Insights into catalytic reforming from a new oscillating reaction

Abstract A new oscillating catalytic reaction is discovered: steam reforming of CH₄ in the presence of SO₂ over Rh nanoparticles. The reducing products from reforming convert SO₂ into adsorbed sulfur, which deactivates the catalyst. Theoretical calculations show how sulfur adsorption causes a subtle shift in the atoms at the stepped edge of the nanoparticle by just one atomic spacing. This subtle change alters the step from a 211 to a 110 configuration, which lowers the reaction rate 25-fold. This quells the reforming reaction and sulfur is removed by steam as SO₂. The edge atoms then shift back and reactivity reemerges, which initiates a new cycle. This illustrates how heterogeneous catalysts can be extremely sensitive to the detailed configuration of the active site, identifies the 211 step as the active site for the practically important steam reforming and shows how theoretical calculations can now predict the structural changes causing oscillations in catalytic reactions.