Physico-Chemical nanomaterials science

Sulfurization and hydrosulfidation of nanoporous carbon for the preparation of sorbents and solid acid catalysts
Chernenko S. I.1, Diyuk V. E.1, Vakaliuk A. V.1, Grishchenko L. M.1, 
Tsapyuk G. G.1, Mischanchuk A. V.2, Mariychuk R.3, Lisnyak V. V.1,3
1 Faculty of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska Street, 64/13, Kyiv 01601, Ukraine.
E-mail: sofiiachernenko@ukr.net; lisnyak@chem.univ.kiev.ua
2 Chuiko Institute of Surface Chemistry of NAS of Ukraine, General Naumov Street, 17, Kyiv 03164, Ukraine.
3 Presov Universirty in Presov, Ul. 17 novembra, 1, Presov 15 080 01, Slovakia.

Carbon nanoporous materials have several advantages over other types of porous materials. These advantages include the increased hydrolytic and thermal stability and diverse types of surface groups, those tuning surface acidity. In fact, the practical applications of carbon sorbents and heterogeneous catalysts depend on the surface chemistry inside small mesopores and micropores. To create effective sorbents, carriers, and acid-base catalysts based on carbon nanoporous materials, one requires the targeted introduction into their surface layer of heteroatoms, e.g., nitrogen, sulfur, phosphorus, etc. The presence of the surface groups with heteroatoms can determine the surface characteristics, e.g., by increasing acidity/basicity and the sorption capacity for heavy metal ions. For example, nanoporous carbons (NCs) with grafted sulfo groups are highly active acid-base catalysts. In this communication, we proposed new staged methods of introducing sulfo groups. These methods include sulfurization and hydrosulfidation at 500–800 °C. By these methods, one can effectively introduce up to 4.5 mmol g–1 of sulfur, which is the maximal amount of sulfur that can be introduced at about 500–600 °C. Thermogravimetric analysis showed that the chemisorbed sulfur is thermally stable below 550–600 °С. To prepare solid acid catalysts, S-containing samples were oxidized with aqueous solutions containing HNO3 and KClO3 and H2O and HAc. Oxidation with strong KClO3 oxidant is a reason for high surface oxidation, resulting in the formation of sulfo groups and different oxygen-containing groups. A result of oxidation with weak oxidant as H2O2 is the formation of a few sulfo groups. The obtained samples have high catalytic activity and reasonable thermal stability of acidic groups in the isopropanol dehydration, which allows the use of the proposed method to get advanced solid acid catalysts.