Intrinsically Active Surface in a Pt/γ-Mo₂N Catalyst for the Water–Gas Shift Reaction: Molybdenum Nitride or Molybdenum Oxide?

Apart from active metals, supports also contribute significantly to the catalytic performance of supported metal catalysts. On account of the formed strain and defects, the heterostructured surface of the support may play a crucial role to activate the reactant molecules, while it is usually neglected. In this work, the Pt/γ-Mo₂N catalyst was prepared via a facile solution method. This Pt/γ-Mo₂N catalyst showed excellent activity and stability for catalyzing the water-gas shift (WGS) reaction. The reaction rates at 240 °C were 16.5 molCO molPt⁻¹s⁻¹ in product-free gas and 5.36 molCO molPt⁻¹ s⁻¹ in full reformate gas, which were almost 20 times that of the catalysts reported. It is found that the molybdenum species in the surface of the Pt/γ-Mo₂N catalyst is molybdenum oxide as MoO₃. This surface MoO₃ is very easily reduced even at room temperature, and it transformed into highly distorted MoOx (2 < x < 3) in the WGS reaction. The MoOx on the catalyst surface greatly enhanced the capability of generating active oxygen vacancies to dissociate H₂O molecules, which induced unexpectedly superior catalytic performance. Therefore, the intrinsically active surface in the Pt/γ-Mo₂N catalyst for the WGS reaction was molybdenum oxide as MoOx (2 < x < 3).