High surface area molybdenum carbides are attractive for use as catalysts and supports. Due to their pyrophoricity, carbides are typically passivated prior to use. Research described in this paper compared the synthesis, structural and compositional properties, and water gas shift activities of catalysts produced by depositing Pt onto unpassivated and passivated MO2C. Passivation had a profound effect on the character of interactions between the Pt precursor salt (H2PtCl6) and MO2C. Nanoscale Pt metal particles were deposited onto the unpassivated MO2C while very large Pt particles were deposited onto the passivated MO2C (p-MO2C). In situ X-ray absorption spectroscopy revealed reduction of Pt4+ in contact with the unpassivated MO2C with commensurate oxidation of Mo. Water gas shift activities were significantly higher for the Pt/MO2C compared to the Pt/p-MO2C catalyst. Overall, the results indicate that the passivation of MO2C prior to metal deposition had deleterious effects on the Pt loadings, structures, and activities. (C) 2015 Elsevier Inc. All rights reserved.