What Is a Sulfuric Acid Catalyst?
Refers to catalysts that have a catalytic function due to the acidity and basicity of the substance. They can transform the reactant into an ionic activated transition state, thereby catalyzing.
Acid-base catalyst
- Due to the acidity and basicity of the substance
- According to the nature of acid and base can be divided into two categories:
- Solid acid: Generally considered to be a solid capable of chemisorbing an alkali, it can also be understood as a solid capable of changing the color of an alkaline indicator thereon. Solid acids are divided into Bronsted acids and Lewis acids. The former is abbreviated as B acid and the latter is abbreviated as L acid. The definition of B-acid and B-base is: all that can give protons are acids, and those that can accept protons are all bases, so B-acid and B-bases are also called proton acid-bases. L acid and L base are defined as: all that can accept electron pairs are acids, and all that can give electron pairs are bases, so L acid L bases are also called aprotic acid bases.
- B acid strength refers to the ability to give protons; L acid strength refers to the ability to accept electron pairs.
- Acid-base catalyst
- If a solid acid surface can adsorb an undissociated base and transform it into the corresponding conjugate acid, and the transformation is transferred from the solid acid surface to the adsorbed base by means of protons, that is: [B] a and [ BH +] a is the concentration of unresolved base (base indicator) and conjugate acid, respectively. pKa is the negative logarithm of the dissociation equilibrium constant of the conjugate acid BH +, similar to pH. If the transition is to the surface of the solid acid by means of the electron pair that adsorbs the base, that is [A: B] is the concentration of the complex AB formed by the adsorption base B and the electron pair acceptor A. The smaller the H0, the stronger the acidity.
- Acid amount: The amount of acid on a solid surface, usually expressed as the number of millimoles of acid sites per unit weight or unit surface area, that is, m mol / wt or m mol / m 2. The amount of acid is also called acidity, which refers to the concentration of acid.
- The strength of a solid base is defined as the ability of a surface-adsorbed acid to convert to a conjugate base, and it is also defined as the ability of a given electron on the surface to adsorb an acid. The amount of alkali is expressed by the number of millimoles of alkali per unit weight or unit surface area, that is, m mol / wt or m mol / m 2. The amount of alkali is also called alkalinity, which means the concentration of alkali center. Acid-base pair synergy: Certain reactions, although known to be catalyzed by acid sites on the catalyst surface, have more or less synergistic effects. Catalysts with such acid-base pair coordination sites sometimes show better activity, and even their acid-base strength is lower than that of a single acid or base site. For example, ZrO2 is a weak acid and weak base, but the activity of splitting the bond of CH is higher than the more acidic SiO2-Al2O3, and also higher than the more basic MgO. The synergistic effect of the acid and base positions is very advantageous for some specific reactions and therefore has higher selectivity. This type of catalyst is called acid-base bifunctional catalyst. Solid super acid and super base: If the strength of solid acid exceeds the strength of 100% sulfuric acid, it is called super strong acid. Because the acid strength of 100% sulfuric acid is represented by the Hammeett acid strength function as H0 = -11.9, solid solid strength H0 <-11.9 is referred to as a solid superacid or superacid.
- Solid super
- Acid-base catalyst