Hydrogen Sulfide Formation Over Automotive Oxidation Catalysts

A number of laboratory and engine dynamometer studies were conducted to determine the effect of various catalyst and engine operating parameters on the formation of H₂S over alumina-supported Pt and Pd catalysts.

These experiments indicate that H₂S formation occurs at high temperatures under O₂ deficient conditions. The fraction of exhaust gas SO₂ converted to H₂S was relatively constant for various fuel sulfur levels, and thus H₂S formation decreases as fuel sulfur content decreases. Calculation of thermodynamic equilibria, as well as various experimental results, indicate that H₂S formation is kinetically limited under the experimental conditions investigated.

Since the operating conditions that favor H₂S formation (high catalyst temperature and O₂ deficiency) do not normally occur in current oxidation catalytic emission control system operation, the formation of H₂S over automotive oxidation catalysts is unlikely unless engine or system malfunctions occur.