Heterogeneous catalysis is a chemistry term which describes catalysis where the catalyst is in a different phase (ie. solid, liquid and gas) to the reactants.Heterogenous catalysts provide a surface for the chemical reaction to take place on. Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the science that deals with the properties of organic and inorganic substances and their interactions with other organic and inorganic substances. ... Generic graph showing the effect of a catalyst in an hypotetical exothermic chemical reaction. ... A catalyst (Greek: καταλύτης, catalytēs) is a substance that accelerates the rate (speed) of a chemical reaction (see also catalysis). ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... A liquid will assume the shape of its container. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... In chemistry, the reactants are the substances that exist at the start of a chemical reaction. ...

In order for the reaction to occur one or more of the reactants must diffuse 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. Understanding these transport phenomena and surface chemistry such as dispersion is an important area of heterogeneous catalyst research. If diffusion rates are not taken into account, the reaction rates for various reactions on surfaces depend solely on the rate constants and reactant concentrations. In chemistry, adsorption of a substance is its concentration on a particular surface. ... The reaction rate for a reactant or product in a particular reaction is defined as the amount (in moles or mass units) per unit time per unit volume that is formed or removed. ... Surface chemistry is the study of chemical phenomena that occur at the interface of two phases, usually between a gas and a solid or between a liquid and a solid. ... In materials science, dispersion is the fraction of atoms of a material exposed to the surface. ... 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. ...

The synthesis of ammonia is an example of heterogeneous catalysis: Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ...

3H₂(g) + N₂(g) ↔ 2NH₃(g) - catalysed by Fe(s).

See also

• Homogeneous catalysis