Paper SS-TuP7
Interaction of Ethylene with Partially Chlorinated RuO₂(110) Surfaces

Tuesday, November 8, 2016, 6:30 pm, Room Hall D

Partial replacement of surface oxygen atoms with chlorine atoms may provide a means for modifying the activity and selectivity of oxide surfaces toward hydrocarbon oxidation. In this study, we investigated the adsorption and oxidation of ethylene on partially chlorinated RuO₂(110) surfaces using temperature programed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS). Chlorination of the RuO₂(110) surface occurs when exposing the stoichiometric surface to gaseous HCl at 700 K, where the bridging oxygen atoms are selectively replaced by chlorine atoms. The degree of chlorination is controlled by the amount of HCl gas introduced, and characterized by XPS. Compared with stoichiometric RuO₂(110), we find that bridging Cl atoms weaken the binding and suppress the oxidation of ethylene, without shifting the selectivity toward partially oxidized products. We also find that on-top oxygen atoms significantly enhance the activity of both s-RuO₂(110) and chlorinated RuO₂(110) surfaces toward the complete oxidation of ethylene. The enhanced reactivity arises from an increase in the ethylene coverage achieved on the O-rich surfaces as well as more facile C‒H bond cleavage of ethylene via H-transfer to on-top vs. bridging oxygen atoms. Our results provide evidence that ethylene molecules achieve high coverages on the O-rich surfaces by preferentially binding to stranded Ru sites located between on-top oxygen atoms, and that such configurations are responsible for the high activity of the O-rich RuO₂ and RuO_xCl_y surfaces. These findings demonstrate that the relative reactivity of on-top vs. bridging oxygen atoms plays a decisive role in determining the chemical activity of partially-chlorinated RuO₂ surfaces, and that high reactivity can be achieved on O-rich RuO_xCl_y surfaces.