Selective Activation of Methane on Single-Atom Catalyst of Rhodium Dispersed on Zirconia for Direct Conversion

Direct methane conversion into value-added products has become increasingly important. Because of inertness of methane, cleaving the first C-H bond has been very difficult, requiring high reaction temperature on the heterogeneous catalysts. Once the first C-H bond becomes activated, the remaining C-H bonds are successively dissociated on the metal surface, hindering the direct methane conversion into chemicals. Here, a single-atom Rh catalyst dispersed on ZrO₂ surface has been synthesized and used for selective activation of methane. The Rh single atomic nature was confirmed by extended X-ray fine structure analysis, electron microscopy images, and diffuse reflectance infrared Fourier transform spectroscopy. A model of the single-atom Rh/ZrO₂ catalyst was constructed by density functional theory calculations, and it was shown that CH₃ intermediates can be energetically stabilized on the single-atom catalyst. The direct conversion of methane was performed using H₂O₂ in the aqueous solution or using O₂ in gas phase as oxidants. Whereas Rh nanoparticles produced CO₂ only, the single-atom Rh catalyst produced methanol in aqueous phase or ethane in gas phase.