RU2146174C1 - Method of catalyst preparation and catalyst for cleaning of exhaust gases of internal combustion engines - Google Patents

Abstract

FIELD: methods of catalysts preparation, and catalysts for cleaning of exhaust gases of internal combustion engines. SUBSTANCE: method of catalyst preparation includes preliminary high-temperature treatment of block metallic inert carrier, application to carrier of coating from aluminum oxide in aqueous solution of caustic soda with direct dissolving of aluminum chips, subsequent impregnation of carrier with solutions of salts of rare-earth and noble metals, drying, calcination and reduction. Method is distinguished by the fact that carrier is treated in calcining kiln in flow of air or oxygen. Coating from aluminum oxide is applied at temperature of not in excess of 40 C. Catalyst for cleaning of exhaust gases of internal combustion engines is also described. The invention allows to reduce number of stages and time of process and process costs, to increase quality of catalyst, its efficiency and service life, to improve uniformly of its coating and strength of adhesion with surface of initial metallic block and to improve structural characteristics of secondary coating from aluminum oxide. EFFECT: higher efficiency. 5 cl, 1 tbl, 12 ex

Description

 The invention relates to methods for producing catalysts containing active components on the surface of block metal carriers, and can be used to obtain catalysts for the deep oxidation of carbon monoxide, hydrocarbons and the reduction of nitrogen oxides in the complex treatment of exhaust gases of internal combustion engines (ICE) and chemical and other productions.

Known methods for producing catalysts on carriers of a honeycomb structure with multi-channel openings in the direction of gas flow. The most common methods for producing cellular monolithic catalysts for the purification of exhaust gases of internal combustion engines and other mixtures of carbon oxides, hydrocarbons and nitrogen include two stages. In the first stage, a secondary carrier is applied to the block, into which then, in the second stage, the active components are introduced. Due to the fact that ceramic and metal block carriers obtained under high temperature conditions have a small specific surface area (0.01-0.65 m ² / g), they are increased before application of the active components by layering mainly aluminum oxide (Al ₂ O ₃ ).

In addition to Al ₂ O _3, mixtures thereof are used with silica (Al ₂ O ₃ : SiO ₂ = 20: 1), other oxides (TiO ₂ , ZrO ₂ , SnO ₂ , MnO ₂ , CoO, SrO ₂ , BaO) [Pat. 217998 France, 1984; Pat. 51-20358 Japan, 1976; Pat. 1446856 Great Britain, 1976], as well as oxides of rare-earth elements (La, Ce, Pr, Sm). For bonding Al ₂ O ₃ with the surface of block supports, organophosphorus compounds (trimethyl phosphate), azo compounds, which are applied to the surface before Al ₂ O _{3, are used} . In some cases, for the formation of an Al ₂ O ₃ layer on honeycomb carriers, organic aluminum salts of dialkyl hydride, C ₂ -C ₂₀ trialkyl, aluminum propylate, and others [Pat. 1320383 Great Britain, 1973]. According to various sources, the thickness of the layer of the applied secondary carrier (coating) reaches 2-300 microns (0.25-25 mm). To increase the adhesion strength of the applied Al ₂ O ₃ with a monolithic ceramic support, it is recommended to use Al ₂ O ₃ with colloidal SiO ₂ and treat the oxide coating with nitrates of Al, Ba, La [Pat. 3956186 USA, 1976].

 The known method described in [US Pat. 4587231 USA, 1986], where, in order to obtain a block catalyst for the treatment of exhaust gases of internal combustion engines, the initial monolithic carrier is repeatedly treated with an alumina suspension in which aluminum oxide powder containing cerium oxide is dispersed. The carrier treated with the suspension is calcined and the active substances — platinum group metals — are precipitated onto the aluminum oxide coating.

 The main disadvantage of this method of preparing a block catalyst is the low adhesion strength of the alumina coating to the surface of an inert carrier. The weighted amount of applied oxide coating does not exceed 10 wt.%, Which is clearly not enough to obtain the required specific surface area and catalyst efficiency.

The closest in technical essence and the achieved effect is the method (prototype) described in [US Pat. 2005538 RF, 1992], where in order to obtain a block catalyst for the treatment of exhaust gases of internal combustion engines, steel corrugated and rolled into a block foil with the content of chromium 15-23 wt.% And aluminum 4.5-5.1 wt.% Are used as the initial inert carrier . An inert metal block is calcined in a muffle furnace (in a confined space) to create a roughness of the metal surface, then the block is degreased by boiling for 1 hour in a solution of caustic soda, washed, dried. Next, a secondary coating of alumina (in a 0.7-1.5% NaOH solution) is applied to the metal block by directly dissolving aluminum chips in it at a temperature of 60-80 ^o C, followed by washing, drying and heat treatment at 500 ^o C. Alumina is impregnated with aqueous solutions of the salts Ce (NO ₃ ) ₂ , H ₂ PtCl ₆ , PdCl ₂ and RhCl ₃ , followed by drying, calcination and reduction of the active substances (Pt, Pd, Rh) with hydrogen.

 The main disadvantage of this method of preparation of the catalyst is the rather low adhesion strength of the alumina coating to the surface of the inert carrier, the unevenness of its coating, which reduces the quality of the catalyst and the duration of its operation. In addition, the process of preparing the catalyst according to the above method is quite lengthy, multi-stage and time-consuming.

 The technical task of the present invention is to reduce the process time, shorten the stages, improve the quality of the catalyst by stabilizing the coating of aluminum oxide, improving its structure and adhesion.

 The essence of the proposed method for producing a catalyst is as follows.

A cold-rolled Al-containing steel foil is taken as an inert carrier. It is corrugated, rolled into a block and subjected to oxidation in a stream of air or oxygen at a speed of 1000-2000 l / h at a temperature of 920-990 ^o C for 20-24 hours. It is the proposed regime of heat treatment of an inert metal carrier in the air stream that allows high-quality oxidation of aluminum, which is contained in the surface layer of the metal carrier. In this case, a uniform layer of surface aluminum oxide is obtained on the surface of the metal block, the particles of which then become crystallization centers upon further application of the secondary coating of aluminum oxide in an aqueous solution of NaOH upon direct dissolution of Al-chips. As a result of heat treatment of the carrier in the air stream, a uniform, strongly bonded Al ₂ O ₃ coating with good structural characteristics is obtained, which provides an increase in the quality and efficiency of the finished catalyst. In addition, the proposed method of heat treatment of the initial block metal carrier allows you to completely get rid of oil and other contaminating surfaces of substances, as a result of which the stage of degreasing the initial carrier, described in the prototype, following the stage of heat treatment, can be completely eliminated, which significantly reduces the process time.

Then, a secondary coating of alumina in an aqueous solution of alkali (NaOH) with a concentration of 7.5-8.0 g / l is applied to the heat-treated metal block with the direct dissolution of Al chips in it at the rate of 3.0-4.8 g / 1 l of the solution at room temperature for 1-3 hours. Next, the temperature is raised to 35-40 ^o C (not higher than 40 ^o C) and the unit is kept for 4-6 hours. Then the solution is cooled and final block is held at a temperature of 25-30 ^o C for 15-20 hours, after which the block is washed, dried and calcined at a temperature of 520-550 ^o .

The alumina coated block is impregnated with aqueous solutions of H ₂ PtCl ₆ and PdCl ₂ salts, followed by drying and reduction of platinum and palladium to a metallic state. This gives a platinum, platinum-palladium catalyst for purification of exhaust gases of diesel engines. In order to clean the exhaust gases of gasoline ICEs, a platinum-rhodium or platinum-palladium-rhodium catalyst with cerium oxide additives is prepared (except Ce, additives of Za oxide and other REEs can be used). The latter is necessary as a heat-stabilizing additive, since during the operation of gasoline ICE there can be overheating of up to 1000 ^o C. In the case of catalysts for passenger cars with a gasoline engine, an aluminum oxide-coated block is impregnated with an aqueous solution of Ce (NO ₃ ) ₂ , dried, calcined, and finally , impregnated with aqueous solutions of noble metal salts (Pt, Pd, Rh), followed by drying and reduction in a stream of H ₂ at 350-400 ^o C. In the exhaust gas purification catalysts ICE often use palladium, as less expensive, in order to reduce the cost of the catalyst, t .to. Pt and Rh prices have risen substantially in recent years.

The inventive method allows to reduce the time of the technological process, to reduce the number of stages and to obtain a catalyst having high efficiency in the processes of purification of gas emissions from CO, CH _x , NO _x due to the stabilization of the secondary coating of Al ₂ O ₃ , improving its structure, adhesion and uniformity of application .

(100-150

~40%; 1100-1200

~30%, а на остальные размеры радиуса пор ~20%), при содержании оксида алюминия 10-20 мас. %, что обеспечивает необходимые эксплуатационные характеристики катализаторов очистки ОГ ДВС.The fabricated alumina coating has high beats. surface: 100-180 m ² / g, has a total pore volume of 0.3-0.6 cm ³ / g, the predominant pore radius in the range of 100-1200

(100-150

~ 40%; 1100-1200

~ 30%, and for the remaining sizes of the pore radius ~ 20%), with an alumina content of 10-20 wt. %, which provides the necessary operational characteristics of the exhaust gas purification catalysts for internal combustion engines.

 Thus, the efficiency and quality of the obtained catalyst depends on the characteristics of the secondary coating of aluminum oxide, which in turn depend on the parameters of the process: temperature and heat treatment time of an inert metal carrier, air flow rate in the calcining furnace, and the temperature and time of dissolution of aluminum chips in a solution of caustic soda. The relationship of the quality of the catalyst and the conditions of its preparation are shown in the table.

 Example 1

From corrugated foil brand X23YU5 (or X20YU5) with a thickness of 0.05 mm and a width of 30 mm, a block with a diameter of 25 mm is rolled up. In a calcining furnace, the metal block carrier is calcined at a temperature of 920-950 ^° C. for 24 hours in a stream of air passing continuously through the furnace at a speed of 1500 l / h. Next, a block weighing 10.0 g is placed in a glass beaker with 100 ml of an aqueous solution of NaOH with a concentration of 7.5-8.0 g / L. Then, Al-shavings are poured into the glass (at the rate of 3.0-4.8 g / 1 L NaOH solution).

The process of dissolution of Al is carried out first at room temperature (20-25 ^o C) for 2 hours. The solution in the glass after loading Al-shavings into it acquires a milky-white color due to the intense evolution of hydrogen gas. The reaction proceeds intensively at room temperature for 1-3 hours, after which the solution brightens, i.e. gas evolution decreases. Then raise the temperature to 35-40 ^o C and incubated at this temperature for 4 hours.

If the temperature rises above 40 ^o C, the process of dissolving Al chips in an alkali solution is significantly accelerated, gas evolution increases, the solution simply "boils". This will subsequently lead to uneven coating of the metal surface of the source block with aluminum hydroxide.

During block exposure, almost complete dissolution of Al chips occurs. If this process is carried out at a temperature of 25-30 ^o C, then the exposure block is carried out for 15-20 hours. Next, the block is removed, thoroughly washed with distilled water, dried at 100-120 ^o C for 1-2 hours. The dried block is subjected to heat treatment in a calcining furnace. The temperature is raised at a rate of 20 ^o C per hour to 550 ^o C.

After the end of the heat treatment mode, the furnace heating is turned off and the unit is cooled to 100 ^o C, then it is discharged from the furnace, weighed, and the percentage of supported aluminum oxide is determined. In example 1, the content of Al ₂ O ₃ is 15.0 wt.%.

During the application of the secondary oxide coating, the surface of the block metal carrier is uniformly coated with a high adhesion Al ₂ O ₃ layer. The obtained properties of Al ₂ O ₃ further provide high efficiency of the catalysts. Then carry out the application of active substances - noble metals, in example 1 - only platinum. Prepare an impregnation solution at the rate of 1.0 g Pt (met.) Per 1 liter of block. Met. the block is impregnated with an aqueous solution of salts of platinum chloride hydrochloric acid by moisture capacity (20 ml of solution per 1 block with a volume of 25 l), dried at 100-120 ^o C for 1-2 hours. The dried block is placed in a reduction furnace, where Pt ⁴⁺ ions are reduced to a metallic state (Pt ^o ). The oven is first purged with nitrogen gas for 1 hour at room temperature. Then hydrogen is heated up to 400 ^o C, and held at 350-400 ^o C for 5 hours, after which the furnace is purged again with nitrogen and cooled to room temperature.

The values of the characteristics of the substrate were measured by the method of mercury vaporometry (r _pore , v _pore ) and low-temperature nitrogen adsorption (S _beats ).

v_пор. - 0,47 см³/г.The resulting finished catalyst based on steel grade X23U5 (Cr - 23.0%, Al - 5.1%) contains
Al ₂ O ₃ - 15 wt.%,
Pt - 0.1 wt.%,
and the aluminum oxide substrate has the following characteristics:
S _beats - 120 m ² / g,
r _then - 100-1200

v _then - 0.47 cm ³ / g.

 Similarly, the catalyst samples were prepared in examples 3-12 with a change in the parameters indicated in the table.

As can be seen from the table (Sample N 7-12), going beyond the limits stated in the invention parameters (temperature, calcination time of the source medium and the air feed rate) leads to a decrease in the specific surface of the secondary substrate (Al ₂ O ₃ ), erosion of the distribution the radius of the pores and, as a result, a decrease in the catalytic activity of the catalyst samples (an increase in the temperature at which 90% conversion of carbon monoxide, propane and nitric oxide is achieved).

Claims (5)

1. A method of preparing a catalyst for purification of exhaust gases of internal combustion engines, including preliminary high-temperature treatment of a block metal inert carrier, coating it with alumina in an aqueous solution of caustic soda with direct dissolution of aluminum chips, followed by impregnation of rare-earth and noble salts with aqueous solutions metals, drying, calcining and recovery, characterized in that the processing of the carrier is carried out in a calcining furnace in the outflow of air or oxygen and the coating of alumina is carried out at a temperature not exceeding 40 ^o C.  2. The method according to p. 1, characterized in that the processing of the carrier is carried out at a flow rate of air or oxygen of 1000 to 2000 l / h 3. The method according to PP.1 and 2, characterized in that the processing of the carrier is carried out at 920 - 990 ^o C.  4. The method according to claim 3, characterized in that the processing of the carrier is carried out for 20 to 24 hours 5. The catalyst for purification of exhaust gases of internal combustion engines, consisting of a block metal inert carrier, the surface of which contains a coating of aluminum oxide with an active phase of rare earth and noble metals deposited on it, characterized in that the coating of aluminum oxide has the following characteristics: content Al ₂ O ₃ 10 - 20 wt. %, specific surface area 100 - 120 m ² / g, predominant pore radius from 100 to 1200

, the total pore volume of 0.3 - 0.6 cm ³ / year

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