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‐MnO 2 , γ‐MnO 2 and β‐MnO 2 ) were synthesized for catalytic oxidation of toluene. The catalytic activity was strongly influenced by the crystal phases of MnO 2 . α‐MnO 2 exhibited the highest catalytic activity with a 50 % toluene conversion (T 50 ) at 229 °C and a 90 % toluene conversion (T 90 ) at 238 °C, followed by γ‐MnO 2 (T 90 =252 °C) and β‐MnO 2 (T 90 =278 °C). The remarkable catalytic activity of α‐MnO 2 was attributed to its superior redox property and lattice oxygen mobility. Different intermediates were detected on the surfaces of α‐, γ‐ and β‐MnO 2 by in situ diffuse reflectance infrared Fourier transform spectroscopy (in‐situ DRIFTS). Benzoate species were found to be the key intermediates on α‐MnO 2 at 240 °C, while benzoyl oxide species and benzoate were the major intermediates on γ‐MnO 2 at 260 °C. The surface of β‐MnO 2 was mainly covered by carbonate and benzoate species after the adsorption of toluene at 280 °C.