LNT and SCR catalysts for combined LNT-SCR applications

Patent metadata

Field	Value
Publication number	US-9597664-B2
Application number	US-201213358708-A
Country	US
Kind code	B2
Filing date	Jan 26, 2012
Priority date	Jan 26, 2011
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

The current invention refers to the LNT and the SCR catalysts designed for combined LNT-SCR applications. LNT catalysts are based on proton-conducting oxides of fluorite structure, namely Ca (Sr)—La—Ce (Zr, Pr) mixed oxides in which up to 40 mol-% of lanthanum is replaced by calcium and/or strontium, and up to 66 mol-% of cerium is replaced by zirconium and/or praseodymium, further combined with Pt—Pd or Pt—Pd—Rh precious metal components. SCR catalysts are Cu/zeolite modified by citrate treatment or Cu—Ce, Mn—Ce or Co—Ce/modified zeolite.

First claim

The invention claimed is:

1. A catalyst system for an exhaust gas treatment system, comprising:
a LNT-catalyst including a mixed metal oxide having proton conducting properties and a combination of at least two platinum group metals (PGM) on a support, wherein the mixed metal oxide is a lanthanum-cerium-oxide, in which up to 40 mol-% of lanthanum is replaced by calcium and/or strontium, wherein at least some lanthanum is replaced by calcium and/or strontium; and
a SCR-catalyst, wherein the SCR-catalyst is positioned downstream of the LNT-catalyst;
wherein the catalyst system has no external ammonia source.

2. The catalyst system according to claim 1 , wherein the mixed metal oxide has defect fluorite structure, and wherein 10-20 mol-% of the lanthanum is replaced by calcium and/or strontium.

3. The catalyst system according to claim 1 , wherein up to 66 mol-% of cerium is replaced by zirconium and/or praseodymium.

4. The catalyst system according to claim 1 , wherein the platinum group metals further comprise Pt and Pd or Pt—Pd—Rh combination.

5. The catalyst system according to claim 1 , wherein a total loading of platinum group metals is 100 g/ft3 or less and wherein a Pt-loading is 10-70 g/ft3.

6. The catalyst system according to claim 1 , wherein a Pd-loading is 5-40 g/ft3 and wherein a Rh-loading is 0-10 g/ft3.

7. A catalyst system for an exhaust gas treatment system, comprising:
a LNT-catalyst including a mixed metal oxide having proton conducting properties and a combination of at least two platinum group metals (PGM) on a support, wherein the mixed metal oxide is a lanthanum-cerium-oxide, in which up to 40 mol-% of lanthanum is replaced by calcium and/or strontium; and
a SCR-catalyst, wherein the SCR-catalyst is positioned downstream of the LNT-catalyst;
wherein the catalyst system has no external ammonia sources, and wherein the support is cordierite provided with an alumina washcoat.

8. A catalyst system for an exhaust gas treatment system comprising:
a LNT-catalyst that generates ammonia, wherein the LNT-catalyst includes a mixed metal oxide having proton conducting properties and a combination of at least two platinum group metals (PGM) on a support; and
a SCR-catalyst comprising a zeolite-containing support, wherein the support has been removed of aluminum extra-lattice/extra-framework species to form a modified zeolite-containing support, wherein a Cu, Cu—Ce, Mn—Ce, or Co—Ce catalyst has been reinserted into the modified zeolite-containing support.

9. The catalyst system of claim 8 , wherein the LNT-catalyst generates ammonia during rich pulses and wherein the catalyst system has no external ammonia source.

10. The catalyst system of claim 9 , where the LNT-catalyst comprises the mixed metal oxide having proton conducting properties and the combination of the at least two platinum group metals (PGM) on the support and wherein a total loading of platinum group metals is 100 g/ft3 or less and wherein a Pt-loading is 10-70 g/ft3.

11. The catalyst system of claim 10 , wherein removal of Cu and/or aluminum extra-lattice species is carried out with a citrate containing solution, comprising citric acid and diammonium hydrogen citrate, wherein the support has been removed of Cu and/or aluminum extra-lattice species and calcined in steps that are repeated at least once.

12. The catalyst system of claim 8 , wherein the zeolite-containing support contains Cu/zeolite including a commercial catalyst on cordierite or another support, wherein the zeolite-containing support is further removed of copper before reinsertion, and wherein the modified zeolite-containing support has been calcined at a temperature of at least 550° C.

13. The catalyst system of claim 8 , wherein the modified zeolite-containing support is removed of aluminum extra-lattice/extra-framework species at a temperature of 80-100° C.

14. The catalyst system of claim 8 , wherein the Cu, Cu—Ce, Mn—Ce, or Co—Ce catalyst is reinserted into a calcined modified zeolite-containing support by ion-exchange and/or impregnation in a presence of urea by using an aqueous solution with nitrate salts of Cu, Ce, Mn and Co, respectively.

15. The catalyst system of claim 8 , wherein the SCR-catalyst is Cu/modified zeolite, Cu—Ce, Mn—Ce or Co—Ce/modified zeolite for reduction of NOx in exhaust gases.

16. The catalyst system of claim 15 , wherein the SCR-catalyst uses the ammonia generated by the LNT-catalyst for the reduction of NOx in exhaust gases.

Assignees

• Chigapov Albert N
• Ukropec Robert
• Carberry Brendan Patrick
• Shishkina Nina
• Ford Global Tech Llc

Inventors

• Chigapov Albert N
• Ukropec Robert
• Carberry Brendan Patrick

Classifications

• B01D2255/1023

  Palladium · CPC title

• B01J2229/37

  Acid treatment · CPC title

• B01J37/0242

  Coating followed by impregnation · CPC title

• B01J2523/3706

  Lanthanum · CPC title

• Y02T10/24

  Cross-Sectional Technologies · mapped topic