Key Differences Between Catalysts, Promoters, and Poisons
In a chemical reaction, when a substance is added to a solid catalyst to boost the rate of the reaction, that substance is called a promoter. A promoter in catalyst does not have a catalytic effect. Sometimes it interacts with the other components to change their chemical effect on the substance that had already catalyzed them. This interaction leads to changes in the crystal or electronic structures of the solid components.
Oxidising and reducing gases or liquids, metallic oxide catalyst, metallic ions are added to the catalyst or reaction before they are used. Examples of some promoters or activators are- during the manufacture of methyl alcohol, chromic oxide is used as a promoter from the water gas including catalyst zinc oxide. Similarly, when a little amount of molybdenum is added to finely divided iron, it increases the process of synthesis of ammonia and here molybdenum acts as a catalyst.
Difference Between Catalyst and Promoter
A catalyst is a material that does not change itself when the rate of the chemical reaction is increased. It participates in the reaction but does not react itself. A promoter, on the other hand, is a substance that helps in increasing the action of a catalyst. It does not have any catalytic value of itself.
For example, in the case of Haber's process, iron acts as a catalyst. When molybdenum is added to it, the efficiency of iron increases. Here, molybdenum acts as a promoter.
Difference Between Catalyst and Catalysis
The only difference between catalyst and catalysis is that a catalyst is a material that accelerates a chemical reaction but does not change itself and does not get it involved in the overall reaction whereas catalysis is the process of changing the rate of the reaction by involving a catalytic material in it.
[Image will be uploaded soon]
Promoter and Catalyst Poison
Let us now go through the difference between catalyst promoter and catalyst poison. The substance that destroys the catalyst activity only by its presence is called catalytic poison. For example, a small amount of arsenic oxide, if present in the reacting gas, will reduce platinized asbestos activity that is used as a catalyst for the manufacture of sulphuric acid.
Similarly, the presence of sulphuric acid or carbon dioxide will destroy the catalytic activity of iron in the synthesis of ammonia by Haber's process. Likewise, the presence of carbonic oxide in the platinum catalyst is used in the oxidation of hydrogen.
By increasing the temperature, the catalytic power of the catalyst will increase but after attaining a certain temperature its power will start decreasing. So, at a particular temperature, the catalytic activity of a catalyst will become maximum. This temperature is known as optimum temperature.
[Image will be uploaded soon]
Catalytic Promoters
To explain catalytic promoters, it is important to understand that a catalytic promoter is a material that is mixed with catalysts in small quantities to increase the efficiency of the catalyst. In other words, it helps to enhance the chemical reaction. These are also known as activators.
The promoters in catalyst increase the surface area stabilization that is present against crystal growth mechanical strength and sintering.
[Image will be uploaded soon]
Catalyst Promoter Definition
The catalyst usually works by giving an alternative way for the chemical reaction to occur. This reduces the activation energy by increasing the reaction rate. A catalyst promoter acts as an accelerator for the catalysts but it is not a catalyst by itself.
Catalysts are of Two Types: a positive catalyst that fastens the chemical reaction and a negative catalyst that slows down the reaction rate.
According to the theory of collision reaction, an effective collision occurs between the reacting molecules. For effective collision, the molecules must have a minimum amount of energy that is called activation energy to form activated complexes that mix to give product molecules. The catalyst gives a new way that contains a small amount of activation energy. So, the maximum number of effective collisions occurs in presence of a catalyst at the same temperature without a catalyst. So, a catalyst is highly essential to make the reaction faster.
FAQs on What Is a Catalytic Promoter in Chemistry?
1. What is a catalytic promoter in chemistry?
A catalytic promoter is a substance that, while having little to no catalytic activity itself, significantly enhances the efficiency and activity of a catalyst when added in small quantities. It does not initiate the reaction but works to improve the performance of the primary catalyst, leading to a faster reaction rate or better product yield.
2. What is a classic example of a catalytic promoter used in industrial chemistry?
A classic and important example is the use of molybdenum (Mo) or a mixture of potassium and aluminium oxides in the Haber's process for ammonia synthesis. In this process, finely divided iron (Fe) acts as the catalyst, while molybdenum acts as a promoter to increase the catalytic activity of the iron, ensuring a higher yield of ammonia at an economical rate.
3. How does a catalytic promoter actually increase the efficiency of a catalyst?
A catalytic promoter enhances a catalyst's efficiency primarily by modifying its physical and chemical properties. The most common mechanisms include:
- Increasing Surface Area: The promoter can prevent the catalyst particles from sintering (fusing together), thereby maintaining a larger surface area for the reaction to occur.
- Creating More Active Sites: It can change the crystal lattice structure of the catalyst, creating more defects or 'active sites' where reactant molecules can bind more effectively.
- Altering Electronic Properties: The promoter can influence the electronic structure of the catalyst, making it easier for it to facilitate the chemical reaction.
4. What is the key difference between a catalytic promoter and a catalytic inhibitor?
The key difference lies in their effect on the catalyst's activity. A catalytic promoter enhances or increases the activity of a catalyst, making the reaction faster. In contrast, a catalytic inhibitor (or poison) decreases or completely destroys the catalyst's activity. For example, in the Haber's process where molybdenum is a promoter, substances like hydrogen sulfide (H₂S) would act as an inhibitor, poisoning the iron catalyst and stopping the reaction.
5. Why are catalytic promoters so important in large-scale chemical manufacturing?
Catalytic promoters are crucial in industrial chemistry for economic and efficiency reasons. By enhancing the performance of a catalyst, they allow chemical reactions to be run under less extreme conditions (lower temperature or pressure), which saves energy and reduces operational costs. They also increase the reaction rate and can improve the selectivity of the catalyst, leading to a higher yield of the desired product and fewer unwanted by-products. This maximises output and minimises waste, making the entire process more sustainable and profitable.
6. Can any substance act as a promoter for any catalyst?
No, the action of promoters is highly specific. A substance that acts as a promoter for one particular catalytic reaction may have no effect or could even act as an inhibitor in another reaction. The choice of a promoter depends on the specific catalyst and the chemical reaction involved. This specificity is due to the complex chemical and physical interactions that must occur between the promoter, the catalyst, and the reactants to enhance the catalytic activity.
