Speaker
Description
Studies on metal oxide clusters in the gas phase are aimed at gaining a better atomistic understanding of single-site catalysts. Here, we study the structure and reactivity of cationic model systems using a combination of mass spectrometry, infrared photodissociation (IRPD) spectroscopy, ion mobility and electronic structure calculations ranging from density functional theory to multi-reference electron correlation methods.
The reactivity of the aluminium oxide cations [Al3O4]+ is studied upon the substitution of Al atoms by the transition metal ones, Fe or Co. The electronically closed-shell [Al3O4]+ has a cone like structure and is unreactive towards methane activation,[1] while [FeAl2O4]+[2] and [CoAl2O4]+ show a planar bicyclic structure with a terminal oxygen radical (AlO•-I) that can abstract H from CH4. However, the doubly transition metal substituted species, [Fe2AlO4]+ and [Co2AlO4]+ are unreactive towards methane, and the structure assignment could not be done solely comparing IRPD spectra to harmonic vibrational spectra for different isomers. Therefore, we used ion mobility spectrometry and ab initio molecular dynamics simulations to unambiguously determine the structure of these systems. They exhibit a “key-like” structure with a planar four-membered ring connected to a nearly linear terminal O–TM+III–O-II unit, that display large amplitude motions that can only be captured by anharmonic simulations. Ion mobility data for the cobalt system, [Co2AlO4]+, were also obtained and confirm the assignment made.
