Constructing a fragmentary g-C3N4 framework with rich nitrogen defects as a highly efficient metal-free catalyst for acetylene hydrochlorination

Abstract

Graphitic carbon nitride (denoted as “g-C₃N₄”), as a graphite-like CN material, is widely used in catalysis. In this paper, a fragmentary g-C₃N₄ framework with a porous structure and rich nitrogen defects was synthesized for acetylene hydrochlorination, using melamine formaldehyde (MF) resin as an oxygen-containing precursor. The fragmentary g-C₃N₄ shows a highly efficient activity with acetylene conversion reaching 94.5%, which is 30 times higher than that of pure g-C₃N₄ prepared by direct pyrolysis of melamine. Both experimental and characterization studies by XRD, XPS and TG-MS reveal that the high activity of the catalyst is mainly derived from the porous structure and rich nitrogen defects, which are attributed to the etching of the g-C₃N₄ framework by oxygen species in the MF resin. Moreover, density functional theory (DFT) calculations demonstrated that the nitrogen defects in the g-C₃N₄ framework greatly improved the adsorption of HCl and acetylene, and at the same time significantly reduced the energy barrier from 62.0 to 38.1 kcal mol⁻¹ at the rate-determining step.