Catalyst theory
Introduction
Catalysis is the process by which the speed of a chemical reaction is increased, due to the participation of a substance called catalyst;[1] those that deactivate catalysis are called inhibitors. An important characteristic is that the mass of the catalyst does not change during the chemical reaction, which differentiates it from a reactant, whose mass decreases throughout the reaction.
In the synthesis of many of the most important industrial chemicals there is catalysis, since this can reduce the time required. Catalyst poisoning, which is generally an undesirable process, is also used in the chemical industry. For example, in the reduction of ethyne to ethene, the palladium (Pd) catalyst is partially "poisoned" with lead(II) acetate, Pb(CHCOO). Without deactivation of the catalyst, the ethene produced would subsequently be reduced to ethane.[2][3].
Generalities
Catalysis is involved in many industrial processes. Likewise, most "biologically" significant processes are catalyzed. Catalysis research is one of the major fields in applied science and involves many areas of chemistry, especially organometallic chemistry and materials science. Catalysis is important to many aspects of environmental science, for example the catalytic converter in automobiles and the dynamics of the ozone hole. Catalytic reactions are preferred in green chemistry for a friendly environment due to the reduced amount of waste generated[4] instead of stoichiometric reactions in which all reactants are consumed and more secondary products are formed. The most common catalyst is the proton (H). Many transition metals and transition metal complexes are used in catalysis. Catalysts called enzymes are important in biology.
The catalyst works by providing an alternative reaction path to the reaction product. The rate of the reaction increases as this alternative pathway has a lower activation energy than the non-catalyst-mediated reaction pathway. The dismutation of hydrogen peroxide to water and oxygen is a reaction that is strongly affected by catalysts:
This reaction is favored, in the sense that the reaction products are more stable than the starting material, however, the uncatalyzed reaction is slow. The decomposition of hydrogen peroxide is in fact so slow that hydrogen peroxide solutions are commercially available. Upon addition of a small amount of manganese dioxide, hydrogen peroxide reacts rapidly according to the above equation. This effect is easily seen by the effervescence of oxygen.[5] Manganese dioxide can be recovered unchanged, and reused indefinitely, and is therefore not consumed in the reaction. Consequently, manganese dioxide .[6].