Understanding the Catalytic Activity of N-doped Mesoporous Carbon on the Atomic Level by 15N Solid-State NMR for Electro- chemical Denitrification and Oxidative Dehydrogenation of Ethylbenzene

Spherical mesoporous carbon (with a particle size in the range of 40–75 μm) was synthesized by nanoreplication of a hard silica template using sucrose as the carbon precursor. The mesoporous carbon with BET surface areas higher than 1200 m2/g was doped with N by a treatment in an aqueous solution of nitric acid and/or in a flow of gaseous ammonia. The highest N content (3.2 wt% of N in bulk) was obtained when both modification methods were combined. Complementary physicochemical characterization techniques, including scanning electron microscopy (SEM), low-temperature N2 adsorption, powder X-ray diffraction (XRD) and Raman spectroscopy revealed the morphology, structure and textural properties of the synthesized N-loaded carbon materials. For the identification of the detailed chemical structure on the surface of the carbons, 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements were performed and the data were supported by chemical shift calculations with accurate quantum chemistry methods, and X-ray photoelectron spectroscopic (XPS) analyzes. All NMR experiments were performed at natural isotope abundance. The verified experimental data clearly showed that after the introduction of the N-containing moieties by the combined methods of treatment, a high concentration of pyridinic N at the edge and pyrrolic N being external to the edge was achieved for the mesoporous carbon. The distributed N surface species promoted the catalytic activity in the oxidative dehydrogenation of ethylbenzene to styrene, but did not significantly influence the efficiency of the carbon materials in the electrochemical reduction of nitrate ions