Molecular Chemistry in a Zeolite: Genesis of a Zeolite Y-Supported Ruthenium Complex Catalyst

Dealuminated zeolite Y was used as a crystalline support for a mononuclear ruthenium complex synthesized from cis-Ru(acac)₂(C₂H₄)₂. Infrared (IR) and extended X-ray absorption fine structure spectra indicated that the surface species were mononuclear ruthenium complexes, Ru(acac)(C₂H₄)₂²⁺, tightly bonded to the surface by two Ru−O bonds at Al³⁺ sites of the zeolite. The maximum loading of the anchored ruthenium complexes was one complex per two Al³⁺ sites; at higher loadings, some of the cis-Ru(acac)₂(C₂H₄)₂ was physisorbed. In the presence of ethylene and H₂, the surface-bound species entered into a catalytic cycle for ethylene dimerization and operated stably. IR data showed that at the start of the catalytic reaction, the acac ligand of the Ru(acac)(C₂H₄)₂²⁺ species was dissociated and captured by an Al³⁺ site. Ethylene dimerization proceeded 600 times faster with a cofeed of ethylene and H₂ than without H₂. These results provide evidence of the importance of the cooperation of the Al³⁺ sites in the zeolite and the H₂ in the feed for the genesis of the catalytically active species. The results presented here demonstrate the usefulness of dealuminated zeolite Y as a nearly uniform support that allows precise synthesis of supported catalysts and detailed elucidation of their structures.