temperature in the catalyst zone is controlled by controlling the combustion of the fuel-air mixture, ie. the adiabatic flame temperature as well as the uniformity of the mixture. Fuel with relatively high energy content can be mixed with larger amounts of air to maintain the desired temperature in the combustion zone. At the upper end of the temperature range. For example, it has been found desirable to have shorter residence times for the gas in the combustion zone, to reduce the possibility of NO formation.

The residence time is largely determined by temperature, pressure and throughput, and it is generally measured in milliseconds. The residence time of the gases in the catalytic combustion zone and any subsequent thermal combustion zone may be less than about 0.1 seconds, preferably below 0.05 seconds. The turnover can. often, for example, are in the range of about 0.5 to about 10 or more million volume units of gas (standard conditions of temperature and pressure) per unit of volume of the total combustion zone per hour. For a stationary turbine in which diesel fuel oil is burned, a typical residence time can be about 30 milliseconds or less, whereas in a vehicle turbine in which petrol is burned, a typical residence time can be about 5 milliseconds or less. The total residence time in the combustion system should be sufficient for essentially complete combustion of the fuel, but it should not be so long that it is formed Ν0_χ.

A process according to the present invention is exemplified in a series of experiments in which the fuel is substantially completely combusted and a low-polluting or undesirable constituent exhaust gas is obtained. The combustion system included a source of pre-heated air under pressure. Part of the air was introduced through a pipe to the combustion zone, and the residue was used for cooling and dilution.

448 348. 22 of the combustion effluent. Lead-free gasoline is atomised in the countercurrent in the air flowing to the combustion zone, thereby ensuring intimate mixing.

In the first test series, a catalyst consisting of two bodies of monolytic honeycomb material arranged in a metal housing is used. The bodies had a nominal diameter of 150 mm and longitudinal, parallel parallel, 57 mm long flow channels. Between the end faces of the bodies facing each other was a small space, about 6 mm long. Both bodies had about 15 flow channels p per cm cross-section and the channel walls had a thickness of 0.25 mm. The catalysts had mutually the same composition and consisted of a zircon mullite honeycomb bearing a composite coating of Al₂O₂, C₂O₂ and GeOlande containing palladium.

The catalyst for these experiments was prepared by slurrying 2400 g of activated alumina powder with a particle size such that it passed through a 0.42 mm mesh aperture screen. The slurry was carried out in a mixer and. As a liquid, a solution prepared by dissolving 2526 g of Cr (NO 2) 9, 91 13 and 1382 g Ce (NO 2) 2 was used. 6H2O in 890 ml of H 2 O. The mixture was dried at 120 ° C over the weekend and the dried solid was crushed and sieved through a 0.42 mm mesh opening. Then the powder was calcined for 4 hours at 1000 ° C. 3200 g of the mixture was charged into a ball mill with a 13 liter mill drum together with 3200 ml of H 2 O and 145.4 g of palladium nitrate. The ball mill was rotated for 17 hours at 54 rpm. The slurry so obtained had a density of 1.63 g / ml, a pH of 4.20 and a viscosity of 12 cP. 1625 g of the slurry so prepared was diluted with 1180 ml of a 1% nitric acid solution. The zircon mullite honeycomb material was dipped in the diluted slurry and kept submerged. in this for 1 minute, after which it was taken out of the lick and blown with air to remove the lick excess. The thus-coated honeycomb material was dried for 16 hours at 110 ° C and then calcined for 2 hours at 500 ° C, then cooled. By this treatment, it had absorbed 11.0 weight percent coating.

The first or upstream catalyst in the casing had a catalytic coating of 13.9% by weight of the catalyst. This coating consisted of 70% by weight of AlgOy 14% by weight CrgO 2 and 16% by weight of CeOg calculated on these components. The catalyst additionally (calculated) contained 0.23% by weight of palladium in the mixture. The second catalyst or upstream catalyst had the same coating of Al₂O₂, CeO₂ and OrgO₂ constituting 11.0% by weight of the catalyst.

448 348 lys atom. The catalyst also contained (calculated) 0.18% by weight palladium in the coating.

The fuel in admixture with the total amount of air was brought into contact with the catalyst. The portion of the total amount of air not mixed with the fuel was introduced into the combustion effluent immediately after leaving the catalyst noon. This secondary air or dilution air cooled, the combustion effluent and samples of the mixture were taken for analysis. Thermocouples are provided adjacent to the inlet of the first catalyst body and at the sampling site, to determine the temperatures at these two locations.

The catalyst was heated to the reaction temperature by contact with preheated air, after which the temperature of the catalyst increased further due to the combustion which occurred at the subsequent contact between the catalyst and the air-fuel mixture. Those at

1.3 reversal of this system for two operating periods in accordance with before. The results of the present invention obtained are summarized in Table II below under column heads A and 2 respectively. B.

The same reaction system and the same procedure were used in further combustion tests using other catalyst bodies 20 disposed in the combustion zone so that there was a space between the bodies for thermal reaction. The catalysts included skeletons in the form of zircon mullite honeycomb material and the upstream catalyst 2 had about 90 parallel gas flow channels per cm of cross-sectional area. O

The upstream catalyst, on the other hand, had about 15 channels per cm. The length of the gas flow channel through the first catalyst body was mm and through the second catalysis body 25 mm. The free space between the catalyst bodies was 40 mm in the direction of flow of the gas. The catalysts had a nominal diameter of 150: mm and were prepared in the manner described above to prepare the catalysts used in experiments A and B. Both catalysts contained a coating mixture of 0 wt% A 2 O 2, 16 wt% CeOg and 14. by weight of CrgOO recalculated on these components. The coating mixture for the first catalyst was 13.5% by weight combined. of palladium in the coating mixture, and the coating mixture of the second catalyst was 15.5% by weight and contained 0.25% by weight palladium. The results obtained using this system for two operating periods in accordance with the present invention are summarized in Table II under column heads C and C, respectively. D.

The data summarized in Table II shows the efficiency of the process according to the invention to provide substantially complete combustion of relatively large amounts of fuel for a given amount.

448 348 catalyst. No backfires occurred during these trials and. the combustion effluents had extremely low levels of such materials, which are considered to be unsuitable atmospheric pollutants, i.a. nitrogen oxides.

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448 348 . .......

Those used in the invention can also be used for selected oxidation reactions. at lower temperatures. In a typical oxidation, they can be used to promote different chemical reactions, whereby a chemical compound ?, is produced. in contact with the catalyst in the presence, of free oxygen, preferably molecular oxygen. Although some oxidation reactions can occur at relatively low temperatures, many of them are carried out at high temperatures, namely at about 150 DEG-90 DEG C., and generally these reactions occur with the vapor phase reaction components. The reaction components are generally materials which undergo oxidation and. contains carbon, and. they can therefore be referred to as carbonaceous either of organic or inorganic nature. The catalysts of the present invention are particularly useful, if. it is desired to promote the oxidation of hydrocarbons, oxygen-containing organic compounds, for example, aldehydes, organic acids, and other intermediates, which occur during combustion, for example carbon monoxide and the like. These materials are often present in the exhaust gases from combustion of carbonaceous fuels and consequently the catalysts of the invention are particularly useful if one wishes to promote the oxidation of such materials and thereby purify the exhaust gases. Such oxidation can be achieved by contacting the gas with the catalyst and molecular or free oxygen.

The acid can be contained in the gas as. some of the fluent one or it may be added in the form of air or in the form of another oxygen mixture with higher or lower oxygen content. The products of such oxidation have a higher weight ratio of oxygen carbon than the material subjected to oxidation, and in exhaust gas purification these final oxidation products are much less harmful to the partially oxidized materials. Many such reaction systems are known in the art in question.

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448 348