Fabrication of P-Doped Porous Carbon Catalysts, with Inherent N Functionality, from Waste Peanut Shells and Their Application in the Metal-Free Aerobic Oxidation of Alcohols

Abstract

Based on low-cost, N-containing biomass waste peanut shells and phosphoric acid, the P element was successfully introduced into the carbon skeleton to obtain P-doped porous carbon materials, with inherent N functionality. In comparison to carbon catalysts functionalized with just N or P (NC-800 or PC), the as-prepared P-doped, N-containing porous carbon materials (NPC-T) possessed superior catalytic activity toward the aerobic oxidation of benzyl alcohol (BA). According to these findings, a synergistic effect of N and P species on the catalytic efficiency of carbon materials was observed. The amounts of graphitic N and C3PO species on the surface of NPC-T were shown to be correlated with catalytic activity. In the case of NPC-800, 100% conversion and 99.7% selectivity could be achieved along with a high TOF value (2.49 × 10–3 mol·g–1·h–1). Even when applied to various alcohols, the NPC-800 still showed good catalytic activity. Based upon the mechanistic investigations, both radical and nonradical reaction pathways occurred during the aerobic oxidation of BA over the NPC-800. Furthermore, to facilitate catalyst recycling, the granular P-doped, N-containing carbon (granular NPC-800) was generated, utilizing a kneading heat treatment and extrusion molding technique that did not require the addition of any extra adhesive. This work highlighted the potential high-value utilization of biomass waste in constructing P-doped, N-containing carbon materials and the application as metal-free catalysts in the aerobic selective oxidation reactions.