S-doped and N+S-co-doped carbon catalysts in redox reactions

In this contribution, the effects of heteroatom doping of porous carbon materials with S and N on their ability to catalyze redox-reactions involving the activation of molecular oxygen were investigated. For this purpose, a library of in total 54 undoped, S-doped and N+S-co-doped porous carbons was obtained via a template-based synthesis procedure using mesoporous silica gel as the template. To understand the influence of S on the properties of the doped carbons three different S-containing precursors, namely dimethyl sulfoxide (DMSO), p -toluene sulfonic acid and thiophene, were used. In order to investigate possible synergistic effects of S- and N-co-doping, urea was employed as the sole N-containing precursor. The obtained carbon catalysts were characterized by selected methods such as N 2 -physisorption at 77 K, X-ray diffraction (XRD), Raman spectroscopy, elemental analysis and X-ray photoelectron spectroscopy (XPS). Each carbon catalyst was tested in the oxidation of sulfurous acid (OSA) to sulfuric acid, the electrochemical oxygen reduction (ORR) and the oxidative dehydrogenation (ODH) of ethylbenzene. Owing to the similar textural and structural properties achieved through template-based synthesis of the carbon catalyst library, the results of the catalytic redox-reactions could directly be related to the respective heteroatom dopant. The observed trends indicate that in these redox-reactions S-species behave somewhat similar to O-species bound on the carbon surface. Furthermore, it can be shown that N+S co-doping rather combines the positive and negative effects of the individual dopants on the activity, than creating a synergistic effect that surpasses the individual contribution. • A great number of N-, S- and N+S-co-codoped porous carbons was synthesized. • S content follows precursor volatility, while N+S-co-doping increases N uptake. • Samples share comparable textural properties and mainly amorphous carbon framework. • N+S co-doping increases oxidized S and O species by facilitating oxygen activation. • N improves OSA and ORR, while S enhances ODH; effects depend on the reaction type.