The catalytic and photocatalytic autoxidation of S x2− to SO 42− by water-soluble cobalt porphyrin

Abstract

The catalytic and photocatalytic transformation of S 4 2−, S 3 2−, S 2 2− and S 2− to SO 4 2− by water-soluble cobalt tetrakis ( N-methyl-4-pyridyl) porphyrin (Co(4-TMPyP)) was performed by a two-step process. The catalytic autoxidation of S x 2− ( x=2, 3 and 4) to S 2O 3 2− by Co(4-TMPyP) in the presence of oxygen was followed by the photocatalytic oxidation of S 2O 3 2− by Co(4-TMPyP) under illumination in presence of oxygen at a strong basic solution. The direct transformation of S x 2− to SO 4 2− was also performed. The catalytic activity of Co(4-TMPyP) was compared to Fe(2-TMPyP) and Mn(4-TMPyP). All three catalysts have activity towards autoxidation of S 4 2− to S 2O 3 2−. The trend in photocatalytic oxidation activity of the porphyrin complexes is Co(4-TMPyP)>Fe(2-TMPyP)>Mn(4-TMPyP). The electrocatalytic reactions of S x 2− by Co(4-TMPyP) were also observed.