catalyst

Examples of catalyst in the following topics:

• Homogeneous Catalysis

  • However, catalysts do not affect the degree to which a reaction progresses.
  • Homogeneous catalysts are those which exist in the same phase (gas or liquid) as the reactants, while heterogeneous catalysts are not in the same phase as the reactants.
  • Try running the reaction with and without a catalyst to see the effect catalysts have on chemical reactions. 1.
  • Run the model to observe what happens without a catalyst. 2.
  • Run the model again, and observe how the catalyst affects the reaction.

• Heterogeneous Catalysis

  • Unlike reactants, a catalyst is not consumed as part of the reaction process.
  • The process of speeding up a reaction by using a catalyst is known as catalysis.
  • Homogeneous catalysts are those that occupy the same phase as the reaction mixture (typically liquid or gas), while heterogeneous catalysts occupy a different phase.
  • Generally, heterogeneous catalysts are solid compounds that are added to liquid or gas reaction mixtures.
  • The reason such catalysts are able to speed up a reaction has to do with collision theory.

• The Effect of a Catalyst

  • Common examples of catalysts include acid catalysts and enzymes.
  • To reiterate, catalysts do not affect the equilibrium state of a reaction.
  • Try running the reaction with and without a catalyst to see the effect catalysts have on chemical reactions. 1.
  • Run the model to observe what happens without a catalyst. 2.
  • Run the model again, and observe how the catalyst affects the reaction.

• Ziegler-Natta Catalytic Polymerization

  • Ziegler-Natta catalysts are prepared by reacting certain transition metal halides with organometallic reagents such as alkyl aluminum, lithium and zinc reagents.
  • The catalyst formed by reaction of triethylaluminum with titanium tetrachloride has been widely studied, but other metals (e.g.
  • Others have been suggested, with changes to accommodate the heterogeneity or homogeneity of the catalyst.
  • Polymerization of propylene through action of the titanium catalyst gives an isotactic product; whereas, a vanadium based catalyst gives a syndiotactic product.

• Hydrogenation

  • Catalysts can be divided into two categories: homogeneous or heterogeneous catalysts.
  • Homogeneous catalysts are soluble in the solvent that contains the unsaturated substrate.
  • Often, heterogeneous catalysts are metal-based and are attached to supports based on carbon or oxide.
  • For heterogenous catalysts, the Horiuti-Polanyi mechanism explains how hydrogenation occurs.
  • First, the unsaturated bond binds to the catalyst, followed by H2 dissociation into atomic hydrogen onto the catalyst.

• Alkylidene Reactions

  • Many structural features of a metathesis catalyst may be changed and adjusted to suit the type of reaction desired.
  • A ROMP catalyst, for example, should complex preferentially with the ring double bond, inducing ring cleavage and formation of a new catalytic site.
  • Much effort has been devoted to creating metathesis catalysts with improved binding and turnover characteristics to fit specific transformations.
  • Schrock's molybdenum catalysts generally show high reactivity, but tend to be air sensitive and intolerant of some functional groups.
  • Tech. ) has produced a family of easily handled ruthenium catalysts that have proven effective and valuable tools in the field of synthetic organic chemistry.

• Hydrogenation

  • This restriction may be circumvented by the use of a catalyst, as shown in the following diagram.
  • Catalysts are substances that changes the rate (velocity) of a chemical reaction without being consumed or appearing as part of the product.
  • Finely divided metals, such as platinum, palladium and nickel, are among the most widely used hydrogenation catalysts.
  • First, the alkene must be absorbed on the surface of the catalyst along with some of the hydrogen.
  • Similar complexes have been reported for nickel and palladium, metals which also function as catalysts for alkene hydrogenation.

• Addition

  • Although it does so less readily than simple alkenes or dienes, benzene adds hydrogen at high pressure in the presence of Pt, Pd or Ni catalysts.
  • Nickel catalysts are often used for this purpose, as noted in the following equations.
  • We have already noted that benzene does not react with chlorine or bromine in the absence of a catalyst and heat.

• Carbon-Carbon Bond Formation

  • Transition metal catalysts have been applied to many functional group transformations, including hydrogenation (Wilkinson's catalyst), asymmetric epoxidation (Sharpless & Jacobsen catalysts) and asymmetric dihydroxylation (Sharpless catalyst).
  • In the following discussion, however, we shall focus on several new and very useful applications of these catalysts to reactions in which carbon-carbon bonds are formed.
  • Nickel catalysts have been demonstrated to be effective in coupling allylic halides to each other and to various aryl, vinyl and alkyl halides.
  • Because nickel carbonyl is an extremely toxic gas, alternative nickel catalysts have been examined with variable results.
  • The best nickel catalyst was Ni(CO)4, a toxic gas, and recent work by K.P.C.

• Introduction to Chemical Reactivity

  • Reaction Conditions: The environmental conditions, such as temperature, pressure, catalysts & solvent, under which a reaction progresses optimally.
  • Catalysts are substances that accelerate the rate ( velocity ) of a chemical reaction without themselves being consumed or appearing as part of the reaction product.
  • Catalysts do not change equilibria positions.