Preoxidation-assisted nitrogen enrichment strategy to decorate porous carbon spheres for catalytic adsorption/oxidation of methyl mercaptan

Abstract

Porous carbon spheres with high surface area and microporous structure were synthesized from alkyl phenols and formaldehyde via suspension polymerization and steam activation. The effects of air oxidation and ammonia solution heat treatment on the pore structure and surface chemistry of the carbon spheres were studied for catalytic oxidation of CH₃SH. The structure property and surface chemistry of the obtained carbon spheres were characterized by N₂ adsorption–desorption, FTIR, scanning electron microscopy, XRD, elemental analysis, X-ray photoelectron spectroscopy and Boehm titration, and then thermal analysis and gas chromatography-mass spectrometry were applied to investigate the catalytic oxidation product. Results show that the as-prepared microporous carbon spheres through direct ammonia treatment have a high surface area value of 1710 m² g⁻¹ and a total pore volume of 0.83 cm³ g⁻¹. Moreover, the preoxidation-assisted nitrogen enrichment strategy not only increases the surface area and total pore volume of the carbon spheres, but also introduces more active nitrogen species such as pyridinic nitrogen and quaternary nitrogen, leading to the highest nitrogen content of 7.13 wt% and the highest CH₃SH capacity of 622.8 mg g⁻¹ due to the pyridinic nitrogen and quaternary nitrogen as function of catalysts. In addition, water and oxygen have a beneficial effect on CH₃SH oxidation over the nitrogen modified carbon spheres, and the basic oxidation product is CH₃SSCH₃ that can be further oxidized into CH₃SO₂SCH₃ according to DTG and GC/MS analysis. The great recycling stability after ten cycles with a reserved CH₃SH capacity of 97% demonstrates that the porous carbon spheres obtained by preoxidation-assisted enriched nitrogen strategy are promising for catalytic oxidation of CH₃SH.