Ceramic catalyst for the selective decomposition of n2o and method thereof

 

The invention relates to catalysts for the selective decomposition of N2About in a mixture of nitrous gases. This problem is solved by the fact that the catalyst consists of a porous ceramic carrier and a catalytically active phase, and the media, at least 95% consists of one or more compounds of alkaline earth metals. The proposed catalyst is preferably applicable in the formation of nitric acid. The technical result - the catalyst has high activity and is applicable in the temperature range 700-1000oWith without violating its catalytic properties. 2 C. and 7 C.p. f-crystals, 6 ill.

The invention relates to a ceramic catalyst for the selective decomposition of N2O (laughing gas) in a mixture of nitrous gas N2and O2and also how to obtain it.

N2About (laughing gas) is released during various processes, such as in furnace installation fluidized bed, as well as with the processes of chemical synthesis of nylon, adipic acid and nitric acid. Based on his reaction inertness he comes without decomposition to the stratosphere, where it contributes to the violation of the protective ozone layer of the Earth. At the world conference in Kadkhodai catalyst for treatment of exhaust gases.

As a potential catalytically active substances it is, along with noble metals, various ceramic materials, such as modified zeolites and mixed oxides with perovskite structure. Thanks to the advantage of price perovskites compared with noble metals and their better thermal stability, the compounds of the perovskite considered as preferred. In Catal. Lett. (1995), 34 (3,4), pages 373-382 N. Gunasekaran, etc. described catalytic decomposition of laughing gas over mixed oxides with perovskite or perovskite-like structure, and as a catalyst as favorable considered La0,8Srof 0.2MO3-(M=Cr, Fe, Mn, Co, Y) and Laa 1.8Srof 0.2CuO4-. As the target direction still worked from energy considerations, primarily in the catalysts, which are in the range of from 250oWith up to 450oTo cause the most complete conversion of N2O. especially preferred is a mixture of aninteractive perovskite composition of La1-xCuxCoO3-with x=0...0.5 and spinel composition of Co3O4in mass cootner (800oS-1200o(C) that, in particular, needed to reduce the content of N2O in the process gas during the manufacture of nitric acid (900oC). Due to the above-mentioned resolutions of the Kyoto named for the last process is the increasing demand for catalysts for such reactions.

Previously known catalysts for the decomposition of N20 at temperatures above 700oWith undergo irreversible deactivation, which is caused by sintering (catalysts based on noble metals), insufficient heat resistance of the structural grid (zeolites) or irreversible reactions between oxides of the transition metal active component carriers, such as with a high content of Al2O3.

Feature introduction in the formation of nitric acid is additionally required selectivity against other oxides, one of which is the target product of the synthesis. Such selectivity with other processes in the off-gas treatment is not required or even expected.

At the heart of this invention lies thus the task of creating a catalyst for the selective decomposition of N2O in a mixture of nitrous gases which d is arsenia its catalytic activity.

This problem is solved using the steps described in the patent claims.

Department of the conventional Al2O3-containing media (e.g., clay or aluminum silicate) using compounds of alkaline earth metals, in particular magnesium oxide, makes it difficult to deactivation of the catalyst in the chemical reaction between the active phase and the media at temperatures above 700oWith this happening at the present level of technology, for example, by the formation of spinel between oxides of aluminum and cobalt. Besides the various oxides of alkaline earth metals, depending on their porous structures themselves have a certain catalytic activity in the decomposition of laughing gas.

Getting oxides of alkaline earth metals is carried out by calcination salt, preferably a carbonate, and the temperature of calcination depends on the stability of the carbonate of the corresponding element from the desired particle size distribution of the oxide of the alkali earth metal and a subsequent temperature of introduction of the catalyst.

The oxides and mixed oxides catalytically active components preferably get wet chemical method by mixed precipitation, soldofsky reactions at high temperatures, pyrolytic methods, as well as all other known methods for producing powders.

Active components can be added before or after calcination of the carrier in the form of semi-products (salts, oxides or mixed oxides. Along with the mechanical mixing of both components proposed different methods of impregnation of the carrier surface active components, as well as deposition on whether the media with subsequent fixation by drying and thermal treatment.

To obtain the formed catalytic element desired mixture plastificated and homogenized by adding plasticizer and water, as is known in ceramic technology. You can add increase the strength of a binder such as silica Sol, inorganic polymer, for example, in the form of phosphate of magnesium, aluminum or boron, or a clay binder, and their share should be as small as possible, since they are not compounds of the alkaline earth metal. This increases the strength of the binder may be homogeneous mixed before or after calcination salts of alkaline earth metal. Revision carried out by known ceramic methods, such as granulation or extrude in the form of pellets, bulk material or of cellular structures.

The proposed activity of the catalysts was determined on three examples with different fractions of catalytically active phase. Below are 6 examples of execution proposed to improve strength additives.

The drawings show: Fig. 1 - curve transformation laughing gas proposed by the catalyst with 0.1 wt.% the catalytically active phase (active component) as a function of temperature (example 1); Fig. 2 - selectivity of the catalyst of Fig.1 relative to the NOxas a function of temperature; Fig. 3 - curve transformation laughing gas proposed by the catalyst with 1.5 wt.% the catalytically active phase (active component) as a function of temperature (example 2); Fig. 4 - selectivity of the catalyst of Fig.3 relative to the NOxas a function of temperature; Fig. 5 - curve transformation laughing gas proposed by the catalyst with 5.0 wt.% the catalytically active phase (active component) as a function of temperature (example 3); Fig. 6 - selectivity of the catalyst of Fig.5 relative to the NOxas a function of temperature.

The proposed catalyst in pellet form was tested using the test gas formed by the technologically advanced, and N2.

In the case of examples 1 and 2 the active phase consists of a catalyst based on heavy metals with the basic components of Mn, Fe, Cr and Co. In the case of example 3, the active phase is lanthanum-strontium-manganese-cobalt-perovskite.

When the volumetric velocity of 10,000 h1at a temperature of 800oWith is 100% catalytic conversion of N2On (Fig.1, 3, 5). Contained in the gas stream NR2only decreases. Strikingly shown that the full transformation of laughing gas almost regardless of the concentration of the active component is achieved when specified in the first example of execution of a low content of 0.1 wt. % at 800oC. higher content of the active phase, as in the second and third examples of performance, is valid only in the first moments of reaction, not ending at lower temperatures.

Because the proposed connection alkaline earth metals are not able to form a fairly solid ceramics, upon receipt of the proposed ceramic catalysts has is the introduction of such binder phases, which in the annealed condition give sufficient hardness without the terms of the basic requirements of destruction "at least 95 wt.% soede measures in paragraphs 13-15 of the claims.

Example 4 (paragraph 13) Compounds of rare-earth metals for the media mixed with 15 wt.% Zola SiO2with the content of SiO213%. After the usual ceramic firing technology, the share of SiO2in a ceramic carrier with good toughness value is 1.95 wt.%.

Example 5 (paragraph 14) Compounds of rare-earth metals for the media mixed with 14 wt.% phosphate of magnesium, which contains, in addition, 6% N2About 37% P2O2. After firing, the fraction of N2About in ceramic media mainly of Cao is 0.84 wt.%, or, if the carrier consists essentially of N2Oh, its share increases by the same percentage.

Example 6 (paragraph 14)
Compounds of alkaline earth metals for media blended with 12 wt.% phosphate of magnesium, which contains, in addition, 8% Al2O3and 35% P2O3. After firing the proportion of A12O3in the ceramic media is 0.96 wt.%.

Example 7 (paragraph 14)
Compounds of alkaline earth metals for media mixed with 8 wt.% the boron phosphate, which contains, in addition, 36% N2O3and 57% P2O2. After firing, the proportion Of2in the ceramic media is 2.9 wt.%.

Example 8 (paragraph 15)
Compounds of alkaline earth metals on the Sabbath.O. After firing the proportion of Al2O3in the ceramic media is 4.7 wt.%.

Example 9 (paragraph 15)
Compounds of alkaline earth metals for media mixed with 5 wt.% polymeric silicate of magnesium, which contains, in addition, with 23.7% N2About 57% of SiO2. After firing, the fraction of N2On the ceramic carrier, consisting mainly of Cao, 1.2 wt.%, and to 2.85 wt.% SiO2or, if the media mainly consists of N2Oh, its share increased by a specified percentage.


Claims

1. Catalyst for the selective decomposition of N2O N2and O2in a mixture containing water vapor nitrous gases containing carrier for the catalytically active phase is at least 95 wt.% consists of one or more compounds of alkaline earth metals, and a catalytically active phase comprises a mixed oxide of the elements Mn, Fe, Cr and/or Co or of lanthanum-strontium-manganese-cobalt-perovskite, and the proportion of the catalytically active phase is from 0.1 to 5 wt.%, characterized in that the carrier consists of a porous ceramic.

2. The catalyst p. 1, characterized in that the connection or one of the compounds of alkaline earth metals is Zemelny metal is calcium oxide.

4. The catalyst according to one of the preceding paragraphs, characterized in that the medium under the condition of 95 wt.% alkaline earth metal contains improving the hardness of the additive in the form of sols of metal oxides and/or inorganic polymers.

5. The catalyst according to one of the preceding paragraphs, characterized in that it presents in the form of a powder mixture.

6. The catalyst according to one of the preceding paragraphs, characterized in that the catalyst carrier contains on its surface a layer of the active phase.

7. The catalyst according to one of the preceding paragraphs, characterized in that the active phase is dispersed in a porous catalyst carrier.

8. A method of manufacturing a carrier for a catalyst made of porous ceramics, characterized in that the ceramic mass before forming as inorganic polymers add phosphates of magnesium, aluminum and/or boron in the amount of from 3 to 20 wt.%, however, assuming 95 wt.% compounds of alkaline earth metals.

9. The method according to p. 8, characterized in that the inorganic polymer type aluminium hydroxide and/or polymeric silicates of magnesium in the amount of from 8 to 15 wt.%, however, assuming 95 wt.% compounds of the alkaline earth is

 

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