ESR identification of vanadium species deposited on Al2O3 and MoS2-Al2O3 catalysts : relevance to catalytic demetallation of vanadyl porphyrinR Hubaut, CF Aissi, S Dejonghe and J GrimblotJ. Chim. Phys., 88 (1991) 1741-1755DOI: https://doi.org/10.1051/jcp/1991881741