WO2013029756A1 - Catalyst for decomposing dinitrogen monoxide in oxygen-containing gases - Google Patents

Abstract

A catalyst for decomposition of laughing gas in oxygen-containing gas mixtures, particularly air, at temperatures of 180 to 300°C, comprises A rhodium and B an oxide or mixed oxide having oxygen-storage properties. B is preferably cerium dioxide or a cerium-zirconium mixed oxide having a Ce/Zr ratio of 5/95 to 95/5.

Description

 Catalyst for the decomposition of nitrous oxide in oxygen-containing gases

The invention relates to a catalyst for the decomposition of N ₂ 0 (nitrous oxide, nitrous oxide) in oxygen-containing gases, preferably air.

For the decomposition of nitrous oxide, different materials have been studied and described as catalysts. The applications and requirements are different, depending on whether it concerns exhaust gas purification, nitrous oxide removal from anesthetic gases or industrial process gases. The temperatures to be used in the various catalysts, in which complete or at least sufficient decomposition of the laughing gas contained as harmful component occurs on these catalysts, are extremely different and highly dependent on the gas composition and conditions of use.

For example, EP 2 062 639 B1 describes a Pd-containing catalyst which can convert nitrous oxide into oxygen-containing gases having a high moisture content at temperatures of up to 450 ° C.

DE 10 2008 048 159 A1 describes Rh catalysts which are capable of reacting nitrous oxide under various conditions. At low oxygen contents and in the absence of moisture, the decomposition already succeeds at temperatures below 200 ° C, in the presence of higher oxygen contents, however, these catalysts also require temperatures for complete conversion in the range of> 350 ° C. In the same patent application, doping of the carrier material Al ₂ O _{3 used} with cerium oxide are described, but in the illustrated examples of DE 10 2008 048 59 A1, Fig. 6, achieve no significant effect on the conversion temperature.

CONFIRMATION COPY DE 10 2004 024 026 A1 describes mixed Pd / Rh catalysts which have high catalytic activity under the conditions of the Ostwald process. In this application, the catalyst is placed directly in the oxidation reactor and is therefore exposed to high temperatures (880 ° C) and corrosive atmosphere. As support for this catalyst, therefore, only materials which are stable under these conditions, such as α-alumina or zirconia are suitable. When used in oxygen-containing gases at low temperatures, however, these catalysts are too inactive.

It is an object of the present invention to provide a catalyst in oxygen- term nitrous oxide temperatures in the constituents can decompose N ₂ and 0. ₂ Particular emphasis was placed on the use of this catalyst for the pre-purification of air in air decomposition plants in order to remove the small amounts of N ₂ O (about 300 ppb) present in the air. But also in other applications, for example in exhaust gas streams from nitric acid plants containing up to 5000 ppm nitrous oxide, a low conversion temperature is advantageous in order to keep energy costs for heating the gas stream as low as possible. Catalysts which accomplish a complete conversion of the nitrous oxide under the oxygen concentrations of the air (20-21%) at temperatures below 300.degree. C. are particularly advantageous.

Surprisingly, the inventors found that Rh in combination with oxidic see materials with oxygen-storing properties has a particularly high activity in the decomposition of nitrous oxide at low temperatures. As such oxygen storage materials, e.g. Ceria or cerium zirconium mixed oxides with Ce / Zr ratios of 5/95 to 95/5 are used. These oxides are used in the production of three-way catalytic converters, but the oxygen storage capacity of these materials serves as a buffering function to operate at low lambda, i. low oxygen content in the exhaust gas to provide the oxygen for the oxidation of the harmful components.

The invention thus relates to catalysts according to claim 1, to processes according to claim 4 and to a use according to claim 10. Further developments can be found in the remaining claims.

Ceria-based catalysts with a Rh content of 0.1-0.5% have proved particularly advantageous. Even at temperatures below 300 ° C., complete conversion of nitrous oxide under air conditions (20% oxygen) could be achieved with these catalysts. Comparable Rh catalysts on other support materials, such as Al ₂ 0 ₃ , Zr0 ₂ or only partially coated with Ce0 ₂ Al ₂ 0 ₃ showed significantly higher temperatures to achieve full conversion.

Figure: Fig. 1 shows a diagram with turnover curves.

example

 The experiments for the results shown in FIG. 1 related to nitrous oxide decomposition. The explanation of the abbreviations can be found in the following table:

The experiments were carried out with the catalysts described in the table. The measuring conditions were:

60 ml of catalyst, 10000 1 / h space velocity, 1000ppb N ₂ 0 in synthetic air, 1 K min cooling ramp

The sales are shown in the diagram on the y-axis, the temperatures on the x-axis. It can be seen that in rhodium on Ce0 ₂ granules the turnover curve at the lowest temperature, namely about 190 ° C, begins.

In view of the numerous attempts at improvement in the form of the catalyst systems of the prior art, this result is to be regarded as surprising.

Claims

claims 1. Catalyst for Lachgaszersetzung in oxygen-containing gas mixtures at temperatures of 180 to 300 ° C, characterized in that it A rhodium and B has an oxide or mixed oxide with oxygen-storing properties. A catalyst according to claim 1, wherein B is ceria or a cerium-zirconium mixed oxide having a Ce / Zr ratio of 5/95 to 95/5. 3. A catalyst according to any one of claims 1 and 2, the rhodium content is 0.1 to 0.5%. 4. A process for Lachgaszersetzung in oxygen-containing gas mixtures, characterized in that the gas mixture is brought to temperatures of 180 to 300 ° C and passed through a catalyst according to one of claims 1 to 3. 5. The method of claim 3, wherein the temperature range is from 180 to 270 ° C. 6. A method according to claim 3, wherein the temperature range is from 180 to 250 ° C. 7. The method according to claim 3, wherein the gas mixture is air with small amounts of N ₂ 0. 8. The method according to claim 3, wherein the gas mixture is air with 250 to 700 ppb N ₂ 0. 9. The method according to claim 3, wherein the gas mixtures are exhaust gas streams from nitric acid plants containing up to 5000 ppm nitrous oxide. 10. Use of a catalyst according to any one of claims 1 to 3 for the decomposition of nitrous oxide in oxygen-containing gas mixtures at temperatures of 180 to 300 ° C. 11. Use according to claim 10, wherein the gas mixture is air with 250 to 350 ppb N ₂ 0. 12. Use according to claim 10, wherein the gas mixtures are exhaust gas streams from nitric acid plants containing up to 5000 ppm nitrous oxide.