Iron hematite-magnetite composite supported on mesoporous SBA-15 synthesized by using silica from cogon grass as a solid catalyst in phenol hydroxylation

Abstract

Phenol hydroxylation involves the oxidation of phenol (C₆H₅OH) using hydrogen peroxide (H₂O₂) to yield benzenediol (C₆H₄(OH)₂), mainly catechol (CTL) and hydroquinone (HQ). These products are in high demand in the pharmaceuticals industry sector. Thus, it is still worth investigating for further improvement in terms of heterogeneous iron catalysts. Herein, this research focuses on an iron hematite (Fe₂O₃)-magnetite (Fe₃O₄) composite catalyst supported on SBA-15 using silica from cogon grass for phenol hydroxylation. The extracted silica exhibited a fine white powder appearance and an amorphous structure, used as a silica source for SBA-15 synthesis. After catalyst preparation, the presence of Fe₂O₃, Fe₃O_4, and Fe₂O₃–Fe₃O₄ composite on SBA-15 was confirmed by using X-ray absorption near-edge structure (XANES). X-ray photoelectron spectroscopy (XPS) analysis provided insights into the surface of the catalyst, revealing that Fe₂O₃–Fe₃O₄/SBA-15 had the highest dispersion of iron species. In terms of catalytic performance, Fe₂O₃–Fe₃O₄/SBA-15 displayed the highest conversion of 88 % and HQ selectivity of 46 % compared with lone Fe₃O₄/SBA-15 or Fe₂O₃/SBA-15. The magnetic separation approach demonstrated the easy separation of catalysts containing Fe₃O₄. Reusability studies showed that Fe₂O₃–Fe₃O₄/SBA-15 maintained its activity up to the 4th cycle, suggesting minimized iron leaching compared to Fe₃O₄/SBA-15. Overall, this study provides insights into the catalytic performance of phenol hydroxylation and iron-based catalysts, emphasizing the potential of Fe₂O₃–Fe₃O₄/SBA-15 as an effective and reusable catalyst.