V. L. Kuznetsov

Properties of catalysts prepared by pyrolysis of Co2(CO)8 on silica containing surface Ti ions

Catalysts prepared by thermal decomposition of Co2(CO)8 on modified silica were studied by magnetic susceptibility and by IR and ESR spectroscopy, and were tested in CO hydrogenation. The modification of SiO2 by Ti ions made it possible to diminish the size of metallic Co particles. The effect was the most pronounced for modification by hydride complexes of a low-valent titanium. An increase of Co dispersion was accompanied by a drop in the metal activity in CO hydrogenation and by a rise of the relative yield of light hydrocarbons and alcohols, especially that of ethanol.

CO hydration over catalysts prepared via supporting Fe3(CO)12 and (NEt4)2[Fe2Mn(CO)12] on oxide supports

A comparison of the properties of iron-containing catalysts prepared through carbonyl clusters Fe3(CO)12 and (NEt4)2[Fe2Mn(CO)12] and iron and manganese nitrates in CO hydration indicates that the addition of Mn incorporated in (NEt4)2[Fe2Mn(CO)12] decreases the methane yield and increases the portion of higher hydrocarbons.AbstractПроведено сопоставление свойств железосодержащих катализаторов, приготовленных с использованием карбонильных кластеров Fe(CO)12 и (NEt4)2[Fe2Mn(CO)12] и нитратов железа и марганца, в реакции гдрирования CO. Введение в катализатор Mn в составе кластера (NEt4)2[Fe2Mn(CO)12] у меньшает выход метана и увеличивает долю высших углеводородов.

Thermal decomposition of metal carbonyls on oxide supports containing surface hydrides: a route to highly dispersed metal catalysts with unusual properties

Abstract A method of preparation of fairly dispersed metal catalysts on oxide supports is described. The Co, Fe, FeCo and Rh carbonyls, when chemisorbed on silica with anchored hydrides of Ti or Al and then subjected to thermal decomposition, produce very small species consisting of several up to several tens of metal atoms. Thermal decomposition of a heteronuclear FeCo cluster leads to formation of bimetallic FeCo particles. The Co, Fe and CoFe samples so obtained possess unusual magnetic properties. On varying temperature and strength of the magnetic field, their magnetization alters in a manner specific for the super paramagnetic particles, but there is no signal of ferromagnetic resonance in ESR spectra. With increasing loading of the supported Fe and Co carbonyls, both chemisorbed and weakly bound carbonyl complexes are on the surface of the support. Larger metallic crystallites are formed in this case at pyrolysis and a FMR signal appears in the spectra. The crystallites are, however, much smaller (near 1 nm) than those obtained on non-modified silica. The metal particles in the samples show high stability to sintering under vacuum but grow in size under conditions of CO hydrogenation (up to about 1.5–2 nm). The growing is accompanied by the appearance of the FMR signal for all the samples containing Co or Fe. Carbide formation presumably takes place on the Fe catalyst during CO hydrogenation. The catalytic properties in the CO + H2 reaction are affected by both the size of metal particles in the catalysts and the chemical nature of the support. In particular, highly dispersed Co and CoFe catalysts demonstrate an increased selectivity towards ethanol production; the ethanol yield being higher than on the Rh catalysts prepared analogously.

Hydrogenation of carbon monoxide catalysts prepared by pyrolysis of Co2(CO)8 on various oxide supports

Catalysts prepared by pyrolysis of Co2(CO)8 on oxide supports have been studied in the hydrogenation of CO. It is shown that MgO and γ-Al2O3-based catalysts are less active than those supported on SiO2, TiO2 and ZrO2. The application of γ-Al2O3 as a support increases the relative yield of light hydrocarbons.AbstractКатализаторы, полученные пиролизом Co2(CO)8 на окисных носителях, исследованы в реакции гидрирования CO. Показано, что катализаторы на основе MgO и γ-Al2O3 имеют меньшую активность по сравнению с катализаторами на основе SiO2, TiO2 и ZrO2. При использовании катализаторов на основе γ-Al2O3 в подуктах увеличено содержание легких углеводородов.

CO hydrogenation on cobalt catalysts. Effect of the conditions of Co2 (CO)8 pyrolysis on the surface of TiO2 on the catalytic and magnetic properties of the catalysts

It was found that fast pyrolysis of Co2 (CO)8 on TiO2 leads to the formation of dispersed superparamagnetic cobalt particles characterized by a narrow ferromagnetic resonance signal. Catalysts thus prepared possess increased activity in the hydrogenation of carbon monoxide.AbstractПоказано, что при быстром пиролизе Co2 (CO)8 на поверхност и TiO2 образуются дисперсные суперпарамагнитные частицы кобальта, характеризуюшиеся узким ситналом ферромагнитного резонанса. Полученные таким способом катализаторы обладают повышенной активностью в гидрировании окиси углерода.

Studies of the state of rhodium in Rh/Al2O3 catalysts prepared via the adsorption of Rh4(CO)12 and Rh6(CO)16 under co oxidation conditions

Studies of the oxidation of Rh4(CO)12 and Rh6(CO)16 clusters on γ-Al2O3 indicate that under CO oxidation conditions Rh(III) and Rh(I) ions are present on the support.AbstractПроведено исследование окисления кластеров Rh4(CO)12 и Rh6(CO)16 на поверхности γ-Al2O3. Показано, что в условиях реакции окисления CO на носителе существуют ионы Rh(III) и Rh(I).

Propylene metathesis catalysts prepared by interaction of Re2(CO)10 with γ-Al2O3

Abstract In this work new data on the state of Re and on the nature of active sites in Re2(CO)10 derived catalysts are discussed. Active catalysts for propylene metathesis can be obtained by several treatments of Re2(CO)10/Al2O3: (1)O2 treatment at 393 K of partially decarbonylated samples of Re2(CO)10/Al2O3. In this case, part of the oxygen reversibly binds to the catalyst, probably in molecular form. The activity of this catalyst increases linearly up to an O:Re ratio close to 0.03. Subsequent addition of oxygen has no effect on activity. (2)O2 treatment at 300 K of Re2(CO)10/Al2O3 samples completely decarbonylated at 773 K. According to the EXAFS and TEM data, completely decarbonylated samples contain associated Re(II) ions, with Re—Re distances different from those in metallic rhenium. O2 treatment leads to rearrangement in the clusters. Part of the oxygen is adsorbed in the molecular form as O2− on Al ions of the support (TPD and ESR data). The adsorption occurs reversibly and without exchange with the oxygen of the Al2O3. The activity of the catalysts correlates with their molecular oxygen content. (3) Partial reduction at 473–573 K of Re2(CO)10/Al2O3 preoxidized at 573 K. The concentration of catalytically active Re atoms is assumed to be less than 2–3% of the rhenium content in the catalysts. Metal-carbene complexes active in metathesis are formed, via the oxidation of propylene, by rhenium ions in a high oxidation state.

Interaction of hydrogen with Rh/La2O3 and Pd/La2O3 catalysts

TPR, XPS and PMR spectroscopic studies of the interaction of H2 with Rh/La2O3 and Pd/La2O3 catalysts have revealed that the reduction of oxidized metals on La2O3 takes place at T<400 K with the formation of hydrides and hydrogen transfer to the support. The latter is evidenced by the hydrogenation of CO32− groups present on La2O3.AbstractС использованием методов температурно-программируемого восстановления РФЭС и ЯМР1H спектроскопии исследовано взаимодействие H2 с катализаторами Rh/La2O3 и Pd/La2O3. Восстановление окисленньх металлов на La2O3 происходит при температуре выше 400 К. Было зарегистрировано образование гидридов и перенос водорода на носитель. Последнее проявилось в гидрировании CO32− групп, присутствующих на La2O3.

Molecular isotope exchange of14CO in surface carbonyl complexes of rhodium

Molecular isotope exchange of CO with14CO for Rh6(CO)16/Sn(II)−SiO2, Rh6(CO)16/Al2O3, Rh(I)(CO)2/Al2O3, Rh4(CO)12/Al2O3 carbonyl complexes of rhodium has been studied. Estimates of the activation energies and a mechanism of the CO exchange are suggested.AbstractДла систем, содержащих поверхностные карбонильные комплексы родия (Rh6(CO)16/Sn(II)−SiO2, Rh6(CO)16/Al2O3, RhI(CO)2/Al2O3, Rh4(CO)12/Al2O3), исследован молекулярный изотопный обмен окиси углерода с14CO. Оценены знергии активации и сделаны предположения о возможных механизмах обмена CO в поверхностных комплексах родия.

RHODIUM-TIN CATALYSTS IN CO HYDROGENATION

A drastic change in the catalytic properties of rhodium in CO hydrogenation has been revealed for catalysts prepared via Rh4(CO)12 and Rh6(CO)16 interactions with silica modified by tin ions.AbstractДля катализаторов, полученных взаимодействием Rh4(CO)12 и Rh6(CO)16 с поверхностью силикагеля, модифицированного ионами олова, обнарузено сильное изменение каталитических свойств родия в реакции гндрирования CO.