A study on the oxidation of phenol by heterogeneous iron silica catalyst

A series of iron silica catalyst with (5–20) wt.% Fe3+ were prepared by means of a simple solvent extraction and sol–gel technique. These catalysts were probed for the oxidation of phenol employing hydrogen peroxide. Catalytic performance increased up to 10 wt.% Fe3+ loading. Further increase in the iron content was found to reduce the phenol conversion rate. Higher Fe3+ loading (>10% Fe3+) resulted in smaller pore size and exhibited extra framework Fe3+ in the catalyst, which lead to catalytic deficiency in phenol oxidation. Phenol oxidation by RH-10Fe gave 95.2% conversion at 343 K with selective formation of 61.3% catechol (CAT) and 38.7% hydroquinone (HQ). Reusability studies with RH-10Fe resulted in only 16% loss in catalytic activity. However, no leaching of iron was detected. The CAT/HQ ratio was found to be constant during the reaction which suggested a non-free radical catalytic mechanism to be operative.