HYDROCARBONS FROM SYNTHESIS GAS - SELECTIVITY CHANGES INDUCED BY THE ZEOLITE MATRIX ON THE METALLIC FUNCTION IN RH Y CATALYSTS/

RhNaY and RhHY zeolites have been prepared either by ion exchange with RhCl3 or by Rh-6(CO)(12) sublimation under vacuum. Except in the latt er case, very small rhodium aggregates were obtained within the superc ages of faujasitic zeolite. Photoelectron spectra and IR of chemisorbe d carbon monoxide revealed that the interaction of these clusters with the zeolite matrix differs substantially, depending on the acidity of the zeolite. These clusters become aggregated during reduction or on- stream mainly at the outer zeolite surface irrespective of the degree of protonation of the zeolite. The RhNaYi catalyst proved to be intere sting for the conversion of CO/H-2 mixtures to low carbon number alken es and alkanes with a propensity to form butenes/butanes. However, the parent RhHYi homologue produced a higher proportion of saturated and branched hydrocarbons, mainly the C-4 fraction. These important differ ences in product distribution in the RhHYi zeolite have been associate d with the presence of cationic rhodium species as revealed by X-ray p hotoelectron spectroscopy and carbon monoxide chemisorption.