RU2146559C1 - Method of preparing platinum-rhodium or palladium-rhodium catalyst on ceramic carrier - Google Patents

Abstract

FIELD: hydrogenation catalysts. SUBSTANCE: carrier is successively impregnated with aqueous solution of platinum or palladium-containing compound and then with aqueous solution of rhodium-containing compound, provided that, in order to homogeneously distribute Pt(Pd)+Rh at 1:1 ratio, dichlorotetramminoplatinum or - palladium aqueous solution is first used for impregnation, after which catalyst is dried and then impregnated with aqueous solution of rhodium pentachloride ammonium salt to form, on the surface of carrier, low- soluble binuclear complex [M(NH₃)₄][RhL₆] wherein M is Pt or Pd and L is chloride ion or water molecule. Catalyst is finally dried and calcined. EFFECT: increased catalytic activity at low temperatures (150-160 C). 4 tbl, 6 ex

Description

 The invention relates to catalytic chemistry, in particular to methods for producing catalysts for neutralizing exhaust gases of internal combustion engines.

 One of the main requirements for modern TWC (three-functional catalysts) exhaust gas conversion catalysts is their high activity in neutralizing harmful emissions not only during operation, but also at the time of engine start-up. This problem is solved by the additional activity of the Pt / Pd / Rh catalyst deposited on a developed ceramic substrate.

Known methods for producing catalysts for the conversion of fuel combustion products, based on the impregnation of a ceramic substrate, mainly γ - Al ₂ O ₃ , a solution of mononuclear compounds of platinum metals, followed by reduction to metal.

 The disadvantage of these methods is the lack of homogeneity in the distribution of two or more different platinum metals in the surface layer, which reduces the activity of the catalyst [R. M. Heck, R.J. Farrauto. Catalytic air pollution control New York. Van Noctrand Reinhold. 1995. p. 42].

The closest in technical essence to the present invention is a method for producing a Pt / Rh catalyst by sequentially impregnating a ceramic substrate (γ-Al ₂ O ₃ ) with aqueous solutions, first Pt (NO ₂ ) ₂ (NH ₃ ) ₂ , then rhodium nitrate, followed by calcination at a temperature of 600 ^o C [US 5063192, 11/05/1991]. This catalyst provides 95 - 100% conversion of NO _x , CO and HC at temperatures above 250 ^o C.

The disadvantage of this method is the uneven distribution of platinum and rhodium in the surface layer of the catalyst and, as a consequence, the lack of catalytic activity in the conversion of hydrocarbons, nitric oxide and carbon monoxide in the temperature range 150-160 ^° C, i.e. at the moment the start of operation of the internal combustion engine, which is mandatory according to the generally accepted in Europe (including Russia) directive EURO-2. In addition, the known catalyst is inactive (conversion ~ 50%) at a temperature of 200 - 250 ^o C in relation to all the main toxic components of the exhaust gas.

The aim of the present invention is to increase the activity of the catalysts at low temperatures (150 - 160 ^o C).

According to the invention, this goal is achieved in that the catalyst is obtained by impregnating the support (mainly γ-Al ₂ O ₃ ) first with a solution of dichlorotetraamine platinum (II) or palladium (II) [Pt (NH ₃ ) ₄ Cl ₂ or [Pd (NH ₃ ) ₄ ] Cl ₂ , followed by drying and treatment with a solution of the ammonium salt of rhodium hexachloride to obtain a poorly soluble binuclear complex with the formula [M (NH ₃ ) ₄ ] [RhL ₆ ], where M is Pt (II) or Pd (II), and L = Cl ^- , H ₂ O with further drying and calcination of the catalyst at a temperature of 550 - 620 ^o C.

Distinctive features of the method are:
- impregnation of the carrier with a solution of dichlorotetraamine platinum or palladium [M (NH ₃ ) ₄ ] Cl ₂ ;
- sequential drying of the impregnated carrier;
- treatment with a solution of the ammonium salt of rhodium hexachloride (NH ₄ ) ₃ [RhCl ₆ ].

. Из приведенной выше формулы образующегося биядерного комплекса видно, что соотношение в нем M : Rh = 1 : 1. Поэтому после прокаливания на поверхности носителя равномерно распределены два металла (M и Rh) в соотношении 1 : 1. Однако если перед процессом получения на поверхности носителя биядерного комплекса предварительно нанести платину, можно получить соотношение 5 : 1 или 5 : 2 (Pt : Rh или Pd : Rh соответственно), характерное для катализаторов, используемых в автомобильной промышленности.At the same time, a poorly soluble binuclear complex [M (NH ₃ ) ₄ ] [RhL ₆ ] is formed in the pores of the support, where M is Pt (II) or Pd (II), and L = Cl ^- , H ₂ O. The composition of the compound is confirmed by chemical and x-ray phase analysis, IR spectroscopy. During thermal decomposition of this complex, a catalyst is obtained with a uniform distribution of platinum elements in the thickness of the substrate layer up to 4000

. From the above formula of the resulting binuclear complex, it can be seen that the ratio in it is M: Rh = 1: 1. Therefore, after calcination, two metals (M and Rh) are uniformly distributed on the surface of the carrier in a ratio of 1: 1. However, if before the process of preparation on the surface of the carrier of the binuclear complex, platinum can be preliminarily applied; a ratio of 5: 1 or 5: 2 (Pt: Rh or Pd: Rh, respectively) can be obtained, which is typical for catalysts used in the automotive industry.

The method is as follows: a ceramic substrate, for example γ-Al ₂ O ₃ , is impregnated with an aqueous solution of [Pt (NH ₃ ) ₄ ] Cl ₂ or [Pd (NH ₃ ) ₄ ] Cl ₂ ,
calculating the concentration of metal ions in the substrate layer by the moisture capacity of the ceramic. Then the sample is dried in air for 1.5 - 2 hours at 100 - 120 ^o C, placed in a vessel with an aqueous solution of (NH ₄ ) ₃ [RhCl ₆ ], dried and calcined for one hour at a temperature of 550 - 620 ^o C.

The choice of the concentration of the rhodium compound is determined by the fact that there should be a ratio of Pt (Pd): Rh = 1: 1. When the sample is impregnated with an aqueous solution of (NH ₄ ) ₃ [RhCl ₆ ] in the pores of the ceramic substrate, a poorly soluble compound of the composition [M (NH ₃ ) ₄ ] [RhL ₆ ], which prevents a change in the concentration of Pt (Pd) in the ceramic matrix and forms the ratio of Pt (Pd): Rh in the surface layer in accordance with the composition of the complex formed.

 Example 1

100 grams of granular γ-Al ₂ O ₃ grade SHN-2 is impregnated in 150 ml of an aqueous solution containing [Pt (NH ₃ ) ₄ ] Cl _{2 of} 1.88 mg / ml. Then the granules are dried in air for 1.5 - 2 hours at a temperature of 100 - 150 ^o C, after which they are placed in 150 ml of an aqueous solution containing (NH ₄ ) ₃ [RhCl ₆ ] 2.14 mg / ml. After that, the granules are dried in air and calcined for an hour at a temperature of 550 - 620 ^o C. The resulting catalyst contains 0.05 wt.% Pt + Rh in a ratio of ~ 1: 1.

 Example 2

 The catalyst is obtained analogously to example 1.

However, the concentration of [Pt (NH ₃ ) ₄ ] Cl ₂ was 3.45 mg / ml, and (NH ₄ ) ₃ [RhCl ₆ ] was 4.29 mg / ml. The resulting catalyst contains 0.1 wt.% Pt + Rh in a ratio of ~ 1: 1.

 Example 3

 The catalyst is obtained analogously to example 1.

However, the concentration of [Pt (NH ₃ ) ₄ ] Cl ₂ was 13.73 mg / ml, and (NH ₄ ) ₃ [RhCl ₆ ] was 17.15 mg / ml. The resulting catalyst contains 0.4 wt.% Pt + Rh in a ratio of ~ 1: 1.

 Example 4

100 grams of granular γ-Al ₂ O ₃ grade SHN-2 is impregnated in 150 ml of an aqueous solution containing 2.0 mg / ml [Pd (NH ₃ ) ₄ ] Cl ₂ . Then the granules are dried in air for 1.5 to 2 hours at a temperature of 100 to 150 ^o C, after which they are placed in 150 ml of an aqueous solution containing 3.1 mg / ml (NH ₄ ) ₃ [RhCl ₆ ]. After that, the granules are dried in air and calcined for an hour at a temperature of 550 - 620 ^o C. The resulting catalyst contains 0.05 wt.% Pd + Rh in a ratio of ~ 1: 1.

 Example 5

 The catalyst is obtained analogously to example 4.

However, the concentration of [Pd (NH ₃ ) ₄ ] Cl ₂ was 40.0 mg / ml and (NH ₄ ) ₃ [RhCl ₆ ] 6.2 mg / ml. The resulting catalyst contains 0.1 wt.% Pd + Rh in a ratio of ~ 1: 1.

 Example 6

The catalyst was prepared analogously to the procedure described in Example 4. However, the concentration of [Pd (NH ₃ ) ₄ ] Cl ₂ was 16.0 mg / ml and (NH ₄ ) ₃ [RhCl ₆ ] 24.8 mg / ml. The resulting catalyst contains 0.4 wt.% Pd + Rh in a ratio of ~ 1: 1.

The proposed method allows to obtain a catalyst with a uniform and homogeneous distribution of platinum metals in the surface layer (see table 1, 2), which leads to an increase in the activity of the catalyst for the conversion of NO _x , CO, HC at a temperature of 150 - 160 ^o C (see table 3, 4).

The catalysts were tested both in laboratory conditions in a flow reactor with programmed temperature change and gas chromatographic analysis, and on the SCHENK model WC-130 motor stand equipped with a DYNAMOT-CONTROL control system under load characteristics in the engine speed range of 1400 - 3400 min ^-1 with the stoichiometric composition of the fuel mixture (λ = 1). The exhaust gas sampling was performed in each mode twice: before and after the converter. Gas analysis was performed using a HORIBA gas analyzer model MEXA-5120. Evaluation of the effectiveness of the catalyst was carried out on an engine with a displacement of 1800 cm ³ equipped with a BOSCH injection system and an adaptation system of the BOSCH model VS-100.

. На основании приведенных результатов можно заключить, что полученный катализатор уже при температуре 175 - 200^oC имеет такую же активность, как и известный при температуре выше 250^oC. Однако катализатор, полученный по предлагаемому способу? проявляет высокую активность уже при температуре ~ 150^oC. Так, в таблицах 3 и 4 показано, что в интервале температур 150 - 160^oC удается нейтрализовать ≥ 40% NO_x и ≥ 50% CO и HC. При этих условиях катализатор, полученный по известному способу, не проявляет активность. При повышении температуры (175 - 200^oC) наблюдалась 95% конверсия NO_x и 100% конверсия CO и HC, т.е. в этом температурном режиме предлагаемый катализатор в два раза эффективнее известного. Это имеет важное значение, т.к. его использование позволит нейтрализовать выхлопные газы в более широком диапазоне работы двигателя.The data on the content of platinum (palladium) and rhodium in the surface catalyst layer presented in Tables 1 and 2 indicate a uniform and homogeneous distribution of these elements in layers up to 4000

. Based on the above results, we can conclude that the obtained catalyst already at a temperature of 175 - 200 ^o C has the same activity as that known at a temperature above 250 ^o C. However, the catalyst obtained by the proposed method? exhibits high activity even at a temperature of ~ 150 ^o C. Thus, tables 3 and 4 show that in the temperature range 150 - 160 ^o C it is possible to neutralize ≥ 40% NO _x and ≥ 50% CO and HC. Under these conditions, the catalyst obtained by a known method does not show activity. With increasing temperature (175 - 200 ^o C) was observed 95% conversion of NO _x and 100% conversion of CO and HC, i.e. in this temperature regime, the proposed catalyst is twice as effective as the known one. This is important because its use will allow to neutralize exhaust gases in a wider range of engine operation.

Thus, we can conclude that the proposed method for the production of Pt / Rh and Pd / Rh catalysts provides high conversion efficiency of harmful emissions not only in the high temperature region (> 250 ^o C), which is typical for known catalysts, but also at a temperature of 150 - 160 ^o C i.e. at the time of starting the engine.

Claims (1)

A method of producing a platinum-rhodium or palladium-rhodium catalyst on a ceramic support by sequentially impregnating the support with aqueous solutions of a platinum or palladium-containing compound and a rhodium-containing compound, followed by drying and calcining the catalyst, characterized in that the support is impregnated with platinum (II) dichlorotetraamine Pt (NH ₃ ) ₄ Cl ₂ or palladium (II) Pd (NH ₃ ) ₄ Cl ₂ , dried, followed by treatment with a solution of the ammonium salt of rhodium hexachloride (NH ₃ ) [RhCl ₆ ] with the formation on the surface of the carrier of the bi binuclear complex
[M (NH ₃ ) ₄ ] [Rh L ₆ ],
where M = Pt (II) or Pd (II);
L = Cl ^- and H ₂ O.

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