Definition of Catalystc

Definition: According to the definition proposed by IUPAC in 1981, a catalyst is a substance that accelerates the rate of a reaction without changing the standard Gibbs free enthalpy change of that reaction. This effect is called catalysis. A screening involving a catalyst is a catalytic reaction.

A catalyst (catalyst) induces a change in a chemical reaction, which results in a faster chemical reaction or a chemical reaction at a lower temperature environment.

We can observe in the Boltzmann distribution and energy profile diagram that catalysts allow chemical reactions to proceed through a pathway that requires less activation energy without alteration. Usually, at this energy, the molecules are either unable to complete the chemical reaction or take longer to complete the reaction. But in the presence of a catalyst, the molecules need less energy to complete the reaction.

Catalysts are divided into homogeneous and non-homogeneous catalysts. Non-homogeneous catalysts present reactions in different phases (Phase) (e.g., solid catalyst in a liquid mixture), while homogeneous catalysts present reactions in the same phase (e.g., liquid catalyst in a liquid mixture). 

A simple non-homogeneous catalytic reaction involves the adsorption of reactants (or zh-ch:substrate; zh-tw:acceptor) onto the surface of the catalyst, where the bonds within the reactants are very weak resulting in the creation of new bonds, but then the products emerge because the bonds between the products and the catalyst are not strong. Many structural positions are known for the different possibilities of adsorption reactions occurring for surface reactions.

A substance that speeds up or slows down the rate of a chemical reaction simply by its presence, without changing its own composition or quality, is called a catalyst. When the catalyst is in the same homogeneous gas or liquid phase as the reactants, it is called single-phase catalysis; when the catalyst is in different phases from the reactants, it is called multi-phase catalysis.

A catalyst that speeds up a chemical reaction is called a positive catalyst; a catalyst that slows down a chemical reaction is called a negative catalyst. For example, the hydrolysis of esters and polysaccharides, commonly used inorganic acid as a positive catalyst; sulfur dioxide oxidation for sulfur trioxide, commonly used as a positive catalyst for vanadium pentoxide, this catalyst is a solid, the reactants are gases, the formation of multi-phase catalysis.

Therefore, vanadium pentoxide is also called catalyst or contact agent; edible fats and oils to add 0.01% ~ 0.02% n-propyl gallate, it can effectively prevent souring, in Here, n-propyl gallate is a negative catalyst (also called retarder or inhibitor).