Rhodium exchange in zeolites

Abstract

Rhodium exchange was attempted by using solutions of RhCl 3, [Rh(NH 3) 5Cl]Cl 2, and Rh(ClO 4) 3 in a series of zeolites with decreasing channel size: Y, mordenite, ZSM-34, ZSM-11, erionite, A, and ZK-5. Facile exchange was found in the large-pore zeolites Y and mordenite. Rh is found in the channels and on the surface of the medium-pore zeolites ZSM-34 and ZSM-11, suggesting that both exchange and surface hydrolysis occur. Surface hydrolysis to form islands of what is probably a Rh-oxy-hydroxy hydrate complex appears to be the primary type of deposition on the small-pore zeolites erionite, A, and ZK-5. Exchange in Y with the use of RhCl 3(aq) solutions at 90 °C, occurs via the Rh(H 2O) 6 3+ complex, does not result in an appreciable Cl − concentration in the zeolite and, contrary to previous work, does not result in Rh on the external surface of the zeolite. RhY prepared from RhCl 3(aq) solutions can be used to prepare highly dispersed Rh in Y without the preliminary preoxidative treatment necessary for Rh(NH 3) 5ClY. Reaction of CO with Rh-exchanged forms of Y, mordenite, ZSM-34, and ZSM-11 produces several species: Rh(I)(CO) 2(O z) 2 in mordenite and Y; Rh(I)(CO) 2(O z)(H 2O) in all four zeolites; and Rh(I)(CO) 3(O z) in mordenite, ZSM-34, and ZSM-11.