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EP-3651899-B1 - CATALYST AND METHOD OF USE THEREOF IN THE CONVERSION OF NOX AND N2O

EP3651899B1EP 3651899 B1EP3651899 B1EP 3651899B1EP-3651899-B1

Inventors

  • LEE, Steven Russell
  • ZHANG, WENZHONG
  • BAKKER, GEERT MARTEN

Dates

Publication Date
20260506
Application Date
20180709

Claims (10)

  1. A catalyst for the conversion of NO X and N 2 O comprising iron chabazite and iron beta zeolite.
  2. The catalyst of claim 1 further comprising alumina.
  3. The catalyst of claim 2 wherein the iron chabazite is made without an organic structure directing agent.
  4. The catalyst of claim 1 wherein the iron beta zeolite is made without an organic structure directing agent.
  5. A method of simultaneously reducing the NOx and N 2 O concentration in a process gas stream comprising contacting the process gas stream with a catalyst comprising iron chabazite and iron beta zeolite under conversion conditions.
  6. The method of claim 5 further comprising adding ammonia, urea or an ammonia generating compound to the process gas before or at the same time as the process gas is contacted with the catalyst.
  7. The method of claim 6 wherein the ammonia generating compound is selected from the group consisting of ammonium carbamate, ammonium formate, ammonium carbonate and metal-amine complexes and, optionally, wherein the contacting is carried out in the presence of at least 0.5 vol. % water.
  8. The method of claim 6 wherein the ammonia to NO X ratio is 1:1.
  9. The method of claim 8 wherein the contacting is carried out in the presence of at least 2 vol. % water.
  10. The method of claim 9 wherein the conversion conditions comprise a temperature in the range of from 250 to 650 °C.

Description

Field of the Invention The invention relates to a catalyst and a method of simultaneously reducing the NOX and N2O concentration in a process gas stream. Background of the Invention Nitric oxides and nitrous oxide are known polluting gases and efforts have been made to limit the amount of these compounds entering the atmosphere. These are found in exhaust gases and process gas streams in a number of industrial processes. In addition, these are found in the exhaust gases of mobile vehicles; cars, trucks, buses, etc. Selective catalytic reduction is a known method for removing these compounds from process gas streams by converting nitrous oxides and nitric oxides to nitrogen and water. EP 2 520 365 A2 discloses a selective catalytic reduction catalyst for converting NOx present in exhaust gas emitted from a mobile source in the presence of a nitrogenous reductant. US 2016/0367939 A1 discloses a method of converting nitrogen oxides in a gas to nitrogen. US 20110286914 discloses an organic-free, metal-containing zeolite Beta with a silica-to-alumina ratio ranging from 5 to 20, and a metal content of at least 0.5 wt%. The published patent application also discloses a method of selective catalytic reduction of nitrogen oxides in exhaust gases using the zeolite Beta. US 20130142727 discloses a microporous crystalline material having a pore opening ranging from 3 to 5 Angstroms, where the material comprises a first metal chosen from alkali earth group, rare earth group, alkali group, or mixtures thereof, and a second metal chosen from iron, copper or mixtures thereof; and has a molar silica to alumina ratio from 3 to 10. The published patent application also discloses a method of selective catalytic reduction of nitrogen oxides in exhaust gas. It is advantageous to develop improved catalysts that are more effective and more stable in this reaction so that the units can be operated over a longer duration without maintenance or catalyst replacement. Summary of the Invention The invention provides a catalyst for the conversion of NOX and N2O comprising iron chabazite and iron beta zeolite. The invention provides a method of simultaneously reducing the NOX and N2O concentration in a process gas stream comprising contacting the process gas stream with a catalyst comprising iron chabazite and iron beta zeolite under conversion conditions. Brief Description of the Figures Figure 1 depicts the N2O decomposition of three different catalysts.Figure 2 depicts the N2O decomposition and the NOX conversion of a catalyst comprising iron chabazite and iron beta zeolite.Figure 3 depicts the hydrothermal stability of a catalyst comprising iron chabazite and iron beta zeolite. Detailed Description of the Invention The invention provides an improved catalyst for the conversion of NOX and N2O. The catalyst comprises iron chabazite and iron beta zeolite. The beta zeolite is preferably made without an organic structure directing agent. The resulting beta zeolite does not contain any residual organic materials in the pores of the material, and thus the treatments usually required to remove the organic components are not needed. In prior art catalysts, organic structure directing agents, such as tetraethylammonium hydroxide, dibenzylmethylammonium, and dibenzyl-dimethyl ammonium hydroxide, were used in the precursor materials. The cost of these compounds and the fact that they usually remain in the pores after manufacture is a problem in the synthesis of these beta zeolite materials. The beta zeolite preferably has a silica-to-alumina ratio of from 5 to 20. The silica-to-alumina ratio is preferably not more than 12, and more preferably in a range of from 5 to 11. The beta zeolite preferably has an average crystal size of greater than 0.1 microns, more preferably of from 0.2 to 5 microns. The iron beta zeolite using the above described beta zeolite preferably comprises at least 0.5 wt% iron, more preferably from 1 to 10 wt% iron. The catalyst may also contain alumina. The iron is preferably added to the catalyst components (chabazite and beta zeolite) by one or more methods, including liquid phase or solid ion exchange, impregnation or incorporation by direct synthesis. In a preferred embodiment, the iron is preferably added by ion exchange. The iron used in the ion exchange method is typically an iron salt and it may be ferric nitrate, ferric chloride, ferrous chloride, ferrous sulfate or mixtures thereof. One method for making the beta zeolite starts with making an aqueous solution comprising NaOH and a source of alumina. The alumina source may be sodium aluminate, aluminum hydroxide, alumina, aluminum nitrate, aluminum alcoholates, or aluminum sulfate. Then a source of silica is added to the solution. The silica may comprise a silica gel, silica sol, silica hydrosols, fumed silica, reactive amorphous solid silicas, silicic acid, water glass, sodium silicate, sodium metasilicate, colloidal silicate, pyrogenic silica, precipitated silicate