Intrazeolite Chemistry of Nickel(0) Complexes and Ni(0,II) Clusters Studied by EXAFS, Solid-State NMR, and FT-IR Spectroscopy

Article abstract of DOI:10.1021/ja00214a024

Adsorption, thermal decomposition, and reactivity of Ni(CO)4 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)4 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)4/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)4/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 , and by synthesis inside the NaY supercage x>.The NaY/Ni(CO)3(PPh2CHMe2) adduct is a ship-in-a-bottle complex, i.e., 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 (31)P MAS NMR.EXAFS is an excellent method to monitor ligand coordination and provides information that is complimentary to IR spectroscopy.