In a catalysed process, the catalyst usually reacts chemically with the reactants but is eventually regenerated, thus the catalyst level remains constant. Because the catalyst isn’t consumed, each molecule of catalyst can cause the transformation of a large number of reactant molecules. The number of molecules changed every minute by a single molecule of active catalyst can be as high as several million. Show
The distribution of products may be changed by the employment of a catalyst that selectively accelerates one reaction relative to the other when a given material or a mixture of substances experiences two or more simultaneous reactions that generate distinct products (s). A certain reaction can be induced to occur to the point that it practically excludes another by using the right catalyst. This type of selectivity is used in a lot of significant catalytic applications. What is Catalyst?Catalyst is a term that we have come across several times while studying chemistry, particularly when learning about chemical reactions. While some chemical reactions occur quickly, others take a long time and necessitate the use of additional materials or effort. This is where a catalyst can help. When heated to a high temperature, potassium chlorate slowly decomposes, releasing dioxygen. The decomposition takes place between 653 and 873K as, 2KClO3 → 2KCl + 3O2 When a small amount of manganese dioxide is added, however, the decomposition occurs at a much lower temperature range, i.e., 473-633K, and at a much faster rate. In terms of mass and composition, the manganese dioxide that has been added remains unchanged. Similarly, the mere presence of a foreign substance can alter the rates of a variety of chemical reactions. Berzelius conducted the first systematic study of the effect of various foreign substances on the rates of chemical reactions in 1835.
Characteristics of Catalyst
Types of Catalysts
Types of CatalysisCatalysis can be broadly divided into two groups: Homogeneous catalysis Homogeneous catalysis occurs when the reactants and the catalyst are in the same phase. Some examples of homogeneous catalysis are as follows:
2SO2 (g) + O2(g) → 2SO3 (g) (in the presence of gaseous NO)
CH3COOCH3 (l) + H2O(l) → CH3COOH(aq) + CH3OH(aq) (in the presence of aqueous HCl)
Heterogeneous catalysis Heterogeneous catalysis refers to the catalytic process in which the reactants and catalysts are in different phases. The following are some examples of heterogeneous catalysis:
2SO2 (g) → 2SO3 (g) (in presence of Pt(s))
4NH3 (g) + 5O2 (g → 4NO(g) + 6H2O(g) (in presence of Pt(s))
Vegetable oils(l) + H2 (g) → vegetable ghee (s) (in presence of solid Nickel)
Adsorption Theory of Heterogeneous CatalysisThis theory explains how heterogeneous catalysis works. The adsorption theory of catalysis held that reactants in gaseous or solution form are adsorbed on the surface of the solid catalyst. The rate of reaction increases as the concentration of the reactants on the surface increases. Because adsorption is an exothermic process, the heat of adsorption is used to increase the rate of the reaction. The catalytic action can be explained in terms of the formation of intermediate compounds. The modern adsorption theory is a synthesis of the intermediate compound formation theory and the old adsorption theory. The catalytic activity is concentrated on the catalyst’s surface. The mechanism consists of five steps:
This theory explains why the catalyst, even in small quantities, remains unchanged in mass and chemical composition at the end of the reaction. It does not, however, explain how catalytic promoters and catalytic poisons work. Important features of Solid Catalysts
Shape Selective Catalysis by ZeolitesShape-selective catalysis refers to a catalytic reaction that is influenced by the pore structure of the catalyst as well as the size of the reactant and product molecules. Because of their honeycomb-like structures, zeolites are excellent shape-selective catalysts. They are microporous aluminosilicates with a three-dimensional silicate network in which some silicon atoms are replaced by aluminium atoms, resulting in an Al–O–Si framework. The reactions that occur in zeolites are influenced by the size and shape of the reactant and product molecules, as well as the pores and cavities of the zeolites. They can be found in nature and synthesized for catalytic selectivity. In the petrochemical industry, zeolites are commonly used as catalysts for hydrocarbon cracking and isomerization. ZSM-5 is a significant zeolite catalyst used in the petroleum industry. It dehydrates alcohol to produce a mixture of hydrocarbons, which it then converts directly into gasoline (petrol). Sample QuestionsQuestion 1: How can a positive catalyst alter the reaction? Answer:
Question 2: What is the role of catalyst poison in Rosenmund reaction? Answer:
Question 3: What is the role of promoters in Haber’s process? Answer:
Question 4: What is autocatalysis? Answer:
Question 5: Give an example of a shape-selective catalyst. Answer:
Question 6: Define electrophoresis. Answer:
What are 3 types of catalyst?Catalysts can be categorized as homogeneous, heterogeneous, or enzymatic. Homogeneous catalysts exist in the same phase as the reactants, whereas heterogeneous catalysts exist in a different phase than the reactants.
What are the types of catalyst with example?A catalyst can be either solid, liquid or gaseous catalysts. Some of the solid catalysts include metals or their oxides, including sulphides, and halides. Semi-metallic elements such as boron, aluminum, and silicon are also used as catalysts.
What are the types of catalytic?Catalysts are primarily categorized into four types. They are (1) Homogeneous, (2) Heterogeneous (solid), (3) Heterogenized homogeneous catalyst and (4) Biocatalysts.
How many types of catalysts are there?Catalysts can be divided into two main types - heterogeneous and homogeneous. In a heterogeneous reaction, the catalyst is in a different phase from the reactants.
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