A process was designed for catalytic cleanup of natural gas and refinery hydrocarbon-gas emissions for the removal of hydrogen sulfide, which is based on low-temperature oxygenation in the presence of transition-metal porphyrin complexes obtained from a mixture of porphyrins isolated from petroleum. A mechanism for the catalytic oxygenation of hydrogen sulfide over metal porphyrins to afford elemental sulfur was proposed, suggesting the formation of an oxo complex with a metal in the higher oxidation state as an intermediate.