SOLID-STATE ION-EXCHANGE OF RHODIUM CHLORIDE WITH HIGHLY DEALUMINATEDY-TYPE ZEOLITE DAY BY THERMAL-TREATMENT AND IN THE PRESENCE OF CARBON-MONOXIDE

The solid-state ion exchange of Rh chloride with highly dealuminated Y zeolite has been studied by in situ FTIR spectroscopy. Thermal treatm ent in vacuum and calcination in oxygen up to 600-degrees-C results in an exchange limited to ca. 25% at temperatures higher than 400-degree s-C. The ion exchange can be performed much more effectively (over 50% ) and at lower temperatures (100-150-degrees-C) in the presence of CO in the gas phase. A linear correlation has been found between the form ation of well-defined Rh(CO)2+ species and the simultaneous loss of ac id hydroxyl groups for samples treated at different conditions. From t hese results a model is proposed with the formation of Rh subcarbonyls , the migration of these species to the cation positions of the zeolit e and, finally, the formation of the stable well-defined Rh(CO)2+ spec ies at these positions as essential steps of the ion exchange in the p resence of CO.