RU2026737C1 - Method for preparation of aluminoplatinum catalyst for cleaning effluent gases from organic substances, carbon monoxide and nitrogen oxides - Google Patents

Abstract

FIELD: catalytic chemistry. SUBSTANCE: applied to carrier - active aluminium oxide is modifying additive - cerium or sum of rare-earth elements from nitrate solutions before or after the application of platinum from solution of chloroplatinic acid. Then, wet catalytic mass is treated with activator - 0.5-3.0% solution of formic acid at room temperature for 5-20 min with subsequent final activation in drying at 60-180 C. Produced catalyst possesses high activity, selectivity and heat resistance as compared with the known one (methane oxidation rate at 550 C in the presence of the catalyst produced by the present method amounts to 5,0·10³ cm³CH₄/g·h versus 2·10³ cm³CH₄/g·h; conversion grades of carbon monoxide and nitrogen oxides are 92 and 86 versus 65.6 and 54%, respectively; selectivity 100% versus 83.8% . Catalyst withstands heating up to 1000-1050 C without material reduction of activity. EFFECT: higher activity, selectivity and heat resistance. 4 tbl

Description

The invention relates to methods for producing catalysts for the neutralization of toxic organic impurities, CO and NO _x in gas emissions.

A known method of preparing a catalyst for the afterburning of harmful impurities based on noble metals and aluminum oxide with the addition of rare-earth elements (REE), including the stage of impregnation of aluminum oxide with solutions of salts of REE, drying and high-temperature calcination of not less than 750 ^about With for the complete decomposition of the applied salts and obtain a stable thermostable carrier . This is followed by the stages of deposition of a platinum group metal, re-drying and high-temperature activation in air at 400-600 ^о С. followed by a step of activation at 650 ° ^C. In the known method it is believed that the salt of cerium (III) restores supported platinum metals, and the resulting cerium oxide (IV) stabilizing t dispersion of active metals. However, despite the fact that dispersed metal particles are formed, the activity of the samples per 1 g does not significantly increase. This is probably due to the blocking of a part of the active component by the oxide of the additive in the pores of the carrier, or by the formation of inactive surface phases of the PtO _x ˙ CeO _y ˙mAl ₂ O _{3 type} .

 There is also known a method of wet reduction of a catalyst with solutions of hydrazine, hydroxylamine, reducing sugars when impregnated together with solutions of salts of alkaline earth elements. However, the dispersion of metals in this method is not high enough.

 Closest to the achieved effect to the present invention is a method for the preparation of REE-containing catalyst afterburning of harmful impurities.

According to this method, the catalyst is prepared by impregnation of granules or active alumina powder with solutions of cerium nitrate salts in an amount of 5-20 wt. % CeO ₂ . After drying at ¹¹⁰ ° C carrier is calcined in air not lower than 750 ^C, which is necessary for the complete decomposition of the salt and obtain a stable carrier. Then follows the stage of applying the noble metal in an amount of 0.1-10 wt. % And again calcining in air at 400-600 ° ^C. To eliminate the secondary calcination, the wet catalyst was treated with hydrogen sulfide gas for 15-20 minutes.

The disadvantages of this method are:
high calcination temperatures of the support, which significantly reduces the specific surface, porosity of the support and does not provide a high dispersion of the deposited metals, and, consequently, the activity of the samples;
after processing the hydrogen sulphide catalyst it requires additional activation in air at a temperature of more than or equal to ^about 300-350 C, which is low-tech, the allocated harmful sulfur oxides;
the liberation during calcination of the modified carrier of harmful nitrogen oxides due to the decomposition of nitrate salts of REE.

The purpose of the invention is the development of a method for the preparation of REE-containing alumina-platinum catalyst for the neutralization of exhaust gases from harmful organic impurities, CO and NO _x , providing high activity and thermal stability of the catalyst due to the formation of highly dispersed metal particles of the active metal that are resistant to overheating. Cooking technology provides for the elimination of harmful emissions, simplification of technology.

The catalyst according to the present method is prepared in several stages. The γ-Al ₂ O ₃ carrier (S = 200 m ² / g, the total pore volume of at least 0.5 cm ³ / g) is impregnated with solutions of cerium nitrates, or nitrates of the sum of REEs. The amount of introduced modifying additives (4-5 wt.% CeO ₂ or 8-10 wt.% Based on the sum of REE oxides) is determined by the concentration of the impregnating solutions and the moisture capacity of the carrier. After removing the excess solution, the carrier is treated with a solution of platinum chloride for the chemisorption of platinum in an amount of 0.2-0.5 wt. % Before applying platinum, if it requires uniform distribution over the grain, the carrier is treated with 0.2 n. acetic acid solution. After application of the platinum catalyst at room temperature was treated with 0.5-3% solution of formic acid for 5-20 min so that during the drying of the catalyst in air at 60-180 ^{° C} flowed final stage of formation of the catalyst due to the expansion joint lanthanide nitrate and recovering deposited ionic platinum by the action of sorbed formic acid. There is no stage of hydrogen sulfide treatment or a stage of high-temperature calcinations in air in inert gases or hydrogen.

Distinctive features of this method are the application of the modifying additive before or after the application of platinum on the carrier, the use of a 0.5-3.0% formic acid solution as an activator, processing under certain conditions and the formation of the active component in the drying mode at 60-180 ^about S.

 Catalysts are examined by XRD, EM, and adsorption. The tests are carried out in model oxidation reactions of methane, butane, CO + NO in flow-through circulating plants.

Test conditions:
The oxidation temperature of methane is 500 ^° C, butane is 300 ^° C, methane concentration is 0.5 vol.%, Butane concentration is 0.25 vol.%, The rest is air. As a measure of activity, the reaction rate of oxidation of a hydrocarbon is taken at a current methane concentration of 0.25 vol.%, Butane - 0.05 vol.%. The reaction CO + NO + O ₂ - 395 ^about With the concentration of NO and CO are 0.9 and 1.3 vol.%, Respectively. Activity assessed by the degree of conversion of NO. Selectivity for N ₂ is determined from the ratio of [N ₂ ] / [N ₂ ] + [N ₂ O], where [N ₂ ] and [N ₂ O] are the concentrations of nitrogen and nitrous oxide.

 The essence of the method is illustrated by the following examples.

), 8,0 СеО₂ (d= 40

), остальное - γ - Al₂O₃ (d=50-60

). Распределение платины и церия по радиусу зерна носителя равномерное. Удельная поверхность составляет 200 м²/г.Example 1. Granules γ - Al ₂ O ₃ (S 200-220 m ² / g, bulk density 0.5-0.6 g / cm ³ , total pore volume 0.5 cm ³ / g) weighing 370 g is treated with stirring of the layer for 30 min 0.75 l of a solution of cerium (III) nitrate containing 150 g of anhydrous salt. Excess solution is drained and residual liquid is removed between layers of filter paper. Then at the same time add 0.75 l of 0.2n. acetic acid and 0.25 l of a solution of platinum hydrochloric acid with a concentration of platinum of 7.8 mg / ml The catalyst layer together with the solution is stirred for 2 hours. The catalyst is washed with water and after removing excess water, the catalyst is treated with 0.75 L of a 1.0% formic acid solution for 15 minutes. After removing excess solution, the catalyst bed temperature was adjusted to ⁶⁰ ° C and for 6 hours performed a step of forming the active component. The final drying is carried out at 180 ^about 8 hours. The composition of the obtained catalyst, wt.%: 0.5 Pt (d = 15-20

), 8.0 CeO ₂ (d = 40

), the rest is γ - Al ₂ O ₃ (d = 50-60

) The distribution of platinum and cerium along the radius of the grain of the carrier is uniform. The specific surface is 200 m ² / g.

), 5,0 CeO₂ (d=50

), остальное-γ -Al₂O₃ (d=60

). Удельная поверхность катализатора составляет 180 м²/г.PRI me R 2. The method of preparation is similar to example 1, but differs in that the catalyst after applying platinum is treated with a 3% solution of HCOOH 5 minutes The composition of the obtained catalyst, wt.%: 0.48 Pt (d = 15-20

), 5.0 CeO ₂ (d = 50

), the rest is γ -Al ₂ O ₃ (d = 60

) The specific surface area of the catalyst is 180 m ² / g.

), 5,0 CeO₂ (d= 40

), остальное -γ - Al₂O₃ (d=50-60

). Удельная поверхность 200 м²/г.PRI me R 3. The method of preparation is similar to example 1, but differs in that the catalyst after applying platinum is treated with a 0.5% HCOOH solution for 20 minutes, and the stage of formation-activation of the catalyst is carried out at 120 ^about C. The resulting catalyst has composition, wt.%: 0.5 Pt, (d = 15-20

), 5.0 CeO ₂ (d = 40

), the rest is -γ - Al ₂ O ₃ (d = 50-60

) The specific surface area is 200 m ² / g.

), 4,5 СеО₂ (d=70

), остальное - γ - Al₂O₃ (d=60

). Удельная поверхность составляет 180 м²/г.PRI me R 4. Similar to example 1, but differs in that the treatment with 2% HCOOH is carried out for 10 minutes, and finally the catalyst is formed in the drying mode at 160 ^about 10 hours. The resulting catalyst has a composition, wt.%: 0.5 Pt (d = 20-25

), 4.5 CeO ₂ (d = 70

), the rest is γ - Al ₂ O ₃ (d = 60

) The specific surface is 180 m ² / g.

 Examples 5-7 show methods for preparing a REE-alumina-platinum catalyst, when a modifying additive is applied after chemisorption of platinum chloride on alumina.

), 4,85 СеО₂ (d= 40

), остальное - γ- Al₂O₃ (d= 50

). Распределение платины и церия по радиусу зерна носителя равномерное. Удельная поверхность составляет 200 м²/г.PRI me R 5. 370 g of granules γ-Al ₂ O ₃ (S = 200 m ² / g, the total pore volume of 0.55 cm ³ / g) is filled with water and incubated for 1 h with stirring. Then 0.75 L of 0.2 N are added. acetic acid and 0.25 l of a solution of platinum hydrochloric acid with a concentration of 7.8 mg / ml of platinum. The catalyst is stirred for 2 hours, washed with water, excess water is removed by vacuum. The catalyst is then treated with 0.75 L of a Ce (III) nitrate solution containing 150 g of salt, 20 min. After removal of the catalyst impregnation solution, 0.8 L of a 1.0% HCOOH solution is treated for 15 minutes. This is followed by a drying step at 60 ° ^C for 6 hours, which is accompanied by reduction decomposition of the active ingredient and the salt-additive. Final drying was carried out at 160 ^{° C} for 8 hours The catalyst has a composition, in weight%:.. 0,5 Pt (d = 15-20

), 4.85 CeO ₂ (d = 40

), the rest is γ- Al ₂ O ₃ (d = 50

) The distribution of platinum and cerium along the radius of the grain of the carrier is uniform. The specific surface is 200 m ² / g.

), 4,7 СеО₂ (d=60-70

), остальное γ- Al₂O₃ (d=50-60

). Удельная поверхность равна 180 м²/г.PRI me R 6. Similar to example 5, but differs in that the catalyst is treated with a 0.5% HCOOH solution for 20 minutes, and the formation of the catalyst is carried out at 140 ^about 4 hours. The resulting catalyst has a composition, in wt. %: 0.5% Pt (d = 20-25

), 4.7 CeO ₂ (d = 60-70

), the rest is γ- Al ₂ O ₃ (d = 50-60

) The specific surface is 180 m ² / g.

PRI me R 7. The preparation method is similar to example 5, but differs in that the sum of REE from a nitric acid solution of industrial concentrate with a volume of 0.5 l with a total amount of REE oxides of 200 g / l is introduced into the catalyst. The composition of the obtained catalyst, wt. %: 0.5 Pt, 8.5 REE amount. The specific surface area is 180 m ² / g.

PRI me R 8. The method of preparation is similar to example 7, but differs in that the catalyst is treated with a 0.5% solution of formic acid for 15 minutes, and the formation of the active phase of the catalyst is carried out at 180 ^about 6 hours. The composition of the obtained catalyst, wt.%: 0.5 Pt, 8.5 amounts of REE, the rest is -γ -Al ₂ O ₃ . The specific surface area is 180 m ² / g.

PRI me R 9 (prototype). 5000 g of spherical particles of active alumina (2-3 mm diameter) was immersed in a solution containing 700 g of Ce (NO _{3) 3} ˙6H ₂ O. After drying at ¹¹⁰ ° C for 16 hours carrier was calcined at 950 ^C in air for 2 hours After cooling, 3500 g of the support are placed in a 1400 ml volume of platinum chloride solution containing 17.5 g of platinum. The wet catalyst is treated with gaseous hydrogen sulfide for 25 minutes, then dried at ¹¹⁰ ° C for 14 hours. The final calcination was carried out in air at ⁵⁰⁰ ° C until complete removal of chloride ions. The composition of the obtained catalyst, wt.%: 0.5 Pt, 5 CeO ₂ , the rest (δ), γ -Al ₂ O ₃ . The specific surface area is 130-140 m ² / g.

 In the table. 1 shows the variable parameters of the present catalyst preparation process.

 In the table. 2 shows data on the specific surface of the carrier, the phase composition of the catalyst samples, the average particle size after high-temperature treatments of the prepared catalyst.

 In the table. Figures 3 and 4 show the results of testing the catalyst in model reactions.

The results obtained indicate that the catalyst prepared by this method has a higher activity in the oxidation of hydrocarbons (2-4 times) and a significantly greater selectivity (20-25%) than the existing analogues. The catalyst also has high thermal stability and can withstand overheating up to 1000-1050 ^{° C} without a significant decrease in activity. According to the present method, there are no harmful emissions and intermediate stages of drying and calcination in the preparation technology.

Claims (1)

METHOD FOR PREPARING AN ALUMINO-PLATIN CATALYST FOR DISCONNECTING EMISSION GASES FROM ORGANIC SUBSTANCES, CARBON MONOXIDE AND NITROGEN OXIDES, which includes the steps of applying to the carrier an active alumina of a modifying additive from cerium chloride or a solution of a red platino solution of a nitrous solution activator, drying and formation of the active component, characterized in that, in order to obtain a catalyst with increased active by bone, selectivity and thermal stability, the modifying additive is introduced before or after platinum is applied to the carrier, a 0.5-3.0% formic acid solution is used as an activator, and the treatment is carried out at room temperature for 5-20 minutes and the final activation is carried out in drying mode at 60-180 ^o C.

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