Compounds with support surfaces, reaction

Reaction of Metal Hydrocarbyl Compounds with Support Surfaces. 

The availability of organic ligands in the surface complexes obtained by the reaction of organometallic compounds with supports allows us to consider two possibilities of the initiation process (1) the monomer insertion into the organic ligand-metal bond (bensyl, allyl, etc.) (9a) ... 

The methodology of the addition of tin into supported platinum or rhodium seems to play an important role in the behaviour of the active phase obtained. Controlled surface reactions of organometallic compounds with metal surfaces result in the formation bimetallic systems with specific properties in the hydrogenation of different unsaturated compounds. ° However, the nature of the Sn-Pt or Sn-Rh bimetallic phase formed, and its influence on the final properties of the catalyst, have not been yet well determined and this is still a subject to be investigated. 

In this class the transition metal is present only on the surface of the support. The catalyst is usually prepared by the reaction of transition metal compound with the surface hydroxyls of the support. The support materials are typically metal oxides such as Si, Al, Zn, Ti, Mg. High activity catalysts for ethylene polymerization based on Ti have been patented by Solvay and Cie (Belgium Patent 650,679 (1963) British Patent 1,024,336 (1963))... 

ABSTRACT. Interactions of organometallic compounds with metal surfaces can be used to produce metal films and coatings as well as to modify the properties of metal catalysts for hydrocarbon conversion. The literature is reviewed, and results are evaluated characterizing the interaction of metal carbonyl clusters with surfaces of supported metals under mild conditions. The reactions lead to the preparation of highly dispersed bimetallic particles, which have homogeneous compositions and nonadditive properties in CO hydrogenation and hydrocarbon conversion. 

The literature and our data give evidence for interesting possibilities of interaction of organometallic compounds with the surfaces of supported metals for obtaining bimetallic catalysts. The use of this novel reaction of metal carbonyl clusters with metal surfaces allows the second metal to be selectively supported on the surface of a metal particle under mild conditions. The bimetallic catalysts obtained have some advantages over conventional catalysts ... 

The following reactions with the surface of silica seem to be possible depending on the conditions of the support pretreatment and type of organometallic compounds ... 

The application of these catalysts in the initial state (without any special treatment of the surface organometallic complexes of such cata-lysts) for ethylene polymerization has been described above. The catalysts formed by the reaction of 7r-allyl compounds with Si02 and AUOj were found to be active in the polymerization of butadiene as well (8, 142). The stereospecificity of the supported catalyst differed from that of the initial ir-allyl compounds. n-Allyl complexes of Mo and W supported on silica were found to be active in olefin disproportionation (142a). 

The data obtained up to the present time show that the method of catalyst preparation by the reaction of organometallic compounds with surface reactive groups may be applied to generate both isolated ions of transition metals (in various valent states) or superfine metal particles on the surface of the support. 

In nonpolar solvents, for example alcohols, the hydroxyls of the support can also be used to anchor alkoxy compounds to the surface in a condensation reaction, in which one alkoxy ligand reacts with the proton of the surface OH to give the corresponding alcohol, and the complex binds to the support. An example is the anchoring of zirconium ethoxide, Zr(OC2H5)4, to silica by means of the reaction... 

The basis of the demonstration can be based on already published data on the surface reaction between NOz and adsorbed organic compounds. Yokoyama and Misono have shown that the rates of N02 reduction over zeolite or silica are proportional to the concentration of adsorbed propene [29], whereas Il ichev et al. have demonstrated that N02 reacts with pre-adsorbed ethylene and propylene on H-ZSM-5 and Cu-ZSL-5 to form nitro-compounds [30], Chen et al [2-4] have observed the same nitrogen-containing deposits on MFI-supported iron catalysts. The question on the pairing of nitrogen atoms is not considered here. 

Y. A. Ryndin, and Y. I. Yermakov, Reactions of organometallic compounds with surfaces of supported and unsupported metals. In Surface Organometallic Chemistry Molecular Approaches to Catalysis edited by J. -M. Basset, B. C. Gates, J.-P. Candy, A. ChopUn, M. Lecomte, F. Quignard, and C. Santini (Kluwer, Dordrecht 1998) pp. 127-141. 

To realize surface-bonded initiating sites or their precursors, a variety of methods are applicable. Either organic (polymer) surfaces are irradiated or plasma treated to yield suitable functional groups [187, 195] or inorganic supports are covered with an interlayer of functional polymers bearing the desired groups. However, to gain control over the quantity of surface reaction sites and define the surface chemistry, interlayers of low molar mass a,co-functionalized surface active compounds are suit-... 

Table II indicates the stoichiometry of the reaction of metal hydro-carbyls with the surface of silicas and aluminas dried at various temperatures. The results indicate that at lower drying temperatures approximately 2 moles of hydrocarbon are liberated per mole of hydrocarbyl compound. Subsequent reaction with the proton source, n-butyl alcohol, generates 1 or 2 moles of hydrocarbon, depending on whether a tris- or tetrahydrocarbyl compound is used. The formation of 2 moles of hydrocarbon can arise as a fortuitous combination of metal species singly, doubly, and triply bonded to the support surface.

Although organochromium catalysts are not well characterized, organochromium compounds are thought to bind to the support by reaction with surface hydroxyls as other types do. When Cr(allyl)3 or Cr(allyl)2 is used, propylene is released (59,60). Chromocene loses one ring (52-55), and / -stabilized alkyls of chromium lose the alkane (81). 

Diarenechromium(O) compounds may be somewhat different because hydrogen is released, suggesting an oxidation—probably to Cr(I). Whether a ring is also lost is unknown. Double attachment to the support by reaction with a pair of hydroxyls is also possible, yielding a variety of surface species (58-60). 

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