Yu. A. Ryndin

Hydrogenolysis of ethane on supported (Mo + Pt)SiO2 catalysts

Abstract The hydrogenolysis of ethane on (Mo + Pt) SiO 2 catalysts exhibits the following features as compared to hydrogenolysis on a Pt SiO 2 catalyst: (1) a much higher activity in the temperature range 200–300 °C; (2) constant activity in a series of successive runs; and (3) a lower activation energy and a decrease of inhibiting effect of hydrogen. The change in the electronic properties of platinum due to its interaction with molybdenum on the support surface is considered a major reason for these specific features of (Mo + Pt) SiO 2 catalysts.

EXAFS and XPS studies of the influence of metal particle size, nature of support and H2 and CO adsorption on the structure and electronic properties of palladium

Abstract For the gas-phase hydrogenation of vinylacetylene the highly dispersed supported palladium particles show a low turnover number, regardless of the nature of the support (silica, γ-alumina, carbon). The peculiarities of their structural and electronic properties were studied by EXAFS and XPS. Regardless of the nature of the support (SiO 2 , C), and the size of the Pd metal particles (19–108 A), the Pd-Pd interatomic distances are close to those for the bulk metal. The quantitative correlation between turnover number and the binding energy, E b , of the Pd core level was found.

Supported metallic catalysts obtained by anchoring metal complexes on carbon supports

Abstract Catalysts containing particles of metallic palladium have been synthesized by anchoring metal complex precursors on carbon supports (active carbon, carbon black, ultra-dispersed graphite and diamond). Anchored precursors were obtained by interaction of solutions of tetrachloride or allylcyclopentadienyl palladium complexes with the supports. Based on data on the peculiarities of HgPdCl 4 adsorption on carbon sorbents of different natures, three types of adsorption sites of Pd II ions have been identified and a quantitative evaluation of their strengths made. The size of the Pd crystallite formed upon reduction of the anchored complexes and its catalytic activity in cyclohexene hydrogenation depend upon the strength of the adsorption site. An increase in the strength of the adsorption site leads to a decrease both in the size and catalytic activity of Pd crystallites. The effect observed is associated with a modifying (ligand) action of atoms involved in the adsorption site. Fourier transform IR spectroscopic data indicate that the interaction of C 3 H 5 PdC 5 H 5 with an oxidized diamond surface occurs with participation of the carboxyl groups of the support. According to transmission electron microscopic data, Pd/C catalysts reduced with hydrogen at 300 °C contain Pd particles 10 – 20 A in size. On increasing the reduction temperature to 600 °C, the dispersion of Pd/diamond remains almost unchanged while the size of the metallic particles on Pd/graphite increases to 100 A. This difference is due to peculiarities in the interaction of Pd particles with graphite and diamond surfaces in a hydrogen atmosphere. In the structurally insensitive hydrogenation of benzene, the turnover number (TON) activity of the Pd/C catalyst is commensurable with that of Pd/SiO 2 , but in the structurally sensitive hydrogenolysis of ethane and hydrogenation of CO to methanol, the TON of Pd/C is one to two orders of magnitude lower, probably due to dissolution of carbon atoms in the Pd particles. Introduction of Zr ions into Pd/C leads to the appearance of a new absorption band at 1600 cm −1 in the IR spectrum of adsorbed CO, an increase in TON activity by 1 – 2 orders of magnitude in methanol synthesis and a drastic decrease in activity in ethane hydrogenolysis, the inhibiting effect of Zr ions being completely suppressed by high-temperature oxidation of the samples. These specific features are similar to those observed earlier for (Pd+Zr)/SiO 2 and Pd/ZrO 2 , and seem to be due to the formation of mixed Pd-Zr active sites in the systems under consideration.

Surface hydride complexes of group IV transition metals as active sites for polymerization and hydrogenation reactions

Abstract Catalysts prepared via interaction of Ti, Zr and Hf organometallic compounds with silica followed by hydrogen treatment have been shown to contain surface metal hydrides. The TON activity of these catalysts in cyclohexene and benzene hydrogenation is comparable with that of Group VIII supported metals. The activity correlates quantitatively with the content of hydrides in the catalysts. The composition and coordination state of the surface hydride complexes, as well as their interaction with ethylene, carbon monoxide and benzene, have been studied by IR, 1 H MAS-NMR, EXAFS, ESR and thermodesorption methods.

Hydride complexes of titanium and zirconium attached to SiO2 as hydrogenation catalysts

Abstract Catalysts obtained by interacting Ti(CH 2 C 6 H 5 ) 4 or Zr(π-C 3 H 5 ) 4 with the surface of SiO 2 and treated with hydrogen possess a very high activity with respect to hydrogenation of benzene and cyclohexene. This activity is commensurable with that of supported Group VIII metals. The catalysts were studied by chemisorption, thermodesorption and EXAFS methods, and were shown to contain anchored hydride complexes of Ti and Zr, whose content can be controlled by varying the temperature of their treatment with hydrogen. A quantitative correlation exists between the specific activity of the catalysts under consideration in hydrogenation reactions and the content of hydride complexes in these catalysts.

Methanol synthesis on palladium nanoparticles: Size effect

The turnover number (TON) of Pd/SiO2 in methanol synthesis increases by one order of magnitude with the growth of Pd particle size from 10 to 30 Å. Further particle size increase to 60 Å does not alter the TON. The fraction of bridged adsorbed CO decreases with the growth of Pd dispersion. Low TON of Pd nanoparticles is caused by the decrease of CO chemisorption strength on small electron-deficient Pd particles.

Catalytic properties of PdCu/Al2O3 system obtained via anchored metal complexes

The TON of PdCu/Al2O3 is two orders of magnitude lower in ethane hydrogenolysis and several times lower in vinylacetylene and CO hydrogenation as compared to that of a Pd/Al2O3 catalyst. Nonadditivity of the catalytic properties indicates the formation of bimetallic particles, whose thermal stability is lower than that of the monometallic one.

ESCA study of (Mo+Pt)/SiO2, (W+Pt)/SiO2 and (Re+Pt)/SiO2 catalysts

Supported catalysts obtained from organometallic compounds have been studied by ESCA. The data obtained indicate a decrease in electron density on the Pt atoms as a result of interaction with Mo, W and Re ions bound to silica.AbstractМетодом рентгеноэлектронной спектроскопии исследованы нанесенные катализаторы, полученные с применением металлоорганических соединений. Получены данные, указывающие на взаимодействие атомов платины с ионами Mo, W, Re, приводящее к понижению электронной плотности на атомах платины.

Electron microscopic studies of platinum catalysts prepared via decomposition of Al2O3-anchored metal complexes

Reduced alumoplatinum and alumoplatinum-tin catalysts prepared via interaction of an organometallic platinum complex and platinum-tin compounds of various composition with Al2O3 mainly contain platinum particles of ≤10 Å.AbstractВосстановленные алюмоплатиновые и алюмоплатино оловянные катализаторы, полученные взаимодействиум платиооловянных соединеннй различного состава с поверхностью Al2O3, содержат, преимущественно, частицы платины размером ≤10 Å.

Influence of rare earth ions on the properties of Pd/SiO2 in CO hydrogenation

Systematic studies of the effect of the lanthanoid (Ln) nature on the activity and selectivity of (Pd+Ln)/SiO2 catalysts obtained by decomposition of anchored Ln and Pd complexes in methanol synthesis from CO and H2 have been carried out. It has been established that the highest promoting effect is observed for Pr and Ho ions.AbstractВыполнено систематическое изучение влияния природы лантаноида (Ln) на активность и селективность (Pd+Ln)/SiO2 катализаторов, полученных разложением закрепленных комплексов Ln и Pd, в реакции синтеза метанола из CO и H2. Наибольшим промотирующим действием обладут ионы Pr и Ho.