Direct Photocatalytic Methane Oxidation to Formaldehyde by N Doping Co-Decorated Mixed Crystal TiO₂

In this paper, N-doped TiO₂ mixed crystals are prepared via direct calcination of TiN for highly selective oxidation of CH₄ to HCHO at room temperature. The structures of the prepared TiO₂ samples are characterized to be N-doped TiO₂ of anatase and rutile mixed crystals. The crystal structures of TiO₂ samples are determined by XRD spectra and Raman spectra, while N doping is demonstrated by TEM mapping, ONH inorganic element analysis, and high-resolution XPS results. Significantly, the production rate of HCHO is as high as 23.5 mmol·g^-1·h^-1 with a selectivity over 90%. Mechanism studies reveal that H₂O is the main oxygen source and acts through the formation of ·OH. DFT calculations indicate that the construction of a mixed crystal structure and N-doping modification mainly act by increasing the adsorption capacity of H₂O. An efficient photocatalyst was prepared by us to convert CH₄ to HCHO with high yield and selectivity, greatly promoting the development of the photocatalytic CH₄ conversion study.