Atomic-Scale Structure and Catalytic Reactivity of the RuO₂(110) Surface

Abstract

The structure of RuO(2)(110) and the mechanism for catalytic carbon monoxide oxidation on this surface were studied by low-energy electron diffraction, scanning tunneling microscopy, and density-functional calculations. The RuO(2)(110) surface exposes bridging oxygen atoms and ruthenium atoms not capped by oxygen. The latter act as coordinatively unsaturated sites-a hypothesis introduced long ago to account for the catalytic activity of oxide surfaces-onto which carbon monoxide can chemisorb and from where it can react with neighboring lattice-oxygen to carbon dioxide. Under steady-state conditions, the consumed lattice-oxygen is continuously restored by oxygen uptake from the gas phase. The results provide atomic-scale verification of a general mechanism originally proposed by Mars and van Krevelen in 1954 and are likely to be of general relevance for the mechanism of catalytic reactions at oxide surfaces.

Epitaxial Growth of Ruthenium Dioxides on Ru(0001) Surface

“…The free Al atoms turn to react with O ad to Al 2 O 3 on NiAl(100). As time progresses more RuO 2 islands are nucleated and then islands grow, coalesce and finally a smooth film (≈ 20 μm) is formed which then thickens (≈ 1-2 nm) as has been determined by STM measurements [16].…”

“…The LEED electrons with wave vector k o impacts perpendicularly to the sample surface, the elastically diffracted electrons with wave vector k are accelerated by the grid potential of +3.8 keV and crush the fluorescent screen lighting up the reflection spots. On the other hand, the RHEED experiment was performed with an electron beam energy of 40 keV (with a wave vector k o ) at grazing incidence of 2-3 o and the elastically diffracted electrons give Ru(0001) surface was oxidized to RuO 2 by exposure to large amounts of molecular oxygen at elevated sample temperatures (600-800 K) under UHV conditions, growing epitaxially with (110) face on Ru(0001) [16], while single crystals of (100) RuO 2 are grown in a multizone furnace using a vapor transport method under oxygen flow [12]. On the other hand, the ruthenium oxide films were electrodeposited on tin doped indium oxide (TIO) substrate from an aqueous solution, for which the monocrystalline phase was characterized by XRD measurements [17], while the hydrous RuO 2 .…”

Nanometer and Subnanometer Thin Oxide Films at Surfaces of Late Transition Metals

“…This may result in commensurable or incommensurable overlayers, and both types have already been observed experimentally on the late 4d basal surfaces. 31,32,33,34 In addition, strain may be easier relaxed at more open sites like steps, pointing again at the relevance of the latter for the oxidation process. Apart from the strain energy, another influential factor is the thermodynamic driving force to form an oxide.…”

“…At the lower temperatures the growth is largely affected by kinetic limitations though, so that at Pd(111) at best small PdO clusters without apparent crystalline order were hitherto reported 35 , while at Ag(111) there exists literally no atomic-scale knowledge on the oxidation process beyond the formation of an ordered p(4 × 4) surface oxide (see below). This situation is far better for Ru(0001) and Rh(111), where it is at least known that the oxidation process ends with the formation of crystalline rutile-structured RuO 2 (110) 31 and corundum-structured Rh 2 O 3 (0001) films 32 , respectively.…”

“…Recent experimental studies seem to support this view, i.e., they indicate that thin oxidic structures, now mostly coined surface oxides, start to form roughly at coverages Θ c . 30,31,32,33,34 For the "true" bulk oxide a higher oxygen concentra- tion might be required, but for oxide nucleation and for the formation of oxidic islands such increased oxygen content is only needed locally. In this respect it is remarkable that although for the on-surface adsorption at the late 4d TM basal surface the adatom-adatom interaction is repulsive (see the discussion of Fig.…”