Surface organometallic chemistry SOMC

In contrast to supported homogeneous catalysis, surface organometallic chemistry (SOMC) uses an inorganic oxide (ExOy) as a solid ligand, on which the metal is directly attached by at least a bond with a surface atom, usually an oxygen, through a M-OE bond. 

Various catalytic reactions are known to be structure sensitive as proposed by Boudart and studied by many authors. Examples are the selective hydrogenation of polyunsaturated hydrocarbons, hydrogenolysis of paraffins, and ammonia or Fischer-Tropsch synthesis. Controlled surface reactions such as oxidation-reduction reactions ° or surface organometallic chemistry (SOMC) " are two suitable methods for the synthesis of mono- or bimetallic particles. However, for these techniques. 

Surface organometallic chemistry (SOMC) has shown high potential for the preparation of supported metal catalysts with desired composition and good dispersion [3]. For example, the controlled hydrogenolysis of tetra-n-butyltin (Sn(/i-C4H9)4) on the surface of group VIII metals leads to well-defined bimetallic catalysts [3-6]. In SOMC on metal supported on oxide, judicious selection of reaction conditions (temperature, initial complex concentration etc.) allows the reaction to occur preferentially between organometallic complexes and metal surface [3,5,6]. 

Methods of Controlled Surface Reactions (CSRs) and Surface Organometallic Chemistry (SOMC) were developed with the aim to obtain surface species with Sn-Pt interaction. In CSRs two approaches have been used (i) electrochemical, and (ii) organometallic. Characteristic feature of the organometallic approach is that both CSR and SOMC results in almost exclusively supported alloy type bimetallic nanoclusters. Studies on the reactivity of tin organic compounds towards hydrogen adsorbed on different transition and noble metals have revealed new aspects for the preparation of supported bimetallic catalysts. 

Lepertit and Che [220] discussed the definitions of interfacial co-ordination chemistry (ICC) and surface organometallic chemistry (SOMC) and compared their main characteristics and applications. The concepts of ICC applied to catalyst preparation, adsorption, and relations with catalysis are also useful in the development of interfacial mechanisms. 

Surface Organometallic Chemistry on Metals (SOMC/M) Approach... 

This chapter has presented some interesting aspects of surface organometallic chemistry on metals (SOMC/M) techniques for the preparation of catalysts. Because of the unique properties of the so-obtained systems, this methodology has received a great deal of attention in the recent years. 

Anwander, R. SOMC PMS (2001) Surface organometallic chemistry at periodic mesoporous silica. Chem. Mater., 13, 4419. 

All these facts clearly indicate the importance of preparing well defined PtSn catalysts. Among the routes proposed to produce such bimetallic catalysts, the Surface Organometallic Chemistry on Metals (SOMC/1 techniques is the one most often employed [7]. SOMC/M techniques consist of the reaction between alkyltin compounds and a supported transition metal, providing adequate methodologies that avoid the waste of metal promoter by direct interaction with the supported material. 

These observations, as well as many others, led to the development of two fields of organometaUic chemistry that we call Surface Organometallic Chemistry on Metals SOMC/metals and Surface OrganometaUic Chemistry on Oxides ... 

In this chapter, we try to describe SOMC strategy in the recent years to achieve alkane and cycloalkane metathesis with increasing TONs and selectivities. We will explore the surface organometallic chemistry of Group IV, V and VI metals on various supports and the properties of these single-site systems in the area of alkane and cycloalkane metathesis. 

From an applied perspective, metals are probably the most important surfaces in SOMC. Whereas in SOMC on oxides we introduce the active site, in SOMC on metals the metals themselves are the active catalysts. Organometallic chemistry provides the means to modify the often unselective metal surface by introduction of organometallic complexes (most often chemically inert) to the surface and eventually by transforming the initially obtained species by thermal or chemical means. For example, the hydrogenolysis of cyclic hydrocarbons, in particular cyclohexane, on the surface of unmodified Ir particles supported on a silica carrier has been studied and clearly indicated to bimetallic mechanism of C-C bond cleavage (Scheme 4) [24, 25]. 

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