The thermal decomposition of hydrogen sulfide over alkali metal sulfides and polysulfides

Abstract

The decomposition of hydrogen sulfide to hydrogen and sulfur on alkali metal sulfides M 2S (M = Li, Na and K) and polysulfides M 2S x ( x = 2–4; M = Na and K) has been studied in a flow system at 400–800°C. Hydrogen yields were measured as a function of temperature in order to compare the effectiveness of the alkali metal (poly)sulfides in promoting the decomposition. It was found that both Na 2S and K 2S are rapidly sulfided by H 2S to give the corresponding disulfides M 2S 2, whereas Li 2S acts as a catalyst for the thermal decomposition of H 2S. Although Na 2S 2 was further sulfided by H 2S, sodium polysulfides were not effective in enhancing hydrogen yields and all polysulfides produced an amorphous product of approximate composition Na 2S 2.4–2.6. With potassium polysulfides the final product was K 2S 3 in all cases and the sulfidation of K 2S 2 by hydrogen sulfide resulted in an enhancement of hydrogen yields at 500–700°C.