Palladium oxide supported on spinels for NOx storage
Passive NO x adsorption (PNA) compositions have a formula Pd—NiFe 2 O 4 wherein Pd represents a palladium component, such as palladium oxide, that is adsorbed on surfaces of the nickel ferrite. Such compositions can be synthesized by wet impregnation of nickel ferrite with a palladium salt, and exhibit efficient NO x adsorption at low temperature, with NO x desorption occurring predominantly at high temperature. Two-stage NO x abatement catalysts, effective under engine cold start conditions, include a PNA composition upstream from an NO x conversion catalyst.
1. A NO x storage component for a two-stage NO x abatement device for removal of NO x from engine exhaust during a cold start, the NO x storage component comprising a passive NO x adsorption (PNA) composition comprising:
a nickel ferrite (NiFe 2 O 4 ) substrate; and
a palladium component adsorbed on surfaces of the nickel ferrite substrate;
wherein, during an engine cold start, NO x is retained in the NO x storage component until the exhaust gas and the abatement device have warmed in excess of 200° C.
2. The NO x storage component as recited in claim 1 , wherein the palladium component comprises a palladium oxide.
3. The NO x storage component as recited in claim 1 , wherein the palladium component comprises palladium (II) oxide.
4. The NO x storage component as recited in claim 1 , wherein palladium is present at a weight percentage of from about 0.1 to about 3 wt. %.
5. The NO x storage component as recited in claim 1 , wherein palladium is present at a weight percentage of from about 0.1 to about 1.5 wt. %.
6. The NO x storage component as recited in claim 1 , wherein palladium is present at a weight percentage of from about 0.5 to about 1 wt. %.
7. A method of synthesizing a PNA composition, the method comprising:
performing wet impregnation of nickel ferrite with a palladium salt solution having a volatile or combustible anion, to produce an impregnated composition; and
calcining the impregnated composition in an oxidative atmosphere to produce the PNA composition.
8. The method as recited in claim 7 , wherein palladium in the palladium salt solution is present, relative to nickel ferrite, at a weight percentage of from about 0.1 to about 3 wt. %.
9. The method as recited in claim 7 , wherein palladium in the palladium salt solution is present, relative to nickel ferrite, at a weight percentage of from about 0.1 to about 1.5 wt. %.
10. The method as recited in claim 7 , wherein palladium in the palladium salt solution is present, relative to nickel ferrite, at a weight percentage of from about 0.5 to about 1 wt. %.
11. The method as recited in claim 7 , wherein the palladium salt solution comprises palladium (II) acetylacetonate.
12. A passive NO x adsorption (PNA) composition comprising:
a nickel ferrite (NiFe 2 O 4 ) substrate; and
palladium oxide adsorbed on surfaces of the nickel ferrite substrate.
13. The PNA composition as recited in claim 12 , wherein palladium is present at a weight percentage of from about 0.1 to about 3 wt. %.
14. The PNA composition as recited in claim 12 , wherein palladium is present at a weight percentage of from about 0.1 to about 1.5 wt. %.
15. The PNA composition as recited in claim 12 , wherein palladium is present at a weight percentage of from about 0.5 to about 1 wt. %.