Fe_xC enhancing the catalytic activity of FeN_x in oxidative dehydration of N-heterocycles

To enhance the catalytic activity by designing metal particles combined with atomically dispersed non-noble metal catalyst is a huge challenge, which yet has not been studied widely in organic reactions. Herein, we describe a simple and efficient method to synthesize Fe_xC combined with Fe single atoms anchored on the N-doped porous carbon by regulating pyrolysis temperature. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy corroborate the existence of atomically dispersed Fe and the coordination number between Fe and N atoms. The Fe–N–C-800 catalyst exhibits the highest catalytic activity giving the 97% yield of quinoline in dehydration of 1,2,3,4-tetrahydroquinoline (THQ) reaction at a mild condition (60 ℃, O₂ balloon), and it shows good stability with 80% isolated yield after five consecutive dehydration reactions. Moreover, density functional theory (DFT) calculations reveal that coexistence of Fe_xC and FeN_x structure exhibits high activity owing to the lowest adsorption energy of co-adsorbed O₂ and THQ and the longest N–H bond length of THQ, that is because the existence of Fe_xC induces the charges transfer. Our work may open a new route to design metal particles combined with atomically dispersed non-noble metal catalysts with high activity in organic synthesis.