Selective catalytic reduction of N
A gas stream containing nitrous oxide and ammonia is contacted with a catalyst composition containing a zeolite. N 2 O is reduced to N 2 and H 2 O at low temperatures in a highly efficient manner. Ammonia-mediated reduction of nitrous oxide can be effectuated from gas streams having N 2 O concentrations as low as 1%. The gas stream may also contact a catalytic composition selective for the reduction of NO x . In this way, N 2 O and N x treatment may be effectuated in a single process stream.
1. A method for ammonia-mediated N 2 O and NOx reduction, comprising contacting a gas stream containing N 2 O and NOx with ammonia and a catalyst comprising a BETA zeolite which is selective for the simultaneous reduction of N 2 O and NOx, wherein the gas stream containing ammonia, nitrous oxide and NOx has a temperature of greater than about 250° C.
2. A method as recited in claim 1 , wherein the gas stream has a temperature of from about 350° C. to about 600° C.
3. A method as recited in claim 1 , wherein the ammonia/N2O concentration ratio is up to about 2.0 based on the total volume of the gas stream.
4. A method as recited in claim 1 , wherein the ammonia/N 2 O concentration ratio is at least about 0.5 based on the total volume of the gas stream.
5. A method as recited in claim 1 , wherein the ammonia/N 2 O concentration ratio is from about 0.8 to about 1.0 based on the total volume of the gas stream.
6. A method as recited in claim 1 , wherein the zeolite is ion-exchanged with at least one type of ion selected from the group consisting of Fe, Cu, Co, Ce, Pt, Rh, Pd, Ir, Mg and combinations thereof.
7. A method as recited in claim 1 wherein the zeolite is ion-exchanged with at least one type of ion selected from the group consisting of Fe, Ce, Cu, Co and combinations thereof.
8. A method as recited in claim 1 , wherein the N 2 O concentration of the gas stream is about 1% or less.
9. A method as recited in claim 1 , wherein the N 2 O concentration of the gas stream is about 5,000 ppm or less.
10. A method as recited in claim 1 , wherein the N 2 O concentration of the gas stream is between about 20 ppm and about 5,000 ppm.