Ruthenium-carbon monoxide adsorption

Electrooxidation of carbon monoxide to carbon dioxide at platinum has been extensively studied mainly not least because of the technological importance of its role in methanol oxidation in fuel cells [5] and in poisoning hydrogen fuel cells [6]. Enhancing anodic oxidation of CO is critical, and platinum surfaces modified with ruthenium or tin, which favor oxygen atom adsorption and transfer to bound CO, can achieve this [7, 8]. 

An Electron Energy Loss Spectroscopic Investigation of the Adsorption of Nitric Oxide, Carbon Monoxide, and Hydrogen on the Basal Plane of Ruthenium... 

Leung, L.-W.H. and Weaver, M.J. (1988) Adsorption and electrooxidation of carbon monoxide on rhodium- and ruthenium-coated gold electrodes as probed by surface-enhanced... 

More recently, Dalla Betta and Shelef (51) performed in situ IR measurements with AljOj-supported ruthenium, exposed to 1 bar total pressure mixtures of H2 CO He = 0.075 0.025 0.9 at temperatures from 250°C upward. Up to 250°C adsorbed CO was present at almost complete monolayer coverage. At higher temperatures the coverage decreased. As the phenomenon is irreversible with respect to a lowering of the reaction temperature, the authors conclude that it reflects surface blocking by a reaction residue rather than a temperature dependence of the carbon monoxide adsorption-desorption equilibrium. 

Low temperature carbon monoxide sensors based on the reversible carbon monoxide adsorptive poisoning of precious metal electrodes are also being developed by Los Alamos National Laboratory. The addition of metals such as ruthenium to the platinum electrode material greatly improves the hydrogen oxidation kinetics in the presence of CO. An amperometric sensor that senses the CO inhibition of the hydrogen oxidation can be fabricated from a platinum electrode, a proton conductor and a platinum ruthenium alloy electrode. While the... 

The active area of supported transition metals can be deterrnined by adsorbing carbon monoxide. Carbon monoxide is known to adsorb associatively on ruthenium at 100 C. Use the following uptake data for the adsorption of CO on 10 wt % Ru supported on AI2O3 at 100°C to determine the equilibrium adsorption constant and the number of adsorption sites. 

Lamy et al. [37] have done extensive research on methanol adsorption and oxidation on fuel cell through radioactive labeling study and FTIR measurements. Kinetics of formation of surface and bulk products coming from methanol and surface/bulk exchange processes were found to be significantly different on Pt compared to Pt/Ru [38,39]. Modifications of the electronic surface of platinum atoms by ruthenium were clearly seen in the electrode structure. Adsorption of carbon monoxide from methanol... 

VanderWiel, D.P., Pruski, M., and King, T.S. 1999. A kinetic study on the adsorption and reaction of hydrogen over silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide. J. Catal. 188 186-202. 

Carbon monoxide (CO), even at trace amounts such as a few ppm levels, can poison Pt catalysts because it can strongly adsorb on the Pt surface, leaving a very small percentage of the Pt surface (e.g., less than 5% at 80°C in the presence of 10 ppm CO) for the HOR. Pt alloys with ruthenium (Ru) and tin (Sn) possess higher CO tolerance, and are thus popular (especially PtRu) as the anode catalysts when H2 is not CO-free. The mechanisms are mainly the accelerated oxidation of CO on PtRu and the reduction of CO adsorption strength on PtSn, respectively. Reaction 1.23 shows how Ru accelerates the... 

The adsorption of carbon monoxide on supported ruthenium has been extensively studied by IR spectroscopy (ref. 4). General agreement exists on the presence of three IR bands. The LF band at 1990-2030 cm" is assigned to the vibration of carbon monoxide linearly bonded on ruthenium crystallites. The bands at 2080 and 2140 cm correspond to the vibrations of a multicarbonyl. In a recent investigation (ref. 5) this species was shown to be a tricarbonyl associated with Ru cations bonded directly to the support. 

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