SCR catalysts having improved low temperature performance, and methods of making and using the same
SCR-active molecular-sieve based catalysts with improved low-temperature performance are made by heating a molecular-sieve in a non-oxidizing atmosphere with steam (hydrothermal treatment), or in a reducing atmosphere without steam (thermal treatment), at a temperature in the range of 600-900° C. for a time period from 5 minutes to two hours. The resulting SCR-active iron-containing molecular sieves exhibit a selective catalytic reduction of nitrogen oxides with NH 3 or urea at 250° C. that is at least 50% greater than if the iron-containing molecular-sieve were calcined at 500° C. for two hours without performing the hydrothermal or thermal treatment.
1. A method of making an SCR-active molecular sieve-based catalyst, the method comprising performing a hydrothermal treatment on an iron-containing molecular sieve in a non-oxidizing atmosphere at a temperature in the range of 600-900° C. for a time period from 5 minutes to two hours, where the molecular sieve is a zeolite having an AEI, AFX, CHA, FER, or SFW framework.
2. The method according to claim 1 , wherein the hydrothermal treatment is performed at a temperature in the range of 650-850° C. for a time period from 15 minutes to two hours.
3. The method according to claim 1 , wherein the zeolite is FER and the hydrothermal treatment is performed at a temperature in the range of about 700 to about 900° C. for a time period from 5 minutes to two hours.
4. The method according to claim 1 , wherein the non-oxidizing atmosphere comprises nitrogen.
5. The method according to claim 1 , wherein the non-oxidizing atmosphere is a reducing atmosphere.
6. The method according to claim 5 , wherein the reducing atmosphere comprises hydrogen gas.
7. The method according to claim 1 , wherein the iron-containing molecular sieve subjected to the hydrothermal treatment is in powder form.
8. The method according to claim 1 , wherein the iron-containing molecular sieve subjected to the hydrothermal treatment is in the form of an extruded unsupported catalyst or a coating on a support body.
9. The method according to claim 1 , wherein the iron-containing molecular sieve is prepared by contacting a molecular sieve with an iron salt.
10. A method of making an SCR-active molecular sieve catalyst, comprising performing a hydrothermal treatment on an iron-containing molecular sieve at a temperature in the range of 600-900° C. for a time period from 5 minutes to two hours, then introducing oxygen into the atmosphere during at least a portion of the time when the iron-containing molecular sieve cools from the hydrothermal or thermal treatment temperature to ambient temperature, where the molecular sieve is a zeolite having an AEI, AFX, CHA, FER, or SFW framework.
11. The method according to claim 10 , wherein the hydrothermal treatment is performed using a means providing mixing, temperature and atmospheric control.
12. The method according to claim 10 , wherein the hydrothermal treatment is performed in an inclined rotary calcination oven in which the iron-containing molecular sieve in powder form is exposed to a countercurrent flow of gas constituting a non-oxidizing or reducing atmosphere.
13. A method of making an SCR-active molecular sieve catalyst, comprising performing a hydrothermal on an iron-containing molecular sieve in a non-oxidizing atmosphere at a temperature in the range of 600-900° C. for a time period from 5 minutes to two hours, then introducing oxygen into the non-oxidizing atmosphere during at least a portion of the time when the iron-containing molecular sieve cools from the hydrothermal treatment temperature to ambient temperature, where the molecular sieve is a zeolite having an AEI, AFX, CHA, FER, or SFW framework.