Effect of Si/Al Ratio and Rh Precursor Used on the Synthesis of HY Zeolite-Supported Rhodium Carbonyl Hydride Complexes

Rh(CO)(2) complexes anchored on various dealuininated HY zeolites were, used as prec-utsors, for the surface-, mediated synthesis of Rh(CO)(H)(x) Species. The carbonyl ligands of the initial Rh(O)(2) Coinp-lexes react with gas-phase C2H4 to fOrni. Rh(CO) (C2H4) species and subsequently well-defined Rh(CO)(H)(x) complexes When the former are exposed to H-2 at room temperature. Zeolite-supported Rh(C2H4)(2) and Rh(NO)(2) can also be used as precursors, but both coinplexes must be converted into Rh(CO)(2) first to allow the formation of Rh(CO)(H)(x) species. The Rh(CO)(H)(x) species thus formed are characterized by a set of well-defined nu(CO) and nu(RhH) bands in their Fotirier transfrorn infrared spectra. Density fuctiotial theory calculations provide strong evidence for the formation of a family of Rh(CO)(H-2), Rh(CO)(H)(2), and Rh(CO)(H) complexes, all of which are attached differently to the zeolite framework. The fraction of each individual complex formed varies significantly with the Si/Al ratio of the zeolite and the nature of the precursor used and therefore has an effect on the number and intensity of infrared bands observed experimentally.