Nickel catalyst oxygen adsorption

These results suggest that with a nickel catalyst the hydroxy group is adsorbed on the catalyst through an unshared electron pair on the oxygen atom. On palladium, however, it appears that the adsorption occurs at the carbinol carbon as depicted in Fig. 14.8.2 The fact that the hydrogenolysis of substituted... 

Systematic IR studies of CO adsorption on supported nickel catalysts [3,12] have described the surface sites of the terminal-CO as being electronically perturbed. The perturbation has been attributed [3,12] to oxygen-mediated electron-exchange interactions between NP/Ni couples established on incompletely reduced catalysts. This type of perturbation is referred to below as 0-perturbation. 

Alumina supported nickel, cobalt and iron catalysts containing 10, 30 and 50 wt % of metal were prepared by co-precipitation method at constant pH conditions (pH = 8 for Ni and Co and pH = 7 for Fe) as described earlier [7], Hydrogen and oxygen adsorption measurements were carried out over the catalysts using a conventional high vacuum system according to the procedure described elsewhere [7]. BET surface area was measured... 

Carbon monoxide oxidation is a relatively simple reaction, and generally its structurally insensitive nature makes it an ideal model of heterogeneous catalytic reactions. Each of the important mechanistic steps of this reaction, such as reactant adsorption and desorption, surface reaction, and desorption of products, has been studied extensively using modem surface-science techniques.17 The structure insensitivity of this reaction is illustrated in Figure 10.4. Here, carbon dioxide turnover frequencies over Rh(l 11) and Rh(100) surfaces are compared with supported Rh catalysts.3 As with CO hydrogenation on nickel, it is readily apparent that, not only does the choice of surface plane matters, but also the size of the active species.18-21 Studies of this system also indicated that, under the reaction conditions of Figure 10.4, the rhodium surface was covered with CO. This means that the reaction is limited by the desorption of carbon monoxide and the adsorption of oxygen. 

When oxygen is an impurity, it can be removed by reaction of the oxygen in the presence of a catalyst with hydrogen to form water. The latter then is removed by refrigeration or adsorption. Palladium and metallic nickel have proved to be effective catalysts for the hydrogen-oxygen reaction. 

A third factor controlling surface composition is the atmosphere in which the catalyst is used. The surface will be enriched in that component of the alloy that has the highest heat of adsorption of the gas. In an oxygen atmosphere the surface of a nickel-gold catalyst becomes enriched with nickel rather than gold. 57 In the presence of CO the surface of a palladium-silver alloy becomes enriched with palladium while, normally, silver would be the predominant surface component. 58 This enrichment of the surface by palladium should also be observed in a hydrogen atmosphere. 

Nickel oxide prepared at 250° [NiO(250°)] presents a greater adsorption affinity toward carbon monoxide at 30° than NiO(200°) [at 2 torr, 4.5 cm /gm on NiO(200°), 5.5 cm /gm on NiO(250°)] and the differential heats of adsorption on NiO(250°) (Fig. 12) decrease more progressively than on NiO(200°) (Fig. 11). The initial heat of adsorption is lower on NiO(250°) (29 kcal/mole) than on NiO(200°) (42 kcal/mole). However, on the latter catalyst, surface oxygen ions react with carbon monoxide to give a small quantity (0.3 cm /gm) of adsorbed carbon dioxide, which accounts for the high initial heat of adsorption of carbon monoxide (42 kcal/mole) on NiO(200°). Because of the higher temperature of its... 

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