Fe-containing carbon-coated monoliths prepared by CVD in gaseous toluene abatement - parametric analysis of the Fenton process

The degradation of toluene (present in a gas stream) by the heterogeneous Fenton process was evaluated in a bubble column reactor. The process was catalyzed by macrostructured carbon-coated monoliths that were synthesized by chemical vapor deposition (CVD), which allowed carbon growth in honeycomb cordierite monoliths, while the iron (metal phase) was incorporated by adsorption. A detailed parametric study was carried out to evaluate the effect of the main variables and process operating conditions, namely channel density of the monolith, hydrogen peroxide concentration, pH and catalyst load; as process responses, the amount of toluene transferred - η, hydrogen peroxide consumption and dissolved organic carbon (DOC) concentration in the liquid phase were assessed. The maximum ratio between the toluene transferred per catalysts mass - η/W - (6.8 ×10−2 moltoluene gcat−1), with total oxidant consumption and higher intermediate compounds remaining in solution (DOC = 33 mgC dm−3), was reached when the process was performed with a monolith with a channel density of 230 cpsi, initial pH = 3.0, [catalyst] = 0.8 g dm−3, [H2O2] = 20 mmol dm−3. During all experiments, only a small amount of iron was leached from the catalyst to the liquid phase (ca. ≤1.0 wt%), proving its stability for such application; in fact, it was found that homogenous process contribution due to iron leaching towards the overall performance is ca. 10%.