Hydrogenated Molybdenum Oxide Overlayers Formed on Mo Nitride Nanosheets in Ambient-Pressure CO₂/H₂ Gases

Transition metal nitrides (TMNx) often exhibit high catalytic activity in many important reactions. Due to their low stability in a reaction environment, it remains as a crucial issue to reveal surface active structures in catalytic reactions, particularly for the cases containing both oxidative and reductive gases. Herein, MoN and Mo2N nanosheets have been constructed on Al2O3(0001) and Au foil surfaces, and in situ surface characterizations are performed on the model catalysts in ambient-pressure CO2, H2, and CO2 + H2 gases. In situ Raman spectroscopy and quasi in situ X-ray photoelectron spectroscopy (XPS) analysis indicate that MoO3 and defective MoO3–x overlayers form on both MoN and Mo2N surfaces in CO2, and the surface oxidation occurs under a milder condition on Mo2N than on MoN. Further, a hydrogenated Mo oxide (HzMoO3–y) overlayer forms in a CO2 + H2 atmosphere, as confirmed using quasi in situ XPS and time-of-flight secondary ion mass spectroscopy. The surface analysis over the model nitride catalysts suggests that O and/or H atoms may be incorporated into surface layers to form the active structure in many O and H-containing reactions.