Effect of pyrolysis temperature of the catalytic activity of active carbon+cobalt phthalocyanine in sulfur dioxide oxidation by oxygen

Structural changes during the pyrolysis of the catalyst ‘active carbon+cobalt phthalocyanine’ (Ac+CoPc) in the temperature range 500–800°C are investigated using infrared spectroscopy, XRD and DTG analysis. The decomposition products contain organic residues of the phthalocyanine rings and separate phases of CO3O4 and β-Co. The effect of pyrolysis temperature on: (i) the chemical stability of Co in the pyrolyzed CoPc in 0.5M H2 SO4; (ii) the electrocatalytic activity for oxidation of SO2 by oxygen; and (iii) the partial electrochemical reactions of SO2 oxidation and oxygen reduction, has been studied. The rate of electrochemical oxidation of SO2 is affected only by the active centres formed on pyrolysis of the chelate rings. The presence of Co at lower pyrolysis temperatures decreases the oxygen diffusion limitations. It is shown that the rate of SO2 oxidation by oxygen is limited by mass transport of oxygen.