Improved catalyst for treatment of exhaust gases from internal combustion engines.

DESCRIPTION

Catalytic converters are used to reduce the amount of pollutants emitted by cars. In order to achieve the simultaneous conversion of pollutants based on carbon monoxide, hydrocarbons and nitrogen oxides, it has become customary to use catalysts together with means of controlling the air / fuel ratio acting in response to a signal feedback from an oxygen detector found in the engine exhaust system. The air / fuel ratio control means are typically programmed to provide fuel and air to the engine at a ratio equal to or near the stoichiometric balance of oxidants and hot exhaust gas reducers, under engine speed conditions and with a stoichiometric excess of reducers during engine starting and east acceleration. The result is that the composition of the exhaust gases with which the catalyst comes into contact fluctuates almost constantly, so that the conditions to which the catalyst is exposed are alternatively clearly reducing (fuel richness) and clearly oxidizing (poverty made out of fuel). A catalyst for the oxidation of carbon monoxide and hydrocarbons and for the reduction of nitric oxide should be able to work in such a dynamic environment.

In the art, catalysts that can be used for this application are well known and are normally referred to as "three component control catalysts". For example, US 4,528,279 describes the use of cerium / lanthanum promoters in conjunction with noble metals such as platinum and rhodium as the active phase of the catalyst. The objective of adding promoters such as cerium or lanthanum is to improve the durability of the three component control catalysts after prolonged use in a vehicle. Thus, US Patent 4,528,279 teaches that the cerium / lanthanum ratio must be 0.05 to 0.3: 1 in order to obtain optimal use of the rare earths. In addition, patent 4,528,279 establishes that rare earth oxides whose positive ionic diameter is about twice that of the aluminum ion are not susceptible to form a solution solution in alumina alumina. Finally, the method of dispersing the lanthanum component in the alumina is by impregnation.

In addition, US 4,591,580 shows the use of a catalytic complex containing lanthanum, ceria and an alkali metal oxide. Here too the lanthanum component is impregnated on the alumina-based support material.

Our study of the prior art catalysts containing lanthanum oxide has shown that lanthanum oxide crystallites are at least 50 Angstroms (5 nm). The present invention, however, reveals a catalytic complex in which lanthanum oxide has an average crystal size smaller than 25 Angstroms (2.5 nm). These small crystallites are obtained by cogelation of the lanthanum component with a support that is a refractory inorganic oxide, for example alumina. A beneficial effect of having these small crystals of lanthanum oxide is that the synergistic interaction between lanthanum oxide and noble metal components, especially rhodium, increases with respect to the case in which lanthanum oxide is present as major crystallites. . The specific result of the greater interaction is that the metallical rhodium is capable of converting nitric oxide into nitrogen more effectively, after long use, than a catalyst of the prior art. In addition, the presence of lanthanum oxide as small crystallites increases the thermal stability of the support such as alumina.

The better durability of the rhodium component means that less rhodium will be required to achieve the same efficiency as with the current catalytic complexes in the prior art. This results in economic savings due to the high cost of metallic rhodium. In addition, the best efficiency can allow a car manufacturer to adjust their vehicles for better performance, while still meeting the standards. Therefore, the present invention provides several advantages over the catalytic complex of the prior art.

This invention relates to a catalytic complex and a method of manufacturing said complex for the treatment of an exhaust gas emitted by an internal combustion engine. The catalytic complex comprises a support which is a refractory inorganic oxide selected from the group consisting of alumina, salyl, titania, zirconia, aluminosilicates and mixtures thereof, which has dispersed on sai or lanthanum oxide, at least one oxide from another rare earth and by At least one noble metal component chosen from the group consisting of platinum, palladium, rhodium, ruthenium and iridium. In addition, the lanthanum oxide present in said catalytic complex is characterized by being composed of crystalline particles having an average crystal size smaller than 25 Angstroms (2.5 nm).

Following this, an embodiment of this invention is a catalytic complex comprising a support that is a refractory inorganic oxide deposited in a metallic or ceramic solid honeycomb vehicle, said support having dispersed on lanthanum saoxide, said lanthanum oxide having a medium size of crystallites less than 25 Angstroms (2.5 nm), at least one rare earth oxide and at least one noble metal component chosen from the platinum group, palladium, rhodium, ruthenium and iridium.

Thus, a specific embodiment of the invention is a catalytic complex comprising an alumina support deposited on a monolithic vehicle, said support having dispersed on lanthanum saoxide, cerium and platinum oxide and metallical rhodium.

Another embodiment of this invention is a catalytic complex, which comprises a support that is a refractory inorganic oxide, with said support being in the form of dragees and having dispersed on lanthanum saoxide having an average crystal size smaller than 25 Angstroms (2, 5 nm) and also having said support dispersed on at least one oxide of another rare earth and at least one noble metal component chosen from the group formed by platinum,

019 988 palladium, rhodium, ruthenium and iridium.

Accordingly, another specific embodiment of the invention is a catalytic complex comprising alumina spheres having lanthanum oxide, cerium oxide and platinum rhodium platinum dispersed on it.

Another embodiment of the invention is a method of manufacturing a catalytic complex, which comprises coating a vehicle in solid, metalic or ceric honeycomb, with a support that is a refactant inorganic oxyxide which has dispersed on itself lanthanum oxide having an average size of Crystallites less than 25 Angstroms (2.5 nm), and at least one rare earth oxide, calcine the resulting coated honeycomb, dispersing at least one noble metal component chosen from the group consisting of platinum, palladium, rhodium and iridium on said vehicle in coated honeycomb, and calcining and recovering the resulting catalytic complex.

Thus, in a specific embodiment of said manufacturing method, a ceramic honeycomb vehicle is coated with an alumina support having lanthanum oxide dispersed on it which has an average crystal size of less than 25 Angstroms (2.5 nm) and cerium oxide, the resulting coated honeycomb vehicle is calcined, platinum and rhodium dispersed on said vehicle in calcined coated honeycomb, and the resulting catalytic complex is calcined and recovered.

Another specific embodiment of said manufacturing method is that said lanthanum oxide is dispersed on said alumina support by means of the operations of mixing a solution of a lanthanum salt with an aluminum hydrosol, to form particles of said aluminum hydrosol which contains lanthanum, calcining said particles to form gamma-alumina particles containing lanthanum oxide and grinding, said particles calcined to provide an alumina powder containing lanthanum oxide particles having an average crystallite size of less than 25 Angstroms (2.5 nm).

Other objectives and accomplishments will be obvious after a more detailed description of the invention.

As indicated above, the present invention relates to a catalytic complex and to a method of manufacturing said complex comprising a support that is a refractory inorganic oxide which has lanthanum oxide dispersed on it, at least another rare earth oxide and at least one noble metal component chosen from the group consisting of platinum, palladium, rhodium, ruthenium and iridium.

Following this, first considering the support used in the present invention, this support can be chosen from the group consisting of alumina, silica, titania, zirconia, aluminosilicates and mixtures thereof, with alumina being preferred. When the alumina is the desired support, it is preferable that the alumina has a specific surface air that is between 75 and 200 m²/ g and more preferably between 100 and 180 m²/ g. It also preferably has a total pore volume that is between 0.25 and 0.80 cm³/ g, more preferably between 0.45 and 0.65 cm³/ g.

A second characteristic of the catalytic complex of this invention is that said support has dispersed on it lanthanum oxide present as crystallites having an average size of crystallites, as determined by x-ray diffraction, less than 25 Anstroms (2.5 nm) . Lanthanum oxide can be dispersed on said support by means of coprecipitation or cogelation of a lanthanum compound and a precursor of said support.

A third characteristic of said catalytic complex is the presence of at least one oxide from another rare earth. They are illustrative of the rare earth oxides contemplated within the scope of this invention of cerium oxide, praseodymium oxide, neodymium oxide, dysprosium oxide, europia oxide, holmium oxide and iterbium oxide. This additional rare earth oxide may be dispersed in said support based on refractory inorgainic oxide in several ways well known in the art, which would be fully exposed to me herein.

The catalyst complex of the present invention can be conveniently employed in the form of particles or the catalyst complex can be deposited on a monolithic solid vehicle. When the particle form is desired, the catalytic complex can receive forms such as pills, dragees, grains, rings, spheres, etc. The particle form is especially desirable when large volumes of catalyst complexes are needed and for use in circumstances in which a periodic replacement of the catalyst complex may be desirable. In the circumstances in which a smaller mass is desirable or in which the movement or agitation of the refractory inorganic oxide particles can cause wear and formation of dust and cause the loss of the disposed metals or an undue increase in the pressure drop to through the particles, a monolithic form is preferred.

In the use of a monolithic form, it is usually more convenient to use the catalytic complex as a thin film or as a coating deposited on an inert carrier material that provides the structural support of said catalytic complex. The inert carrier material can be any refractory material such as ceriamic or metalyl materials. It is desirable that the carrier material is not reactive with respect to the catalytic complex and is not degraded by means of the gas to which it is exposed. Examples of suitable ceramic materials include silimanite, petalite, cordierite, mullite, zirconia, zirconia, spodumene, alumina-titanate, etc. In addition, the metal materials that are within the scope of the appended claims include the metals and alloys disclosed in US Pat. 3,920,583 and which are resistant to oxidation and which, at the same time, are capable of withstanding high temperatures.

The vehicle material can be used optimally in any rigid unit configuration that provides a plurality of pores or channels extending in the direction of gas circulation. It is preferred that the configuration be a honeycomb configuration. The structure

019 988 honeycomb can be used advantageously in unit form or as an arrangement of multiple modules. The honeycomb structure is usually oriented in such a way that the circulation of gases occurs, in a genreal manner, in the same direction as the cells or channels of the honeycomb structure. For a more detailed exposition of the monolithic structures, reference can be made to US Patent 3,785,998 and US Patent 3,767,453.

Another embodiment of this invention is a method of manufacturing said catalyst complex. The first stage of this manufacturing method consists in dispersing lanthanum oxide which has an average crystallite size of less than 25 Angstroms (2.5 nm) on said support. It is envisioned that lanthanum oxide may be dispersed on said support in several ways, including coprecipitation or cogelacioan of a lanthanum compound with a precursor of said support, provided that such method originates lanthanum oxide with an average crystal size smaller than 25 Angstroms (2.5 nm).

Thus, a preferred method of dispersing lanthanum oxide over a refractory inorganic oxide is to modify the well-known oil drop method taught in US Patent 2,620,314. When alumina is the support based on refractory inorganic oxide, the modified oil droplet method comprises forming an aluminum hydrosol by any of the methods taught in the art and, preferably, reacting metal aluminum with hydrochloric acid; adding an aqueous solution of a decomposable lanthanum compound to said aluminum hydrosol; Combine the resulting mixture in hydrosol with a suitable gelation agent, and drop the resulting mixture into an oil bath maintained at elevated temperatures. The drops of the mixture remain in the oil bath until they set and form hydrogel spheres. The spheres are then continuously extracted from the oil bath and, typically, are subjected to specific curing and oil drying treatments and in an ammoniacal solution to further improve their physical characteristics. The resulting cured and gelled particles are then washed and dried at a relatively low temperature of 149-205 ° C, and subjected to a calcination process at a temperature of 455705 ° C, for a period of 1 to 20 hours. This treatment effects the conversion of the hydrogel into the corresponding crystalline gamma-alumina containing lanthanum oxide in the form of crystallites whose average size is less than 25 Angstroms (2.5 nm).

In the above process, any water soluble and decomposable lanthanum compound, including lanthanum chloride, lanthanum nitrate and lanthanum acetate, can be used. By means of the expression "decomposable metal compound" a compound is designated which, when heated in air at 500-750 ^ C for 2 to 20 hours, decomposes to give the metal oxide, for example lanthanum oxide.

If the lanthanum dispersed in said support is effective, said lanthanum oxide must be present at a concentration of 0.5 to 15 percent by the support. Preferably, the concentration of lanthanum oxide should be from 2 to 10 percent by weight of said support.

Spherical alumina or other support containing lanthanum oxide can now be impregnated with an aqueous solution of a decomposable compound of at least one metal from another rare earth, dried and at least one oxide from another rare earth. Finally, the spherical support containing lanthanum oxide and at least one rare earth oxide can then be impregnated with an aqueous solution of a decomposable noble metal compound, dried and heated in air to give a spherical catalytic complex. The details on the decomposable compounds that can be used and on other conditions to effect such impregnation are similar to the details of when a monolithic vehicle is used and will be indicated herein.

Alternatively, if a monolithic form is desired, the preferred method of preparation is as follows: the spherical support containing lanthanum oxide is ground, using normal milling processes, such as hammer milling, to give a powder having a size of particle less than about 250 μm. This powder is then added to an aqueous solution containing a decomposable compound of at least one metal from another rare earth, the resulting mixture is dried at a temperature of 100 to 150 ^ C and calcined (by "calcining" is designated the air heating) at a temperature of 500 to 750 ^ C for 2 to 20 hours, to give a perfectly dispersed rare earth oxide. It is contemplated, within the scope of the appended claims, that the drying and calcining steps can be carried out in a single stage.

Alternatively, the ground powder can be added to a colloidal suspension of the desired rare earth oxide, dried and calcined as before. When a colloidal suspension is used, the crystallite size of the rare earth oxide is usually greater than when the rare earth is impregnated using a water soluble compound. Although both methods of preparation give adequate results, it has been found that the use of a colloidal suspension is preferred.

Since the spheres prepared by the oil drop method are finally milled to give a powder, it is provided, within the scope of the appended claims, that the oil drop method can be used to form irregularly shaped particles. In this way, the parameters that must be controlled to form spheres are no longer critical. This has the economic advantage of increasing the production rate of refractory inorganic particles containing lanthanum oxide.

Illustrative of the rare earths that can be used in the present invention are cerium, praseodymium, neodymium, dysprosium, europium, holmium and ytterbium. In addition, examples of such water soluble and decomposable rare earth compounds are cerium acetate, neodymium acetate, europium acetate, holmium acetate, ytterbium acetate, praseodymium acetate, cerium nitrate , lanthanum nitrate, neodymium nitrate, europium nitrate, ni4

019 988 holmium treatment, ytterbium nitrate, praseosimium nitrate, dysprosium nitrate, cerium chloride, lanthanum chloride, neodymium chloride, europium chloride, holmium chloride, ytterbium chloride, praseodymium chloride and dysprosium chloride. Regardless of how to apply this metallic compound from another rare earth to said refractory inorganic oxide support, the refractory inorganic oxide support containing lanthanum oxide and at least one metal compound from another rare earth is dried and calcined at air at a temperature of 400 ^ to 700 C for 1 to 3 hours to give a support containing lanthanum oxide and at least one rare earth oxide. The concentration of the rare earth oxide may vary considerably but is conveniently chosen to be from 5 to 35 percent by weight of the support and, more preferably, from 15 to 25 percent by weight of said support.

In the next stage of this example of the method of preparation, a suspensioan is prepared using the support containing delantane oxyanorobenzene oxide of another rare earth. The suspension can be prepared by means known in the art such as combining the appropriate amounts of the support with an aqueous solution of an acid, such as nitric acid, hydrochloric acid, sulfuric acid, etc. The resulting suspension is ground with a ball mill for 2 to 6 hours to form a usable suspension. Other types of mills, such as crash mills, can be used to reduce the grinding time to 5-30 minutes. This suspension can then be used to deposit a thin film or coating on the molistic vehicle by means well known in the art. One such method includes immersing the monolithic vehicle in said suspensioan, blowing off the excess suspensioan and drying and calcining in the air at a temperature of 500 ^ to 700 C for 1 to 4 hours. This process can be repeated until the desired amount of support containing lanthanum and at least one other rare earth in said monolithic vehicle is achieved. It is preferred that the support, such as alumina, be present in the monolithic vehicle in amounts ranging from 28g to 355g of support per liter of vehicle volume, the volume being measured by means of the exterior dimensions of the monolithic vehicle structure.

It is further envisaged, within the scope of this invention, that additional rare earth may disperse in the support containing lanthanum oxide after the support has been deposited on said monolithic vehicle. Thus, a suspension is prepared from said support containing lanthanum oxide, by means known in the art such as those described above. This suspension is then applied to a monolithic vehicle as described above to give a coating of said support in said monolithic vehicle. Next, at least one oxyxide from another rare earth is dispersed on said support by impregnating said monolithic vehicle coated with said support by means of an aqueous solution of a rare earth decomposable compound, dried and calcined. Alternatively, said monolithic vehicle can be submerged in a colloidal suspension of the desired rare earth oxide, dried and calcined.

The final stage, in this example of the preparation method, is to disperse at least one noble metal component onto said support that covers said monolithic vehicle. The noble metal can be chosen from the group consisting of platinum, palladium, rhodium, ruthenium or iridium and mixtures thereof. The noble metal can be deposited on the support in any suitable way. An example of a method of dispersing the noble metal on the support involves impregnating the monolithic vehicle, which has a coating of said support, with an aqueous solution of a decomposable compound of the metal or of the desired noble metals.

Illustrative of the decomposable compounds of such noble metals are chloroplatanic acid, ammonium chloroplatinate, platinum (II) hydroxydisulfite acid, bromoplatinic acid, platinum tetrachloride hydrate, sodium dinitrodiaminoplatin, sodium tetranitroplatinate, rhodium trichloride , rhodium hexaamine chloride, rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate, sodium hexachlorodate, sodium hexanitrorrodate, Chloropaladic acid, palladium chloride, palladium nitrate, diaminepladium hydroxide, tetraamine palladium chloride, acid hexachloroiridate (IV), acid hexachloroiridate (III), dichlorodihydrooxoiridate ammonium (III) acid (III) ), Amoanic Acohexachloroiridate (IV), Tetraaminadichloroiridate Chloride (III) and Acute Tratraminenairidate Chloride (III), Ruthenium Tetrachloride, Hexachlororrutenate and Ruthenium Hexaamine Chloride. Of the compounds listed above, to disperse the desired noble metal, the following are preferred: platanic chlorine acid, rhodium chloride, chloropaladic acid, hexachloroiridate (IV) acid and hexachlorrutenatol.

For the three component control operation, it is desirable that the catalyst complex contains a combination of rhodium and platinum, palladium or mixtures thereof. Specific combinations include platinum and rhodium, palladium and rhodium and platinum, palladium and rhodium. However, under certain circumstances, for example when it is not necessary to control the nitric oxide, it is undesirable (from an economic point of view) that the catalytic complex contains rhodium. In this case it is desirable that the catalyst complex contains platinum, palladium and mixtures thereof.

When more than one noble metal is desired, the metals may be in common aqueous solution or in separate aqueous solutions. When separate aqueous solutions are used, the impregnation of said first support with said noble metal solutions can be carried out sequentially, in any order. Finally, hydrogen chloride, natric acid or other suitable materials may be added to said solutions, in order to further facilitate the uniform distribution of the noble metal components throughout the entire support.

When such support must be deposited so5

019 988 on a solid monolithic vehicle, said support can be impregnated with said aqueous noble metal solution, either before, or after, of the deposition of the support on said monolotic solid vehicle. Of the two processes, the most convenient way is to arrange the noble metal by impregnating it on the support containing lanthanum oxide and at least one oxide from another rare earth, after it has been deposited on said monolithic solid vehicle with an aqueous solution of the noble metal component, and air dry and calcine at a temperature of 400 ° to 500 ° C for a time of 1 to 4 hours. It should be noted that the two methods of dispersing noble metals can provide non-equivalent catalytic complexes.

It is preferable that said noble metal component is present in an amount of 0.01 to 4 percent by weight of the support. Specifically, in the case of platinum and palladium, the amount is between 0.1 and 4 percent by weight. In the case of rhodium, ruthenium and iridium, the amount is between 0.01 and 2 percent by weight.

As already indicated above, one of the advantages of the present invention is that well dispersed lanthanum oxide stabilizes refractory inorgaonic oxide, especially alumina, at temperatures as high as 1,250 ° C. In addition, after a prolonged test of durability at a temperature of 760 ° C, the catalytic complex of the present invention is more effective in treating an exhaust gas emitted by an internal combustion engine than a catalytic complex of the prior art. . Particularly important is the ability of the catalytic complex of the present invention to convert the nitric oxide emissions from said exhaust gas into harmless gases.

Finally, in another embodiment of the present invention there is provided a process for the treatment of exhaust gases, especially exhaust gases emitted by an internal combustion engine, which comprises causing said gases to come into contact with the catalytic complex described herein. .

In order to more fully illustrate the advantages derived from the present invention, the following examples are given. It should be understood that the examples are only given by way of illustration and that they are not intended to impose undue limitation in the wide scope of the appended claims.

Example I

This example describes the preparation of alumina spheres containing lanthanum oxide. The basic oil drop process is that found in US Patent 2,620,314. To 1,250 ml of alumina sol containing 13.5 percent by weight of aluminum, at an Al / Cl ratio of 1.4, 43.1 g of LaCl were added₃.6H₂O. This mixture was treated as described in patent 2,620,314 to give gamma-alumina spheres containing 5 percent by weight of lanthanum oxide.

Example II

The spheres of Example 1 were used to prepare a catalytic complex as follows: 3.145 g of the spheres were milled to give a powder having an average particle size of less than 250 μm. This powder was added to 2,783 g of a colloidal solution of cerium oxide (20 weight percent of Ce), 103.2 ml of concentrated HNO3 and 3.1 liters of deionized H2O and ground using an Eiger Model No. ABML-75 for 10 minutes.

An oval-shaped cordierite monolith with an axis smaller than 8 cm, a length of 14.3 cm, a length of 12 cm and having 400 square channels per square inch (approximately 6.35 cm) was immersed in the suspension described above.²) of facial area. After immersion, the excess suspension was removed by blowing with an air gun. The suspension coated monolith was calcined in air for approximately 1 hour at 540^°C. The above-described immersion, blow and calcination steps were repeated until the monolith contained 160 g of coating per liter of monolith volume.

The washing-coated monolith described above was then impregnated with the metal platinum and rhodium. The monolith described above was immersed in an aqueous solution containing 1.40 mg of platinum (in the form of chloroplatinic acid) per gram of dissolution and 0.06 mg of rhodium (in the form of rhodium chloride) per gram of dissolution. After immersion, the excess solution was removed by blowing with an air gun, dried and calcined for about an hour at 540^°C. This catalytic complex was designated "Catalyst A". The calculated composition of Catalyst A in percentage units by weight of alumina was Pt = 1.0%, Rh = 0.05%, Ce = 19.4% and La = 5.3%. Catalyst A contained 120g of Al2O3 per liter of vehicle volume.

Example III

The conventional catalytic complex was prepared by the following method: In a flask 6,300 grams of pseudobohemite alumina and 10,800 grams of an aqueous solution of LaCl3.6H2O (3.1 percent by weight of La) were mixed, stirred for 30 minutes , were transferred to a cuvette deep, dried for 4 hours at 150^°C and finally calcined in the air at 600^°C for 1 hour. Next, 4,000 grams of calcined lanthanum alumina / oxide powder was stirred in a vessel containing 3,565 ml of a colloidal solution of cerium oxide (20 weight percent of Ce), 246.2 g of concentrated HNO3 and 4 liters of deionized H2O and ground using an Eiger Model n mill^° ABML-75, for 10 minutes.

An oval-shaped cordierite monolith with an axis less than 8 cm, a length of 14.3 cm, a length of 12 cm and having 400 square channels per square inch (approximately 6.35 cm) was immersed in the suspension described above.²) of facial area. After immersion, the excess suspension was removed by blowing with an air gun. The monolith coated with calcined suspension for about 1 hour at 540^°C. The above-described immersion, blowing and calcination stages were repeated until the monolith contained 160 g of

019 988 coating per liter of monolith volume.

Next, the wash-coated monolith described above was impregnated with the metallic platinum and rhodium. The monolith described above was immersed in an aqueous solution containing 1.40 mg of platinum (in the form of chloroplatonic acid) per gram of dissolution and 0.06 mg of rhodium (in the form of rhodium chloride) per gram of dissolution. After immersion, the excess dissolution was removed by blowing with an air gun and was calibrated for about an hour at 540^°C. This catalytic complex was designated "Catalyst B". The calculated composition of Catalyst B in percentage units by weight of alumina was Pt = 1.0%, Rh = 0.05%, Ce = 19.4% and La = 5.3%. Catalyst B contained 120 g of Al2O3 per liter of vehicle volume.

Example IV

Spheres were prepared as in Example I and characterized as follows: The surface air of the spheres containing lanthanum turned out to be 140-170 m²/ g. The pore volume of said spheres was 0.467 cm³/ g of sample. A sample of said spheres was ground to give a powder and analyzed by x-ray diffraction to determine the identity of the crystalline species. The x-ray diffraction spectrum only showed the presence of gamma-alumina. This means that all the lanthanum is perfectly dispersed and that the particles are less than 25 Angstroms (2.5 nm) (the detection limit of the x-ray diffraction technique).

A second sample of the spheres was treated at 1,100^°C for 2 hours in an atmosphere of 10% water vapor and 90% air. After this treatment, the superficial air turned out to be 76 m²/ g and the pore volume was 0.204 cm³/ g of sample. In addition, X-ray diffraction demonstrated that theta-alumina was the main phase of alumina, with some gamma and delta-alumina being present. No lanthanum species were detected.

A third sample of spheres was treated at 1,250^°C for 2 hours in an atmosphere of 10% water vapor and 90% air. After this treatment, the superficial air was found to be 38 m²/ g and the pore volume was 0.101 cm³/ g of sample.

Example V

An alumina powder was impregnated with La (NO3) 3.6H2O as described in the Example

III. This sample had a 260 m surface area²/ g and a pore volume of 0.74 cm³/ g. The analysis by x-ray diffraction demonstrated the presence of gamma-alumina and lanthanum oxycarbonate. The reason why lanthanum oxycarbonate was formed instead of lanthanum oxide is that the impregnated material was calcined in an oven heated with gases whose exhaust contained unburned methane and carbon monoxide.

A second sample of the alumina powder containing lanthanum was treated at 1,100^°C for 2 hours in an atmosphere of 10% water vapor and 90% air. After this treatment, the surface area of ​​the powder was 90 m²/ g and pore volume was 0.510 cm³/ g. The X-ray diffraction spectrum demonstrated the presence of theta-alumina as the main phase and of LaAlO3, gamma-, delta- and alpha-alumina as minor phases.

Finally, a third sample of said alumina powder containing lanthanum was treated at 1,250^°C for 2 hours, in a 10% atmosphere of water vapor and 90% air. After this treatment, the superficial air was 6 m²/ g and the pore volume was 0.015 cm³/ g.

Comparing the results of Example V with those of Example IV, we observe that the complex of the present invention does not form LaAlO3 at high temperatures and stabilizes the alumina more effectively than the prior art complex at temperatures as high as 1,250^°C. Example VI

A reference catalytic complex was prepared by means of the following method: In a flask 5,000 grams of pseudobohemite alumina and 13,562 grams of a cerium acetate solution (7 percent by weight of cerium) were mixed, stirred for 30 minutes, transferred to a shallow bucket, dried for 4 hours at 150^°C and finally calcined at 600^°C for 1 hour. The calcined alumina / cerium oxide oxide was then stirred in a vessel containing 5.33 liters of water and 48 ml of concentrated nitric acid (HNO3). This mixture was ground for 4 hours in a ball mill.

An oval-shaped cordierite monolith with an axis less than 8 cm, a major axis of 14.3 cm, a length of 12 cm and having 400 square channels per square inch (approximately 6, was immersed in a suspension described above. 35 cm²) of facial air. After immersion, the excess suspension was removed by blowing with an air gun. The suspension coated monolith was calcined for approximately 1 hour at 540^°C. The above-described immersion, blow and calcination steps were repeated until the monolith contained 8 g of coating per liter of monolith volume.

The washing-coated monolith described above was then impregnated with the metallic platinum and rhodium. The monolith described above was immersed in an aqueous solution containing 1.40 mg of platinum (in the form of chloroplatonic acid) per gram of dissolution and 0.06 mg of rhodium (in the form of rhodium chloride) per gram of dissolution. After immersion, the impregnated monolith was dried and calcined for about an hour at 540^°C. This catalytic complex was designated "Catalyst C". The calculated composition of Catalyst C in percentage units by weight of alumina was Pt = 1.0%; Rh = 0.05%; and Ce = 19.4%. Catalyst C contained 120 g of Al2O3 per liter of vehicle volume.

Example VII

Samples of the AyCseguón Catalysts Examples II and VI were prepared. Each one was mounted on a converter and placed in the exhaust current of a gasoline engine. This was achieved by placing a converter in the exhaust current from a block of an engine in V-8 and the other converter in the current of es7

019 988 cape of the other V-8 engine block. The engine was worked following the following cycle:

The engine used for the durability cycle was a 5.01, V8 Ford engine, equipped with a dual fuel body fuel injector. The durability cycle consisted of a speed operation for 60 seconds and a fuel cut operation for 5 seconds. During the operation of the scheme, the engine worked stoichiomatically, while during the fuel cutting operation the engine worked in a state of fuel poverty that included a temperature and oxygen tip. The fuel cutting operation will be achieved by cutting the circuit between one of the fuel injectors and the electronic control of the engine. The engine speed and the load on it were adjusted to give an exhaust gas temperature of 760 ° C during regime operation and 704 ° C during fuel cutting operation. This cycle was repeated for 100 hours.

Example VIII

Samples of Catalysts B and C were prepared as in Examples III and VI and tested for durability as in Example VII.

Example IX

Catalysts A and C of Example VII and Catalysts B and C of Example VIII were evaluated in their new state, after 20 hours and after 100 hours of exposure to the duration capacity cycle of Example VII. The evaluation test was carried out using an engine dynamometer that measures the behavior of the catalyst (hydrocarbons, carbon monoxide and nitric oxide) based on air / fuel (A / C). The test included the evaluation of the catalyst at seven different points of the A / C ratio (14.71, 14.66, 14.61, 14.56, 14.51, 14.46 and 14.41), at a temperature 450 input^°C. At each A / C point, the air / fuel ranged by plus or minus 0.1 A / C at a frequency of 1 Hertz. The conversions of hydrocarbons, carbon monoxide and nitric oxides at each A / C were calculated and then a conversion of integral behavior was obtained by averaging all conversions.

Since a sample of the reference catalyst (Catalyst C) had been tested for durability and evaluated with Catalyst A (catalyst of the present invention), and Catalyst B, (catalyst of the prior art), it was obtained a relative difference between Catalysts A and B. This relative difference was calculated as follows: First, the conversion of Catalyst C was subtracted from the conversion of Catalyst A. This difference was called X. Next, the conversion of Catalyst C was subtracted from the conversion of Catalyst B. This difference was called Y. Finally, Y was subtracted from X to give the relative difference between Catalysts A and B.

Thus, if AB (obtained from XY) is a positive number, it means that Catalyst A is a more effective catalyst than Catalyst B in the conversion of contaminants into harmless gases, while a negative number means that Catalyst A is a less effective catalyst than Catalyst B. The results of these evaluations are presented in Table 1.

Table 1

<td>H</td><td colspan="3">D Integral behavior (%)</td>

<td> 0</td><td>HC two</td><td>CO one</td><td>NOx 3</td>

<td> 20</td><td> 4</td><td> 0</td><td> 2</td>

<td> 100</td><td> 2</td><td> -2</td><td> 7</td>

Being:

H = Hours in the durability cycle D = Relative differences between Catalysts A and B (A - B)

The results presented in Table 1 clearly show that, after 100 hours of durability test, the catalyst of the present invention (Catalyst A) is more effective in the conversion of the nitric oxides into harmless gases than the catalyst of the previous technique (Catalyst B). The difference observed in the conversion of hydrocarbons and carbon monoxide is within the experimental error of the evaluation test and, therefore, the two catalysts are equivalent with respect to these two pollutants. Therefore, the catalyst of the present invention shows unexpected results with respect to the catalyst of the prior art.

Example X

Catalysts A and C of Example VII and Catalysts B and C of Example VIII were evaluated, in their new state, after 20 hours and after 100 hours of exposure to the duration capacity cycle of Example VII. The evaluation test was a continuous temperature run test with an A / C ratio of approximately 14.55. During this test, the temperature of the exhaust gases entering the converter was continuously varied from 200^°C up to 460^°C, by varying the heat transfer rate of a stainless steel thermal exchanger. The conversion of hydrocarbons, carbon monoxide and naxide oxides was calculated as a function of temperature. The time needed to reach a conversion of 25% is a common criterion used to evaluate catalytic complexes (called “light off performance”, that is to say “basic behavior”) and is indicated here. The results of these evaluations are presented in Table 2.

The results presented in Table 2 were obtained as described in Example IX. For the results in Table 2, a negative number means that Catalyst A (catalyst of the present invention) will achieve the conversion of

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25% at a lower temperature than Catalyst B (catalyst of the prior art). Thus, a negative number means that Catalyst A is more active, that is, it is a better catalyst than Catalyst B.

Table 2

<td>H</td><td colspan="3">D</td>

<td></td><td>HC</td><td>CO</td><td>NOx</td>

<td> 0</td><td> -40</td><td> -53</td><td> -66</td>

<td> 20</td><td> -19</td><td> -19</td><td> -19</td>

<td> 100</td><td> 26</td><td> -34</td><td> -38</td>

Being:

H = Hours in the capacity cycle

D = Relative difference in T25 * between Catalysts A and B (A - B) * Temperature (° C) necessary to reach a conversion of 25%.

The results indicate that the catalytic complex of the present invention (Catalyst A) reaches a conversion of 25% hydrocarbons, carbon monoxide and nitric oxide at a temperature much lower than the catalyst of the prior art (Catalyst B). The magnitude of the difference between Catalysts A and B is very large, indicating that Catalyst A has substantially better activity than Catalyst B. In addition, this best activity is observed when both catalysts are new and after 100 hours of durability test. Therefore, the catalyst of the present invention shows unexpected results with respect to the catalyst of the prior art.

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