Hydrogen-Promoted Chlorination of RuO₂(110)

Abstract

High resolution core level photoemission spectroscopy and temperature programmed reaction experiments together with density functional theory calculations were used to elucidate the chlorination mechanism of ruthenium dioxide RuO 2 (110) by hydrogen chloride exposure on the atomic scale. The surface selective chlorination accounts for the extraordinary stability of the RuO 2 catalyst in the Sumitomo process -the heterogeneously catalyzed oxidation of hydrogen chloride by oxygen. The selective replacement of bridging oxygen atoms by chlorine atoms depends on the formation of water molecules serving as leaving groups. Water is produced by the chlorine assisted recombination of two neighboring surface hydroxyl groups at around 450 K -a temperature where water instantaneously leaves the surface. Finally, the bridging vacancy is filled in by chlorine atoms, thereby forming bridging chlorine atoms. Pre-adsorbed hydrogen has shown to facilitate the chlorination process for stoichiometry reasons. The general strategy of transforming bridging O atoms into a good leaving group has been corroborated by the chlorination of RuO 2 (110) via CO pretreatment and subsequent Cl 2 exposure with CO 2 as leaving group.2

Kinetic Monte Carlo simulations of heterogeneously catalyzed oxidation reactions

“…A few of the Cl ot atoms, which cannot desorb, remain on the surface, but can be incorporated into the bridging vacancies. [64][65][66] With an HCl exposure of 1.5 L, the total ratio of on-top O desorbing at 420 K and those at 700 K is 1 : 1, roughly reconciling the experimentally found ratio in TPR. The number of produced Cl 2 molecules equals the number of oxygen molecules produced from trapped O.…”

“…24 Upon exposure to HCl molecules at temperatures above 500 K, the stoichiometric RuO 2 (110) surface is transformed into a chlorinated surface where the bridging O atoms are partially replaced by chlorine. [64][65][66] The surface reaction of HCl oxidation over surface chlorinated RuO 2 (110) is summarized by the catalytic cycle depicted in Fig. 6.…”

Combined experiment and theory approach in surface chemistry: Stairway to heaven?

“…In the case of RuO 2 (110) it was found that the anionic sublattice at the RuO 2 (110) surface of the catalyst is modified under reaction conditions in that the bridging surface O atoms (O br ) are selectively replaced by chlorine (Cl br ), one of the key factors to stabilize this oxide catalyst against corrosion [67][68][69]. Actually this substitution of surface oxygen sites at the RuO 2 (110) surface by chlorine has been shown not only to improve the stability of the catalyst but also to modify slightly the activity of the catalyst [66].…”

Electrospun ceria-based nanofibers for the facile assessment of catalyst morphological stability under harsh HCl oxidation reaction conditions

“…The main advantage of this catalyst is its high activity in the oxidation of HCl, so the reaction temperature can be reduced to about 300 • C. At 300 • C, in-depth chlorination is suppressed due to selective and self-limiting surface chlorination, and hence RuO 2 -based catalysts are quite stable [12][13][14][15].…”