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

Alumina was synthesized from Al(NO 3 ) 3 , AlCl 3 and Al 3 (SO 4 ) 2 with NaOH, and from NaAlO 2 with HNO 3 by addition of acidic solution to alkaline solution with a syringe pump. The as-produced Al 2 O 3 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 CO 2 drying. However, the γ-alumina with the largest pore volume (5.4 cm 3 /g), BET surface area (423.7 m 2 /g) and pore size (37.8 nm) was obtained using Al(NO 3 ) 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.