Preparation of large pore volume γ-alumina and its performance as catalyst support in phenol hydroxylation

Abstract

Alumina was synthesized from Al(NO3)3, AlCl3 and Al3(SO4)2 with NaOH, and from NaAlO2 with HNO3 by addition of acidic solution to alkaline solution with a syringe pump. The as-produced Al2O3 precursors were supercritically dried and calcined at 500 °C to obtain mesoporous γ-alumina material. Results showed that all the inorganic aluminum salts could be used to synthesize high pore volume γ-alumina by controlling the precursor addition rate at room temperature and supercritical CO2 drying. However, the γ-alumina with the largest pore volume (5.4 cm3/g), BET surface area (423.7 m2/g) and pore size (37.8 nm) was obtained using Al(NO3)3 and NaOH. This γ-alumina was further used as a support for Fe-based catalyst with hydrogen peroxide to produce hydroquinone and catechol in the phenol hydroxylation reaction in 30 min at 80 °C. The conversion of phenol was 53.4% whereas the selectivity to dihydroxybenzenes-DHBs (hydroquinone-HQ and catechol-CAT) was as high as 96.2%, revealing that the larger pore volume takes effect in the γ-alumina as support for the Fe-based catalyst in the hydroxylation reaction, and that the γ-alumina may be a good candidate as the support for other important catalysts such as those used in the petroleum refining industry.