Cobalt-containing beta zeolite, method of its preparation, and use thereof in catalyzed reduction of nitrogen oxides

Field of Art

The invention relates to the elimination of nitrogen oxides from emissions of combustion and technological processes using a zeolite-based catalyst, which can be prepared without use of organic templates. The catalyst has a high content of aluminium and it contains cobalt in non-lattice positions. The invention further relates to a method of preparation of the above mentioned catalyst and to a method of a selective catalytic reduction of nitrogen oxides into nitrogen gas.

Background Art Emissions of nitrogen oxides (NO _x ), i.e. NO, N0 ₂ , N ₂ 0 _3} N 0 ₄ and N ₂ 0, as side products of combustion of the so called poor fuel mixtures or from chemical production processes, represent a severe environmental problem. The emissions are being limited by legislative regulations. A selective catalytic reduction of nitrogen oxides (NO, N0 ₂ ) into nitrogen and water vapors using ammonia is an efficient and a widely used process for abatement emissions of NO and N0 ₂ . N ₂ 0 is usually converted into nitrogen and oxygen at high temperatures by its catalytic decomposition.

The selective catalytic reduction using ammonia is utilized mainly for stationary sources of NO and N0 ₂ (chemical processes such as nitric acid production, emissions from nitration processes etc.), and during fuel combustion during energy production (power station, heating plant) or incineration. Literature often describes a process of selective catalytic reduction of nitrogen oxides using hydrocarbons (CH-SCR-NO _x ). It is a promising method of nitrogen oxide elimination from oxygen-containing emissions. During the CH-SCR-NO _x process, the reducing agent (hydrocarbons or derivatives thereof) is administered into a flow of emissions containing nitrogen oxides, oxygen and optionally non-reacted hydrocarbons and derivatives thereof. The resulting gas mixture flows over a catalytic bed on which the reduction of nitrogen oxides occurs. The main drawback of this process is the insufficient activity/selectivity of the hitherto known catalysts or insufficient stability of NO _x conversion at high temperatures. Precious metal-based catalysts show a certain activity at low temperatures, but they are suitable only for a very limited range of temperatures. Ionic form of cobalt shows a catalytic activity when placed in non-lattice positions of zeolites. The activity of such catalysts, however, is not sufficient to be used in practice. Therefore, the significance of the above mentioned catalysts in the current technologies is negligible.

Catalysts based on cobalt ions in beta zeolites, destined for selective catalytic reduction of nitrogen oxides (NO, N0 ₂ ) using hydrocarbons, are described in US 5869013. Their preparation is based on common ion exchange processes between cobalt salt solutions and beta zeolite. Beta zeolite (according to IZA called BEA* and composed of three polymorphs A, B, and C) consists of 4-, 5- and 6-membered rings, forming a three- dimensional channel structure with 12-membered entrance holes of 6.6 x 6.7 A (Ch. Baerlocher, L.B. McCusker and D.H. Olson, Atlas of Zeolite Framework Types, 6th revised edition, 2007). Such channel structure and the absence of large cavities (unlike in zeolite Y) means a substantial advantage for fast transport of molecules in catalytic processes in crude oil processing, paraffin elimination, paraffin isomerization, benzene alkylation using low olefines as well as in organic chemistry during special compounds production. Beta zeolite was first described in US3308069. One disadvantage with respect to industrial use of beta zeolites prepared by classical methods is the need to use a relatively expensive tetramethylammoniumhydroxide (TMAOH) or an analogical organic template during the hydrothermal synthesis of such zeolite. Another disadvantage of such procedures is the limitation of maximum aluminium content in the lattice of zeolites, corresponding to the Si/Al ratio > 11. US5869013 uses this type of beta zeolite.

Since 2008, procedures for synthesis of beta zeolites with high aluminium content in lattice are known, the Si/Al ratio falling down to 3 (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). These procedures replace the organic template during the synthesis by addition of beta zeolite into aluminium silicate gel as a source of crystal nuclei. The above mentioned procedures enable high-crystalline beta zeolite synthesis, leading towards well-formed crystals of 0.3 to 0.5 μηι and high aluminium lattice content.

The present invention aims to solve the problem of elimination of all nitrogen oxides from emissions by their selective catalytic reduction, using preferably hydrocarbons as the reducing agents.

Disclosure of the Invention

The present invention provides a unique and highly efficient catalyst, based on cobalt ions distributed in beta zeolite with high lattice content of aluminium. Such catalytic process provides a high conversion of NO, N0 _2j N ₂ 0 ₅ and N ₂ 0 into nitrogen.

The present invention uses beta zeolites, which are prepared without the use of organic templates. The beta zeolites used in this invention are prepared by the method of synthesis using addition of beta zeolite into aluminium silicate gel as a source of crystal nuclei, and have a high lattice content of aluminium (being molar ratio Si/Al from 3 to 8). They are used to prepare cobalt-based catalysts for selective catalytic reduction of nitrogen oxides. Such catalysts according to the present invention provide high activities, significantly exceeding those of the materials known in the art.

Thus, the object of the present invention is a catalyst which contains beta zeolite having the content of aluminium in the lattice corresponding to Si/Al ratio in the range of from 3 to 8, and containing cobalt ions as active centers.

Preferably, such catalyst is obtainable by addition of beta zeolite as a source of crystal nuclei into aluminium silicate gel, followed by crystallization, and ion-exchange process using Co ²⁺ ions. This means that the catalyst is obtainable without the use of organic templates. In a preferred embodiment, the catalyst has main peaks in its XRD diffraction pattern obtained using CU _& radiation in Bragg-Brentano geometry in the following ranges: 7.2- 8.4; 21.7-22.4; 24.8-25.2; 28.2-28.7 and 29.1-29.4 degree 2-theta. In another preferred embodiment, the content of the cobalt ions in the catalyst lies between 1 and 20 % (w/w), more preferably between 7 and 12 % (w/w).

In one embodiment, the catalyst contains up to 25 % (w/w) of a dopant selected from a group containing IIA, IIIA, IV A, IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIIIB metal ions. The presence of the dopant may increase the efficiency of the beta zeolite based catalyst according to the present invention.

In a preferred embodiment, the dopant is selected from alkaline earth metal ions and or transition metal ions and/or precious metal ions, in particular from a group containing Ca ²⁺ , Ba ²⁺ , Zn ²⁺ , Cu ²⁺ , Fe ²⁺ , Pd ²⁺ . Most preferable dopant is barium in an ion-exchange form in non-lattice positions of the zeolite.

In another embodiment, the catalyst according to the present invention further contains zeolites of different crystalographical structures, preferably zeolites of structural topology MOR, FER and/or MFI.

The present invention further provides a method of preparation of the catalyst according to the present invention. In a first step, beta zeolite is added into aluminium silicate gel as a source of crystal nuclei, in a second step the crystallization of the beta zeolite is carried out, and in a third step, ion-exchange process with Co solution occurs. The method of preparation of the catalyst utilizes solution and/or solid state ion exchange. It can also rely on the impregnation using cobalt salts. The Co solution is typically a solution of Co(II) salt, such as nitrate, halogenide, sulfate, carbonate, acetate, or any other soluble Co(II) salt. The Co ²⁺ solution may be used, for example, in an amount of about 1 to about 100 ml per 1 g of beta zeolite, and in a concentration of 0.01 to 10 M. Most suitable amount is 50 ml of 0.05 M Co ^2÷ solution per 1 g of beta zeolite. In another embodiment, the method of preparation of the catalyst uses in the ion-exchange step Co ²⁺ and dopant solution, wherein the dopant is selected from the group containing IIA, IIIA, IV A, IB, IIB, IIIB, IVB, VB, VIB, VIIB, VIIIB metal ions, preferably selected from Ca ²⁺ , Ba ²⁺ , Zn ²⁺ , Cu ²⁺ , Fe ²⁺ , Pd ²⁺ . The dopant salts used can be any salts soluble in the solvent which is used for the ion-exchange, such as nitrates, halogenides, sulfates, carbonates, acetates, or any other soluble salts. The solvent used for ion exchange is typically water, however other polar solvents might also be used. When the method of impregnation is used, cobalt salts and salts of metals suitable as dopants are utilized. The present invention further includes a method of catalytic reduction of nitrogen oxides using the catalyst according to the present invention. The temperature of the reduction reaction lies in a range of from 150 °C to 550 °C, preferably from 300 °C to 450 °C, the pressure is equal or higher than atmospheric and the reducing agent is present in a concentration of 50 to 10 000 ppm (from 0.5 mol. equiv. to 10 mol. equiv. of nitrogen oxides, which are being reduced).

In one preferred embodiment, nitrogen oxides are selected from the group containing NO, Ν0 ₂ , N ₂ 0, 2O5 and mixtures thereof. In another preferred embodiment, the reducing agent is preferably selected from the group containing diesel fuel, bio-diesel fuel, gasoline, oil, paraffin, ammonia, urea, and C| to C ₂ o hydrocarbons, such as alkanes, alkenes, aromates, alcohols, ethers, aldehydes, ketones, and mixtures thereof. The present invention further includes the use of the catalyst according to the present invention for the elimination of nitrogen oxides from emissions.

The beta zeolite-based catalyst with a high aluminium content (molar ratio Si/Al is from 3 to 8) and cobalt ions as active centers, prepared without the use of organic template, can be placed as a catalytic bed in a reactor space in the form of extrudates. It can also be applied on the surface of a monolite of a suitable shape and channel diameter or it can be used in the form of pellets, tablets or other suitable shapes. The beta zeolite based catalyst according to the present invention can thus be used in selective catalytic reduction of nitrogen oxides present in emissions from various sources, such as from combustion processes in heat and electric energy production, diesel combustion motors, and chemical technological processes (nitric acid production etc.).

A skilled person will appreciate that the various embodiments and preferred embodiments described in this disclosure can be combined. The invention is further explained using the following examples which should, however, not be construed as limiting the scope of the invention.

Brief description of figures Fig. 1 : XRD diffractogram of the Co-BEA-5 catalyst, prepared according to Example 1. Fig. 2: XRD diffractogram of the CoBa-BEA-4 catalyst, prepared according to Example 2. Fig. 3: XRD diffractogram of the Co-BEA/MOR-4.5 catalyst, prepared according to Example 13. Examples

Example 1

The catalyst Co-BEA-5 was prepared by an ion-exchange of beta zeolite with high content of lattice aluminium (molar ratio Si/Al was 5) prepared by addition of beta zeolite into aluminium silicate gel as a source of crystal nuclei and subsequent crystallization, i.e. without use of an organic template. The ionic exchange was repeated three times, using 0.05 M Co(N0 ₃ )2 (50 ml of the solution per 1 g of zeolite). The obtained catalyst contained 8.1 % (w/w) of cobalt in a form of highly dispersed Co ²⁺ ions in non-lattice positions of the zeolite. The catalyst showed an XRD diffractogram (see Fig. 1). The XRD diffraction pattern was obtained using Cu _Ka radiation in Bragg-Brentano geometry in the following ranges: 7.2-8.4; 21.7-22.4; 24.8-25.2; 28.2-28.7 and 29.1-29.4 degree 2-theta. Comparative example 1 A

In order to compare the catalytic activity of Co-BEA-5 with known catalysts, a catalyst Co-BEA-11 was prepared. Co-BEA-11 was prepared by an ion-exchange of beta zeolite (molar ratio Si/Al was 11) prepared using an organic template. The ionic exchange was repeated three times, using 0.05 M Co(N03) ₂ (50 ml of the solution per 1 g of zeolite). The obtained catalyst contained 4 % (w/w) of cobalt in a form of highly dispersed Co ions in non-lattice positions of the zeolite. The intensities and patterns of the X-ray diffraction lines for Co-BEA-1 1 obtained using Cu _.a radiation in Bragg- Brentano geometry were characteristic of the well-developed crystalline structure of BE A* topology. All observed reflections are shifted by 0.3 degree 2-theta to the lower values compared to BEA-5 indicating the low concentration of Al for Co-BEA-11.

Example 2

The catalyst CoBa-BEA-4 was prepared by an ion-exchange of beta zeolite with high content of lattice aluminium (molar ratio Si/Al was 4) prepared by addition of beta zeolite into aluminium silicate gel as a source of crystal nuclei and subsequent crystallization, i.e. without use of an organic template. The ionic exchange was repeated three times, using a solution containing 0.05 M Co(N0 ₃ ) ₂ and 0.05 M Ba(N0 ₃ ) ₂ (50 ml of the solution per 1 g of zeolite). The obtained catalyst contained cobalt in a form of highly dispersed Co ²⁺ ions (7.5 % (w/w)) in non-lattice positions of the zeolite and Ba ²⁺ ions (2 % (w/w)) in non- lattice positions of the zeolite.

Comparative example 2A

The catalyst CoBa-BEA-1 1 was prepared by an ion-exchange of beta zeolite (molar ratio Si/Al was 11) prepared using an organic template. The ionic exchange was repeated three times, using a solution containing 0.05 M Co(N03) ₂ and 0.05 M Ba(N0 ₃ )2 (50 ml of the solution per 1 g of zeolite). The obtained catalyst contained cobalt in a form of highly dispersed Co ²⁺ ions (3 %(w/w)) in non-lattice positions of the zeolite and Ba ²⁺ ions (1 % (w/w)) in non-lattice positions of the zeolite. The intensities and patterns of the X-ray diffraction lines for Co/Ba-BEA-11 obtained using CU Q radiation in Bragg-Brentano geometry were characteristic of the well-developed crystalline structure of BEA* topology. All observed reflections are shifted by 0.3 degree 2-theta to the lower values compared to CoBa-BEA-4 indicating the low concentration of Al for Co/Ba-BEA-11.

Example 3

A flow of emissions composed of 960 ppm NO, 40 ppm N0 ₂ , 1000 ppm C ₃ H ₈ , 0.7 % H ₂ 0, 3 % 0 ₂ at the temperature of from 300 °C to 450 °C was driven to a reactor with a catalytic bed containing the catalyst prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 90 000 h ^"1 . The same experiment was repeated with the catalyst prepared in Comparative example 1A. The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 1.

Analysis of NO, N0 _2s N ₂ 0, N ₂ , NH ₃ , 0 _2} CO _x and C _x H _y at the reactor outlet was performed using an Advanced Optima (ABB) IR analyzer (N ₂ 0), AH (MLU) chemiluminescence analyzer (NO, N0 ₂ ), UV photometric analyzer ABB AO2000-Limasl 1UV (NO, N0 ₂ , NH ₃ ) and Hewlett Packard 5890 II Gas chromatograph (C _x H _y , CO _x , N ₂ , 0 ₂ , N ₂ 0).

Example 4

A flow of emissions composed of 960 ppm NO, 40 ppm N0 ₂ , 1000 ppm C ₃ ¾, 3 % H ₂ 0, 3 % 0 ₂ at the temperature of 400 °C was driven to a reactor with a catalytic bed containing the catalyst prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 90 000 h ^"! . The conversion of nitrogen oxides into nitrogen was 96%.

Example 5

A flow of emissions composed of 960 ppm NO, 40 ppm N0 _2s 3000 ppm CH ₄ , 10 % H ₂ 0, 3 % 0 ₂ at the temperature of 400 °C was driven to a reactor with a catalytic bed containing the catalyst prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 90 000 h ^"1 . The conversion of nitrogen oxides into nitrogen was 95%.

Example 6

A flow of emissions composed of 250 ppm NO, 800 ppm N0 ₂ , 1000 ppm N ₂ 0, 3000 ppm CH4, 0.7 % H ₂ 0, 3 % 0 ₂ at the temperature of from 350 °C to 400 °C was driven to a reactor with a catalytic bed containing the catalyst Co-BEA-5 prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 11 250 h ^"1 . The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 2.

Example 7

A flow of emissions composed of 1000 ppm NO, 3000 ppm CH ₄ , 0.7 % H ₂ 0, 3 % 0 ₂ at the temperature of from 400 °C to 450 °C was driven to a reactor with the catalytic bed containing a catalyst Co-BEA-5 prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 11 250 h ^"1 . The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 3.

Example 8

A flow of emissions composed of 250 ppm NO, 800 ppm N0 ₂ , 1000 ppm N ₂ 0, 3000 ppm CHU, 0.7 % ¾0, 3 % 0 ₂ at the temperature of from 350 °C to 450 °C was driven to a reactor with a catalytic bed containing the catalyst prepared according to Example 2. The weight of the catalyst was 100 mg and the spatial velocity was 15 000 h ^"1 . The same experiment was repeated using the catalyst of Comparative example 2A. The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 4.

Example 9

A flow of emissions composed of 1000 ppm NO, 1000 ppm N ₂ 0, 1000 ppm C ₃ H ₈ , 0.7 % H ₂ 0, 3 % 0 ₂ at the temperature of from 350 °C to 450 °C was driven to a reactor with a catalytic bed containing a catalyst prepared according to Example 2. The weight of the catalyst was 100 mg and the spatial velocity was 200 000 h ^"1 . The same experiment was repeated using the catalyst of Comparative example 2 A. The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 5.

Example 10

The catalyst Co/Pd/Fe-BEA-6 was prepared by an ion-exchange of beta zeolite with high content of lattice aluminium (molar ratio Si/Al was 6) prepared by addition of beta zeolite into aluminium silicate gel as a source of crystal nuclei and subsequent crystallization, i.e. without use of an organic template. The ionic exchange was performed using 0.1 M Co(N0 ₃ ) ₂ (10 ml of the solution per 1 g of zeolite) to obtain Co-BEA-6. Fe was introduced into Co-BEA-6 by its impregnation with anhydrous FeCl ₃ in acetylacetone, following calcination in air at 550 °C for 2 h. Pd was introduced into Co/Fe-BEA-6 by impregnation with aqueous solution of Pd(N0 ₃ ) ₂ , following calcination in air at 450 °C for 2 h. The obtained catalyst contained 4% (w/w) of cobalt, 7% (w/w) of iron and 0.5% (w/w) of palladium.

Example 11

A flow of emissions composed of 450 ppm NO, 60 ppm N0 ₂ , 520 ppm N¾, 10 % H ₂ 0, 8 % 0 ₂ at the temperature of from 150 °C to 300 °C was driven to a reactor with a catalytic bed containing a catalyst prepared according to Example 10. The weight of the catalyst was 20 mg and the spatial velocity was 600 000 h ^"1 . The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 6.

Example 12

A flow of emissions composed of 450 ppm NO, 60 ppm N0 _2; 200 ppm decane, 10 % H ₂ 0, 8 % 0 ₂ at the temperature of from 250 °C to 350 °C was driven to a reactor with a catalytic bed containing a catalyst prepared according to Example 1. The weight of the catalyst was 100 mg and the spatial velocity was 42 000 h ^"1 . The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 7.

Example 13

The catalyst Co-BEA/MOR-4.5 was prepared by an ion-exchange of beta zeolite with high content of lattice aluminium (molar ratio Si/Al was 5) and zeolite structural topology MOR prepared by addition of beta and mordenite (MOR) zeolite into aluminium silicate gel as a source of crystal nuclei and subsequent crystallization, i.e. without use of an organic template. The ionic exchange was repeated three times, using 0.05 M Co(N0 ₃ ) ₂ (50 ml of the solution per 1 g of zeolite). The obtained catalyst contained 9.2 % (w/w) of cobalt in a form of highly dispersed Co ²⁺ ions in non-lattice positions of the zeolite. The catalyst showed an XRD diffractogram (see Fig. 3). The XRD diffraction pattern was obtained using Cuj _a radiation in Bragg-Brentano geometry in the following ranges: 7.2-8.4; 21.7- 22.4; 24.8-25.2; 28.2-28.7 and 29.1-29.4 degree 2-theta reflecting the beta zeolite, and 6.2- 6.6, 9.4-9.9, 13.1-13.9, 15.0-15.4, 19.4-19.7 and 26.0-26.4 degree 2-theta reflecting the mordenite zeolite. Example 14

A flow of emissions composed of 960 ppm NO, 40 ppm N0 ₂ , 1000 ppm 0 ₃ ¾, 0.7 % H ₂ 0, 3 % 0 ₂ at the temperature of from 300 °C to 450 °C was driven to a reactor with a catalytic bed containing the catalyst prepared according to Example 13. The weight of the catalyst was 100 mg and the spatial velocity was 90 000 h ^"1 . The dependence of the conversion of nitrogen oxides into nitrogen on temperature is listed in Table 8.

Table 1

Table 2

Temperature (°C) Conversion of NO and N0 ₂ (%) Conversion of N ₂ 0 (%)

450 89.2 99.6

425 73.5 90.0

Table 3

Temperature (°C) Conversion of NO andN0 ₂ (%)

450 97

440 94

425 91

400 82 Table 4

Table 5

Table 6

Temperature (°C) Conversion of NO and N0 ₂ (%)

150 94

200 99

250 99

300 97

Table 7

Temperature (°C) Conversion of NO and N0 ₂ (%)

250 94

300 97

350 97 Table 8

Temperature (°C) Conversion of NO and N0 ₂ (%)

350 25

375 50

400 93

425 94