Embedded catalyst

To prepare unbedded catalyst, polymerization was first carrirf out in a small a tetui glass reactor at room temperature for 1 hr in n-heptane at very low styreaie (xmcentration using Et[Ind]2ZrCl2/MAO catalyst with Al/Ti mole ratio of20-200. After the rraiction, a small part of the solid fraction (embedded catalyst) was isolated fi om the liquid phase for the... 

The ethylene polymerization was carried out using a 12 OZ glass reactor equipped with a two blade impeller under a constant ethylene pressure of 20 psi. A predetermined amount of solvent (n-heptane), monomer, MAO and embedded catalyst were charged in series into the reactor. Polymerization was carried out at 70"C with agitation speed of 800 rpm. The polymer obtained was washed with excess amount of methanol containing hydrochloric acid solution and dried in vacuo for 24 hrs. The polymerization rate was determined from the amount of consumed ethylene, measured using a mass flow meter. DSC analyses (Dupont V4.0B) was carried out at a rate of 10 C /min, and the results were obtained in the second scan. 

Fig. 1. DSC thermogram of polymers (a) polyethylene with homogeneous catalyst (b) polyethylene with embedded catalyst (c) catalyst embedded polystyrene.

On the other hand, the polymer prepared by the embedded catalyst shows T around 130 °C, which is a typical melting temperature of high density polyethylene. There was little activity difference between the polyethylene produced by embedded particles and those by homogeneous catalysts. The results of ethylene polymerization using embedded catalyst and homogeneous catalyst are summarized in Table 1 and Fig. 2,... 

Table 1. Results of ethylene polymerization with embedded catalyst and homogeneous...

An example of the use of PGSE NMR spectroscopy can be found in the studies of Selke et al. [33], who investigated the dependence of enantioselectivity on the distribution of a chiral hydrogenation catalyst between aqueous and micellar phases. When a compound is incorporated into a micelle, its mobility is much lower compared to its mobility in solution. This effect is exactly what is probed with PGSE NMR. The calculated diffusion coefficient is a time-averaged value of the lower diffusion coefficient of the catalyst incorporated into the micelles, and of the diffusion coefficient of the free catalyst. An increased amount of micelle-embedded catalyst was found to lead to an increased enantioselectivity. 

Other examples involve the immobilization of ruthenium porphyrin catalysts [74]. While Severin et al. generated insoluble polymer-embedded catalysts 16 by co-polymerizing porphyrin derivatives with ethylene glycol dimethacrylate (EGD-MA) [74 a], Che et al. linked the ruthenium-porphyrin unit to soluble polyethylene glycol (PEG) 17 [74b]. Both immobilized catalysts were employed in a variety of olefin epoxidations with 2,6-dichloropyridine N-oxide (Gl2pyNO), providing similar conversions of up to 99% and high selectivities (Scheme 4.9). 

Figure 6.2 Embedded catalyst design developed by our group.

The embedded catalyst synthesized in this way shows higher thermal stability than the traditional catalyst obtained by incipient wetness impregnation. 

Although TA-NaBr-MRNi is rather more unstable than TA-MRNi in the persistency of EDA, TA-NaBr-MRNi was extremely stabilized not only with EDA but also with hydrogenation activity by embedding it in a silicone polymer as shown in Fig. 34 (48). The embedded catalyst can be stored very stably for a long period without special precautions. The embedded catalyst with high EDA is expected to be obtained in the near future. 

Harmer et al.196 used 1,1,2,2-tetrafluoroethanesulfonic acid in the alkylation of para-xylene with 1-dodecene. The silica-embedded catalyst prepared by the sol-gel method showed much higher activity than the neat acid (almost complete conversion in 15 min at 100°C over the sol-gel-derived material versus 10% conversion, using the same molar amounts of acid). Practically no leaching was detected and the catalyst could be recycled with a slight decrease in conversion. It is in sharp contrast with silica-supported triflic acid, which showed much lower activity due to the loss of volatile triflic acid. 

Influence of the calcination on H -up-take and surface area of colloid embedded catalysts Catalyst Surface area, m g H2-uptake, cm g ... 

This time, the addition of a solvent hardly improves the performance of the non embedded catalyst. Dilution of the reaction medium and a more imporant blank reaction are the only consequences. This confirms that a membrane resident catalyst under solvent free conditions can actually be used to reduce interferences from the blank reaction. 

An embedded catalyst reacts with the healing agent,... 

By incorporating ligating groups in dendrimers or polymers and subsequent metal catalyst formation, new structures are formed with sometimes less assignable constructions. It should be remembered that inorganic or organic matrices can also alter the catalytic properties of an embedded catalyst. 

Disadvantages No catalyst recovery (only possible in a separate device) Less flexibility (only the reaction mediated by the embedded catalyst is possible)... 

The reactor capillary with the embedded catalyst ( , )-5 was coupled between the preseparation and the enantioselective separation capillary. Using this experimental setup, the diastereo- and enantioselective formation of 4a from ( ,Z)-3 and 4b from (Z, )-3 was detected. The advantage of this approach is that... 

The embedded catalyst R,R)-5 provided excellent conversions and enantiomeric ratio values for the catalytic asymmetric Gosteli - Claisen rearrangement of E,Z)-Z to 4a. Notably, the catalyst maintained its activity and selectivity within the investigated temperature range between 65 and 85 °C. 

Polypynole films have been employed as carriers of catalytically active materials like finely dispersed metal particles [567], whose own catalytic properties in various electrochemical reactions have been studied [568]. These systems sometimes were investigated using spectroelectrochemical techniques. Mostly, measurements were aimed at elucidating catalytic aspects of the embedded catalyst. These reports are beyond the scope of this review. 

Transformation of SPs, swelling-shrinking, was used to control the activity of the embedded catalysts (Lu et /., 2006,2009a). Metal nanoparticles such as Ag, Au, Rh or Pt were embedded inside the pNIPAM shell and their exposure to the medium meant that their catalytic activity was dependent on the temperature-induced conformational changes of the polymer (Fig. 13.8). 

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