Excellent low temperature performance for total benzene oxidation over mesoporous CoMnAl composited oxides from hydrotalcites

摘要

Mesoporous CoMnAl mixed metal oxide catalysts with various Co/Mn atomic ratios have been obtained by calcination at 450 degrees C of layered double hydroxide (LDH) precursors prepared by the NH4OH co-precipitation-hydrothermal method without distinct MnCO3 peaks. The catalysts exhibited high efficiency for total oxidation of volatile organic compounds (VOCs). The physicochemical properties of the catalysts were characterized using several analytical techniques. Among them, CoMn2AlO shows the optimal activity and the temperature required to achieve a benzene conversion of 90% (T-90) was about 238 degrees C, with a reaction rate and activity energy (E-a) of 0.24 mmol g(cat)(-1) h(-1) and 65.77 kJ mol(-1) respectively. This temperature was 47 degrees C lower than that on the Co3AlO sample with a tower reaction rate of 0.19 mmol g(cat)(-1) h(-1) and a higher E-a 130.31 kJ mol(-1) at a high space velocity (SV = 60 000 mL g(-1) h(-1)). The effects of calcination temperature on the textural properties and catalytic activity of the CoMn2AlO catalyst were further investigated. The as-prepared CoMn2AlO-550 sample displayed superior catalytic activity, with T-90 at 208 degrees C, compared CoMn2AlO-450. The formation of a solid solution with high surface area, rich oxygen vacancies, high Mn4+/Mn3+ and Co3+/Co2+ ratios and low-temperature reducibility made a great contribution to the significant improvement of the catalytic activity.