FT-IR spectroscopic study of the oxidation of chlorobenzene over Mn-based catalyst

Adsorption and oxidation of chlorobenzene on Al₂O₃, TiO₂-Al₂O₃, and MnO_x/TiO₂-Al₂O₃ have been studied by in situ Fourier transform infrared (FT-IR) spectroscopy. At room temperature, chlorobenzene is only physisorbed on Al₂O₃, TiO₂-Al₂O₃, and MnO_x/TiO₂-Al₂O₃, and gives the same IR spectrum as that for liquid-phase chlorobenzene. On Al₂O₃ no further interaction and reaction take place with treatment at higher temperatures (up to 773 K), while phenolates are observed for TiO₂-Al₂O₃ and MnO_x/TiO₂-Al₂O₃ at 773 K. When the adsorbed chlorobenzene coexists with oxygen, formates are detected for Al₂O₃, while acetates are additionally observed for TiO₂-Al₂O₃ above 573 K. For MnO_x/TiO_2-Al₂O₃, maleates are present at 573 and 673 K, while formates and acetates develop at 473 and 573 K. Almost all IR bands due to formates, acetates, and maleates disappear at 773 K, indicating that these oxygen-containing species are potential intermediates for the total oxidation of chlorobenzene.