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Adsorption, thermal decomposition, and reactivity of Ni(CO), in the cage system of dehydrated zeolite Y has been studied with EXAFS and near-edge spectroscopies, in particular monitoring changes in oxidation states and Ni ligation. Ni(CO), is adsorbed as an intact molecule in cation-free zeolite Y, LiY, and Nay. Symmetry changes of the molecule in LiY and NaY are assigned to the formation of cation-OC-Ni bridges. Thermal treatment of the Ni(CO),/NaY adduct leads to loss of CO concomitant with the formation of a bimodal Ni phase. A major part of the Ni forms small clusters (approximately 0.5 to 1.5 nm), in addition to larger crystallites (5-30 nm), sticking at the outer surface of the zeolite crystals. Oxidation of Ni(CO),/NaY to NiO/NaY with molecular oxygen occurs almost to completion below 295 K. The small NiO particles are stable to sintering up to 670 K. Nickel-phosphine/NaY adducts have been prepared by direct adsorption from solution (Ni(CO)3PMe3, Ni(C0)2(PMe3)2), and by synthesis inside the NaY supercage (Ni(CO)3PMe3, Ni(CO),(PPh,CHMe,), Ni(co),P(t-B~)~, Ni(PMe,),). The NaY/Ni(CO)3(PPh2CHMe2) adduct is a ship-in-a-bottle complex, Le., the Ni complex is too large to exit the zeolite supercage. The substitution of carbonyl ligands by phosphines was monitored in the near-edge and EXAFS modulations as well as with "P MAS NMR. EXAFS is an excellent method to monitor ligand coordination and provides information that is complimentary to IR spectroscopy. The interplay between organometallic molecules and oxide surfaces has attracted growing attention during the last decade. A major incentive to study these systems is to anchor catalytically active species on heterogeneous supports for the purpose of facile recovery from the reaction mixture.* Homogeneous catalysts, if immobilized for instance in the cage system of zeolites, might be expected to be stabilized against aggregation or bimolecular deactivation. Furthermore, the zeolite cage system may favor unique selectivity of a catalytic reaction due to changed complex geometries, transition-state modifications, and/or diffusional selectivity for the substrate molecules. Thermal decomposition of supported Ni(C0)4 as a precursor for dispersed Ni catalysts3-' and a limited number of attempts to anchor mixed Ni(CO),L, complexes directly on partially hy- droxylated oxide surface^*^^ have been reported previously. The reaction of Ni(C0)4 with NaX zeolite, its thermal stability, and the generation of encapsulated phosphine complexes have recently been studied with IR techniques.I0 The effect of pore blocking at high loading densities and selectivity for ligands of certain size have been demonstrated. The limitations of IR spectroscopy for these systems prevented a definitive identification of the reaction products. A major challenge for research on supported metal systems is the detailed characterization of the metal environment. In an attempt to understand the behavior of nickel carbonyl compounds in the cage system of faujasites, we have used a combination of EXAFS and X-ray absorption near edge spectroscopy, comple- mented by 31P MAS-NMR and FT-IR experiments.

Intrazeolite chemistry of nickel(0) complexes and Ni(0,II) clusters studied by EXAFS, solid-state NMR and FT-IR spectroscopy