Vanadyl Porphyrin: Efficient Spin Probe to Study the Alumina Surface of Supported Catalysts

• Published in: Applied magnetic resonance 2024-10, Vol.55 (10), p.1293-1306
• Main Authors: Chetkova, Anna G., Trukhan, Sergey N., Martyanov, Oleg N.
• Format: Article
• Language: English
• Subjects: Adsorption; Alumina; Aluminum; Aluminum oxide; Atoms and Molecules in Strong Fields; Crude oil; Dehydration; Hydration; Investigations; Laser Matter Interaction; Ligands; Metals; Molybdenum; Nickel; Organic Chemistry; Original Paper; Parameter identification; Physical Chemistry; Physics; Physics and Astronomy; Solid State Physics; Spectroscopy/Spectrometry; Temperature; Transitional aluminas; Vanadyl porphyrins
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-024-01681-9

The EPR method and vanadyl tetraphenylporphyrin complex (VOTPP) as a spin probe were employed to study the transformation of the γ-Al 2 O 3 surface during temperature treatment. It has been shown that VOTPP complex is stable at least up to a temperature of 450 °C and P O 2 ≲ 3 Pa. Four distinct forms of vanadyl complex were identified on the γ-Al 2 O 3 surface, depending on the annealing temperature. The intensity ratio between these forms, exhibiting significantly different spin-Hamiltonian parameters, depend on the degree of surface hydration, which in turn determines the ratio between sites with different acidity on the γ-Al 2 O 3 surface. It has been shown that VOTPP complex demonstrate reversible transitions between different adsorption forms on the alumina surface during dehydration/hydration cycles. The observed phenomenon can be explained by the coordination vanadyl spin probe along the axial axis to the surface centers of different polarity/acidity.