CHARACTERIZATION OF ACTIVATED STATES OF RUTHENIUM-CONTAINING ZEOLITE NAHY

As has been proven earlier, ruthenium-containing NaHY zeolites are abl e to catalyze the decomposition of ammonia at temperatures from 300 to 450 degrees C. In such catalysts, ruthenium cations are still present , even after heat treatment in high vacuum at 400 degrees C; they can be detected using ammonia and/or pyridine as probes for Fourier transf orm IR spectroscopy. They reside both in supercages and in sodalite ca ges. Various intermediates of the decomposition of the Ru(NH3)(6)NaY c omplex on heat treatment in high vacuum were identified via in situ IR spectroscopy; in particular, evidence for the formation of complexes with nitrosyl ligands was obtained. It was shown that partially decomp osed (deammoniated) Ru(NH3)(6)NaY complexes can be recovered to some e xtent by readsorption of ammonia. Ruthenium-containing species were lo calized either in the supercages or in the small cavities as shown by LR spectroscopy employing ammonia and pyridine as probes, The acidic p roperties of variously treated Ru(NH3)(6)NaY zeolites were characteriz ed via temperature-programmed desorption (TPD) of ammonia, which was m onitored by mass spectrometry. A strong interaction between ruthenium- containing species and the zeolite framework, leading to a lack of ove rtone and combination modes in the near infrared, is confirmed. Invest igations of Ru(NH3)(6)NaY samples by X-ray photoelectron spectroscopy under the same conditions as applied for IR and TPD studies revealed t hat, at variance with the results usually obtained after heat treatmen t of Ru(NH3)(6)NaY in high vacuum, no significant formation of rutheni um metal species through autoreduction occurred. Rather, a particular form of a cation-exchanged Ru, Na-Y zeolite was obtained. (C) 1997 Aca demic Press.