Heterogeneous Catalysis

Heterogeneous catalysis is a process in which the phase of the catalysts differs from the phase of the reactants or products. In comparison, homogeneous catalysis occurs when the reactants, products, and catalysts reside in the same phase. Not only does phase discriminate between solid, liquid, and gas components, but also between immiscible mixes (e.g., oil and water) or any interface exists. Heterogeneous catalysis is essential because it permits rapid, large-scale manufacturing and the synthesis of selected products. Catalysis contributes around 35% of the world’s GDP. This article will describe everything about heterogeneous catalysis, including its processes and applications.

Types of catalyst in Chemistry

There are two types of catalyst in Chemistry: homogeneous and heterogeneous catalysis. The catalyst is different from the reactants in a heterogeneous reaction. However, the catalyst and reactants are in the same phase in a homogeneous reaction. When chemists observe a combination and see a border between two components, this indicates that those substances are in separate stages. For example, two phases exist in a combination consisting of a solid and a liquid. However, because there is no visible border between the phases in combining several chemicals in a single solution, the mixture consists of just one phase.

Heterogeneous Catalysis: What is it?

Numerous catalytic reactions do not involve the coexistence of the catalyst and the reactants in the same phase—the state of matter. These types of catalytic processes are heterogeneous catalytic reactions. They may occur at the surface of a solid catalyst and include either gasses or liquids or both. Because the surface is the reaction site, chemists generally prepare it to produce a high surface area per catalyst unit. Many kinds of metals and medical compliments are helpful in modern heterogeneous catalysis.

Heterogeneous Catalysis Process

Scientists achieve this process by using a catalyst in a phase distinct from the reactants. Typical instances utilize a solid catalyst and either liquids or gasses as reactants. As previously noted, the majority of cases of heterogeneous catalysis follow a similar pattern: At active sites, one or more of the reactants perform absorption into the catalyst’s surface. Adsorption is the process by which something adheres to a surface. It is not synonymous with absorption, which occurs when one substance gets absorbed into the structure. An active site is a surface region that is highly effective in adsorbing and reacting with molecules. The catalyst’s surface interacts with the reactant molecules, increasing their reactivity. It may entail direct interaction with the surface or weakening the links between the molecules attached. The response takes place. Both reactant molecules connect to the surface at this point, or one may be attached and struck by the other as it moves freely through the gas or liquid.

Desorbed Product Molecules

Desorption is the process through which product molecules separate. This process frees up the active site for another group of molecules to connect. A suitable catalyst is able to absorb reactant molecules which helps in starting the reaction. But it is not strong enough, so product molecules adhere to the surface permanently. For example, silver is ineffective as a catalyst because it does not create strong enough bonds with reactant molecules. On the other hand, Tungsten is an ineffective catalyst due to its high adsorption capacity.

Heterogeneous Catalyst Example:- The hydrogenation of a carbon-carbon double bond is a heterogeneous catalyst example. The reaction between ethene and hydrogen in a nickel catalyst is the simplest example of this. In reality, this reaction is futile since it converts the immensely valuable ethene to the comparatively inert ethane. However, any chemical having a carbon-carbon double bond will undergo the same reaction. One important industrial use is the hydrogenation of vegetable oils to produce margarine. It similarly includes reacting the vegetable oil’s carbon-carbon double bond with the hydrogen in the presence of a nickel catalyst. The nickel surface absorbs ethane components. As a result, the double bond between the carbon atoms breaks apart. The carbon is bonded to the nickel surface using electrons. Additionally, hydrogen molecules also come into absorption on the nickel’s surface. It results in the disintegration of hydrogen molecules into atoms. These are movable on the nickel’s surface. Suppose a hydrogen atom diffuses close to one of the bonded carbons. In that case, the bond between the carbon and the nickel breaks apart, and the carbon becomes hydrogen-bonded. That end of the original ethene has now separated from the surface. Moreover, the opposite will soon do the same. In this example, one of the hydrogen atoms establishes a connection with the carbon, and this bond also breaks free. As a result, there is no room on the nickel’s surface for fresh reactant molecules to undergo the whole process again.

Catalytic Converters

Catalytic converters convert harmful compounds found in car exhausts. Such as carbon monoxide and different nitrogen oxides, to more benign molecules such as carbon dioxide and nitrogen. They use high-priced metals such as platinum, palladium, and rhodium as heterogeneous catalysts. Thin layers of metal are placed onto a ceramic honeycomb. It increases the surface area and minimizes the quantity of metal utilized. Catalyst poisoning may have a detrimental effect on catalytic converters. It occurs when material that is not a reaction component is heavily adsorbed onto the catalyst’s surface, blocking the reaction’s regular reactants from accessing it. Lead is a well-known catalyst toxin that has its use in catalytic converters. It coatings the honeycomb with costly metals and renders it inoperable. Sulfur dioxide transfers into sulfur trioxide during the Contact Process used to manufacture sulphuric acid. The vanadium(V) oxide oxidizes the sulfur dioxide to sulfur trioxide. The vanadium(V) oxide turns into vanadium(IV) oxide throughout the procedure. The oxygen then reoxidizes the vanadium(IV) oxide. It is how a catalyst can modify during heterogeneous catalysis. However, it will be chemically identical to when it began after the process.

Conclusion

As shown in the case of heterogeneous catalysis, expectations indicated manipulating the elemental composition. Moreover, the structure of an active metal oxide phase can finally accomplish the goal of selectivity in hydrocarbon transformation. There are several advantages to heterogeneous catalysis. For one thing, heterogeneous catalysts may be easily isolated from a reaction mixture using filtering. In this manner, costly catalysts can efficiently recover, critical for industrial production operations.