RU2430781C1 - Catalyst, preparation method thereof and method of decomposing nitrogen oxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a catalyst for selective decomposition of nitrogen oxide under Ostwald process conditions, as well as in conditions with ammonia slip after platinoid mesh. Described is a catalyst which is a block with cellular structure consisting of porous ceramic oxide carrier on which a catalytically active phase of formula LaMe¹ _xFe_1-xO₃ is deposited, where: Me = Cu, Co, Mg, Ni, Zn, x=0-0.4, wherein the volume of transport pores with characteristic size 300-2000 Å in the catalyst is equal to at least 0.25 cm³/g.The invention also describes a method of preparing said catalyst and a method of decomposing nitrogen oxide using said catalyst.

EFFECT: preparation of an active and thermally stable catalyst for decomposing nitrogen oxide under Ostwald process conditions in the temperature range 800-1000°C and pressure 0,9-9 bars.

9 cl, 5 ex, 5 tbl, 2 dwg

Description

The invention relates to a ceramic block catalyst for the selective decomposition of nitrous oxide under the conditions of the Ostwald process at a temperature of 800-1000 ° C and a pressure of 0.9 ÷ 9 bar and a method for its preparation. The invention also includes a method of carrying out a process using this catalyst.

Nitrous oxide is the main source of NO _x in the stratosphere, which leads to the destruction of the ozone layer. In addition, its potential for global warming exceeds the values characteristic of CO ₂ and CH _{4 by} 310 and 21 times, respectively (J. Perez-Ramirez, F. Kaptein, K.Shoffel, JAMoulijn, Applied Catalysis B: Environmental 44 (2003) 117-151). As a result, worldwide efforts are being made to reduce the level of anthropogenic emissions of N ₂ O by decomposing it to N ₂ and O ₂ .

The Ostwald process is traditionally used to produce nitric acid by catalytic combustion of ammonia on grids consisting of Pt-Rh (-Pd) alloys. Nitrogen and N ₂ O are emitted as by-products of ammonia oxidation into the atmosphere after all stages of the process. The concentration of N ₂ O after conventional catalytic networks varies from 500 to 3000 ppm, but their further modification is primarily aimed at increasing NO _x selectivity due to reduce nitrogen formation. Since the process of producing nitric acid is a highly optimized production, any change in the process chain will require large investments. Therefore, the most simple from a technological point of view is the decomposition of N ₂ O directly in the converter, when the catalyst is placed immediately after the platinum chains instead of a layer of Raschig rings. Such a solution, however, puts forward very stringent requirements for the catalyst, determined primarily by the process conditions in the ammonia oxidation reactor: temperature - 800 ÷ 1000 ° C, linear gas velocities - up to 7 m / s, aggressive environment - nitrogen oxides, water, ammonia. The negative effect of the latter factor is expressed in the fact that insufficiently resistant materials can release compounds which, when released into the final product (mainly ammonium nitrate), cause its decomposition with an explosion.

Thus, catalysts that effectively remove N ₂ O under the conditions of the Ostwald process, in addition to high activity, must meet the following requirements both in terms of the efficiency of the process and its safety:

- thermal stability;

- stability in aggressive environments;

- inertia with respect to NO;

- low gas-dynamic resistance of the catalyst layer.

The latter requirement is most easily solved by using a catalyst in the form of blocks with a honeycomb structure, which are installed immediately after the packet of meshes instead of a layer of Raschig rings. In addition, an increase in the channel density allows, due to the geometric factor, to significantly increase the active surface without a significant increase in the pressure drop across the layer, which is practically impossible in the case of using catalysts of a different geometric shape, for example, granules, Raschig rings.

A block with a honeycomb structure can directly consist of an active component mixed with a binder (so-called massive monoliths), and also represent a carrier with an active component deposited. From the point of view of the distribution of the active component, catalysts are distinguished in which the active component is localized on the outer surface of the block or distributed uniformly along the wall depth (P. Avila, M. Montes, EEMiro, Chem. Journal 109 (2005) 11-36) .

In relation to the possibility of preparing block catalysts, we analyzed information on previously developed catalytic systems, including supported ones, which can be used under the conditions of the Ostwald process (Т = 850 ÷ 950 ° С, Р = 1 ÷ 15 atm, contact time ≤0.1 s).

In a series of patents and applications filed by HERAEUS GMBH W C [DE] (DE 102004024026 A1, US 20050202966, US 2009130010 A1, RU 2304465 C2, EP 15863665 A2), a catalyst is proposed that contains a carrier consisting of alpha-Al ₂ O ₃ , ZrO ₂ , CeO _2, or mixtures thereof, and a coating on a support of rhodium or rhodium oxide or a mixed Pd-Rh catalyst.

Mixed oxides of zirconium and cerium, taken in a ratio of 20/80 to 80/20 and forming a solid solution, appear as a catalyst for the decomposition of N ₂ O in the temperature range from 700 to 1,000 ° C and costs of more than 50,000 h ^-1 (US 7192566 )

PORZELLANWERK CLOSTER FILESDORF GMBH (DE) (US 20040179986, RU 2221642) has patented a powdered catalyst, which consists of a porous ceramic support and a catalytically active phase, the support being at least 95% composed of one or more alkaline earth metal compounds (MgO, CaO). The active component is an oxide / mixture of oxides Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, In, Ag, Ti, Y, Zr, La, Ca, Sr and Ba.

Catalysts based on various mixed oxides with a perovskite or spinel structure are of particular interest, since such systems have high thermal stability and are resistant to aggressive environments. So, for the decomposition of N ₂ O in NO gases, YARA INTERNATIONAL ACA (NO) (US 20040023796, RU 2237514) offers a catalyst containing 0.1-10 mol.% Co _3-x M _x O ₄ , where M represents Fe or Al and x = 0.25-2, on the carrier - cerium oxide. Mixed oxides of other metals with variable valency (Cu, Mn, Fe, La, Y) with a perovskite structure can also be applied to cerium oxide and zirconium oxide (EP 1504805 A1).

The active components based on copper-containing spinel of the composition CuAl ₂ O ₄ modified with Zn, Pb and / or one of the elements of the second group of the periodic system of elements (WO 99/55621, US 6743404, US 6723295) formed the basis of granular (cuttings, Rashig rings, trefoils) of O3-85 and O3-86 catalysts for industrial applications developed by BASF AG (www.basf.de; G. Kuhn: Proceeding of the Krupp Uhde Technologies Users' Group Meeting 2000, Vienna, March 14-16, 2000). Subsequent BASF patents propose modifying the CuO-Zn (Pb) -Al ₃ O _{3 system} with elements such as Ag, Au, Mg, Co, Ni, Pd, Pt, Ru, Os, Ir, and / or Rh (DE 10016276 A1 ), as well as applying the active component to woven and knitted grids of Fe-Cr-Al alloy and then forming three-dimensional structures from them (US 7364711). Moreover, the range of possible active material deposition was significantly expanded and included simple oxides (MgO, CoO, MoO ₃ , NiO, ZnO, Cr ₂ O ₃ , WO ₃ , SrO, CuO / Cu ₂ O, MnO ₂ , V ₂ O ₅ ), mixed oxides (CuO-ZnO-Al ₂ O ₃ , CoO-MgO, CoO-La ₂ O ₃ , La ₂ CuO ₄ , Nd ₂ CuO ₄ , Co-ZnO, NiO-MoO ₃ ), including with the structure perovskite (LaMnO ₃ , CoTiO ₃ , LaTiO ₃ , CoNiO ₃ ) or spinel (CuAl ₂ O ₄ , ZnAl ₂ O ₄ , MgAl ₂ O ₄ , (Cu, Zn) Al ₂ O ₄ , (Cu, Zn, Mg) Al ₂ O ₄ , (Cu, Zn, Ba) Al ₂ O ₄ , (Cu, Zn, Ca) Al ₂ O ₄ , La ₂ NiO ₄ ).

In relation to massive monoliths, the use of any copper-containing compounds as an active component is very problematic from a safety point of view, since copper can be released from the catalyst and, when it enters the final product, ammonium nitrate, catalyzes its decomposition [Applied Catalysis B: Environmental, 44 (2003 ), 117-151]. This is what significantly limits the use of bulk catalysts based on CuO [US 6743404, WO 9955621], including the proposed BASF 03-85 and 03-86. It is also economically disadvantageous to use an active component based on rhodium (DE 102004024026 (A1), US 20050202966, US 2009130010 (A1), RU 2304465, EP 15863665 (A2)). It is rather difficult to form alkaline earth metal oxides (MgO, CaO) in the form of blocks with a sufficiently high channel density, which are offered as carriers for supported catalysts based on the oxides Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, In, Ag , Ti, Y, Zr, La, Ca, Sr and Ba (US 20040179986, RU 2221642).

Catalysts consisting of mixed oxides with the structure of perovskite or spinel, as well as fluorite (CeO ₂ , ZrO ₂ ) can be formed into blocks with a honeycomb structure with a sufficiently high channel density.

Closest to the proposed invention in its technical essence and the achieved effect is a method of decomposition of nitrous oxide on a block catalyst of a honeycomb structure with an active component of the composition M ¹ M ² _1-x M ³ _x O ₃ with a perovskite crystal lattice, where x = 0.05 ÷ 0.9, M ¹ is selected from La, Ce, Nd, Pr, Sm and / or a combination thereof, M ² from Fe, Ni and / or a combination thereof, M ³ from Cu, Co, Mn and / or a combination [WO 2007 / 104403 A1, B01J 23/00, 09/20/2007; RU 2006107288 A, B01J 21/00, 09/20/2007]. In this case, the active component can be introduced either directly into the plastic mass for extrusion, or applied by all known methods to ready-made blocks of the carrier of the honeycomb structure. Regardless of the material of the carrier, preference is given to samples with a high (more than 5 m ² / g) specific surface area.

The specific surface area of the material is highly dependent on its calcination temperature. To avoid sintering during operation, the latter, in turn, should be higher than the upper limit of the temperature range in which it is supposed to be used (750 ÷ 950 ° C). For most materials used as carriers, after calcination at T> 1000 ° C, the specific surface area does not exceed 20 m ² / g. In this case, the porous structure can differ dramatically, depending on the nature of the carrier material, as well as additives used to improve the formability of the blocks and their final strength.

Meanwhile, ammonia oxidation refers to processes for which diffusion restrictions not only reduce the overall reaction rate, especially with increasing pressure, but also significantly worsen the selectivity of the reaction with respect to nitrogen oxides, including due to the formation of an additional amount of nitrous oxide under breakthrough conditions ammonia. Therefore, the availability of active sites on the surface of the catalyst is crucial. In addition, the catalysts must have high thermal stability, mechanical strength, as well as the absence of interaction between the active component and the carrier material, leading to deactivation. In principle, the vast majority of available honeycomb media designed for high-temperature processes satisfy the last three criteria. However, as a rule, the high pressure required for the extrusion of blocks with a high channel density leads to an increased density of the material in the surface layers of the channel walls. As a result of high-temperature processing, the surface layers of the walls are sintered to form a fused crust with a low specific surface (Fig. 1A). Such a gas-tight crust limits the access of reagents to the inner layers of the block and thus significantly reduces the active surface. In addition, the specifics of the process of producing nitric acid (high speeds, aggressive environment, the presence of water in the reaction mixture) makes high demands on the strength of the fastening of the active component on the carrier, which is very problematic on smooth surfaces.

The invention solves the problem of creating an active and thermally stable block catalyst of a honeycomb structure for the decomposition of nitrous oxide in the process of ammonia oxidation.

The problem is solved through the use of a carrier in which, with a relatively low specific surface area, a branched system of transport pores is created in the surface layer of the channel walls, which makes it possible to efficiently use the internal volume of the catalyst wall in the case of uniform distribution of the active component along the depth of the carrier (Fig. 1B).

The proposed catalyst for the decomposition of nitrous oxide under the conditions of the process of ammonia oxidation at 800 ÷ 920 ° C and a pressure of 1 ÷ 9 bar, including conditions with an ammonia slip, contains a honeycomb carrier with an active component deposited, the active component has the composition LaM ¹ _{1- x} M ² _x O ₃ , where M ¹ is selected from the group consisting of Fe, Mn, Co; M ² - Co, Cu, Ni, Zn, Mg; x = 0 ÷ 0.4; the porous structure of the carrier includes open transport pores 300-2000 Å in size, and the volume of such pores is not lower than 0.25 cm ³ / g,

M ¹ , preferably Fe, M ² , preferably Cu, x, preferably 0.2.

The catalyst contains not more than 6 wt.% Of the active component, and the total copper content in such a catalyst does not exceed 0.3 wt.%.

The catalyst has the shape of a hexagonal prism with a side of 30 mm and a height of 50 mm, triangular channels measuring 2.5 × 2.5 × 2.5 mm and a wall thickness of 0.5 mm.

The problem is also solved by the method of preparation of the catalyst. The catalyst is prepared by impregnating the block support with the active component. A support for a block catalyst with open transport pores in the surface layer of channel walls 300–2000 Å in size, with a pore volume of at least 0.25 cm ³ / g, is prepared by mixing alumina powder (cerium, zirconium, titanium) with a characteristic particle size of 5 to 100 microns with any of the traditionally used inorganic binders based on alumina (hydrargillite, bayerite, pseudoboehmite, aluminum oxynitrate, X-ray amorphous aluminum hydroxide and / or mixtures thereof), water, acid (nitric, acetic), plasticizing (ethylene glycol, intact lulose, methyl cellulose, or mixtures thereof), as well as high-temperature burn-out additives, for example, graphite, wood chips, ground brown coal, waste from coal processing plants, TPP ash, lignin, and the active component is applied to the carrier by impregnation with aqueous solutions containing polymerized ester precursors active component.

The process of decomposition of nitrous oxide under the conditions of the Ostwald process is carried out at 800 ÷ 920 ° C and a pressure of 1 ÷ 9 bar, including under conditions with an ammonia slip, in which N ₂ O - containing mixture formed after platinum networks as a result of ammonia oxidation is introduced in contact with a catalyst for the decomposition of nitrous oxide N ₂ O in the presence of the catalyst described above.

Figure 1 presents the images of the fracture of the walls of the channels of the typical available (A) and optimal, i.e. containing an extensive network of open transport pores (B), carriers based on Al ₂ O ₃ . Scanning electron microscopy data.

To confirm this assumption, we tested the activity of block catalysts in which α-alumina with a surface area of at least 1 m ² / g and a similar pore volume was used as a support, however, the pore size differed significantly. In particular, to increase the working surface of the carrier, the technique of applying an additional alumina sublayer was used. An iron-containing perovskite was used as the active component, which was applied by impregnation from nitrate solutions. The activity measurements were carried out both under model conditions (atmospheric pressure, Т = 900 ° С, composition of the reaction mixture: 0.15% N ₂ O + 3% O ₂ + 3% H ₂ O, the rest - He), and on a pilot installation under close to those in the industrial unit (pressure from 3 to 6 bar, the temperature and composition of the gases supplied to the catalyst is determined by the temperature of ammonia combustion and the composition of the package of platinum networks installed directly in front of the test sample). In all cases, fragments of blocks were tested.

It turned out that the activity measured under model conditions similar to those used in [WO 2007/104403 A1] correlates with that under conditions close to real ones (ie, in the presence of nitrogen oxides, water, at elevated pressure). However, the specific surface of the sample, even in the case of the same carrier nature and close channel density in the block, is not a factor determining the activity of the catalyst.

It was shown that in the case of using samples with an initially low specific surface as carriers, it is possible to significantly increase activity by applying an additional substrate with a highly developed surface, for example, from aluminum oxide, using conventional methods. The application of such a substrate also favorably affects the activity of samples with an isolated internal volume of the channel walls in blocks (as shown in Fig. 1A). However, under real conditions, samples with a substrate quickly lose activity due to entrainment of the active component and / or interaction of the active component with the substrate material. High activity and stability are possessed by samples in which a developed system of transport pores is formed (Fig. 1B). Particularly preferred are carrier samples in which the transport pore size is in the range of 500 ÷ 2000 Å, and the total volume of such pores is not lower than 0.25 cm ³ / g. However, it should be taken into account that an increase in the porosity of the material leads to a decrease in its strength. Therefore, it is advisable not to increase the volume of transport pores above a value of 0.5 cm ³ / g. It is also better that micropores (<200 Å) are absent in the carrier, which quickly sinter under the catalyst operating conditions, which leads to a decrease in activity.

A carrier having the necessary porous structure can be prepared by mixing alumina powder (cerium, zirconium, titanium) with a characteristic particle size of 5 to 100 micrometers with any of the commonly used inorganic binders based on alumina (hydrargillite, bayerite, pseudoboehmite, hydroxy nitrate aluminum, X-ray amorphous aluminum hydroxide and / or mixtures thereof), water, acid (nitric, acetic), an agglomerating agent (ethylene glycol, cellulose, methyl cellulose, or mixtures thereof). It is possible to minimize the likelihood of a gas-tight crust forming on the surface of the carrier walls by adding a pore-forming additive to the paste, the burn-out temperature of which is close to the final calcination temperature of the carrier. As such an additive, graphite, wood sawdust, crushed brown coal, waste from coal processing plants, ashes of thermal power plants, and lignin can be used. From the above list, the use of graphite is preferred since graphite also serves to improve the formability of the blocks. Blocks of the desired shape and with the required channel density from the paste prepared in this way are obtained by extrusion through an appropriate die, dried and then calcined at a temperature of 1100 ÷ 1300 ° C. Of the above oxides, it is more preferable to use alumina or zirconium oxide. Since the active surface depends on the density of the channels, it is preferable to use dies that can reach 200 holes per square inch or more, if this does not lead to a noticeable compaction of the surface layers of the wall (see Fig. 1A).

A mixture of complex oxides of the composition LaM ¹ _1-x M ² _x O ₃ (where M ¹ is selected from the group consisting of Fe, Mn, Co; M ² - Co, Cu, Ni, Zn, Mg; x = 0 ÷ 0.4). All other things being equal, in media containing nitrogen oxides and water, samples with M ¹ = Fe and M ² = Cu and x = 0.1–0.2 show higher activity. The resulting ultimately active component may be a mixture of oxides, spinels and / or perovskites formed from the above elements. On carriers with an optimal porous structure, samples with the composition LaCu _0.2 Fe _0.8 О ₃ show a stably higher activity. Moreover, the total content of the active component applied per impregnation, as a rule, does not exceed 6 wt.%, And the copper content, respectively, does not exceed the value of 0.3 wt.%. Separate experiments showed that the activity is weakly dependent on the amount of applied active component. It should be noted that none of the catalysts with the optimally selected porous structure and composition showed a decrease in the yield of nitrogen oxides compared to the value observed after platinum networks.

A uniform distribution of the active component along the wall depth is obtained by impregnating with water solutions of the salts of the precursors of the active component, taken in the required proportions. Preference is given to methods using impregnation with solutions containing polymerized ester precursors of the active component, for example, the Pekini method (Pechini M.P. US 3330697, 1967).

The invention is illustrated by the following examples. Description of experimental facilities for testing the activity of samples.

The catalytic decomposition of N ₂ O on the proposed catalysts is carried out under various conditions.

For testing in model mixtures (0.15% N ₂ O + 3% O ₂ + 3% H ₂ O in He) at atmospheric pressure, a quartz reactor, which is a U-shaped tube with an inner diameter of 11.5 mm, is placed in a circulating sand furnace . The temperature in the furnace and the reactor is controlled by measuring the temperature with a thermocouple located on the outer wall of the reactor in the central part of the unit. All measurements are carried out at 900 ° C. The flow of the reaction mixture is carried out by gas flow regulators, the feed rate is 2 l / min. The required concentration of water in the mixture is achieved by blowing it through a temperature controlled saturator. To avoid possible condensation, all parts of the installation and the sampling system are heated to 65 ° C. The test sample of the catalyst is a fragment of a block with a diameter of 11 mm and a height of 22 mm The contact time for such measurements is 0.02 s.

Testing in real mixtures is carried out on a setup that allows you to vary the pressure up to 7 bar and gas flow up to 3 m ³ / h. A fragment of a catalyst block with a diameter of 11 mm and a height of 50 mm is placed in a steel reactor with quartz inlays. The temperature and composition of the gases supplied to the catalyst is determined by the temperature of the combustion of ammonia and the composition of the packet of platinum networks installed directly in front of the test sample. The temperature in the reactor is controlled by thermocouples located at three points: 1) 1 mm downstream after the platinum mesh, 2) 1 ÷ 2 mm downstream after the catalyst, 3) on the outside of the reactor at a height approximately corresponding to half the height of the block fragment. To reduce heat dissipation through the walls of the reactor, the latter is additionally heated in the length section corresponding to the location of the test block. The experiments are carried out so that the difference between the temperature values after the platinum mesh, after the catalyst block and on the wall of the reactor does not exceed 10 ° C. For most measurements of activity, the temperature after the grids lies in the range 850–880 ° С. In typical experiments, the conversion of ammonia proceeds on 5 grids. The pressure in the reactor and the flow rate of the mixture vary. So, at a pressure of 3.6 atm, the flow rate of the mixture is 890 l / h, and at a pressure of 5.9 atm it is 2100 l / h, which corresponds to values of contact time under operating conditions τ (on an empty reactor) of 0.02 s and 0.013 s, respectively.

To identify the effect of ammonia slip, the number of nets is reduced to three, so that the total yield of NO and NO ₂ is reduced from 92% (for 5 nets) to 81-82% (for 3 nets).

Example 1

This example shows the dependence of the activity and stability of block catalysts supported by the active component (AK) of LaCu _0.2 Fe _0.8 О ₃ composition in model mixtures on the porous structure of the support. T = 900 ° C.

Table 1 Media sample The characteristics of the porous structure The density of the channels, pcs / inch ² AK,% The conversion of N ₂ O in model conditions,% S, m ² / g The total pore volume, cm ³ / g Characteristic pores, Å The volume of characteristic pores, cm ³ / g Freshly cooked After working in real mixes Non-optimal porous media Al ₂ O ₃ -1 * 6.6 0.23 9000 ÷ 22000 0.19 310 3.0 2.2 - 6.0 7.5 - Al ₂ O ₃ -1 + sublayer γ - Al ₂ O ₃ - 310 1.5 49.8 - 3.5 61.2 Al ₂ O ₃ -1 + (sublayer γ - Al ₂ O ₃ + AK) ** - 310 7.5 48.8 - 14.2 88.3 60.7 Al ₂ O ₃ -2 * 3.8 0.19 600 ÷ 3000 0.14 200 2.9 25.9 - 5.0 40.5 - Al ₂ O ₃ -3 30.6 0.27 60 ÷ 400 0.09 200 3.5 87.0 600 ÷ 4500 0.09 Cordierite - 1 10.9 0.17 200 ÷ 1500 0.02 200 11.3 27.6 1500 ÷ 5400 0.10 Cordierite - 1 + (sublayer γ - Al ₂ O ₃ + AK) ** - 200 9.7 69.2 - 14.6 93.3 49.2 16.5 97.2 67.6 Cordierite 2 + under a layer of γ-Al ₂ O ₃ 400 5.7 one hundred 73.7 3.9 94.0 84.0 Optimum porous media Al ₂ O ₃ -4 6.2 0.32 600 ÷ 2000 0.27 200 12.9 one hundred one hundred Al ₂ O ₃ -5 11.3 0.32 500 ÷ 3000 0.30 200 6.2 96.4 96.0 * - sample with an isolated internal volume of the walls of the channels (figa) ** - the amount of the applied active component and the γ - Al ₂ O ₃ sublayer are indicated.

Example 2

This example shows the dependence of the activity and stability of block catalysts coated with an active component (AK) of LaCu _0.2 Fe _0.8 O ₃ composition under conditions close to those in an industrial reactor on the porous structure of the support. 5 platinoid nets. T = 860 ÷ 870 ° C.

table 2 Media sample The characteristics of the porous structure The density of the channels, pcs / inch ² Active component,% The conversion of N ₂ O,% S, m ² / g The total pore volume, cm ³ / g Characteristic pores, Å The volume of characteristic pores, cm ³ / g P = 3.6 ata P = 5.9 ata Non-optimal porous media Al ₂ O ₃ -1 + (sublayer γ - Al ₂ O ₃ + AK) * - 310 7.5 -0 - 14.2 17 - Al ₂ O ₃ -3 30.6 0.27 20 ÷ 500 0.10 200 3.5 39.5 - 500 ÷ 3000 0.11 Cordierite - 2 + sublayer γ - Al ₂ O ₃ 400 5.7 42.1 - 5.3 61 - 3.5 81 → 76 (7 hours of work) - 3.9 70 → 62 (4 hrs of work) Optimum porous media Al ₂ O ₃ -4 6.2 0.32 600 ÷ 2000 0.27 200 12.9 81 58 Al ₂ O ₃ -5 11.3 0.32 500 ÷ 3000 0.30 200 6.2 76 58 Al ₂ O ₃ -6 10.1 0.32 500 ÷ 3000 0.30 200 3.5 76 58 * - indicates the amount of applied active component and sublayer γ - Al ₂ O ₃ .

Example 3 describes a method of preparing a carrier with an optimal porous structure and a catalyst based on it.

21 kg of hydrargillite, preliminarily calcined at 1200 ° С and then ground on a disintegrator, 18.2 kg of aluminum hydroxide, 11.9 liters of 16% nitric acid, 1 liter of ethylene glycol, 1.05 kg of graphite are loaded into a two-blade zeta-type mixer and mixed for 30-40 minutes until a homogeneous masses. The grinding conditions of the calcined hydrargillite on the disintegrator are selected so that the particle size of the product after grinding lies in the range of 5 ÷ 100 μm. From the resulting mass, blocks are formed in the form of a hexagonal prism with a side of 30 mm and a height of 56 mm, triangular channels 2.5 * 2.5 * 2.5 mm and a wall thickness of 0.5 mm. The molded blocks are dried for a week in the temperature range of 25-75 ° C, then for 2 days at 500-550 ° C, and finally calcined at 1100-1200 ° C for 4 hours.

According to x-ray phase analysis, the material of the obtained block is α-alumina without noticeable impurities of low-temperature phases. The structure of the fracture of the wall of the carrier channel is shown in Fig.1B.

Characteristics of the prepared carrier (sample Al ₂ O ₃ -6 in Example 2):

S _beats = 10.1 m ² / g,

V _then = 0.32 cm ³ / g

The characteristic pore size is 500 ÷ 3000 Å,

The volume of characteristic pores is 0.30 cm ³ / g.

The calcined blocks are impregnated with a solution containing dissolved salts of the precursor salts of the composition LaCu _0.2 Fe _0.8 O ₃ , dried in air for a day and finally calcined at 900 ° C for 4 hours. For an impregnating solution, 528 g of lanthanum nitrate 6 water, 60.4 g of copper nitrate of 3-water and 389.6 g of iron nitrate of 9-water are dissolved in 1 liter of distilled water, a solution of citric acid (80 g of citric acid in 40 ml of water) and 60 ml of ethylene glycol are added.

On the catalyst obtained by the aforementioned method, the degree of conversion of nitrous oxide under conditions close to those in an industrial reactor, with a pressure in the reactor of 3.6 at and 5.9 at, is 76% and 58%, respectively

Example 4

This example shows the effect of element M in LaM ² _0.2 Fe _0.8 О ₃ on the activity of catalysts prepared on the basis of Al ₂ O ₃ -5.5 support of platinum chains. P = 3.6 ata, T = 860 ÷ 870 ° C. The contact time under operating conditions (τ) is 0.02 s. Blocks of catalysts with a channel density of 250 / inch ² .

Table 3 M ² The degree of conversion of N ₂ O,% Cu 87 With 62 Ni 56 Mg 65 Zn 56

Example 5

This example shows the effect of the degree of iron substitution with copper, the content of the active component (obtained by changing the degree of impregnation) and the leakage of ammonia (varies by changing the number of platinum chains) on the degree of decomposition of nitrous oxide (Table 4). Catalyst blocks with optimal porous structure, channel density 200 / inch ² . T = 860 ÷ 870 ° C.

The approximate slip of ammonia after 3 and 5 platinum networks was estimated from the composition of the reaction mixture, measured in artificial mixtures of Ar + 21% O ₂ + NH ₃ (Ar as a diluent gas was chosen in order to measure the concentration of nitrogen formed). It was assumed that, on the way to the analysis system, all ammonia that did not react on the grids reacts with nitrogen oxides, which leads to a decrease in selectivity for nitrogen oxides. At a close concentration of input ammonia (NH ₃ ⁰ ), the value equal to the total concentration of the formed nitrogen was conventionally taken as the upper limit of the breakthrough after the grids (Table 5).

Table 4 Sample The content of the active component, wt.% The degree of decomposition of nitrous oxide,% 5 grids 3 grids 3.6 ata (τ = 0.02 s) (ammonia slip - 0.28 vol.%) 5.9 ata (τ = 0.013 s) 3.6 ata (τ = 0.02 s) (ammonia slip - 0.85 vol.%) Active ingredient - LaCu _0.2 FeO ₃ LaCu _0.2 FeO ₃ / Al ₂ O ₃ -6 3.5 76 58 73-75 6.37 82 65 82 LaFeO ₃ / Al ₂ O ₃ -6 4.04 66 49 63 LaCu _0.4 Fe _0.6 O ₃ / Al ₂ O ₃ -6 3.38 72 53

Table 5 Determination of the amount of ammonia slip after a different number of platinum networks. T = 860 ° C. P = 3.6 ata (τ = 0.02 s) The number of grids NH ₃ ⁰ ,% (NO + NO ₂ ),% N ₂ O,% N ₂ ,% Nitrogen balance,% The output of NO _x ,% ¹ The output of NO _x ,% ² 3 9.73 7.94 0.129 0.85 101.7 80.2 81.6 5 10.01 9.00 0.101 0.28 97.5 92.2 89.9 1 - Output NO _x (%) = (NO + NO ₂ ) / ∑ _N * 100 3 - Output NO _x (%) = (NO + NO ₂ ) / C ⁰ _NH3 * 100

Claims (9)

1. The catalyst for the decomposition of nitrous oxide under the conditions of the oxidation of ammonia at 800 ÷ 920 ° C and a pressure of 1 ÷ 9 bar, including under conditions with an ammonia slip, which is a honeycomb structure carrier containing aluminum oxide or cerium oxide or oxide zirconium, or titanium oxide coated with an active component, the active component has the composition

where M ¹ is selected from the group consisting of Fe, Mn, Co; M ² - Co, Cu, Ni, Zn, Mg; x = 0 ÷ 0.4, characterized in that the porous structure of the support includes open transport pores 300–2000 Å in size, the volume of such pores not lower than 0.25 cm ³ / g. 2. The catalyst according to claim 1, characterized in that M ¹ preferably Fe; M ² preferably Cu. 3. The catalyst according to claim 1, characterized in that x is preferably 0.2. 4. The catalyst according to claim 1, characterized in that the total copper content in the catalyst does not exceed 0.3 wt.%. 5. The catalyst according to claim 1, characterized in that it has the shape of a hexagonal prism with a side of 30 mm and a height of 50 mm, triangular channels with a size of 2.5 · 2.5 · 2.5 mm and a wall thickness of 0.5 mm. 6. A method of preparing a catalyst for the decomposition of nitrous oxide under the conditions of the oxidation of ammonia at 800 ÷ 920 ° C and a pressure of 1 ÷ 9 bar, which includes preparing a carrier, molding, drying, calcining and impregnating a block carrier with an active component, characterized in that the carrier for block a catalyst with open transport pores in the walls of the channels with a size of 300-2000 U, with a volume of such pores not lower than 0.25 cm ³ / g is prepared by mixing a powder of aluminum oxide, or cerium oxide, or zirconium oxide, or titanium oxide with a characteristic particle size from 5 to 100 μm with any of the traditionally used inorganic binders based on alumina, water, acid, plasticizing and high-temperature burn-out additives, and the active component is applied to the carrier by impregnation with aqueous solutions containing polymerized ester precursors of the active component, and the catalyst is obtained by to any one of claims 1 to 5. 7. The method according to claim 6, characterized in that the active component of the catalyst has a composition of LaM ¹ _1-x M ² _x O ₃ , where M ¹ is selected from the group consisting of Fe, Mn, Co; M ² - Co, Cu, Ni, Zn, Mg; x = 0 ÷ 0.4. 8. The method according to claim 6, characterized in that graphite, wood chips, ground brown coal, waste from coal preparation plants, TPP ash, lignin can be used as burnable additives. 9. A method for carrying out the decomposition of nitrous oxide under the conditions of the process of ammonia oxidation at 800 ÷ 920 ° C and a pressure of 1 ÷ 9 bar, including under conditions with an ammonia slip, in which the N ₂ O-containing mixture is formed after platinum chains as a result oxidation of ammonia is brought into contact with a decomposition catalyst N ₂ O, characterized in that the catalyst according to any one of claims 1 to 5 or prepared according to any one of claims 6 to 8 is used.

Images