A Novel Bimetal Cu–Fe Nano-Silica Catalyst Synthesis by Supercritical Method and Its High Catalytic Activity for Phenol Hydroxylation

Abstract— Nano-sized bimetal Cu–Fe silica catalyst (Cu–Fe–SiO₂/S) had been directly prepared by supercritical one-step method from sodium silicate to catalyze phenol hydroxylation. Compared with the ordinary silica, it had the same structure and composition with smaller particle size, more fluffy morphology and larger oil absorption. Its particle size mainly was 20 nm with 192.4 m²/g specific surface area, and much higher than that of ordinary silica (90.0 m²/g). This method employing bimetal Cu–Fe–SiO₂/S as catalyst for phenol hydroxylation was better catalytic activity than Fe–SiO₂/S and Fe-containing precipitated silica catalyst (Fe–SiO₂/P), which was benefited the favorable performance attributes such as larger specific surface area and more regular pore structure as catalyst support, and the synergistic catalysis between Cu and Fe. Under optimal reaction conditions, 46.9% of dihydroxybenzene yield, 43.3% of catechol yield, 3.6% of hydroquinone yield, and 82.3% of catechol selectivity was achieved. The possible catalytic reaction mechanism for phenol hydroxylation over Cu–Fe–SiO₂/S was also suggested.