Fig. 4: Investigation of photocatalytic mechanism.

a Calculated energy diagrams for methane conversion to ethane on PdCu and TiO2. Apart from the methyl radicals coupling pathway (blue line and red line, pathway 1), another pathway (pathway 2, purple line) via the coupling of methyl radicals and methane molecule to form ethane on PdCu is also presented. The ball models for the main pathway on both PdCu and TiO2 are shown (red – O, pink – Ti, tan – Pd, orange – Cu, teal – C, white – H) b XPS spectra (C 1 s) of Pd/TiO2 after 10-hour reaction. c XPS spectra (C 1 s) of PdCu/TiO2 after 112-hour reaction. d Scheme of photocatalytic OCM over PdCu/TiO2. Source data are provided as a Source Data file.