The Fe/Mo/DBH catalyst exhibited stable p-selective oxidation activity in forming terepohthaldehyde by gas-phase O-2 oxidation of p-xylene under mild reaction conditions with high selectivity. It also catalyzes other reactions such as oxydehydrogenation, hydroxylation of benzene to phenol, and CO2 activation. The catalyst was characterized by employing combined techniques of Raman spectroscopy, analytical electron microscopy (AEM), high-resolution electron microscopy (HREM), Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and in situ total electron yield near edge spectroscopy (XANES). Two phases, Fe-2(MoO4)(3) and MoO3, were identified by Raman spectroscopy. In situ low-temperature CO2-dosing XANES experiments provided evidence for a strongly chemisorbed CO2 species on Fe/Mo/DBH at the reaction temperature.