Halogenated oxide surfaces Lewis acidity

Radical cations can be generated by many chemical oxidizing reagents, including Brpnsted and Lewis acids, the halogens, peroxide anions or radical anions, metal ions or oxides, nitrosonium and dioxygenyl ions, stable aminium radical cations, semiconductor surfaces, and suitable zeolites. In principle, it is possible to choose a reagent with a one-electron redox potential sufficient for oxidation-reduction, and a two-electron potential insufficient for oxidation-reduction of the radical ion. 

Coal and many coal-derived liquids contain polycyclic aromatic structures, whose molecular equivalents form radical cations at anodes and radical anions at cathodes. ESR-electrolysis experiments support this (14). Chemically, radical cations form by action of H2SO4 (15,19), acidic media containing oxidizing agents (15,20,21,22), Lewis acid media (18,23-35) halogens (36), iodine and AgC104 (37,38), and metal salts (39,40). They also form by photoionization (41,42,43) and on such solid catalytic surfaces as gamma-alumina (44), silica-alumina (45), and zeolites (46). Radical anions form in the presence of active metals (76). 

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