Enhanced Lattice Oxygen Reactivity over Ni-Modified WO3-Based Redox Catalysts for Chemical Looping Partial Oxidation of Methane

Partially oxidizing methane into syngas via a two-step chemical looping scheme is a promising option for methane transformation. Providing the optimum lattice oxygen to selectively produce syngas represents the major challenge for the development of oxygen carrier materials in chemical looping processes. This paper describes the design of WO3-based oxygen carriers as the primary source of lattice oxygen with high melting points and attractive syngas selectivity. To further enhance the lattice oxygen availability and methane conversion capacity, NiO nanoclusters are introduced, considering the doping effect on chemical bonding disruption in both bulk and surface regions. For Ni0.5WOx/Al2O3, the nickel cations incorporated into the bulk of WO3 can strongly weaken the tungsten oxygen bond strength and increase the availability of lattice oxygen. The surface-grafted nickel species can effectively activate methane molecules and catalyze the partial oxidation reaction. Total methane conversion and syngas yield can be substantially increased by about 2.7-fold in comparison with unmodified WO3/Al2O3. This work demonstrates that the bulk and surface modifications are feasible to tailor the active lattice oxygen of oxygen-carrying materials in chemical looping processes.