Surface of the support

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

Membranes made by interfacial polymerization have a dense, highly cross-linked interfacial polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less cross-linked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. Because the dense cross-linked polymer layer can only form at the interface, it is extremely thin, on the order of 0.1 p.m or less, and the permeation flux is high. Because the polymer is highly cross-linked, its selectivity is also high. The first reverse osmosis membranes made this way were 5—10 times less salt-permeable than the best membranes with comparable water fluxes made by other techniques. 

Metal island films form spontaneously during slow evaporation of the metal on to supports with low adhesion. The metal islands can produce the surface-enhancement required for Raman characterization of the surface of the support. 

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. 

The formation of surface compounds of low-valent ions of transition metals on the surface of the support. In particular, fixing organometallic compounds on the support surface, it may be possible to stabilize coordi-natively insufficient complexes of transition metals and to obtain highly active catalysts. In the ideal case a complete use of the transition metal in the formation of the propagation centers can be achieved. 

For reasons which will become apparent in Chapters 4,8 and 11 of this book it is very likely that the increasing commercial importance of Zr02 and Ce02 supports for conventional supported metal catalyst is due to the ability of these supports to continuously provide backspillover anionic oxygen on the surface of the supported metal catalyst. 

This study, in conjunction with that discussed in 12.2.1.2, show that when using aqueous electrolytes or Nafion saturated with H20, the induction of NEMCA on finely dispersed noble metal catalysts is rather straightforward. The role of the electronically conducting porous C support is only to conduct electrons and to support the finely dispersed catalyst. The promoting species can reach the active catalyst via the electrolyte or via the aqueous film without having to migrate on the surface of the support, as is the case when using ceramic solid electrolytes. 

This involves deposition of the catalyst on the accessible surface of the support. The complex is held on the surface by rather weak interactions, such as van der Waals forces, hydrogen bonding, or a donating bond. The stability of the complex on the surface is determined by its solubility in the reaction solvent and/or the complexation of reagents and products. 

Filling the pores of the support with a solution of the catalytically active element, after which the solvent is removed by drying, is a straightforward way to load a support with active material. However, in this process various interactions are possible between the dissolved catalyst precursor and the surface of the support, which can be used to obtain a good dispersion of the active component over the support. To appreciate the importance of such interactions we need to take a closer look at the surface chemistry of hydroxylated oxides in solution. 

In figure 3 and show that the relative thermal motion of the surface atoms is significantly greater than in the bulk metal over the range from 100 - 800 K, This result is expected considering the partial coordination, hence lack of constraint of the surface atoms. A similar result has been found from LEED measurements on a Pt surface. ( ) Significantly, the surface atom disorder when extrapolated to 0 K remains sizable. This static disorder or strain appears to be a result of the interaction of the Ft atoms with the support, a kind of epitaxy to the oxygen (or hydroxyl) surface of the support. 

Platinum catalysts were prepared by ion-exchange of activated charcoal. A powdered support was used for batch experiments (CECA SOS) and a granular form (Norit Rox 0.8) was employed in the continuous reactor. Oxidised sites on the surface of the support were created by treatment with aqueous sodium hypochlorite (3%) and ion-exchange of the associated protons with Pt(NH3)42+ ions was performed as described previously [13,14]. The palladium catalyst mentioned in section 3.1 was prepared by impregnation, as described in [8]. Bimetallic PtBi/C catalysts were prepared by two methods (1) bismuth was deposited onto a platinum catalyst, previously prepared by the exchange method outlined above, using the surface redox reaction ... 

The first step of the grafting process is probably the physisorption of Bu4Sn on the surface of the support (higher surface area), which then migrates from the support to the metal surface. Then, when the physisorbed complex interacts with the surface Pt atoms covered by hydrogen atoms (Pts-H ), there is... 

Without sonication, Pt particles adsorb primarily on the external surface of SBA-15 and at the mesopore openings. Sonication promotes homogeneous inclusion and deposition of Pt nanoparticles on the inner surface of the support mesopores, because ca. 90% of the total surface area is from the inner pore walls. Heat treatment... 

Figure 1. Design of suitable complexes easily approaching to surfaces of the support.

Information on the chemical state of iridium on going from the molecular precursors, and its adsorption on the surface of the support can be obtained by Ir Mossbauer spectroscopy. It allows to estimate the composition of the Ir-containing alloys that are possibly formed during the activation treatment of supported bimetallic systems. The main results obtained in the application of Ir Mossbauer spectroscopy to characterize two Ir-containing bimetallic supported nanoparticles, i.e., Pt-Ir on amorphous silica and Fe-Ir on magnesia are presented and discussed... 

The micrographs of the samples Pd/C type 1 and Pd/C type 2 are shown in Figure 2 and Figure 3, respectively. The structure of the catalysts is rather uniform. The surface of the support is covered evenly by the palladium. The... 

Several works have been reported for macroscopically orientated biological membranes.106-109 The biomembrane alignment can be carried out mechanically or magnetically. The first one relies on the deposition of lipid bilayers on the surface of a rigid support (glass plates) such that the bilayer normal is perpendicular to the surface of the support itself. Small peptides and the lipid bilayers can be dissolved in organic solvents which are successively removed under vacuum.105 The re-hydration of the system in a chamber of an optimized temperature, humidity and time gives rise to the desired orientation. 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

In order to be able to isolate both PS1 and PS2 from the thermophilic cyanobacterium Thermosynechococcus elongatus by a one-step procedure and in order to immobilize both photosystems on the surface of the support materials (i.e. the electrodes) in an oriented... 

The results of Mossbauer spectroscopy investigations of Fe(C0)5 decomposition on Ti02 samples pretreated in three different fashions are given in Table I. These three samples were pretreated in a manner intended to produce different populations of Ti + ions and hydroxyl groups on the surface of the support. This is explained in the discussion section. 

Sulphuric acid catalysts are not truly heterogeneous catalysts but so-called supported liquid phase (SLP) catalysts, where the oxidation of S02 takes place as a homogeneous reaction in a liquid film covering the internal surface of the support material [2], This was proposed already in 1940 by Frazer and Kirkpatrick [6], who found that the promoting action of the common alkali metals was due to their ability to form relatively low-melting pyrosulphates, which dissolve vanadium oxides, e.g. for potassium... 

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