The catalyst for purification of gases from nitrogen oxides and method thereof

 

(57) Abstract:

The objective of the invention is to develop a catalyst for purification of gases from nitrogen oxides with a low ignition temperature, high strength, selectivity and stability, having high activity at low concentration of active component is palladium compounds. The problem is solved at the expense of the catalyst for purification of gases from nitrogen oxides, which comprises a compound of palladium, the modifying compound and the carrier based on alumina. As media use-Al2O3containing one or more compounds of an element from the group of Mg, Ca, La, Pr, Ce, Zr, Ba, and the compound of palladium is in crust thickness of 200-1500 μm, and the catalyst has the following composition, wt. %: palladium (in terms of metal) of 0.1-2.0, one or more compounds for the modification of the carrier is 0.1 to 5.0, alumina rest. Also the claimed method of producing a catalyst for purification of gases from nitrogen oxides, which includes the impregnation of the carrier based on alumina acidic solution of palladium compounds, followed by heat treatment at temperatures up to 400oWith the current of air. The concentration of free nitric acid in propi dehydration trihydroxide aluminum. The proposed method allows to obtain catalysts with increased activity in the reaction of high-temperature reduction of nitrogen oxides and significantly improves the environment in the production of the catalyst through the use of impregnating solutions with minimal acidity and reduction in the duration of heat treatment up to 10 hours. 2 S. and 4 C.p. f-crystals, 1 table.

The invention relates to catalytic chemistry, in particular to methods of producing catalysts for the process of reduction of nitrogen oxides, mainly in the presence of methane and oxygen, and can be used for purification of exhaust gases (NOx) in the production of weak nitric acid, flue gases of high-temperature furnaces and boilers.

Currently actively developed processes neutralization of nitrogen oxides recovery of methane, because methane is associated with fewer complications than the use as a reducing agent ammonia.

A method of obtaining APK-2 (Technology catalysts. /Under the editorship of Muglinova I. I. L.: Chemistry, 1979, S. 164-165), which is used for tail gas treatment unit production of dilute nitric acid from oxido what W. The method consists in the following. Preformed aluminum oxide is loaded into the apparatus, the pre-filled 1/3 of demineralized water, where the sulfur compound. After loading media reactor is completely filled with water, isinjected for heating and mixing the mass for 1 hour. In the same apparatus, the carrier is washed to the lack of sulfur in the wash water, then dried it in the dryer. A solution of Pd(NO3)2get in the reactor dilution palladium paste demineralized water to a concentration of (862) g/l (in terms of palladium). The amount of salt is determined by the palladium content in the finished catalyst. The impregnated carrier is dried with hot air for 40 hours at 200-220oSince then, the catalyst was calcined in a furnace at 380-400oC in nitrogen atmosphere. Catalyst weight provides the cleaning gas from the nitrogen oxides to a residual content of not more than 0,005% vol.

The disadvantages of this method are the low strength and the specific activity of the catalyst associated with the misallocation of palladium on the pellet carrier, high palladium content.

Known catalyst for reduction of nitrogen oxides in industrial othodoxy noble metals, which provide atomic dispersion of the active component on the carrier surface.

The disadvantages of the catalyst are its low activity and the complexity of preparation.

Closest to the claimed invention is a method of obtaining a palladium catalyst for the process of reduction of nitrogen oxides in the exhaust gas (RF patent 2072260, IPC6B 01 J 23/44, 37/02, 1997). The method includes the impregnated alumina carrier with an aqueous solution of palladium acetate, drying and restoration.

The disadvantages of the catalyst are low strength and activity.

The objective of the invention is to develop a catalyst for purification of gases from nitrogen oxides with a low ignition temperature, high strength, selectivity and stability, having high activity at low concentration of active component is palladium compounds.

The problem is solved at the expense of the catalyst for purification of gases from nitrogen oxides, which comprises a compound of palladium, the modifying compound and the carrier based on alumina. As media use-Al2ABOUT3containing one or more connection is
Palladium (in terms of metal) - 0,1-2,0

One or more connections for the inoculation of media - 0,1-5,0

Alumina - Rest

The catalyst preferably contains a compound of palladium (in terms of metal) in an amount of 0.1-0.5 wt.%, the carrier preferably contains calcium and/or cerium in an amount of from 0,5 -2,0 wt.%, while the compound of palladium is in crust thickness of 200-1500 μm.

The problem is solved by the method of producing a catalyst for purification of gases from nitrogen oxides, which comprises the impregnation of the support based on aluminium oxide compound of palladium, followed by drying and calcination. For the preparation of the catalyst using a carrier-Al2ABOUT3containing one or more compounds of an element from the group of Mg, Ca, La, Pr, CE, Zr, Ba in an amount of 0.1-5.0 wt.%, which is impregnated with an acidic solution of palladium compounds, and the concentration of free nitric acid in the impregnating solution is 5-10 g/l, followed by heat treatment at temperatures up to 400oWith the current of air.

As predecessor-Al2ABOUT3use the product fast dehydration trihydroxide aluminum.

In the proposed izobreteny the SUB>ABOUT3use aluminum hydroxide, which can be obtained by known methods: presidenial, thermoactivation Al(Oh)3and others, however, to obtain a carrier is preferred, the product composition of Al2ABOUT3mo2Oh, where n=0,03 to 2.0, which is obtained by rapid dehydration of trihydroxide aluminum and has a layered x-ray amorphous structure. This product may contain at least one modifier compound of an element from the group of Mg, Ca, La, WG, CE, Zr, Ba in an amount of 0.1-5.0 wt.%, that may be partially present in the original product, or they are administered before rapid dehydration by any known means, for example by impregnation or coprecipitation.

The application of active component is palladium compounds is carried out with the use of impregnating solutions of the active component with a minimum acidity (5-10 g acid/l) followed by heat treatment at intensive removal of decomposition products in a current of hot air.

The proposed method allows to obtain catalysts with low palladium content of from 0.1 to 2.0 wt.%, (preferably from 0.1 to 0.5 wt.%), high rates of activity, strength, thermal stability.

The acidity of the impregnating solution (5-10 g acid/l) reduces the amount of nitrogen oxides during calcination, reduction of its duration upon receipt of the catalyst, i.e. the improvement of the ecological situation in the production of the catalyst while increasing the activity of the catalyst.

In the presence of the proposed modifying additives (alkaline-earth and rare-earth elements) increases the strength of the media, change the acid-base and adsorption properties of the surface of the carrier. Modifying elements modify the distribution of palladium grains, besides the active ingredient is a compound of palladium is distributed in the crust thickness of 200-1500 μm. Alkaline-earth elements (CA, Mg) prevent sintering of palladium due to the neutralization of acid centers on the surface of the media.

Thus, to increase activity, strength and thermal stability of the catalyst for purification of gases from nitrogen oxides using media with additives (REE, SSE), and palladium is distributed in the crust.

Developed catalysts "Korotkova type were tested for activity in% is selecionou installation. Test conditions catalysts: the composition of the gas mixture at the inlet to the reactor cleaning: 0.1% of NOx+ 1,87% O2+ 1,05% CH4+ He leave; CH4/ABOUT3= 0,561; the flow rate is 12.3 l/h; the reaction temperature 200-700oC.

The distribution of palladium on radius granules media investigated using x-ray microanalyzer (RMA) type 35-DDS company "JEOL".

Catalytic and physico-chemical properties of the resulting catalysts are presented in the table.

Data analysis shows that the proposed method of producing the catalyst for purification of exhaust gases from nitrogen oxides provides obtaining highly dispersed catalyst (uniform layer of the active component on the surface of the modified media), the resulting catalysts have a high activity, selectivity and thermal stability in comparison with the known.

Example 1

30.0 g of alumina carrier modified with magnesium (0.1% of Mg) and obtained using the product of rapid dehydration trihydroxide aluminum impregnated with a solution of palladium nitrate Pd(NO3)2containing 0.15 g of Pd and 0,077 g NGO3. The acidity of the impregnating solution is of 8.27 g/Laura impregnated carrier is dried at a temperature of 120oC for 5 hours, then calcined in air flow at a temperature of 400oWith 10 hours to decompose the palladium nitrate by reaction

2Pd(NO3)2=2PdO+4NO2+O2.

The catalyst is cooled down and stored in a closed container.

The prepared catalyst contains, wt%:

Palladium - 0,5

Magnesium - 0,1

Alumina - Rest

Example 2

of 26.5 g of the carrier Al2ABOUT3modified magnesium (0.5% of Mg), treated with an impregnating solution of the active component containing 0,132 g Pd and 0,068 g NGO3that corresponds to the acidity of the impregnating solution, 8.3 g/l

Heat treatment conditions described in example 1.

The prepared catalyst contains, wt%:

Palladium - 0,5

Magnesium - 0,5

Alumina - Rest

Example 3

29,02 g of alumina-modified calcium in forming medium, treated with an impregnating solution of palladium nitrate containing 0,145 g Pd metal and 0,074 g HNO3. The acidity of the impregnating solution is 6.9 g/HP heat treatment Conditions as in example 1.

The prepared catalyst contains, wt%:

Palladium - 0,504

Calcium - 2,0

is emkosti solution of palladium nitrate, containing 0.15 g of Pd metal and 0,074 g NGO3. The acidity of the impregnating solution is to 7.15 g/l Conditions of the heat treatment of the impregnated carrier as in example 1.

The prepared catalyst contains, wt%:

Palladium - 0,53

Cerium - 2,0

Alumina - Rest

Example 5

The catalyst is prepared analogously to example 1, but differs in that the medium contains 2% praseodymium.

The prepared catalyst contains, wt%:

Palladium - 0,49

The praseodymium - 2,0

Alumina - Rest

Examples 6-8

Similar to example 1, only differ in the content of palladium and modifying compounds in the media.

For comparison, the table shows the properties and composition of used industrial catalyst APK-2 and the catalyst prepared according to the prior art (patent RF 2072260).

Analysis of the above data shows that the modification of the media proposed modifying compounds solves the problem. Due to the fact that the proposed method of producing the catalyst for purification of exhaust gases from nitrogen oxides ensures catalyst "Korotkova type, the resulting catalysts exhibit improved and the palladium.

Thus, the proposed method allows to obtain catalysts with increased activity in the reaction of high-temperature reduction of nitrogen oxides and significantly improves the environment in the production of the catalyst through the use of impregnating solutions with minimal acidity and reduction in the duration of heat treatment up to 10 hours.

1. The catalyst for purification of gases from nitrogen oxides, comprising a compound of palladium, the modifying compound and the carrier on the basis of aluminum oxide, wherein the catalyst as a carrier contains-Al2O3including one or more modifying compounds of an element from the group of Mg, Ca, La, Pr, Ce, Zr, Ba, catalyst formed during the heat treatment of the above carrier, impregnated with an acidic solution of palladium compounds, and has the following composition, wt.%:

Palladium (in terms of metal) - 0,1-2,0

One or more modifying compounds is 0.1 to 5.0

Alumina - Rest

2. The catalyst p. 1, characterized in that the catalyst contains a compound of palladium (in terms of metal) in an amount of 0.1-0.5 wt.%.

3. The catalyst PP.1 and 2, characterized in that h is p. 1, characterized in that the compound of palladium is in crust thickness of 200-1500 μm.

5. A method of producing a catalyst for purification of gases from nitrogen oxides, comprising a carrier impregnated on the basis of aluminum oxide compound of palladium, followed by drying and calcination, characterized in that for the preparation of a catalyst using a carrier - Al2O3including one or more modifying compounds of an element from the group of Mg, Ca, La, Pr, Ce, Zr, Ba in an amount of 0.1-5.0 wt.%, which is impregnated with an acidic solution of palladium compounds, and the concentration of free nitric acid in the impregnating solution is 5-10 g/l, followed by heat treatment at temperatures up to 400oC for 10 h in air flow.

6. The method according to p. 5, characterized in that, as predecessor-Al2O3use the product fast dehydration trihydroxide aluminum.

 

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