Pillared modification

Zyomyx introduced a microfabricated microarray system based upon the use of pillars that serve as platforms for depositing capture antibodies. Relying on substrate features such as ultraflatness and surface modification, the... 

Fast deactivation rates due to coking and the limited hydrothermal stability of pillared clays have probably retarded the commercial development of these new type of catalysts and prevented (to date) their acceptance by chemical producers and refiners. However, there is a large economic incentive justifying efforts to convert inexpensive (i.e. 40-100/ton) smectites into commercially viable (pillared clay) catalysts (56). Therefore, it is believed that work on the chemical modification of natural (and synthetic) clays, and work on the preparation and characterization of new pillared clays with improved hydrothermal stability are, and will remain, areas of interest to the academic community, as well as to researchers in industrial laboratories (56). 

A small increase of the (d 001) basal spacing is observed for the Li containing Zr pillared clays. However, the thermal stability of these solids drastically decrease. At high temperature, the collapse of the strucutre is also supported by the decrease of the surface area which is, at 700°C, almost identical to those measured for the montmorillonite. Different hypothesis may be proposed to explain the increase of the interlayer distance at low temperature (i) a better polymerization of the intercalated complex (ii) a modification of the distribution of the pillars (iii) a lower interaction between the pillar and the silica layer. The first hypothesis may easily be eliminated since the small variation of the height of the pillars (less than 1 A) cannot be explained by structural changes of the... 

In the present work, three approaches supercritical drying, templating with surfactants of quaternary ammonium salts and a two-step modification are applied to the sol pillared clay to tailor the pore structure. Mechanisms involved in these processes are discussed in detail. 

Loading of Ca2+ ions into the pillared clay and modification with TEOS... 

On the macroscopic scale, pillared layer structures are frequently found in ancient buildings, such as the Parthenon in Athens. Even on the microscopic scale, the pillared layer motif is very useful for the construction of various porous frameworks, because simple modification of a pillar module can be used to control porous structures and properties. The Cu11 coordination polymers, [Cu2(pzdc)2(L)] (L = pillar ligand), known as coordination pillared layers (CPLs), have pillared layer structures and are a suitable system for the design of porous functionalities.78 107 108 Two-dimensional... 

The inherent limitations of the use of zeolites as catalysts, i.e. their small pore sizes and long diffusion paths, have been addressed extensively. Corma reviewed the area of mesopore-containing microporous oxides,[67] with emphasis on extra-large pore zeolites and pillared-layered clay-type structures. Here we present a brief overview of different approaches to overcoming the limitations regarding the accessibility of catalytic sites in microporous oxide catalysts. In the first part, structures with hierarchical pore architectures, i.e. containing both microporous and mesoporous domains, are discussed. This is followed by a section on the modification of mesoporous host materials with nanometre-sized catalytically active metal oxide particles. 

Smectite clay catalysts are potential alternative adsorbents, although some modifications of the natural mineral are necessary. Interlayer sites in smectite dehydrate at temperatures above 200°C, collapsing to an illitic structure. Since the ion-exchange capacity of smectite centres on the interlayer site, collapse must be prevented if clay catalysts are to be used in thermal treatments of chemical organic toxins. The intercalation of thermally stable cations, which act as molecular props or pillars, is one... 

The modification of the AI13 species by substitution of secondary metal ions into the complex (311. rather than by addition polymerization (251. or post ion exchange (241. as originally proposed, adds a new and wide ranging versatility to the pillar itself. These materials may be expected to show not just a different catalytic reactivity, but changes in the way the pillars... 

The present study makes an attempt to increase mesoporosity within the pillared structure of montmorillonite and to study the catalytic property of the resulting material. Enhancement of mesoporous areas has been observed in a smectite seunple pillared by aluminium polyoxy cations by chemical modification in presence of varied amounts of a nonionic surfactant. The effeet of the enhaneement in mesoporous areas on the pillar density and the deaetivation of the pillared materials in a typical alkylation reaction has been studied. 

Chemical modification with different amounts of tween-80, a nonionic surfactant, was foimd to enhance the mesoporous area in pillared montmorillonite samples. Deactivation of the modified clays in the vapour phase catalysis of alkylation of toluene by methanol showed that the pillar density and the rate of deactivation could be controlled by the amount of surfactant used during the preparation of pillared samples. Presence of surfactant within the gallery affects the distribution of pillars perhaps during washing and dehydration. This offers a method to suppress deactivation in pillared samples to catalyze organic reactions. 

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