Rate determining step during surface catalysis

Pairs A and B were assigned to adsorbed SO and sulfide bonded to ruthenium atoms, respectively. The activation of Ru catalysts was dependent on the heating temperature of catalysts. Pair B appeared when the catalysts were still inactive. Hence, ruthenium metal microparticles were first sulfided and then exhibited the catalytic reactivity to form elemental sulfur from SO. The difference of sulfidation temperature for the [Ru CjA iOj (503 K) and conv-Ru/TiO catalysts (573 K) may be originated from each Ru particle size. In general, smaller [RuJ cluster is more reactive than larger Ru particles (10 - 50A) of conventional catalysts [14]. Pair A was exclusively observed in addition to the weak shoulder peaks of Pair B (Fig. lA). Therefore, the surface during the catalysis of the SO + Hj reactions should be predominantly occupied by SO. The elementary step of SO dissociation to SO(ads) may be the rate-determining step of overall reaction. 

Let us be more precise about the reasons for the high activity in such systems. In redox catalysis, especially during the oxidation of hydrocarbons, oxygen species are adsorbed on the surface and the rate-determining step is the transfer of a partial charge (3) to - and from - the catalytic site, usually a metal cation M, as follows M"+ -I- 0.502 M + -I- O.5O2 and so... 

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