Direct Photocatalytic Methane Oxidation to Formaldehyde by N Doping Co-Decorated Mixed Crystal TiO 2 .

In this paper, N-doped TiO 2 mixed crystals are prepared via direct calcination of TiN for highly selective oxidation of CH 4 to HCHO at room temperature. The structures of the prepared TiO 2 samples are characterized to be N-doped TiO 2 of anatase and rutile mixed crystals. The crystal structures of TiO 2 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 H 2 O 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 H 2 O. An efficient photocatalyst was prepared by us to convert CH 4 to HCHO with high yield and selectivity, greatly promoting the development of the photocatalytic CH 4 conversion study.