DRIFTS investigation of toluene oxidation on CeO₂ nanoparticles

The oxidation mechanism of toluene on the surface of heat-treated CeO₂ nanoparticles was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). When introduced to the CeO₂ surface, toluene either chemisorbs to an oxygen bound to a single cerium atom creating monobound (m) benzyloxy or to an oxygen bound to two neighboring cerium atoms forming bridged (b) benzyloxy. From the DRIFTS analysis, benzoate production is directly dependent on the presence and oxidation of b-benzyloxy groups. Using temperature dependent peak height analysis of the DRIFTS spectra, the oxidation state of specific v_s(OCO) bands of bidentate (bdt) benzoate groups are identified through pairing with their v_a(OCO) counterparts. Surface lattice oxygens and b‑hydroxyl groups are found to facilitate the chemisorption of toluene as the two surface benzyloxy groups. Once toluene reacts with the substrate, surface hydroxyls react with m-benzyloxy groups to create additional b-benzyloxy groups as well as enabling the transformation of b-benzyloxy groups to bdt-benzoate groups. The previously unclear intermediate transformation steps of toluene to bdt-benzoate on the surface of CeO₂ and surface hydroxyls species role in said transformation is unveiled through the use of peak height analysis of the collected DRIFTS spectra.