Experimental and ab initio investigations of H2S-assisted propane oxidative dehydrogenation reactions

The oxidative dehydrogenation (ODH) reaction of propane was investigated at temperatures between 923 and 1023 K using either O2 or O2/H2S mixture as oxidant. GC analysis of the product mixtures showed that ethylene was the major olefin product in the conventional ODH reaction whereas propylene became dominant when H2S was included in the feed gas. With an oxygen-rich feed (4:2:2 C3H8:O2:H2S), ∼ 70% propane conversion, and ∼ 50% propylene selectivity could be achieved at 1023 K, a level of performance comparable to that for the ODH reaction employing reducible solid oxide catalysts. Theoretical calculations utilizing CBS-QB3 method were also conducted to explore the causes of the enhanced propylene yield and selectivity of the H2S-assisted ODH reaction. It was found that the increased propane conversion was due to a large enthalpy gain from the in situ formation of S2 that compensated for the high energy cost of hydrogen abstraction by SH and S2H. Also, the promoted propylene selectivity was attributed to the instability of the sulfur-containing products, which made the reaction route to propylene the most thermodynamically favored.