The adsorption and oxidation of ortho-dichlorobenzene (o-DCB) over sulfated zirconia (SZ), Co-SZ, and Pd/Co-SZ were studied by means of in situ MR spectroscopy to determine the nature of surface intermediates formed on these catalysts. The results indicate that o-DCB adsorbs on Lewis acid sites, forming surface intermediates that are strongly held on the surface. These intermediates can be subsequently oxidized to yield various partial oxidation products in either the presence or absence of gas-phase oxygen, confirming that surface oxygen is involved in the oxidation process. On Pd/Co-SZ samples, the oxidation is faster in the presence of gas-phase oxygen, yielding higher concentrations of partial oxidation products on the catalyst surface. (C) 2008 Elsevier Inc. All rights reserved.