Hydrogenated Molybdenum Oxide Overlayers Formed on Mo Nitride Nanosheets in Ambient-Pressure CO 2 /H 2 Gases.

Transition metal nitrides (TMN x ) 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 Mo 2 N nanosheets have been constructed on Al 2 O 3 (0001) and Au foil surfaces, and in situ surface characterizations are performed on the model catalysts in ambient-pressure CO 2 , H 2 , and CO 2 + H 2 gases. In situ Raman spectroscopy and quasi in situ X-ray photoelectron spectroscopy (XPS) analysis indicate that MoO 3 and defective MoO 3- x overlayers form on both MoN and Mo 2 N surfaces in CO 2 , and the surface oxidation occurs under a milder condition on Mo 2 N than on MoN. Further, a hydrogenated Mo oxide (H z MoO 3- y ) overlayer forms in a CO 2 + H 2 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.