Influence of magnesium and chromium oxides on the physicochemical properties of γ-alumina

Abstract

Boehmite, magnesium–aluminum and chromium–aluminum hydroxides prepared from the corresponding chloride solutions using ammonia solution at pH ∼ 9. The precipitated hydroxides subjected to thermal treatment at 450 °C to produce γ-alumina and magnesium–aluminum mixed oxide and at 600 °C to produce chromium–aluminum mixed oxide materials. The materials characterized by Fourier transformer infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and BET surface analyses. The catalytic activity of these materials toward cyclohexane dehydrogenation reaction was performed in a pulse micro-catalytic reactor operated under atmospheric pressure at reaction temperature ranged from 250 to 550 °C. The results indicated that, chromium–aluminum oxide material which possess crystallite size, 27.0 nm and surface area 89.0 m 2 /g, is the most active material toward benzene formation (23.7%) at reaction temperature 500 °C. Meanwhile, magnesium–aluminum oxide is the most selective one toward benzene formation (crystallite size, 3.0 nm and surface area, 209.7 m 2 /g) as compared with the other prepared materials. Boehmite, magnesium–aluminum and chromium–aluminum hydroxides prepared from the corresponding chloride solutions of aluminum, magnesium and chromium, respectively, using ammonia solution at pH ∼ 9. The precipitated hydroxides subjected to thermal treatment at 450 °C to produce γ-alumina and magnesium–aluminum mixed oxide and at 600 °C to produce chromium–aluminum mixed oxide materials. The materials characterized using Fourier transformer infrared spectroscopy, X-ray diffraction pattern, differential scanning calorimetry and BET surface analyses. The catalytic activity of these materials toward cyclohexane dehydrogenation reaction was performed in a pulse micro-catalytic reactor operated under atmospheric pressure at reaction temperature ranged from 250 to 550 °C. The results indicated that, chromium–aluminum oxide material which possess crystallite size, 27.0 nm and surface area 89.0 m 2 /g, is the most active material toward benzene formation (23.7%) at reaction temperature 500 °C. Meanwhile, magnesium–aluminum oxide is the most selective one toward benzene formation (crystallite size, 3.0 nm and surface area, 209.7 m 2 /g) as compared with the other prepared materials.