FTIR AND EPR CHARACTERIZATION OF COPPER-EXCHANGED MORDENITES AND BETA-ZEOLITES

Sodium mordenites and beta zeolites, partially exchanged with Cu2+, we re characterised by means of Fourier transform infrared (FTIR) and bot h continuous-wave and pulse electron paramagnetic resonance (EPR) spec troscopies, in order to shed light on the catalytic role of copper ion s in the ammoxidation of 1-methylnaphthalene. FTIR analysis showed tha t ammonia interacts with both Bronsted and Lewis acid sites, while 1-m ethylnaphthalene is mainly coordinated through pi-complexes. The acidi ty of the catalysts was also determined through FTIR analysis of the a dsorbed pyridine. The main changes in the coordination sphere of Cu2ions were observed by EPR analysis after ammonia adsorption and after catalyst use, while adsorption of 1-methylnaphthalene had a very minor effect. Primary electron spin echo envelope modulation spectra after catalytic use showed the presence of organic radicals, having a relaxa tion time of longer than the Cu2+ ions. The latter are confirmed as th e active reaction centres and should be located in the Side pockets of the mordenites, and be unaccessible to the aromatic system of 1-methy lnaphthalene, This explains the higher selectivity observed with morde nites. In the more acidic beta zeolites the presence of copper ions on the walls of large channels initially favours side reactions, but als o makes adsorbed ammonia more available for ammoxidation.