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O: Oberflächenphysik

O 9: Adsorption an Oberfl
ächen (I)

O 9.7: Talk

Monday, March 11, 2002, 16:45–17:00, H36

Adsorption and reaction of CO and H₂O on RuO₂(110) — •Arun Lobo and Horst Conrad — Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin

Recently it has been demonstrated that RuO₂ can be grown epitaxially on Ru(0001) in (110) orientation, terminated with bridging oxygen atoms (O_bridge) and coordinatively unsaturated Ru atoms (Ru_cus) [1].

We have studied the adsorption and reaction of H₂O and CO on this surface using HREELS and TDS. The HREEL spectrum of a RuO₂(110) layer consists of a prominent peak at 560 cm⁻¹, which corresponds to the vibration of the bridge bonded oxygen (O_bridge) at the topmost Ru atoms [2]. Adsorption of water at 300K results in a red shift of the oxygen peak to 538 cm⁻¹ and the appearance of a new peak at 508 cm⁻¹, which we assign to the Ru-OH₂ vibration. In addition, the spectrum shows the (O-H) stretching mode and the bending mode at 3602 cm⁻¹ and 873 cm⁻¹, respectively. The characteristic H₂O scissor mode appears at 1580 cm⁻¹. The spectrum also shows a low frequency tail at the OH stretch peak, which indicates the formation of hydrogen bonded water clusters. The TDS data shows two desorption maxima at 375K and 410K, which can be attributed to water desorption from clusters and monomers adsorbed at Ru_cus sites, respectively. On the RuO₂(110) surface covered with O_bridge and O_cus atoms H₂O adsorbs mainly as monomers. When the RuO₂(110) surface is first exposed to CO, H₂O dissociates predominantly to OH, which desorbs upon heating at about 600 K. 1. H. Over et. al Science, 286 (2001) 1. 2. Y.D. Kim et.al, J. Phys. Chem. B, 105 (2001) 3752.