Synthesis, of supports

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

The goal of precise synthesis of supported mononuclear and polynuclear metal complexes can be traced to the early work of Yermakov [1], Ballard [2], and others. Their work stimulated the hvely field referred to as surface organometalhc chemistry [3-6]. The success and importance of precise synthesis of supported molecular catalysts are illustrated by the apphcation of supported metallocene catalysts for industrial alkene polymerization [7j. 

The mechanical incorporation of active nanoparticles into the silica pore structure is very promising for the general synthesis of supported catalysts, although particles larger than the support s pore diameter cannot be incorporated into the mesopore structure. To overcome this limitation, pre-defined Pt particles were mixed with silica precursors, and the mesoporous silica structures were grown by a hydrothermal method. This process is referred to as nanoparticle encapsulation (NE) (Scheme 2) [16] because the resulting silica encapsulates metal nanoparticles inside the pore structure. 

Guerin S, Hayden BE, Pletcher D, Rendall ME, Suchsland J-P, WiUiams LJ. 2006b. Combinatorial approach to the study of particle size effects in electrocatalysis synthesis of supported gold nanoparticles. J Comb Chem 8 791-798. 

Supported model catalysts are frequently prepared by thermally evaporating metal atoms onto a planar oxide surface in UHV. The morphology and growth of supported metal clusters depend on a number of factors such as substrate morphology, the deposition rate, and the surface temperature. For a controlled synthesis of supported model catalysts, it is necessary to monitor the growth kinetics of supported metal... 

It is also observed in Fig. 5.3 that Pd(II) ions are partly adsorbed on AI2O3 before ultrasonic irradiation the concentration of Pd(II) just before irradiation becomes ca. 0.8 mM, although 1 mM Pd(II) was added in the sample solution. From a preliminary adsorption experiment, the rate of Pd(II) adsorption on A1203 was found to be slow compared with those of Pd(II) reduction in the presence of alcohols. Therefore, it is suggested that the sonochemical reduction of Pd(II) in the presence of alcohols mainly proceeds in the bulk solution. The mechanism of the Pd/Al203 formation is also described in the section of sonochemical synthesis of supported metal nanoparticles. 

Three main methods of synthesis of supported metal complex catalysts can be distinguished from the literature, which we will successively analyze ... 

In an effort to confront these deficiencies, we have developed a procedure for the surface derivatization of small glass (sol-gel) [41] pellets and applied it to the synthesis of supported Ru catalysts [42]. As shown in Scheme 11.8, the Unker and the active metal carbene were installed in a sin e step. Treatment of (71) with allylchlorodi-methylsilane and a full equivalent of (4,5-dihydroIMES)PCy3Cl2Ru=CHPh (29) led to rapid ROCM and metaUation of the styrenyl ether (-> 72). Preweighed monolithic (smallest dimension > 1 mm) sol-gels were then added to the solution, and substi-... 

Synthesis of Supported Bimetallic Catalysts from Molecular Cluster Precursors... 

At present, there is no answer to the dilemma that arises in the case of single crystallites of MoS2 containing very few Mo atoms. However, as the fields of organometallic complex chemistry and further improvements in the synthesis of supported Co-Mo-S or SBMS catalysts come closer and closer together, the answer may emerge. 

Several strategies enable the attachment of guanidines and amidines to insoluble supports (Figure 3.29, Table 3.28). These include attachment as A-benzyl, A-acyl, and A-alkoxycarbonyl derivatives. Furthermore, support-bound isothioureas can be used to convert amines into guanidines. The synthesis of support-bound guandines is considered in Section 14.3. 

Thiol esters RC(0)SR are stronger acylating agents than simple alkyl esters, and have been prepared on solid phase mainly as synthetic intermediates. The preparation of thiol esters as intermediates for the synthesis of support-bound thiols is discussed in Section 8.1. Further examples of the preparation of thiol esters on insoluble supports include the aldol addition of ketene thioacetals to polystyrene-bound aldehydes... 

Molecularly or ionically dispersed metal carbonyl clusters on metal oxides have been prepared in high yields by reaction of metal carbonyl clusters with support surfaces or by syntheses on support surfaces from mononuclear precursors (Gates and Lamb, 1989 Iwasawa, 1993 Ichikawa, 1992 Gates, 1994). Synthesis of supported metal carbonyl clusters has been reviewed recently (Gates, 1995,1998), and only a few examples are included here. 

The selected example by Chen and Janda [175] reported the validation of a method for the synthesis of prostanoid libraries on a soluble polymeric support made by non-crosslinked chloromethylated polystyrene (NCPS). The synthesis of supported PGE2 methyl ester is shown in Figure 7.23. 

FIGURE 7.23 Synthesis of supported PGE2 methyl ester. 

Another example is the synthesis of supported oxide catalysts by spreading of one oxide across the surface of another (support) oxide in physical mixtures. Also, the phenomenon of solid-state ion exchange in zeolites may be discussed within the framework of the wetting and spreading concept. 

Wegener SL, Marks TJ, Stair PC. Design strategies for the molecular level synthesis of supported catalysts. Accounts of Chemical Research. 2012 45(2) 206-214. 

Homogeneous reactions are monitored by simple and effective methods, such as TLC, and characterized using a wide variety of analytical techniques, whereas the synthesis of supported intermediates and/or final products can only be monitored by sophisticated on-bead methods or after cleavage from the support. 

Baltes, M., O. Collar , P. Van Der Voort, and E. F. Vansant, Synthesis of Supported Transition Metal Oxide Catalysts by the Designed Deposition of Acetylacetonate Complexes , Langmuir (1999), 15, 5841-5. 

The use of polynuclear metal complexes provides a novel approach to the synthesis of supported metals and metal oxides. Mark White (Georgia Tech) shows how these materials can be synthesized and characterized. Quantum mechanics are used to compare predicted and experimental results of the interactions of the metal complexes and surfaces. The use of these materials as both adsorbents and catalysts suggests the importance of understanding both how they are synthesized, and their post-synthesis structure. 

Buchmeiser MR. Recent advances in the synthesis of supported metathesis catalysts. New J. Chem. 2004 28 549-557. 

The examples discussed in this review for wetting and spreading of one mobile oxide phase on the surface of a support oxide should have shown that this "dry" procedure has indeed a significant potential for the synthesis of supported oxide catalysts or catalyst precursors. Certainly the possibilities of this approach for practical preparation of catalysts have not yet been exploited fully. However, efforts in this area will... 

Catalysts usually consist of two or more components in which the various constituents are assembled in the desired structure and shape. In this chapter we will consider the synthesis of a set of building blocks for the catalyst. The building blocks coiasidered are support materials (silica, alumina and carbon), zeolites and mesoporous materials. Often the catalyst assembly process involves the addition of an active (second) component onto these building blocks. A case in point is the emplacement of a metal onto the support materials in order to obtain so-called supported catalysts. Note that the synthesis of supported catalysts is discussed separately in Chapter 10. 

To avoid the formation of HCl in the synthesis of supported Lewis acidic ILs, ionic liquids bearing an alkoxylsilyl group on the alkyl chain, which can be covalently bound (grafted) to the surface, were used. In this procedure the aluminium halide was introduced subsequently, giving a highly acidic ionic complex on the surface of the support (Scheme 4.13). 

Fig. 2 Schematic of the preparation method for the synthesis of supported metal clusters on thin film oxide surfaces. (View this art in color at www.dekker.com.)...

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