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An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.
Often, substances are intentionally added to the reaction feed or on the catalyst to influence catalytic activity, selectivity, and/or stability. These compounds are called promoters. For example, alumina (Al 2 O 3) is added during ammonia synthesis to providing greater stability by slowing sintering processes on the Fe-catalyst. [2]
These catalysts initiate radical chain reactions, autoxidation that produce organic radicals that combine with oxygen to give hydroperoxide intermediates. Generally the selectivity of oxidation is determined by bond energies. For example, benzylic C-H bonds are replaced by oxygen faster than aromatic C-H bonds. [2]
Usually the true catalyst is an expensive and complex molecule and added in quantities as small as possible. The stoichiometric catalyst on the other hand should be cheap and abundant. [citation needed] "Sacrificial catalysts" are more accurately referred to by their actual role in the catalytic cycle, for example as a reductant.
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H +) donor and the base is the proton acceptor. Typical reactions catalyzed by proton transfer are esterifications and aldol reactions.
The graph for these equations is a sigmoid curve (specifically a logistic function), which is typical for autocatalytic reactions: these chemical reactions proceed slowly at the start (the induction period) because there is little catalyst present, the rate of reaction increases progressively as the reaction proceeds as the amount of catalyst ...
Examples of early transition metal catalysts includes titanium and zirconium complexes. Early transition metals can easily form oxides; therefore, protection groups, like the use of methylaluminoxane (MAO) due to its Lewis acidity, can be used to prevent side reactions from happening. [13]
Acetalisation; Acetoacetic ester condensation; Achmatowicz reaction; Acylation; Acyloin condensation; Adams' catalyst; Adams decarboxylation; Adkins catalyst