Stability of a cryptomelane catalyst in the oxidation of toluene

The oxidation of toluene over a cryptomelane (K-OMS-2) catalyst was investigated at temperatures between 100 and 300 °C. The catalyst was tested both in temperature-programmed experiments (light-off curves) and in isothermal tests. The carbonaceous deposits retained in the porous structure after the isothermal tests were evaluated by temperature-programmed oxidation. The results show that gradual deactivation occurs at temperatures below 268 °C (which corresponds to the peak maximum in the TPO curves). Furthermore, in a restricted temperature range (252–258 °C), the catalyst shows an unstable behaviour, and oscillations in the conversion into CO2 occur. TPD experiments after adsorption of toluene at room temperature show that this compound is strongly retained in the porous structure up to high temperatures, which can explain the deactivation and the unstable behaviour. For comparative purposes, TPD after adsorption of ethyl acetate was also carried out, and it was observed that this compound was not retained as much as toluene, no oscillations being detected.