Ruthenium chemisorptive properties

The interaction of CO with alloy or bimetallic surfaces is of special interest because of the importance of bimetallic catalysts in both the electrochemical and gas-phase oxidation of CO. Platinum-ruthenium alloys have long been known to be superior catalysts for the electrochemical CO oxidation, but the details of their catalytic action are still disputed. We will have more to say about the mechanism of the electrocatalytic CO oxidation on both metals and alloys in section III.8, in particular about the relevant ab initio quantum-chemical studies. Here, we will simply discuss how the chemisorption properties of CO on PtRu depend on the stmcture and composition of the bimetallic surface. 

The dispersion of ruthenium in Y zeolite ion-exchanged with Ru(NH3) + as a function of treatment conditions was re-investigated by McCarthy et al. [212] who re-confirmed the earUer results of Lunsford et al. [119,120] and Verdonck etal. [121]. Increasing the H+/Ru ratio from 3 to lOforRu/HY resulted in a 75 % decrease in hydrogen chemisorptive properties. This was attributed to the larger electron deficiency of the clusters interacting with acidic sites. 

Ruthenium-copper and osmium-copper clusters (21) are of particular interest because the components are immiscible in the bulk (32). Studies of the chemisorption and catalytic properties of the clusters suggested a structure in which the copper was present on the surface of the ruthenium or osmium (23,24). The clusters were dispersed on a silica carrier (21). They were prepared by wetting the silica with an aqueous solution of ruthenium and copper, or osmium and copper, salts. After a drying step, the metal salts on the silica were reduced to form the bimetallic clusters. The reduction was accomplished by heating the material in a stream of hydrogen. 

The results of the EXAFS studies on osmium-copper clusters lead to conclusions similar to those derived for ruthenium-copper clusters. That is, an osmium-copper cluster Is viewed as a central core of osmium atoms with the copper present at the surface. The results of the EXAFS investigations have provided excellent support for the conclusions deduced earlier (21,23,24) from studies of the chemisorption and catalytic properties of the clusters. Although copper is immiscible with both ruthenium and osmium in the bulk, it exhibits significant interaction with either metal at an interface. 

It was discovered that the ability of metals to form solid solutions (alloys) in the bulk is not necessary for a bimetallic system to be of interest as a catalyst. An example is the ruthenium-copper system, in which the two components are virtually completely immiscible in the bulk. This system exhibits an effect of the copper (in particular, selective inhibition of hydrocarbon hydrogenoly-sis) similar to that exhibited by the nickel-copper system, in which the components are completely miscible. Although ruthenium and copper do not form solid solutions in the bulk, they do exhibit a strong interaction at copper-ruthenium interfaces. The copper tends to cover the surface of the ruthenium, analogous to a chemisorbed layer. As a result, the copper has a marked effect on the chemisorption and catalytic properties of the ruthenium. 

Thus although ruthenium and copper are immiscible in the bulk, ruthenium-copper aggregates can be prepared that have surface properties very different from those of pure ruthenium. The ruthenium-copper aggregates exhibit chemisorption and catalytic properties which would not be expected for simple physical mixtures of ruthenium and copper granules. The presence of the copper clearly has a marked effect on surface processes occurring on ruthenium. On the basis of the chemisorption and catalytic results, we conclude that the copper tends to cover the ruthenium surface. We thus adopt the view that copper is chemisorbed on the ruthenium. 

Park, S., Y.T. Tong, A. Wieckowski, and M.J. Weaver, Infrared spectral comparison of electrochemical carbon monoxide adlayers formed by direct chemisorption and methanol dissociation on carbon-supported platinum nanoparticles. Langmuir, 2002.18(8) pp. 3233-3240 Park, S., Y. Tong, A. Wieckowski, and M.J. Weaver, Infrared reflection-absorption properties of platinum nanoparticle films on metal electrode substrates control of anomalous opticalejfects. Electrochemistry Communications, 2001. 3(9) pp. 509-513 Park, S., P.K. Babu, A. Wieckowski, and M.J. Weaver, Electrochemical infrared characterization of CO domains on ruthenium decorated platinum nanoparticles. Abstracts of Papers of the American Chemical Society, 2003. 225 pp. U619-U619... 

Based on the research results of monometallic catalysts, scientists also studied on bimetallic catalysts for N2 activation. They realized that the adsorption energy of N2 determines the catalysts properties. Under specific reaction conditions, it can estimate adsorption energy of N2 on catalyst. The catalytic efficiency of the elements for the synthesis and decomposition of ammonia was correlated with the chemisorption energy of nitrogen. An inverted parabolic function (volcano curve) was obtained by Ozaki et in which iron, ruthenium, and osmium mark the top of the volcano. 

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