Reaction with support surfaces

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 ... 

Figure 7.8 General scheme of the SPREAD procedure of self-replication, (a) A template is immobilized by an irreversible reaction with the surface of a solid support, (b) The template binds complementary fragments from solution, (c) The fragments are linked together by chemical ligation, (d) The copy is released, and re-immobilized at another part of the solid support to become a template for the next cycle of steps. Irreversible immobilization of template molecules is thus a means to overcome product inhibition. (Adapted from Luther et al, 1998.)...

Reaction of Metal Hydrocarbyl Compounds with Support Surfaces. 

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 above procedures for catalyst preparation have generally provided excellent results. Especially important are surface-sensitive reactions. With supported catalysts in which the active components have a narrow particle-size distnbution, the optimum particle size for a demanding reaction can be established. Major improvements of supported catalysts, e.g. with respect to carbon deposition and ammonia decomposition, can be achieved by preparing catalysts with a narrow par-ticle-size distribution. Also, the preparation of catalysts in which the active components have a uniform chemical composition is highly important One instance is the preparation of supported vanadium oxide phosphorus oxide (VPO) catalysts for the selective oxidation of w-butane to maleic anhydride, which has been carried out using vanadium(III) deposition onto silica [31]... 

Deposition by Selective Reaction with the Surface of the Support. The carrier is left in contact with an excess of solution for a definite time, and then the excess liquid is removed, e.g. using a dipping technique. The objective is to make a strong bond with the surface. The process is little used but it has potential for grafting or anchoring active elements to a support. 

The deposition of platinum, rhodium and ruthenium acetylacetonates on titania takes place by reaction with the surface hydroxy groups to give a supported complex. Thermal decomposition of these supported complexes in vacuum gave highly dispersed titania supported metal catalysts having metal particles about 2 nm in diameter. ... 

Furthermore, a closer look to experimental data and a tentative balance between CO consumption, CO2 formation and O2 uptake showed the irreversible loss of oxygen on Pt/A Os as well as the significant retention of carbon on ceria-alumina supports. In fact surface carbonated species were clearly identified by FT-IR spectroscopy (1200-1600 cm" ) upon CO adsorption [34-36]. An even more detailed study of Pt/A Oa and Pt/Ce02 systems [37] evidenced that the OSC of alumina systems mainly originates from the WGS reaction with alumina surface OH groups. Furthermore, in the case of ceria-supported catalysts, three contributions to the OSC could be distinguished the OSC related to the metal particle (M/MO), the OSC of ceria and the OSC originating from the metal-ceria contact. 

The aim of this paper is to provide a correlation between the catalytic pattern of differently loaded silica supported M0O3 and V2O5 catalysts in MPO and POD reactions with their surface and redox features in order to highlight the nature of the active surface species in the selective oxidation of light alkanes. 

Different ways to immobilize ILs are described, particularly for chloroaluminate-based ILs (see Section 5.2.1.3). Two preparation procedures can be envisioned. The simplest one is just an impregnation of the chloroaluminate IL to fiU the pores of the dehydrated inorganic solid. The chloroaluminate anion is grafted on the surface by reaction with the surface hydroxyl group. This method may present some disadvantages, such as destruction of the structure of the support and the modification of the acidity of the Lewis acid. 

Derivatization of the silica surface is of importance particularly in the preparation of materials for chromatographic supports and for the support of biologically active molecules such as proteins and enzymes. The active groups are usually attached to the silica surface by reaction with the surface hydroxyl groups via an... 

Spieker and Regalbuto [16] mention as one of the three adsorption mechanisms the complexation of the hexachloroplatinate ions with the dissolved oxide. The reaction will proceed where the acid solution contacts the alumina and, thus, immobilizes the platinum. The other two adsorption mechanisms involve chemical interactions between the metal complexes of the precursor and the surface of the solid support, and pure electrostatic interaction of charged complexes of the precursor with oppositely charged sites on the surface of the support. Results obtained by Roth and Reichard [17] demonstrate the immobilization by local neutralization of the hexachloroplatinum acid by reaction with the support. When an aqueous ammoniacal solution of platinum diamino dinitrite solution is impregnated, reaction with the surface of the support does not proceed, and a more uniform platinum profile results. 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

Oxychlorination of Ethylene to Dichloroethane. Ethylene (qv) is converted to dichloroethane in very high yield in fixed-bed, multitubular reactors and fluid-bed reactors by reaction with oxygen and hydrogen chloride over potassium-promoted copper(II) chloride supported on high surface area, porous alumina (84) ... 

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