The adsorption and oxidation of 1,2-dichlorobenzene (o-DCB) with 8% O2/He over Co-HMOR, Pd/Co-HMOR and H-MOR catalyst samples were studied by means of in situ FTIR spectroscopy. Strong o-DCB adsorption takes place on both Co-HMOR and Pd/Co-HMOR at 250°C on Co2+ Lewis acid sites, as indicated by the appearance of a characteristic IR band centered at 1663cm−1. o-DCB can also adsorb on these materials through weaker interactions with hydroxyl (Brønsted) acid sites. o-DCB adsorption on such Brønsted acid sites is the only mode of interaction with the parent H-MOR material. Under reaction conditions the 1663cm−1 band is no longer detectable in the spectra due to the low concentration of Co2+ sites – which were converted to (Co-OH)+ and CoOx due to interactions with the water generated by the reaction – and/or the reactivity of the corresponding adsorbed o-DCB species. In the case of Co-HMOR, the presence of gas phase oxygen is necessary for any reaction products to appear, while on Pd/Co-HMOR the onset of the reaction is observed even in the absence of gas phase oxygen, presumably due to the presence of PdO in the sample.