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

Abstract

Mesoporous CoMnAl mixed metal oxide catalysts with various Co/Mn atomic ratios have been obtained by calcination at 450 °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% (T₉₀) was about 238 °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 °C lower than that on the Co₃AlO sample with a lower 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 T₉₀ at 208 °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.