N/P doped porous graphitic carbons as metal-free catalysts for the hydrogenation of sulfoxide to sulfide

N doped graphitic carbon (UCs-T) or N, P co-doped graphitic carbon (PCs-T) were conveniently prepared by pyrolysis. Their main doping modes of heteroatoms and defect structures were characterized. The hydrogenation of sulfoxides to thioethers with H₂ and formic acid (FA) was investigated over the prepared carbon materials (UCs-T and PCs-T), respectively. N-doped carbon UCs-T series showed satisfactory catalytic performance and stability in hydrogenation of sulfoxide with H₂, especially for UCs-1000 with 93.74 % sulfoxide conversion. Characterization and theoretical calculation showed that the nano electric fields induced by defects and doped N atom, affected its polarity and ability to polarize and activate H₂ located there, which was beneficial to hydrogenation. For transfer hydrogenation of sulfoxide with FA, N, P co-doped carbon PCs-900 showed superior performance to commercial Pd/C in both activity and stability, sulfoxide conversion was 97.32 %. Characterization and theoretical calculation demonstrated the structural unit like 1,3-azaphosphorine showed significant capability for adsorption and activation of FA. The activation behaviors of hydrogen and FA by nano electric fields induced by defects and doping heteroatoms in carbon materials was different, and which provided a novel insight for the design of metal-free hydrogenation catalysts.