All Topics  
Heterogeneous catalysis

 

 
   Email Print
   Bookmark   Link
 

 

Heterogeneous catalysis
 
 
  Topics Heterogeneous catalysis Topic Home

Heterogeneous catalysis is a chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 term which describes catalysis
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
 where the catalyst is in a different phase (ie. solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
, liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 and gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
, but also oil
Oil

An oil is a chemical substance that is in a viscosity liquid state at room temperature or slightly warmer, and is both hydrophobic and lipophilic ....
 and water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
) to the reactants. Heterogeneous catalysts provide a surface for the chemical reaction to take place on.

In order for the reaction to occur, one or more of the reactants must diffuse
Surface diffusion

Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters at solid material surfaces. The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1....
 to the catalyst surface and adsorb onto it. After reaction, the products must desorb from the surface and diffuse away from the solid surface.






Discussion
Ask a question about 'Heterogeneous catalysis'
Start a new discussion about 'Heterogeneous catalysis'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Heterogeneous catalysis is a chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 term which describes catalysis
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
 where the catalyst is in a different phase (ie. solid
Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
, liquid
Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
 and gas
Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
, but also oil
Oil

An oil is a chemical substance that is in a viscosity liquid state at room temperature or slightly warmer, and is both hydrophobic and lipophilic ....
 and water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
) to the reactants. Heterogeneous catalysts provide a surface for the chemical reaction to take place on.

In order for the reaction to occur, one or more of the reactants must diffuse
Surface diffusion

Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters at solid material surfaces. The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1....
 to the catalyst surface and adsorb onto it. After reaction, the products must desorb from the surface and diffuse away from the solid surface. Frequently, this transport of reactants and products from one phase to another plays a dominant role in limiting the reaction rate
Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular chemical reaction is intuitively defined as how fast a reaction takes place....
. Understanding these transport phenomena and surface chemistry such as dispersion
Dispersion (materials science)

In materials science, dispersion is the fraction of atoms of a material exposed to the surface. In general:where D is the dispersion, NS is the number of surface atoms and NT is the total number of atoms of the material....
 is an important area of heterogeneous catalyst research. Catalyst surface area may also be considered. Mesoporous silicates
Mesoporous silicates

Mesoporous silicates are silicates with a special Morphology ....
, for example, have found utility as catalysts because their surface areas may be in excess of 1000 m2/g, which increases the probability that a reactant molecule in solution will come in contact with the catalyst surface and adsorb. If diffusion rates are not taken into account, the reaction rates for various reactions on surfaces
Reactions on surfaces

By reactions on surfaces it is understood reactions in which at least one of the steps of the reaction mechanism is the adsorption of one or more reactants....
 depend solely on the rate constants and reactant concentrations. Asymmetric heterogeneous catalysis can be used to synthesize enantiomerically pure compounds using chiral heterogeneous catalysts. The field is of great industrial and environmental importance. It has attracted two Nobel prizes
Nobel Prize

The Nobel Prize , established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Nobel Prize in Physics, Nobel Prize in Chemistry, Nobel Prize in Physiology or Medicine, Nobel Prize in Literature, and Nobel Peace Prize in 1901....
 for Irving Langmuir
Irving Langmuir

Irving Langmuir was an United States chemistry and physics. His most noted publication was the famous 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N....
 in 1932 and Gerhard Ertl
Gerhard Ertl

Gerhard Ertl is a German physicist and a Professor emeritus at the Department of Physical Chemistry, Fritz Haber Institute of the MPG in Berlin, Germany....
 in 2007.

Examples

  • The synthesis of Ammonia is an example of heterogeneous catalysis:
3H2(g) + N2(g) ? 2NH3(g) - catalysed by Fe(s).


  • The use of Nickel
    Nickel

    Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
     in the hydrogenation
    Hydrogenation

    Hydrogenation is the chemical reaction that results from the addition of hydrogen . The process is usually employed to a redox or Saturation organic compounds....
     of vegetable oils to produce margarine
    Margarine

    Margarine , as a generic term, can indicate any of a wide range of butter substitutes. In many parts of the world, margarine has become the best-selling table spread, although butter and olive oil also command large market shares....
    . The unsaturated fat
    Unsaturated fat

    An unsaturated fat is a fat or fatty acid in which there are one or more double bonds in the fatty acid chain. A fat molecule is Monounsaturated fat if it contains one double bond, and polyunsaturated if it contains more than one double bond....
     present in the vegetable oils are converted to saturated fat
    Saturated fat

    Saturated fat is fat that consists of triglycerides containing only Saturation fatty acid radicals. There are several kinds of naturally occurring saturated fatty acids, which differ by the number of carbon atoms - from 1 to 24....
     by the addition of hydrogen. This in turn breaks the Carbon-carbon double bonds. In order for this reaction to be catalysed effectively the nickel
    Nickel

    Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
     must present a large surface area so therefore must be finely divided.
-CH=CH- + H2 ? -CH2-CH2-


Another example is the reduction of nitrile
Nitrile

A nitrile is any organic compound which has a -Carbon=Nitrogen functional group. The -C=N functional group is called a nitrile group....
s for instance in a synthesis of phenethylamine
Phenethylamine

Phenethylamine, or ?-phenylethylamine or 2-phenylethylamine, is an alkaloid and monoamine. Phenethylamine also has a constitutional isomer a-phenylethylamine , which has two stereoisomers: --1-phenylethylamine and --1-phenylethylamine....
 with Raney nickel
Raney nickel

Raney nickel is a solid catalyst composed of fine grains of a nickel-aluminium alloy, used in many industrial processes. It was developed in 1926 by United States engineer Murray Raney as an alternative catalyst for the hydrogenation of vegetable oils in industrial processes....
 and ammonia
Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
:




  • The cracking, isomerisation
    Isomerisation

    In chemistry isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g....
     and re-forming of hydrocarbons to form appropriate and useful blends of Petrol.


Catalytic Converters

These are often used in automobiles. Three main reactions are catalysed by Catalytic converters.

The oxidation of carbon monoxide
Carbon monoxide

Carbon monoxide, with the chemical formula CO, is a colorless and odorless, tasteless, yet highly toxic gas. Its molecules consist of one carbon atom covalent bond to one oxygen atom....
 to carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
.

2CO(g) + O2(g) ? 2CO2(g)

The reduction
Reduction

Reduction, reduced, or reduce may refer to:...
 of nitrogen monoxide back to nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
.

2NO(g) + 2CO(g) ? N2(g) + 2CO2(g)

The oxidation of hydrocarbons to water and carbon dioxide. This can occur on any of the hydrocarbons however primarily Petrol or Diesel
Diesel

Diesel or diesel fuel in general is any fuel used in diesel engines. The most common is a specific fractional distillation of petroleum fuel oil, but alternatives that are not derived from petroleum, such as biodiesel, biomass to liquid or gas to liquid diesel, are increasingly being developed and adopted....
.

2C6H6(g) + 15O2 ? 12CO2(g) +6H2O(l)

See also

  • Homogeneous catalysis
    Homogeneous catalysis

    Homogeneous catalysis is a chemistry term which describes catalysis where the catalyst is in the same phase as the reactants. It is the opposite to heterogeneous catalysis....
  • Temperature-programmed reduction
    Temperature-programmed reduction

    Temperature-programmed reduction is a technique for the characterization of solid materials and is often used in the field of heterogeneous catalysis to find the most efficient Redox conditions, an oxidized catalyst precursor is submitted to a programmed temperature rise while a reducing gas mixture is flowed over it....
  • Thermal desorption spectroscopy
    Thermal desorption spectroscopy

    Thermal desorption spectroscopy , also known as temperature programmed desorption is the method of observing desorption molecules from a surface when the surface temperature is increased....