B. N. Kuznetsov

Supported metallic catalysts prepared by decomposition of surface ornagometallic complexes

Abstract New approaches to the preparation of supported metallic catalysts by decomposition of surface organometallic complexes have made it possible to prepare: (a) highly dispersed particles of Group VIII metals which may be used in the study of the dependence of catalytic properties on the size of metallic particles; (b) surface species which contain a Group VIII metal and a modifying element. With these particles it is possible to study the change in the catalytic properties of active species with variation in their composition. The results of the study of Ni, Pd, and Pt supported catalysts and of catalysts containing Group VIII metals and modifying elements (Sn, Mo, W, Re) are presented.

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.

Composition and catalytic activity of supported sulphided metal catalysts prepared via anchored complexes I. Tungsten catalysts prepared via anchoring of W(C4H7)4 ON SiO2

Anchored organometallic complexes of tungsten were prepared by supporting tetramethallyltungsten on SiO2. The composition of the surface compounds obtained by treatment of the anchored complexes with H2S was studied. The activities of sulphided catalysts containing different surface species of tungsten in the hydrogenolysis of thiophen were measured. An increase in turn-over number (per surface atom of tungsten) was observed for catalysts containing small sulphide aggregates. The electron-deficient state of W and S in these aggregates by comparison with WS2 was shown by the x.p.s. technique.

Nature of active centers of molybdenum catalysts for propylene disproportionation, obtained in the reaction of tetrakis(π-allyl)molybdenum with silica

The activities of surface compounds of Mo(VI), Mo(IV) and Mo(II) obtained via interaction of Mo(π-C3H5)4 with silica have been compared using the disproportionation of propylene. The surface compounds of tetravalent molybdenum were shown to be the active centers for disproportionation.AbstractСопоставлялась активность поверхностных соединении MoVI, MoIV и MoII, полученных взаимодействием Mo(π-C3H5)4 с снликагелем, в реакции диспропорционирования пропилена. Показано, что поверхностные соединения четырехвалентного молибдена являются активными центрами в реакции диспропорционирования.

Properties of silica-supported Pt−Mo and Pd−Mo catalysts obtained from organometallic compounds

An assumption has been made on the possibility of stabilizing highly dispersed metal particles in the presence of low-valent transition metal ions bound to the carrier. This assumption is supported by studies of the dispersion and catalytic activity of Pt−Mo and Pd−Mo catalysts obtained from π-allyl complexes of Mo, Pt, Pd.AbstractСделано предположение о возможности стабилизации выс окодисперс ных частиц металлов в присутствии низковалентных ионов переходных элементов, связанных с носителем. Изучение дисперености и каталитическ ои активности Pt−Mo и Pd−Mo катализаторов, полученных с использованием π-аллильных комплексов Mo, Pt и Pd, подтверждает это предполозение.

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.

Some properties of nickel catalysts obtained in the reaction of bis (π-allyl) nickel with silica

The preparation of high dispersity nickel catalysts by reacting bis (π-allyl) nickel with silica gel is described. The reduced catalysts contain nickel which is fully accessible for oxygen adsorption at 20°C and has a high activity towards benzene hydrogenation.AbstractОписан новый способ получения высокодисперсных никелевых катализаторов путем взаимодействия бис-π-аллилникеля с поверхностъю силикагеля. Восстановленные катализаторы содержат никель, который полностью доступен для адсорбции кислорода при 20 °C и обладают высокой активностью в реакции гидрирования бензола.

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.

The state of metal ions in supported catalysts with respect to their catalytic activity in metathesis

Abstract The relation between the composition and catalytic activity of surface metal complexes prepared by anchoring of allyl and ethoxy compounds Mo, W and Re to silica was studied. It was concluded that the precursors of metathesis active centers in these catalysts are coordinatively unsaturated metal ions with oxidation number + 4. The activity of surface species in olefin metathesis also depends to a great extent on the ligand environment of the metal ion.

Specific activity of supported nickel in the hydrogenolysis of ethane

It has been found that over a wide range of dispersities (15–70 Å) the specific activity of supported nickel is independent of the metal particle size and the method of catalyst preparation. However, samples with nickel particle size ≤10 Å are characterized by higher specific activity, which may be related to the structural features of small nickel clusters.AbstractНайдено, что в широком интервале дисперсности (от 15 до 70 Å) удельная активность нанесенного никеля не зависит от размера частиц металла и способа приготовления катализатора. Однако образцы, имеющие размер частиц никеля≤10 Å, обладают повышенной удельной активностью, что может быть связано со структурными особенностями мелких кластеров никеля.