CZ2014448A3 - Catalyst for selective catalytic reduction of nitrogen oxides and process of its preparation and use - Google Patents

Abstract

Removal of nitrogen oxides by their selective catalytic reduction with a reducing agent using a cobalt ion-based catalyst located in the zeolite beta structural topology from a high-lattice, high-lattice-free synthesis. Catalyst, process for production and use in catalytic process. The catalytic process utilizing this catalyst provides high conversion to NO, NO 2 and N 2 to nitrogen.

Description

Field of technology:

The invention solves the removal of nitrogen oxides from the exhausts of combustion and technological processes using a catalytic process using a catalyst based on zeolite beta prepared without the use of organic templates. The catalyst is characterized by a high content of lattice aluminum and the presence of cobalt in non-lattice positions. The invention deals with the preparation and production of this catalyst and the process of selective catalytic reduction of nitrogen oxides to nitrogen.

Current state of the art:

Emissions of nitrogen oxides (NO _X ), i.e. NO, NO ₂ , N ₂ O ₃ , N ₂ O ₄ and N ₂ O as by-products of the combustion of so-called lean fuel mixtures or from chemical production are a serious ecological problem and their emissions are limited according to the legislative standards applicable to individual states. An effective and widespread process for the elimination of nitrogen oxides NO and NO ₂ is their selective catalytic reduction using ammonia to produce nitrogen and water vapor. The process of catalytic decomposition of N ₂ O into nitrogen and oxygen at high temperatures is mainly used to eliminate N ₂ O.

Selective catalytic reduction with ammonia is mainly used for stationary sources of NO and NO ₂ (chemical processes such as nitric acid production plants, off-gases from nitrate production, etc.) and when burning fuels for the purpose of energy production (heating plants, power plants) or in waste incinerators. The removal of nitrogen oxides from stationary sources of oxygen-containing exhalates and solutions using the technology of selective catalytic reduction of nitrogen oxides with ammonia is described, for example, in patent WO 200^)21^39. In the case of mobile sources of NO and NO ₂ (combustion engines in vehicles), the selective catalytic reduction of nitrogen oxides NO and NO ₂ is solved by dosing a urea solution, which can be transported more easily. The replacement of ammonia in the selective catalytic reduction of nitrogen oxides with more easily dosed and stored urea is described, for example, in patent US 2002^25905. Before the selective reduction process itself, urea is decomposed to form ammonia, and further the selective catalytic process takes place in a similar way to the dosing of gaseous ammonia. Traditional and reliable catalysts for these processes are based on vanadium as an active component deposited on alumina (V2O5/AI2O3) or on titanium oxides (V2O5/TIO2) possibly doped with tungsten to increase stability. More modern catalysts are mainly based on iron or copper ions in off-lattice positions of zeolites (Catalysis Reviews - Science and Engineering 2008 50 492-531). All these technologies are associated with a demanding process of dosing, storage and control of ammonia emissions, and in the case of urea, the process is also associated with the risk of emission of toxic urea decomposition products.

The process of selective catalytic reduction of nitrogen oxides with hydrocarbons (CH-SCR-NO _X ) is very often described in professional publications and patent sources. This is a promising way to eliminate nitrogen oxides from oxygen-containing exhalates. In CH-SCR-NO _X processes into a stream of exhalates, containing nitrogen oxides, oxygen and possibly unreacted hydrocarbons and their derivatives from the fuel, a reducing agent - hydrocarbons or their derivatives is dosed, the resulting gas mixture is passed through a catalytic bed ₍ on which the reduction takes place of nitrogen oxides using the hydrocarbon present. A fundamental problem for this process is the insufficiently high activity/selectivity of the catalysts known to date developed for this process or the insufficient stability of NO _X conversion at higher temperatures. Precious metal catalysts showing some activity at lower temperatures are only suitable for very narrow temperature range. A description of the proposed catalysts and their catalytic activity in the selective catalytic reduction of NO _X is clearly presented in Applied Catalysis B: Environmental 13 (1997) 1-25, Applied Catalysis B: Environmental 39 (2002) 283-303. Analysis of the problem of elimination of nitrogen oxides in combustion engines is presented, for example, in Topics in Catalysis 28 (2004 ) 1-199.

Among the catalysts with the highest activity in CH-SCR-NO _X are materials based on copper, iron, silver on cobalt. Silver deposited on alumina shows relatively high activity at higher temperatures (Applied Catalysis B: Environmental 2 (1993) 199-205). Copper, iron and cobalt show relatively high activity if they are found in the form of ions located in off-lattice positions of zeolites (Catalysis Reviews - Science and Engineering 2004 46 271333). However, the activity of these catalysts is usually not sufficient for practical use and therefore their importance in current technologies is negligible.

L

Catalysts based on cobalt ions in zeolite beta for selective catalytic reduction of nitrogen oxides (NO and NO2) with hydrocarbons are described in US Patent ¹ and a detailed structural study in Journal of Catalysis 272 (2010) 44-54. For the preparation of these catalysts, conventional ion exchanges with solutions of salts of cobalt ions and zeolite of structural topology beta were used. Zeolite structural topology beta (designated by IZA as BEA* and composed of three A, B and C polymorphs) [Ch. Baerlocher, LB McCusker and DH Olson, Atlas of Zeolite Framework Types, 6th revised edition, 2007] is composed of 4-, 5-, and 6-membered rings that form a three-dimensional (3D) channel structure with 12-membered entrance openings of of size 6.6 x 6.7 A. This channel structure and the absence of large cavities that exist in zeolite Y is a great advantage for the rapid transport of molecules in catalytic processes of petroleum refining, paraffin dewaxing and isomerization of paraffins and benzene, alkylation with low olefins, as well as in the organic production of special substances. Zeolite beta was first described in patent U^0^69 and then U^5^145 and ^by W ^{6 and} others. A shortcoming for the significantly wider industrial use of beta zeolites prepared according to these patents is the need to use expensive tetramethylammonium hydroxide (TMAOH) or a similar organic template for the hydrothermal synthesis of this zeolite. Another shortcoming of these procedures is the limitation of the maximum concentration of aluminum in the structural lattice corresponding to the molar ratio Si/Al >11. Such a low aluminum content limits the concentration of active centers in zeolite beta. Since 2008*, procedures have been known for the synthesis of zeolite beta with a high aluminum content in a structural lattice corresponding to the Si/Al molar ratio as early as 3j9. These syntheses were reported by Xie et al. [Chemistry of Materials 20 (2008) 4533-4535], Majano et al. [Chemistry of Materials 21 (2009) 4184-4191] and Kamimura et al. [Catalysis Science and Technology 3 (2013) 2580-2586] and replace the organic template in the synthesis with the addition of zeolite beta to the aluminosilicate gel as a source of crystal seeds. These procedures opened up the possibility of synthesizing beta zeolites with high crystallinity with well-developed crystals with dimensions of about 0.3 x 0.5 µm and with a high concentration of AI in the structural lattice. Beta zeolites prepared in this way are fundamentally different from beta zeolites that were used for the preparation of cobalt-containing catalysts described in 1999 in patent U^869^ 13, when beta zeolites prepared without the use of a template and with a high aluminum content in the structural lattice were unknown. Conversely, zeolite beta prepared without the use of a template was used to prepare a catalyst containing Fe and Cu ions for the selective catalytic reduction of nitrogen oxides with ammonia, and these catalysts are described in patent WO 2013/118&63 AI.

The solution proposed in this patent uses beta zeolites prepared without the use of a template and with a high aluminum content in the structural lattice to prepare a catalyst with an active component based on cobalt for the selective catalytic reduction of nitrogen oxides. The catalyst on this basis provides a fundamentally increased activity and fundamentally surpasses previously known materials.

In contrast to the elimination of NO and NO ₂ from exhaust gases, in the case of N ₂ O removal, the process is usually implemented using the catalytic decomposition of N ₂ O into nitrogen and oxygen at high temperatures or using reducing agents, mainly in the form of hydrocarbons. In recent years, the process of high-temperature decomposition of N ₂ O has been introduced in nitric acid production plants. Decomposition takes place íX typically at temperatures of 800 r 900 °C and is associated with problems with the gradual deactivation of catalysts due to high thermal stress in the gas stream containing water vapor. A typical catalyst for this process is described in US Pat. No. 2,3295 (B1). Catalytic elimination of N ₂ O at lower temperatures (typically 450 °C) by its decomposition or reduction using hydrocarbon additions is solved in industrial applications by means of catalysts based on iron ions located in off-lattice positions of zeolites. Typical processes are described in patent EP 1^91^016 (AI).

This invention solves the problem of removing all nitrogen oxides by their selective catalytic reduction with a reducing agent, mainly hydrocarbons, using a unique highly efficient catalyst based on cobalt ions located in a zeolite of structural topology beta with a high lattice aluminum content. This catalytic process provides a high conversion in the disposal of NO, NO ₂ and N ₂ O to nitrogen.

The essence of the invention

The essence of the invention consists in achieving a very high concentration of cobalt centers in a zeolite of structural topology beta prepared without the use of an organic template. The high ionic capacity for cobalt cations leads to the formation of a high concentration of highly active catalytic centers for the process of selective catalytic reduction of nitrogen oxides with hydrocarbons. The proximity of these centers, and possibly the addition of alkaline earth metal to the catalyst, fundamentally increase the activity of the catalyst. The high activity of the catalysts for the selective catalytic reduction of hydrocarbons described in this patent enables a very efficient control of the elimination process of NO, NO ₂ and N ₂ O and exceeds the known catalysts based on cobalt ions in zeolite structural topology beta described in the patent

The process of selective catalytic reduction of nitrogen oxides is controlled by the high capacity for cobalt ions in zeolite beta prepared by synthesis without the use of an organic template.

A catalyst based on beta zeolite with a high lattice aluminum content (molal ratio Si/Al 3λλ 8) prepared without the use of an organic template and with active centers in the form of cobalt ions can be stored in the reactor space in the form of a catalytic bed in the form of extrudates, deposited on a monolith of a suitable shape and the diameter of the channels or it can be in the form of pellets, tablets or in another suitable form.

The catalyst production process uses methods of ion exchange in solution or in the solid phase or impregnation using cobalt salts and/or salts of the respective metals as dopants.

The efficiency of the catalyst based on zeolite beta with a high lattice aluminum content prepared without the use of an organic template and active centers in the form of cobalt ions depends on the cobalt content and its high dispersion in the catalyst. High conversions are achieved especially with the use of a catalyst with a high proportion of cobalt in the form of ion-exchanged cobalt particles in off-lattice positions.

The effectiveness of a catalyst based on zeolite beta with a high content of lattice aluminum prepared without the use of an organic template and active centers in the form of cobalt ions is increased by the presence of a dopant in the form of cations of alkaline earth metals, especially calcium, barium, or dopants based on precious metals, especially palladium. The activity depends on the dopant content and its high dispersion in the catalyst. High conversions are achieved especially with the use of barium as a dopant in an ion-exchanged form in off-lattice positions of the zeolite.

A catalytic process using a catalyst based on zeolite beta with a high lattice aluminum content prepared without the use of an organic template and active centers in the form of cobalt ions can be used for the selective catalytic reduction of nitrogen oxides contained in exhalates from various sources, mainly in combustion processes conducted for the purpose of production heat and

electrical energy, in the exhaust of diesel combustion engines, chemical technological processes such as nitric acid production plants, etc.

The catalytic process using a beta zeolite catalyst with a high lattice aluminum content prepared without the use of an organic template and active centers in the form of cobalt ions can be used for the selective catalytic reduction of nitrogen oxides using C1-C20 hydrocarbons, their derivatives and or ammonia, and is very effective for elimination of all nitrogen oxides from the group NO, NO ₂ and N ₂ O. The process can be used for exhales containing one, two or three nitrogen oxides from the group NO, NO ₂ and N ₂ O.

The catalytic process using a beta zeolite catalyst with a high lattice aluminum content prepared without the use of an organic template and active centers in the form of cobalt ions can be used for the selective catalytic reduction of nitrogen oxides using hydrocarbons at temperatures of 250*550 °C, preferably at temperatures of 300 *450 °C and at atmospheric or elevated pressure.

This patent concerns the catalytic application of these catalysts, the method of their preparation and production where the total amount of cobalt is 1 to 20^0% by weight and the amount of dopant is 0 to 25|% by weight in the form of alkaline earth metal cations, mainly calcium, barium or zinc-based dopants , iron and copper or precious metals, especially palladium.

) Specific Examples of the invention

Example 1

The Co-BEA-5 catalyst was prepared by ion exchange of zeolite beta with a high lattice aluminum content (molal ratio Si/Al 5) prepared without the use of an organic template. The ion exchange was repeated three times using a 0.05 molar solution of cobalt nitrate at a ratio of 50 ml of solution per gram of zeolite. The obtained catalyst contains 8.1% by weight. of cobalt in the form of highly dispersed Co ²⁺ ions in the off-lattice positions of the zeolite. The catalyst shows a characteristic XRD pattern (Figure 1).

To compare the catalytic activity of the Co-BEA-5 catalyst with previously known catalysts, the Co-BEA-11 catalyst was prepared. The Co-BEA-11 catalyst was prepared by ion exchange %

of zeolite beta (molal ratio Si/Al 11) prepared using an organic template. The ion exchange was repeated three times using a 0.05 molar solution of cobalt nitrate at a ratio of 50 ml of solution per gram of zeolite. The obtained catalyst contains 4% by weight of Tobalt in the form of highly dispersed Co ²⁺ ions in off-lattice positions of the zeolite.

Example 2

The CoBa-BEA-4 catalyst was prepared by ion exchange of zeolite beta with a high lattice aluminum content (molar ratio Si/Al 4) prepared without the use of an organic template. Ion exchange was repeated three times using 0.05 mol cobalt nitrate solution and 0.05 mol bamate nitrate solution at a ratio of 50 ml of solution per gram of zeolite. The obtained catalyst contains cobalt in the form of highly dispersed Co ²⁺ ions in off-lattice positions of the zeolite and Ba ²⁺ ions on off-lattice positions of the zeolite.

The CoBa-BEA-11 catalyst was prepared by ion exchange of zeolite beta (Si/Al molar ratio 11) prepared using an organic template. Ion exchange was repeated three times using 0.05 mol cobalt nitrate solution and 0.05 mol bamate nitrate solution at a ratio of 50 ml of solution per gram of zeolite. The obtained catalyst contains cobalt in the form of highly dispersed Co ²⁺ ions in off-lattice positions of the zeolite and Ba ²⁺ ions on off-lattice positions of the zeolite.

Example 3

A stream of exhaled gases with a composition of 960 ppm NO, 40 ppm NO ₂ , 1000 ppm C ₃ H ₈ , 0.7% H ₂ , 0.1% O ₂ and a temperature of 300–450 °C is fed into a reactor with a catalytic bed containing a catalyst prepared according to example 1 The mass of the catalyst is 100 mg and the space velocity is 90,000 h ¹ . The conversions of nitrogen oxides to nitrogen as a function of temperature are shown in Table 1.

Example 4

The exhaled stream with a composition of 960 ppm NO, 40 ppm NO ₂ , 1000 ppm C ₃ H ₈ , 3j/o H ₂ O and 3% O ₂ and a temperature of 400 °C is fed into a reactor with a catalytic bed containing the Catalyst prepared according to Example 1. The mass of the catalyst is 100 mg and the space velocity is 90,000 h' ¹ . Conversion of nitrogen oxides to nitrogen is 96%.

Example 5

A flow of exhaled gases with a composition of 960 ppm NO, 40 ppm NO ₂ , 3000 ppm CH4, 1 (^ó H ₂ O and 3% O ₂ and a temperature of 400 °C) is fed into a reactor with a catalytic bed containing a catalyst prepared according to example 1. Mass of catalyst is 100 mg and the space velocity is 90,000 h' ^1. The conversion of nitrogen oxides to nitrogen is 95%ó.

Example 6

An exhaled stream with a composition of 250 ppm NO, 800 ppm NO ₂ , 1000 ppm N ₂ O and 3000 ppm CH4, O, 70o H ₂ O, 3% O ₂ and a temperature of 350-450 °C is fed to a reactor with a catalytic bed containing a catalyst prepared according to example 1 and the space velocity is 11,250 h' ¹ . The conversions of nitrogen oxides to nitrogen as a function of temperature are shown for the Co-BEA-5 catalyst in Table 2.

Example 7

A stream of exhalates with a composition of 1000 ppm NO, 3000 ppm CH4, 0.7 ¹ % H ₂ O and 3% O ₂ and a temperature of 400050 °C is fed into a reactor with a catalytic bed containing the catalyst prepared according to example 1. The mass of the catalyst is 100 mg and space velocity 11 250 h' ¹ . The conversions of nitrogen oxides to nitrogen as a function of temperature are shown for the Co-BEA-5 catalyst in Table 3.

Example 8

Exhalate stream with a composition of 250 ppm NO, 800 ppm NO ₂ , 1000 ppm N ₂ O and 3000 ppm CH ₄ , 0.7& V

H ₂ O, O ₂ and a temperature of 350050 °C is fed into a reactor with a catalytic bed containing a catalyst prepared according to example 2. The mass of the catalyst is 100 mg and the space velocity is 15,000 h ¹ . The conversions of nitrogen oxides to nitrogen as a function of temperature are shown in Table 4.

Example 9

The stream of exhalates with a composition of 1000 ppm NO, 1000 ppm N ₂ O, 1000 ppm C ₃ H ₈ , 0.7% H ₂ O, 3^ó O ₂ and a temperature of 350050 °C is fed into a reactor with a catalytic bed containing a catalyst prepared according to of example 2. The mass of the catalyst is 100 mg and the space velocity is 200,000 h *. The conversions of nitrogen oxides to nitrogen as a function of temperature are shown in Table 5.

Table 1

Temperature (°C) Conversion of NO and NO ₂ (%) Co-BEA-5 Co-BEA-11 350 34.2 9 375 67.3 19 400 96.2 27 425 99.3 40 450 99.7 61

Table 2

Temperature (°C) Conversion of NO and NO ₂ (%) N ₂ O conversion (%) 450 89.2 99.6 425 73.5 90.0

Table 3

Temperature (°C) Conversion of NO and NO ₂ (%) 450 97 440 94 425 91 400 82

Table 4

Temperature (°C) Conversion of NO and NO ₂ (%) N ₂ O conversion (%) CoBa-BEA-4 CoBa-BEA-11 CoBa-BEA-4 CoBa-BEA-11 450 98 85 99.8 98 425 96 75 97 90

%

Table 5

Temperature (°C) Conversion of NO and NO ₂ (%) N ₂ O conversion (%) CoBa-BEA-4 CoBa-BEA-11 CoBa-BEA-4 CoBa-BEA-11 400 99 80 98 96 350 90 60 96 88 300 80 25 90 80

Claims (8)

PATENT CLAIMS 1. Catalyst for the selective catalytic reduction of nitrogen oxides, characterized by the fact that it contains zeolite beta with lattice aluminum content with a Si/Al molar ratio ranging from 3 to 8, prepared without the use of an organic template, and active centers in the form of cobalt ions. 2. Catalyst for the selective catalytic reduction of nitrogen oxide according to claim 1, characterized in that it is characterized by an X-ray diffractogram with intensities of 7.j[ to 8.4; 21.7 to 22.8; 24.8 to 25.2; 28.2 to 28.7 and 29.1 to 29.4 of two theta degrees. 3. Catalyst for the selective catalytic reduction of nitrogen oxides according to claim 1 or 2, characterized in that the total amount of cobalt is 1 to 20% by weight, and further contains a dopant in the amount of 0 to 25% by weight in the form of ions of at least one metal selected from metals IIA , IIIA, IVA, IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIIIB groups of the periodic table, preferably in the form of alkaline earth metal cations, preferably calcium and barium ions, or in the form of zinc, copper, iron and or in the form of precious metals, especially palladium. 4. Catalyst for the selective catalytic reduction of nitrogen oxides according to any one of the preceding claims, characterized in that it contains admixtures of zeolites of other crystallographic structures, especially admixtures of zeolites of the structural topology MOR, FER or MFL 5. A method of preparing a catalyst for the selective catalytic reduction of nitrogen oxides according to any one of the preceding claims, characterized in that zeolite beta from a template-free synthesis with a lattice aluminum Si/Al ratio in the range of 3 to 8 is subjected to ion exchange in solution or in the solid phase or impregnation with cobalt salts, or with dopant salts. 6. A method of treating exhalates containing nitrogen oxides, characterized in that nitrogen oxides contained in exhalates with an oxidizing atmosphere are reduced to nitrogen by catalytic reduction using a catalyst according to any one of claims 1 to 4 at a temperature ranging from 250°C to 550°C, with preferably at a temperature ranging from 300 °C to 450 °C, and at atmospheric or elevated pressure. 7. The method of treating exhalates containing nitrogen oxides according to claim 6, characterized in that the nitrogen oxides are selected from the group including NO, NO ₂ , N ₂ O, N ₂ O ₅ and their mixtures. 8. The method of treating exhalates containing nitrogen oxides according to claim 6 or 7, characterized in that the reduction is carried out with a reducing agent selected from the group containing diesel fuel, bio-diesel fuel, gasoline, oil, kerosene, ammonia, urea, Ci to C20 hydrocarbons, such as alkanes, alkenes, aromatic hydrocarbons, alcohols, ethers, aldehydes, ketones, and mixtures thereof.