Ion-exchange and Impregnation

Kaeding and Butter modified ZSM-5 with phosphorus compounds. The selectivity toward Cj-C paraffins decreased from 39 to 5 wt% and toward aromatics from 40 to 20 wt%. The selectivity toward 

Using infrared and microcalorimetric techniques led Vedrine et al. to propose that phosphorus neutralizes medium and strong acid sites at the entrance of the zeolite channels. The strongest acid sites, however, would not be modified. As a result, the activity of the modified catalyst was comparable to that of the parent ZSM-5. The increased olefin selectivity was then assigned to the increased 

Balkrishnan et al. suggested that, even though the tortuosity in the zeolite channels is increased, the observed higher selectivity toward Cj-C olefins in the methanol conversion on P-modified ZSM-5 is due more to a change in the acidity than to any steric effect. According to Cai et al., ° phosphorus affects both Bronsted and Lewis sites of various acid strength. As a result, an increased ethylene selectivity was attained. 

By modifying the ZSM-5 catalyst with Mg, ° the stronger acid sites were eliminated, but the number of weaker Lewis acid sites was increased. The Mg-ZSM-5 catalyst was more selective toward propylene. This was alo observed by Juan, who attributed the higher propylene selectivity to the presence of the relatively weak acid sites, active in the /3-scission of carbenium ions. 

On ZSM-5 modified with molybdenum, Balkrishnan observed selectivities toward Cj-C olefins as high as 90%. The selectivity increased with the M0O3 content, but the methanol conversion was decreased. 

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In Chapter 14, one of the least-used applications of TLC and PLC is described, namely inorganics and organometallics. These separations in the analytical mode often require quite unusual stationary phases (e.g., inorganic ion exchangers and impregnated and mixed layers) combined with a variety of diverse mobile phases. This means that the use of the analogous systems in the preparative mode represents an unusually difficult challenge. 

Figure 2.1.6.9 and Table 2.1.6.4 present the N2-sorption isotherms and the results of the characterization of the Al-MCM-41 parent material and of the by ion exchange and impregnation onto Al-MCM-41 immobihzed (S,S)-Co( 11)-Jacobsen complexes. The N2-sorption isotherms of the loaded materials clearly illustrate that (S,S)-Co(II)-Jacobsen complex is deposited in the inner surface of the pores... 

The (S,S)-Co(II)-Jacobsen complex was immobilized on Al-MCM-41 by both impregnation and ion exchange. For the ion-exchange and impregnation methods different solvents, several metal salts, and different concentrations were tested in order to avoid a structure collapse of the support material. The catalysts were in-... 

The ultimate goal of catalyst preparation is to obtain very small platinum particles to increase the surface to volume ratio (S/V = 3/r for a spherical particle). Platinization by ion exchange and impregnation with colloidal platinum yield the best results in this respect (135). 

The pertinent key parameters which may influence the interaction of a transition metal complex with an oxide support are first briefly discussed, before examples of important applications of ion exchange and impregnation are given. 

Catalysts were prepared (138,139) by both ion exchange and impregnation of zeolites with Ni2 +. Ion exchange resulted in the most active but least selective (approximately 25% selectivity to n-butenes under conditions com-... 

Various techniques are available for the introduction of metals into zeolites. Ion exchange and impregnation, e.g., by the incipient wetness or imbiberaent techniques, are often used. The former method introduces preferentially the cation into the zeolite, whereas the latter method also incorporates an equivalent number of anions. In both cases, the introduction of ions has to be followed by calcination and reduction steps. For zeolite-based catalysts the ion-exchange method is often preferred (97,9S). 

Amino acids have been separated on layers of a wide variety of inorganic and organic adsorbents, ion exchangers, and impregnated plates. The two most commonly used adsorbents are silica gel and cellulose. 

In this communication, we discuss the structure of Co containing ZSM5 zeolites prepared by direct synthesis, ion exchange and impregnation methods and compare it with results obtained from an atomistic simulation. 

The surface area of the samples prepared by ion exchange and impregnation, respectively, EX and IMP, are very similar to the surface area of zeolite HUSY. However, the precipitated catalysts (PP25 and PP90) presented a lower surface area, which can probably be attributed to some blocking of pores. 

The pHjo (pH for which a 50% extraction efficiency is achieved) has been used to measure the separation factors. A practical ApHjg (Mi/M2)>l allows an effective separation efficiency of Ml (>95%) over M2 (<5%). The pHjg and ApHjg values for the set of selected metals for solvent extraction, ion exchange, and impregnated resins systems (Table 9.6) show that sulphonic, phosphoric, and carboxylic groups do not allow efficient separation factors, yet phosphinic acid extractants such as Cyanex 272 could offer an appropriate solution to solve this separation problem [44]. 

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