Metal ligand complexes in CoH–BEA relevant to ethane ammoxidation to acetonitrile: an FTIR study Original Research Article

Local lattice perturbation induced by bonding of a single cobalt ion at cationic sites in dehydrated CoH–beta zeolite (Si/Al 11.5–12.2, Co/Al 0.06–0.4) decreases after cobalt interaction with basic molecules, i.e. C2H4, C2H5NH2, NH3, and CD3CN. Lattice perturbation is manifested by a reverse change of an IR band at the transmission window region for a bare cation at 916 cm−1, giving a relaxation shift for the 1 : 1 complex, Δr, equal to 10–26 cm−1. The order of Δr values was as follows: C2H5NH2 ≅ CD3CN > NH3 ⪢ C2H4. The value of the ‘relaxation shift’ correlates well with the strength of the cobalt–ligand bonding in Co–adsorbate complexes. It has been found that during the desorption experiment on CoH–BEA of Co/Al > 0.2 at temperatures above 300°C, the Co–ethylamine is converted into the Co–acetonitrile complex without oxygen present in the gas phase. This transformation occurs on the single Co ions and is not connected with non-specified Co oxidic species present in some highly Co-loaded CoH–beta zeolites.