Platinum metals nitrogen adsorption

Bunsen worked out a method for the separation of platinum metals (preparation of pure rhodium). He determined the composition, NIg,NH3, of nitrogen iodide, developed a volumetric method of iodimetry, using a solution of sulphurous acid, and worked on water analysis. Bunsen and L. Schischkoff investigated the chemical reactions in the explosion of gunpowder. Bunsen discovered arsenic pentasulphide, and measured the adsorption of carbon dioxide on glass. ... 

Direct ammonia oxidation is well understood for platinum and some other noble metals [17]. The actual reactant is free ammonia (NH3) therefore more ammonia is oxidized at higher pH values. At low overpotentials, nearly all anrnuuiia is oxidized to N2 as the potential increases, some nitrate and nitrite are produced, and at even higher potentials, the electrodes are poisoned by nitrogen adsorption. Of all tested noble metal electrodes, those with platinum and iridium deposits exhibit a particularly high performance (see, e.g., [18]). Direct anunonia oxidation has also been reported for electrodes without noble metals. Two examples are BDD [12] or... 

Several types of nitrogen substituents occur in known dye stmetures. The most useful are the acid-substituted alkyl N-substituents such as sulfopropyl, which provide desirable solubiUty and adsorption characteristics for practical cyanine and merocyanine sensitizers. Patents in this area are numerous. Other types of substituents include N-aryl groups, heterocycHc substituents, and complexes of dye bases with metal ions (iridium, platinum, zinc, copper, nickel). Heteroatom substituents directly bonded to nitrogen (N—O, N—NR2, N—OR) provide photochemically reactive dyes. 

Whereas determination of chemisorption isotherms, e.g., of hydrogen on metals, is a means for calculating the size of the metallic surface area, our results clearly demonstrate that IR studies on the adsorption of nitrogen and carbon monoxide can give valuable information about the structure of the metal surface. The adsorption of nitrogen enables us to determine the number of B5 sites per unit of metal surface area, not only on nickel, but also on palladium, platinum, and iridium. Once the number of B5 sites is known, it is possible to look for other phenomena that require the presence of these sites. One has already been found, viz, the dissociative chemisorption of carbon dioxide on nickel. 

In Figs. 5a and 5b are shown typical examples of adsorption isotherms for hydrogen on reduced metallic catalysts. It should be possible to evaluate accurately measured adsorption isotherms with statistical mechanics in order to reach an understanding of adsorption and of the nature of adsorbent surfaces. Only a few attempts, however, have been made along this line. Wilkins (42) studied the van der Waals adsorption of helium, nitrogen, and other gases on platinum foil and attributed... 

In addition to the enantioselective effect, cinchona alkaloids also produce a rate acceleration, i.e. this is an example of ligand accelerated catalysis [14]. The model of a non-closepacked ordered array of cinchonidine molecules adsorbed on platinum, proposed by Wells and co-workers, was abandoned in their later study [15]. Augustine [16] deduced from the behaviour of this system at low modifier concentrations that the chiral sites are formed at the edge and comer platinum atoms, which involve the adsorbed cinchonidine and a metal adatom. The different authors agreed that the quinoline ring of the modifier is responsible for the adsorption on platinum, the quinuclidine part, through the nitrogen atom, interacts with... 

The study of the oxidation of ammonia to nitrogen and water at low temperature has become more and more important in recent years due to agricultural and industrial waste streams. Noble metals (Pt, Ir) are suitable for the selective, low temperature oxidation of ammonia to nitrogen and water. Alumina supported platinum catalysts are promising in the conversion of gaseous ammonia to N2 and H2O. They possess a high activity and selectivity in N2 formation.I l However, these catalysts are susceptible to rapid deactivation due to irreversible adsorption of reaction intermediates such as NHx species. 

The platinum group metals demonstrate clearly the impact of the key parameters that influence the efficiency of ammonia synthesis catalysts structure sensitivity, the heat of adsorption of reactants and products, and the roles of promoters and supports. The key requirement to minimize the activation energy for nitrogen dissociation limits the active metals to alkali-promoted ruthenium and osmium. Similar activities are then obtained, irrespective of the genesis of the alkali metal promoter (salt or metal), indicating that both convert to a similar... 

H2 on noble metal catalysts, platinum, and rhodium. Since one of the antibonding orbitals of NO bond is occupied by an electron, the N-O bond is weaker than the bond of CO. The rate of dissociative NO adsorption is generally faster than that of CO. Rhodium is more reactive than platinum. Therefore the rate of dissociative adsorption of NO is higher on Rh than on Pt, as is the steady-state coverage of adsorbed nitrogen atoms. 

---