Heterogeneous catalysis in solution. Part 18. The catalysis by carbons of oxidation–reduction reactions

Abstract

A mechanism of electron-transfer-through-the solid is proposed to account for the widespread catalysis by carbons of redox reactions in solution. Charcoal catalysis of the aqueous reaction between Fe³⁺ and I^– ions was predicted, found, and studied kinetically. The activation energy of the heterogeneous process was only 24 kJ mol^–1 compared with 100 kJ mol^–1 for the homogeneous reaction. The [Fe(CN)₆]^3–+ I^– reaction in water was found to be catalysed by carbons as well as by several phthalocyanines. Neither reaction was catalysed by solids such as SiO₂ or Ba[SO₄] which do not conduct electronically.