CATALYTIC-OXIDATION OF AN AMORPHOUS-CARBON BLACK

The oxidation of an amorphous carbon black in the presence of a potassium-copper-vanadium catalyst supported on alpha-alumina has been studied. Burnoff temperatures in the presence of catalyst were lowered by about 300 K with respect to those for uncatalyzed combustion. Cycles of temperature-programmed reduction and oxidation, along with TG-MS analyses demonstrated that a redox mechanism is at the basis of the catalyst strong activity. A differential flow reactor was employed to perform kinetic tests. The progress of the catalytic combustion process was followed measuring the concentrations of carbon oxides in the product stream at the reactor outlet with on-line NDIR analyzers. The dependence of the reaction rate on the relevant variables was investigated. In particular, the apparent activation energy for the catalytic oxidation was found to be less than half that of the corresponding uncatalyzed process, while the carbon reactivity showed a linear dependence upon the amount of catalyst and a square root dependence upon the oxygen partial pressure. The results allowed the formulation of a mechanism for the catalytic oxidation of carbon black and suggest that the limiting step of the overall process is that of catalyst reduction. On the basis of such findings a kinetic equation for catalytic carbon black oxidation is proposed.