Catalytic oxidation of hydrogen sulfide by dioxygen on CoN₄ type catalyst

A new catalyst based on the formation of carbon supported "CoN ₄" structures by heat treatment of Co(CH₃COO) ₂ and imidazole impregnated carbon black is introduced. The performance of the new catalyst is compared to the performance of other catalysts including activated carbon powder, granular activated carbon, and pyrolysed cobalt(II) mesotetra-4-methoxyphenylporphyrin. The optimized form of the new catalyst outperforms all these catalysts. The underlying concept is borrowed from fuel cell technology, which uses electrocatalysts that activate triplet dioxygen and facilitate its reduction. The same concept is used to reduce oxygen by hydrogen sulfide. In electrochemistry oxygen reduction is carried out by heterogeneous electron transfer, whereas in dehydrosulfurization the reduced sulfur moieties serve as the electron donors. We postulate that the reason for the improved performance of the new catalyst compared to pyrolysed carbon supported cobalt porphyrin, which is also a Me-N₄ type catalyst, stems from the ability to load a larger amount of cobalt chelates rather than from a change of oxidation mechanism.