Transient in‐situ DRIFTS Investigation of Catalytic Oxidation of Toluene over α‐, γ‐ and β‐MnO2.

Manganese oxides with different crystal phases (i. e. α‐MnO2, γ‐MnO2 and β‐MnO2) were synthesized for catalytic oxidation of toluene. The catalytic activity was strongly influenced by the crystal phases of MnO2. α‐MnO2 exhibited the highest catalytic activity with a 50 % toluene conversion (T50) at 229 °C and a 90 % toluene conversion (T90) at 238 °C, followed by γ‐MnO2 (T90=252 °C) and β‐MnO2 (T90=278 °C). The remarkable catalytic activity of α‐MnO2 was attributed to its superior redox property and lattice oxygen mobility. Different intermediates were detected on the surfaces of α‐, γ‐ and β‐MnO2 by in situ diffuse reflectance infrared Fourier transform spectroscopy (in‐situ DRIFTS). Benzoate species were found to be the key intermediates on α‐MnO2 at 240 °C, while benzoyl oxide species and benzoate were the major intermediates on γ‐MnO2 at 260 °C. The surface of β‐MnO2 was mainly covered by carbonate and benzoate species after the adsorption of toluene at 280 °C. [ABSTRACT FROM AUTHOR]