Bifunctional active sites for adsorption of NOx
Immobilized nitronyl nitroxide active sites on the surface of a porous inorganic oxide support act as efficient and rapid oxidants for NO, reacting with >99% of the NO under flow conditions through a packed bed; and, in a parallel configuration with nitroxyl radical active sites, act to remove >99% of both NO and NO 2 from a gas mixture, with >95% of the active sites participating in NO x trapping.
1. A NOx adsorption system, comprising:
(a) a NO oxidation site having a nitronyl nitroxide covalently attached to a silica support; and
(b) a NO 2 adsorption site having a nitroxide radical immobilized on a solid support, wherein the NO oxidation site and NO 2 adsorption site are configured such that said NO 2 adsorption site adsorbs NO 2 generated by the NO oxidation and wherein x is 1 or 2.
2. The system according to claim 1 , wherein said nitronyl nitroxide has the formula:
wherein
A is selected from aryl and heteroaryl;
the bond between A and the silica support is covalent; and
R 1 , R 2 , R 3 and R 4 are members independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl and substituted or unsubstituted heteroarylalkyl.
3. The system according to claim 2 , wherein A is substituted or unsubstituted phenyl.
4. The system according to claim 2 , wherein R 1 , R 2 , R 3 and R 4 are members independently selected from C 1 -C 6 unsubstituted alkyl.
5. The system according to claim 2 , wherein said nitronyl nitroxide has the formula:
wherein
X is a member selected from O, S, amine, amide, carbamate, ester, carbonate, thioester, thiocarbonate, ketone, sulfoxide, sulfone, sulfonate, sulfate, disulfide, phosphine, phosphonate, imine, imide, nitrone, nitroxide, nitroxyl radical, boronate, quaternary ammonium, substituted or unsubstituted alkyl and substituted or unsubstituted heteroalkyl.
6. The system according to claim 1 , wherein said silica support and said solid support are different supports in a mechanical mixture with one another.
7. The system according to claim 1 , wherein said silica support and said second solid support are the same support.
8. The system according to claim 1 , wherein said nitronyl nitroxide is PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl).
9. A device comprising:
(a) said system according to claim 1 ; and
(b) a container for said system, wherein said container comprises a gas inlet port and a gas outlet port.
10. The system according to claim 1 , wherein said solid support is made of a material substantially non-reactive with NO x .
11. The system according to claim 1 , wherein said solid support is coated with a non-reactive material.
12. The system according to claim 1 , wherein said nitronyl nitroxide is covalently attached to the silica support surface through a linker arm.
13. The system according to claim 1 , wherein said NO 2 adsorption site is TEMPO (2,2,6,6-Tetramethylpiperidine 1-oxyl).
14. The system according to claim 1 , wherein the nitroxide radical is covalently attached to the solid support.
15. The system according to claim 14 , wherein the solid support is said silica support.
16. The system according to claim 14 , wherein the solid support is a silica support.