Physico-Chemical nanomaterials science

Universal approach to prepare effective solid acid catalysts from the surface-brominated nanoporous activated carbons
Grishchenko L. M.1, Chernenko S. I.1, Zaderko A. N.1, Boldyrieva O. Yu.1, Yatsymyrskyi A. V.1, Mischanchuk A. V.2, Tsapyuk G. G.1, Diyuk V. E.1
1 Faculty of Chemistry, Taras Shevchenko National University of Kyiv . Volodymyrska Street, 64/13, Kyiv-01601, Ukraine.
E-mail: sofiiachernenko@ukr.net; liudmyla.grishchenko@gmail.com
2 Chuiko Institute of Surface Chemistry of NAS of Ukraine, General Naumov Street 17, Kyiv -03164.

Nanoporous activated carbons (NAC) are promising materials for adsorption and catalysis because of advanced porous structure and high chemical stability. Preparation of solid acid catalysts and the search for factors that have influenced on adsorption and acid catalysis are of special interest for advanced synthesis and catalysis processes. In contrast to such sophisticated synthesis methods as, for example, plasma bromination or low-temperature gas discharges, wet bromination rout under mild conditions was proposed in this work, and the effect of further functionalization on the properties of NAC was investigated. The bromine concentration in them can reach 0.5 mmol/g. By treatment of the brominated NACs with sulfur-containing reagents and using subsequent oxidation of sulfur-containing surface species, one can obtain effective catalysts for the gas-phase dehydration of isopropyl alcohol. The concentration of sulfo groups in the obtained for samples has reached 0.3 mol/g. This amount of sulfo groups is much higher than that in the catalysts prepared without the bromination stage. Preliminary halogenation, hydrolysis, and oxidation have much effect on the structure, surface concentration of grafted S-containing groups and the catalytic properties. The catalytic activity depends on many factors; the crucial is the thermal stability and concentration of the sulfo groups as acidic centers. The use of bromine-containing precursors, compared to the pristine NAC, allows obtaining catalysts that have a higher activity in the dehydration reaction, the temperature at the maximal dehydration of isopropyl alcohol is reduced by the value of up to 40 °C. Furthermore, 100% conversion of isopropanol to propylene with 100% propylene selectivity was achieved in the presence of obtained catalysts.