The chemical reaction carried out under the action of a catalyst is called a catalytic reaction. In a chemical reaction, some of the chemical bonds of the reaction molecule must be dissociated and form new chemical bonds, which requires a certain activation energy. In some systems where chemical reactions are difficult to occur, the addition of a third substance (catalyst) that contributes to the chemical bond rearrangement of the reactive molecules can reduce the activation energy of the reaction, thereby accelerating the chemical reaction and controlling the selectivity and stereoregularity of the product.
Figure 1. The schematic of catalytic reaction
Just as shown in Figure 1, according to the Arrhenius formula k=A*e-Ea/RT(k is the rate constant for the reaction; A referred to as the pre-exponential factor/Arrhenius constant, and its unit is the same with k; Ea is the activation energy of the reaction, and its unit is coke (J) or kilojoule (kJ), which is considered a constant when the temperature varies little; R is a gas constant; T is the temperature under the absolute temperature scale, and its unit is Kelvin (K)), the Ea value is reduced due to the catalyst participating in the reaction, so that the reaction rate is significantly increased.
There are also some reactions. After the catalyst participates in the reaction, the activation energy Ea value does not change much, but the pre-exponential factor A value increases significantly (or is explained as the activation entropy increases), which also leads to an increase in the reaction rate.
A catalyst is a chemical that changes the reaction rate of a chemical reaction without changing the thermodynamic equilibrium position of the chemical reaction and is not significantly consumed by the chemical reaction itself. It is estimated that 90% of commercially produced chemical products involve catalysts at certain stages of their manufacturing process. Adding a catalyst to the reaction can achieve the following effects:
According to the reaction mechanism, the catalytic reaction can be divided into acid-base type catalytic reaction and redox type catalytic reaction.
According to reaction type classification, it can be divided into hydrogenation, dehydrogenation, oxidation, carbonylation, polymerization, halogenation, cracking, hydration, alkylation, isomerization, and the like.
According to the phase state of the reaction, it can be divided into homogeneous catalytic reaction and heterogeneous catalytic reaction. In the homogeneous catalytic reaction, organic catalysis is the main, and in the heterogeneous catalytic reaction, electrocatalysis is the main one.
Phase Transfer Catalysts