Catalyst introduced

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

Compared with uncatalyzed reactions, catalysts introduce alternative pathways that, in nearly all cases, involve two nr more consecutive reaction steps. Each of these steps has a lower activation energy than does the uncatalyzed reaction. We can nse as an example the gas phase reaction of ozone and oxygen atoms. In the homogeneons uncatalyzed case, the reaction is represented to occur in a single irreversible step that has a high activation energy ... 

The 8-branch point present in PECH is absent in polymers of higher 1,2-epoxy-u-chloroalkanes. Such polymers are readily prepared by treatment of the neat monomers with the modified tri-ethyl al uminum catalyst introduced by Vandenberg (5, ) results for (2-chloroethyl)oxirane, (3-chloropropyl)oxirane and (4-chlorobutyl)-oxirane (2a-c) are summarized in Table I (7, 8). 

Coupling of bromide 152 with (a-ethoxyvinyl)trimethyltin in the presence of a palladium catalyst introduces an acetyl group at the C-5 position to yield compound 153 (Equation 7) <2002TL1005>. 

Among the highly active catalysts introduced above, bis(phenoxy-imine) early transition metal complexes (Fig. 9) in particular show strikingly high activities for the polymerization of ethylene [14, 51-54]. 

The increase in the amount of catalyst introduced in oxidized cumene (353 K) increases the oxidation rate, decreases the amount of the formed hydroperoxide, and increases the yield of the products of hydroperoxide decomposition methylphenyl ethanol and acetophenone. Similar mechanism was proposed for catalysis by copper phthalocyanine in cumene oxidation [254],... 

Scheme 1. Metathesis catalysts introduced by Grubbs (la-b) and Schrock (2)...

Safety aspects of drum storage, pellet screening, dust removal, reactor loading and unloading, and activation of process catalysts are discussed [1], and reprocessing aspects are considered, with disposal as a last resort [2], Hydrogenation catalysts introduce their own problems [3],... 

A solid acid catalyst introduced in 1985 is used in UOP s Hexall process to selectively dimerize propylene at high conversion.24 The Colefin content of the product can reach higher than 90% with an octane number of 95-96. 

Pt/y-alumina wash-coat catalyst introduced by co-impregnation was used for butane combustion. After brief heating for 10 s, the reaction ignited and proceeded... 

In addition to the illumination of the catalyst surface, another simple method is used for the alteration of the electron concentration and the occupation of the bond orbitals in the semiconductor surface. This method is a modification of the inverse mixed catalysts introduced by Schwab 89 9 . The electron concentration and distribution upon the bond states is achieved 1. by putting the surface bonds into the potential of a boundary layer of a metal-semiconductor junction and 2. by illumination of the semiconductor-metal junction with ultraviolet light (photovoltaic effect). 

In order to understand the molecular mechanisms of how the quadratic autocatalysis is brought about, the concept of dimer catalyst introduced by Kagan and coworkers, may be relevant [ 19,30,32,33]. Assume that monomers R and S react to form homodimers R2 and S2 with a rate Vhom and a heterodimer RS with a rate VheP... 

Functionalised carbenes can anchor free carbenes to the metal site, introduce hemilabil-ity, provide a means to immobilise transition metal carbene catalysts, introduce chirality, provide a chelate ligand or bridge two metal centres. NHC can be attached to carbohydrates and camphor, derived from amino acids and purines, and they can be used as organocata-lysts mimicking vitamin B1 or as weak solvent donors in lanthanide chemistry. There are many possibilities which are still only scarcely explored. 

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