Cation exchangers, aluminosilicates

Clays are usually cation-exchangeable aluminosilicates, and exfoliated clay particles have a platelet shape with nanoscopic size. Cast protein-clay films on electrodes have been used to immobilize proteins. The Clay/Mb electrode has good electrocatalytic properties for the reduction of oxygen and hydrogen peroxide [236] and the biosensors can also be made based on these properties. 

Cation-exchanged aluminosilicates can also act as bases, particularly when the extra lattice cation is large. A low Si Al ratio produces a more basic catalyst. A Cs+ exchanged amorphous aluminosilicate can catalyze the liquid phase aldol condensation of benzaldehyde with cyclooctanone (Eqn. lO.lb). Both mono-and di-benzylidene products are formed over this amorphous basic catalyst. As discussed later, with the crystalline aluminosilicates, the zeolites, selectivity for raono-benzylidene product formation is increased. 

This i>aper describes two broad types of intercalation conpomds which are based on graphite on the one hand and sheet aluminosilicate (clay) hosts on the other. Taken together these provide a rich veiriety of examples of heterogeneously catalysed reactions. Appropriately cation exchanged clays, for example, act as efficient catalysts for a number of commercially important proton catalysed reactions (10-13) (see Table I). Graphite intercalates, whilst also capable of... 

CASH CBM CBO CBPC CC CCB CCM CCP CDB CEC CFBC CFC CFR CMM COP CSH CT Calcium aluminosilicate hydrate Coal bed methane Carbon burn-out Chemically-bonded phosphate ceramics Carbonate carbon Coal combustion byproducts Constant capacitance model Coal combustion product Citrate-dithionate-bicarbonate Cation exchange capacity Circulating fluidized bed combustion Chlorofluorocarbon Cumulative fraction Coal mine methane Coefficient of performance Calcium silicate hydrate Collision theory... 

The important groups of dehydration catalysts are oxides, aluminosilicates (both amorphous and zeolitic), metal salts and cation exchange resins. Most work on mechanisms has been done with alumina. 

Hydration and dehydration employ catalysts that have a strong affinity for water. Alumina is the principal catalyst, but also used are aluminosilicates, metal salts, and phosphoric acid or its metal salts on carriers and cation exchange resins. 

A central feature of the mechanism that accounts for the catalytic cracking of hydrocarbons by appropriately cation exchanged zeolites is the formation of carbonium ions (also designated carbocations and alkylcarbenium ions) as intermediates. Many other reactions for which aluminosilicates, be they clay-or zeolite-based, also predicate (320) the existence of carbonium ion intermediates, formed usually by proton donation from Bronsted acid sites, have been discussed earlier (Section III,K). 

The determination of surface properties of particles is an important key to understanding interactions of trace elements and organic compounds between particulate and dissolved phases in estuarine and coastal systems. Specific surface area (SSA), cationic exchange capacity (CEC) and heat of immersion (AH) have been measured on native and treated suspended sediment and after oxidation with 15% H202- SSA and A H have also been measured on samples leached with NaOH and Na-dithionite in order to remove amorphous aluminosilicates. 

The use of surfactant-modified zeolite (SMZ) as a permeable barrier sorbent may offer several unique advantages when dealing with mixed contaminant plumes. Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers,... 

Aluminosilicate clays (kaolinite) with a cation exchange capacity of 2.2meq/100g were blended with calcium oxide and starch prior to spray addition of the epoxide. The reaction proceeded at ambient temperature without mixing. Greater reaction efficiencies are claimed.43... 

Hydrogen ions participate in the cation-exchange processes of the interlayer space. As will be seen later (Section 2.7.1), they have a very large affinity for the layer charge. Hydrogen and hydroxide ions are potential-determining ions of the external surfaces via the protonation and deprotonation processes of aluminol and silanol sites. In acidic media, the degradation of aluminosilicates can be observed. 

Note CEC = cation exchange capacity HISM = hydroxyinterlayered smectite HIV = hydroxyinterlayered vermiculite Kf = Freundlich metal distribution coefficients LSB = lime stabilized biosolids = total aluminosilicates. 

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