Particles from Neutral Complexes

Volatile transition metal complexes have been widely used for the production of zeolite-encaged metal particles or organometallic compounds (222,223). The resulting catalysts are active for a wide range of reactions (224) and in some cases are superior to other preparations. For those metals 

The decomposition of Co2(CO)8 in faujasites has been studied in some detail. Low-temperature spin-echo ferromagnetic nuclear resonance spectroscopy shows that very small Co particles are formed in supercages of zeolite NaX by microwave plasma activation at low temperatures (86). In situ far-infrared spectroscopy revealed that adsorbed Co2(CO)s interacts with accessible supercage cations in NaY and CoY (239). Carbonyl complexes of different Co nuclearity, such as Co4(CO)i2 and Co(CO)4, are also formed (227,228). In HY the Co atoms are oxidized to Co ions by the zeolite protons. 

Nickel tetracarbonyl and nickel complexes with mixed carbonyl and alkylphosphine ligands in zeolite Y have been studied with EXAFS, NMR, and FTIR spectroscopies (85,240-242). The loading of Ni(CO 4 in dehydrated zeolite X can be as high as 28 wt%, corresponding to 2.75 Ni(CO 4 molecules per supercages. The IR spectrum of Ni(CO 4 was found to be affected by the cations inside the zeolite supercages. The spectrum of 

Ni(C0)4 in dealuminated NaY (Si/Al 400) shows one band at 2046 cm , similar to that of tetrahedrally coordinated Ni(CO)4 in THF solution. No change of the Ni oxidation state and no loss of CO ligands after adsorption of Ni(CO)4 in alkali zeolite Y are detected with XANES and EXAFS spectroscopies. However, the appearance of four IR bands, which shift when the Ni(CO 4 loading or the alkali cations are varied, indicates an interaction of the type -OC—Ni, where = Na or Li. A reactive Ni(CO)3 in- 

Introduction of PPh2CHMc2 into Ni(CO)4-loaded NaY led to the formation of Ni(CO)3PPh2CHMe2, as evidenced by XANES, EXAFS, NMR, and IR spectroscopies (85). 

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Figure 8.1 Simplified picture showing the steps leading to supported bimetallic particles from a heteronuclear neutral carbonyl complex.

Figure 9.4 Core-shell polyplex structures (A) cationic particles with a core from neutralized DNA and polycation and a corona from polycation chains adsorbed on the core (B) electroneutral particles ( polyion complex micelles or block ionomer complex ) with a core from neutralized DNA and poly cation and a corona from nonionic water soluble polymer.

Ionic solutions are liquids consisting of a solvent formed from neutral, polar molecules, and a solute that dissociates into positive and negative ions. They vary widely in complexity in the classic electrolyte solutions, the cations and anions are of comparable size and absolute charge, whereas macromolecular ionic solutions contain both macroins (charged polymer chains or coils, micelles, charged colloidal particles etc.) and microscopic counterions [28]. We will discuss only the classic ionic solutions. 

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

Thorium generally exists as a neutral hydroxide species in the oceans and is highly insoluble. Its behavior is dominated by a tendency to become incorporated in colloids and/or adhere to the surfaces of existing particles (Cochran 1992). Because ocean particles settle from the water column on the timescale of years, Th isotopes are removed rapidly and have an average residence time of = 20 years (Fig. 1). This insoluble behavior has led to the common assertion that Th is always immobile in aqueous conditions. While this is generally true in seawater, there are examples of Th being complexed as a carbonate (e.g.. Mono Lake waters, Anderson et al. 1982 Simpson et al. 1982) in which form it is soluble. 

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