Advanced oxidation process for coke removal: A systematic study of hydrogen peroxide and OH-derived-Fenton radicals of a fouled zeolite

The regeneration process of a fouled catalyst typically involves treatments at high temperature which often cause irreversible damages on the catalyst's properties. In this work, Fenton chemistry-derived OH species, and H2O2, are proposed as oxidizing agents to reactivate a porous catalyst at mild conditions, below 100 degrees C. The chosen catalyst is a microporous ZSM-5 zeolite, which is a challenging candidate due to the mass transfer limitations with possible recombination of the hydroxyl radicals; thereby being an obstacle to oxidize organics occluded in the micropores. The organics deposition over a ZSM-5 zeolite during the D-glucose dehydration reaction was confirmed by a number of characterization techniques, which revealed a considerable decrease in the surface area, pore volume and acid site density in the fouled catalyst. By properly selecting the regeneration conditions, reactivation via Fenton or H2O2 was highly effective in terms of removal of the organics as well as recovery of the initial catalytic activity. The properties of the H2O2 treated-zeolite, the optimal treatment in this case study, were preserved with similar structural and textural features and improved acidity. Hot water extraction was ineffective to remove the humins from ZSM-5. Mechanistically, the presence of Fe impurities in the zeolite structure did not allow to discriminate between a homo, heterogeneous, or a direct H2O2 pathway, or a combination of them. The exhibited conversion by the regenerated zeolite was comparable to that of the fresh one.