Hydrogenation of Chemisorbed

Methanol synthesis over the heterogeneous catalyst is thought to occur by a successive hydrogenation of chemisorbed carbon monoxide. 

Hydrogenation of Chemisorbed Higher Olefins. When chemisorbed butenes, pentenes, and hexenes are treated with hydrogen at 35° C., spectra are obtained which show that in all cases the hydrogenated species... 

These adsorbed alkyl radicals can be dehydrogenated by pumping at 35° C. The species obtained during chemisorption of acetylene and by hydrogenation of chemisorbed acetylene can not be easily dehydrogenated by pumping. The intensity of the bands obtained after hydrogenating... 

Sclteme I shows a broadly-accepted mechanism based on successive hydrogenation of chemisorbed CO. Methanol is formed when no dissociation of CO occurs [10]. This seems to be a major difference to Fischer-Tropsch type reductions. 

In this paper, pyridine adsorption was utilized to investigate the hydrogen spillover phenomenon from metal to acidic centers of zeolite by observing hydrogenation of chemisorbed pyridine on B or L acid sites of USY zeolite using hybrid catalyst composed of USY zeolite and Pt/SiOo. To give insight into spill-over process in the hybrid catalyst system, isomerization of n-pentane, which is one of the typical add catalyzed reaction, was also studied. 

USY. Apparently, chemisorbed pyridine species on Brpnsted and Lewis acid sites of USY+ Pt/SiOi hybrid catalyst was hydrogenated. However, no change in IR spectra of pyridine were observed for USY alone as shown in Fig. 2b. This indicates that Pt/SiCh catalyst is essential for hydrogenation of adsorbed pyridine on USY+ Pt/SiCF hybrid catalyst. Since pyridine selectively chemisorbed on the acidic surface of USY in the hybrid catalyst (Fig.1), and Ht can be dissociated on Pt surface, it can be concluded that hydrogenation of chemisorbed pyridine on acidic surface of USY in the hybrid catalyst was carried out via spillover hydrogen from Pt/Si02. 

D. Godbey, F. Zaera, R. Yeates, and G.A. Somoijai. Hydrogenation of Chemisorbed Ethylene on Clean, Hydrogen, and Ethylidyne Covered Platinum (111) Crystal Surfaces. Surf. Sci. 167 150 (1986). 

A reaction mechanism is suggested which involves dissociative chemisorption of hydrogen and water in competition on one type of active sites and chemisorption of carbon dioxide on the other type. Chemisorption of carbon dioxide is so strong that it prevents chemisorption of carbon monoxide. Chemisorbed carbon dioxide and hydrogen are in equilibrium on the surface. Reverse shift takes place by dissociation of the reaction product into carbon monoxide and a chemisorbed hydroxyl-species. The shift reaction is taking place by reaction between carbon monoxide from the gas phase and hydroxyl-species on the surface. Methanol is formed by step-wise hydrogenation of chemisorbed carbon dioxide. 

Godbey, D., Zaera, R, Yeates, R., and Somorjai, G.A. Hydrogenation of chemisorbed ethylene on clean, hydrogen and ethylidyne covered platinum (111) crystal surfaces. Sci. 1986,167, 150-166. 

The synthesis of ammonia by hydrogenation of chemisorbed N is faster than by the reaction of H2 and N2 over the same catalyst [420, 421]. This... 

Hydrogen gas chemisorbs on the surface of many metals in an important step for many catalytic reactions. A method for estimating the heat of hydrogen chemisorption on transition metals has been developed (67). These values and metal—hydrogen bond energies for 21 transition metals are available (67). 

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

In addition to actual synthesis tests, fresh and used catalysts were investigated extensively in order to determine the effect of steam on catalyst activity and catalyst stability. This was done by measurement of surface areas. Whereas the Brunauer-Emmett-Teller (BET) area (4) is a measure of the total surface area, the volume of chemisorbed hydrogen is a measure only of the exposed metallic nickel area and therefore should be a truer measure of the catalytically active area. The H2 chemisorption measurement data are summarized in Table III. For fresh reduced catalyst, activity was equivalent to 11.2 ml/g. When this reduced catalyst was treated with a mixture of hydrogen and steam, it lost 27% of its activity. This activity loss is definitely caused by steam since a... 

Mixed-valence Ru"-Ru" paddlewheel carboxylate complexes also have potential for oxidation reactions after incorporation in a microporous lattice with porphyrinic ligands. This MOF can be used for oxidation of alcohols and for hydrogenation of ethylene. Both the porosity of the lattice and the abihty of the diruthenium centers to chemisorb dioxygen are essential for the performance of the catalyst [62, 64]. 

Breiter MW. 1975. Influence of chemisorbed carbon monoxide on the oxidation of molecular hydrogen at smooth platinum in sulfuric acid solution. J Electroanal Chem 65 623-634. 

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