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FTlR spectroscopy at low temperature (77-300 K) h a s been used to study the surface species formed during t h e interaction of CO and NO with Rh'(CO), and Rh'(NO), on highly dealuminated zeolite Y (US-Ex). A series of different well defined surface carbonyls and nitrosyls including mixed NO-CO compounds was obtained in addition to t h e dicarbonyl and dinitrosyl. With CO a Rh tricarbonyl with C,, symmetry and a tetracarbonyl with C , , symmetry are suggested and identified by ligand exchange with "C'*O and '3C'60 and a calculation of the force constants within the framework of an energy-separated force field. As an intermediate in the ligand exchange reaction between Rh'(CO), and Rh'(NO), the mixed surface compound Rh'(CO)(NO), could be identified.

The interaction of NO and CO with Rh supported on highly dealuminated zeolite Y (US-Ex) has been investigated by FTlR spectroscopy at temperatures between 300 and 573 K. The interaction of NO with oxidized or reduced Rh/US-Ex results in the formation of a well defined Rh dinitrosyl species with IR bands at 1855 and 1780 cm-'. Other surface nitrosyl species were found to be dependent on the Rh particle size and the interaction conditions. With CO and NO in the gas phase well defined mixed surface complexes Rh'(CO)(NO), (vco = 2103 cm-';v N o = 1772, 1711 cm-') and Rh(CO),(NO) (vco = 2162, 2128 cm-' ; vNo = 1786 cm-') were observed at room temperature in addition to Rh'(CO), and Rh'(NO),. At higher temperatures, gaseous N, O and C02 and isocyanate, adsorbed on the support, were observed depending on the conditions.

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