FexC enhancing the catalytic activity of FeNx in oxidative dehydration of N-heterocycles

Abstract

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 FexC 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 °C, 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 FexC and FeNx 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 FexC 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.