FT IR STUDY OF NO ADSORPTION OVER COZSM-5

The adsorption of NO on CoZSM-5 zeolites with different Co content is studied by FT i.r. spectroscopy. The dominant NO species absorbed on C oZSM-5 is found to be in a dinitrosyl form, as demonstrated by the i.r . bands at 1,813 and 1,896 cm(-1). The mononitrosyl form occurs in the region of 1,939-1,941 cm(-1) as a minor species. From the samples of higher Co loadings (>2% by wt) a new band near 1,858 cm(-1)(w) attribu table to the species of Co3O4-NO is observed. It is found that the amo unt of NO molecules adsorbed on the samples of lower Co loadings (less than or equal to 2%) increases with the exchanged Co2+ contents. Over the OH stretching region, three vibrational frequencies were observed : a weak band near 3,746 cm(-1) for isolated SiOH sites, another near 3,614 cm(-1) for the Bronsted acid sites, and the third near 3,665 cm( -1) for [CoOH](+). The (-Co-O-)(x) species may be formed by the therma l decomposition of either [CoOH](1+) or Co-(NO)(2) under an oxidative state. (C) Elsevier Science Inc. 1996