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

The decomposition of hydrogen sulfide to hydrogen and sulfur on alkali metal sulfides M2S (M = Li, Na and K) and polysulfides M2Sx (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 Na2S and K2S are rapidly sulfided by H2S to give the corresponding disulfides M2S2, whereas Li2S acts as a catalyst for the thermal decomposition of H2S. Although Na2S2 was further sulfided by H2S, sodium polysulfides were not effective in enhancing hydrogen yields and all polysulfides produced an amorphous product of approximate composition Na2S2.4–2.6. With potassium polysulfides the final product was K2S3 in all cases and the sulfidation of K2S2 by hydrogen sulfide resulted in an enhancement of hydrogen yields at 500–700°C.