Mechanistic understanding of surface reduction of Cu Ce O hybrid nanoparticles for catalytic methane combustion

Abstract

Abstract The synergistic effect of Cu Ce O hybrid nanostructure has shown the promise for catalytic methane combustion. In this study, we develop an aerosol-based two-stage thermal treatment method to (1) synthesize the Cu Ce O hybrid nanoparticle (NP) with a tunable oxidation state directly in gas phase, and (2) provide a mechanistic understanding of surface reduction of the Cu Ce O hybrid NP for catalysis of methane combustion. After evaporation-induced self-assembly followed by a thermal decomposition to form metal oxide NP at the 1st stage thermal treatment, a temperature-programmed, aerosol-based hydrogen reduction process was employed for direct tuning the oxidation state of the NP in the gas phase (the 2nd stage thermal treatment). Differential mobility analysis, x-ray diffractomery, x-ray photoelectron spectroscopy, and scanning electron microscopy were employed complementarily for characterization of particle size, morphology, crystallinity, elemental composition, and oxidation state of the NPs. The results show a successful surface reduction of Cu for both Cu-only NP and Cu Ce O hybrid NP by the aerosol-based two-stage thermal treatment method. Using the Cu Ce O hybrid nanoparticle as catalyst, our results show a successfully catalysis on methane combustion over various initial oxidation states of Cu. The results show a high activity with a low light-off temperature, a high light-off stability and operation stability toward catalytic methane combustion. The prototype method proposed in this study provides the mechanistic understanding of the synergistic catalysis of the surface-reduced Cu Ce O hybrid nanoparticle with different oxidation states. The method can be especially useful to fabricate a variety of nanocatalysts with different oxidation states of active metals by design for the study of methane-based energy and environmental applications (e.g., CO2 dry reforming by methane).