Second, the catalytic principle:
1. The phenomenon that the chemical reaction rate is accelerated or slowed down due to the intervention of the catalyst is called catalysis. In the catalytic reaction, the chemical interaction between the catalyst and reactants changes the reaction path, thus reducing the activation energy of the reaction, which is why the catalyst can improve the reaction rate. For example, chemical reaction A+B→AB needs activation energy E. After adding catalyst C, the reaction is divided into two steps, and the required activation energies are F and G, respectively, where both F and G are less than E. ..
2, A+C → AC-AC+B → AB+C, the activation energies of these two steps are much smaller than the e value. According to Arrhenius formula k=Ae-E/RT, due to the participation of catalyst in the reaction, the e value decreases, thus the reaction rate is significantly improved. There are also some reactions. After the catalyst participated in the reaction, the activation energy e value changed little, but the pre-exponential factor a value increased obviously (or explained by the increase of activation entropy), which also led to the acceleration of the reaction rate.
Three. Catalytic type:
1, homogeneous catalysis. In-phase catalysis of catalyst and reactant, such as homogeneous acid-base catalysis and homogeneous complex catalysis. Homogeneous catalysis is mostly carried out in liquid phase. Homogeneous catalyst has uniform active center, high selectivity and few side reactions, but it is difficult to separate, recover and regenerate the catalyst.
2. Heterogeneous catalysis. The catalysis of two-phase interface. Usually, the catalyst is a porous solid, and the reactant is a liquid or gas. In heterogeneous catalytic reaction, solid catalyst chemically adsorbs reactant molecules, activates reactant molecules, reduces reaction activation energy and accelerates reaction rate. The surface of solid catalyst is not uniform, and only some points chemisorb reactant molecules, which are called active centers. Catalysis in industrial production mostly belongs to heterogeneous catalysis.
3. Biocatalysis. The catalytic reaction of an organism under the action of an enzyme. Enzyme catalysis has the characteristics of high selectivity, high catalytic activity and mild reaction conditions, but it is greatly influenced by temperature, pH value of solution, ionic strength and other factors.
4. Automatic catalysis. Autocatalysis of reaction products. In some reactions, the products or intermediates of some reactions have catalytic effect, which greatly speeds up the reaction after an induction period. Autocatalysis is one of the necessary conditions for chemical oscillation.
5. Others include electrocatalysis, photo-assisted catalysis and photoelectrocatalysis.