Catalysts , Chemistry

CATALYSTS

A catalyst is a species that speeds up a chemical reaction but is not itself consumed. Catalysts do not change the thermodynamics of the position of equilibrium or a reaction, but react by providing an alternative pathway of lower activation energy. They allow many reactions to be done at lower temperatures than without a catalyst, and also give selectivity in producing a specific product in reactions where various products are feasible thermodynamically. Enzymes are distinct selective biological catalysts.

A catalyst present in the same phase as the reactants is called homogeneous; one in a distinct phase is heterogeneous. Most heterogeneous catalysts are solids, and react by adsorption of liquid or gaseous reactants on a surface. Homogeneous catalysts are specific molecules, usually organ metallic compounds that can be tailored in a more specific way to produce a required product than is possible with heterogeneous catalysts.

 

Industrial and domestic plastics are mostly prepared by polymerizing alkenes:

 

1154_Untitled.png

The reaction is exothermic and may be started by free radicals but organ metallic catalysts produce more controllable results. Most commonly used is Ziegler-Natta catalysts build by mixing Al2Et6 with TiCl4. Solid TiCl3 is build and catalysis occurs at surface Ti-Et groups, to which alkene molecules undergo and coordinate insertion into the Ti-R bond. An advantage of these catalysts is that they may form stereoregular polymers where all the R parts in -C(R)H CH2- have the same stereo chemical configuration. This produces stronger materials with greater melting points than the random stereochemistry resulting from radical polymerization.

 

Posted Date: 7/23/2012 8:21:06 AM | Location : United States







Related Discussions:- Catalysts , Assignment Help, Ask Question on Catalysts , Get Answer, Expert's Help, Catalysts Discussions

Write discussion on Catalysts
Your posts are moderated
Related Questions
what are the pysical propities of iodofrom

1s 2 , 2s 2 , 2p 6 3s 1 shows configuration of: (1) Al 3+   in ground state (2) Ne in excited state  (3) Mg + in excited state   (4) None of these Ans:  Mg + in

Prepare a table that lists the expressions for the dimensionless concentration profiles and catalyst effectiveness factors for slab, cylinder and spherical catalysts.

The atomic orbitals are progressively filled in order of increasing energy. This principle is called as: (1) Hund's rule (2)Aufbau principle (3) Exclusion principle (4

Q. Explain about Stereoisomerism? Stereoisomers have the same bonds but the arrangement of atoms in space is different.  Stereoisomerism can be divided into two kinds: geometri

Alkanes have single bond, but why are they less reactive as compared to alkenes or alkynes which have respectively double or triple bonds ? Alkanes have only single sigma bond w




what points should be included in an assignment on van der waals forces