Anna Penkova

FTIR spectroscopic study of low-temperature co-adsorption of NO and O2 on H-ZSM-5: evidence of formation of [ONNO]+ species

Abstract Coadsorption of NO and O 2 on H-ZSM-5 at room temperature leads to formation of NO + occupying cationic positions (2133 cm −1 ) and adsorbed nitrogen oxides. At low temperature NO + reacts with NO, thus producing the unknown so far [ONNO] + surface complex (2000 and 1687 cm −1 ). The latter is readily decomposed to NO + and NO. The assignment is supported by experiments involving 15 NO.

FTIR spectroscopic study of CO and NO adsorption on Cr-ZSM-5

Abstract Low temperature adsorption of CO on activated Cr-ZSM-5 sample does not lead to formation of any chromium carbonyls. Very small amount of chromium nitrosyls were produced after NO adsorption at ambient temperature. When NO was adsorbed on a hydrogen-reduced sample (773 K) dinitrosyls of Cr3+(NO)2 type were produced and evidenced by strong bands at 1908 and 1782 cm−1. Surprisingly, CO fails to detect these Cr3+ sites even at low temperature. The results are rationalized by assuming that Cr3+ cations in Cr-ZSM-5 are coordinatively saturated and do not form chemical bonds with weak ligands. Since the Cr3+(NO)2 are very stable (they decompose at 323 K), these species are formed with a simultaneous change in the original coordination of the Cr3+ cations.