The Catalytic autoxidation of sulfite by supported water-soluble iron porphyrins

Abstract

Water-soluble iron porphyrins Fe( n-TMPyP) ( n = 2, 3 and 4), immobilized on a zeolite molecular sieve, have been used as catalysts and for the catalytic autoxidation of SO 2− 3 to sulfate effectively in the presence of oxygen at room temperature in aqueous solutions. The catalytic reaction rate of the sulfite oxidation is affected by the amount of catalyst immobilized on the zeolite molecular sieve. The initial concentration of SO 2− 3 influences the reaction rate. The pH value and ionic strength of the aqueous solution also very obviously influence the catalytic reaction rates. The catalysts are active in the pH range in which Fe(IV)( n-TMPyP) can be generated by electrochemical method and can influence the SO 2− 3 catalytic autoxidation mechanism. Fe(2-TMPyP) is more catalytically active than Fe(3-TMPyP) and Fe(4-TMPyP) under the same conditions. Fe(2-TMPyP) and Fe(3-TMPyP) are robust catalysts, while Fe(4-TMPyP) deactivates significantly. The orientation of N-methyl-pyridinium groups at the meso position of the porphyrin ring exhibit strong effects on the catalyst stability.