Supported leaching process

A second area of concern is reduced tree growth in forests. As acidic deposition moves through forest soil, the leaching process removes nutrients. If the soil base is thin or contains barely adequate amounts of nutrients to support a particular mix of species, the continued loss of a portion of the soil minerals may cause a reduction in future tree growth rates or a change in the types of trees able to survive in a given location. 

Zeolites also lend themselves particularly well to reactions where the catalytically active species are cationic. Under these circumstances there is a strong electrostatic interaction between the active entity and the support which minimizes activity loss via leaching processes. 

The solid HP As showed promising improvement in conductivity and fuel cell performance but dissolved in water formed by the electrochemical process of current generation [9]. This leaching of the acids led to decay in the performance of the fuel cells. To overcome the problem of electrolyte dissolutimi and the consequent short lifetime of the fuel cell, an approach was investigated in which the HPA was blocked inside a host material in such a way that it would maintain high proton conductivity of the original electrolyte. The immobilization of the HPA on a support could be attained by any of the three processes physisorption, chemical attachment, and entrapment. Since weak forces are involved in physisorption, it is not an effective method to avoid the solubilization and leaching of the HPA from the support. The processes of immobilization by chemical attachment or entrapment are more effective as they form covalent or ionic bonds with the host material and very stable materials can be prepared. 

The processiag costs associated with separation and corrosion are stiU significant ia the low pressure process for the process to be economical, the efficiency of recovery and recycle of the rhodium must be very high. Consequently, researchers have continued to seek new ways to faciUtate the separation and confine the corrosion. Extensive research was done with rhodium phosphine complexes bonded to soHd supports, but the resulting catalysts were not sufficiently stable, as rhodium was leached iato the product solution (27,28). A mote successful solution to the engineering problem resulted from the apphcation of a two-phase Hquid-Hquid process (29). The catalyst is synthesized with polar -SO Na groups on the phenyl rings of the triphenylphosphine. 

Our approach, to achieve a high dispersion of the metal compound while the oxide network is formed, is to employ metal complexes of the type LnM[X(CH2)3Si(OR)3]y in the sol-gel process [2]. The metal ions then cannot aggregate because of complexation, and the metal complexes cannot leach because they are linked to the oxidic support. These complexes are formed in situ on reaction of silanes of the type X(CH2)nSi(OR)3 with suitable metal salts. 

The utility of such reagents in the oxidation processes is compromised due to their inherent toxicity, cumbersome preparation, potential danger in handling of metal complexes, difficulties encountered in product isolation and waste disposal problems. Immobilization of metallic reagents on solid supports has circumvented some of these drawbacks and provided an attractive alternative in organic synthesis because of the selectivity and associated ease of manipulation. Further, the localization of metals on the mineral oxide surfaces reduces the possibility of their leaching into the environment. 

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