Gating effect of g-C3N4-encapsulated Pt-based catalysts for the hydrogenation and Bamberger rearrangement of nitroaromatics

Abstract

Encapsulated catalysts are known for their exceptional stability; however, the encapsulation of the active sites typically leads to reduced activity. To address this issue, an effective strategy is to employ g-C₃N₄ (graphitic carbon nitride with a 3-s-triazine structure), which has distinctive pore channels. This material acts as a gatekeeper, allowing only small molecules such as H₂ and H to pass through, while blocking Pt and larger molecules like nitrobenzene, thus preventing Pt loss. The g-C₃N₄ “gating effect” can enhance the dissociation of H₂ on the Pt surface and greatly improve the activity. Moreover, the flow of electrons from Pt to g-C₃N₄ (forming a Pt–N bond) contributes to the enhancement of the H-adsorption capacity of g-C₃N₄, which can promote the hydrogenation of nitrobenzene adsorbed on the surface of g-C₃N₄. In the hydrogenation process of converting nitroaromatics to 4-aminophenol, p-methoxyphenol, and their derivatives, the key to controlling the product selectivity is the desorption of phenylhydroxylamine and its derivatives (intermediates). On the g-C₃N₄ surface, phenylhydroxylamine exhibited significantly reduced adsorption compared to the Pt surface, which promoted improved selectivity (selectivity increased by 29.6%). Therefore, the Pt/C@g-C₃N₄ catalyst disrupted the balance between the activity and selectivity in the nitroaromatic hydrogenation–rearrangement reaction, ensuring both high selectivity and stability while markedly enhancing the activity. These improvements establish favorable conditions for industrial implementation.