Which of the following catalyst is used in Contact process?

V₂O₅

The correct answer is option 2. \(V_2O_5\).

The Contact process is a method used industrially to produce sulfuric acid (\( \text{H}_2\text{SO}_4 \)). This process involves the catalytic oxidation of sulfur dioxide (\( \text{SO}_2 \)) to sulfur trioxide (\( \text{SO}_3 \)), which is then absorbed in water to form sulfuric acid. Here's how the process works and why V2O5 (vanadium pentoxide) is used as the catalyst:

Process Overview

Formation of Sulfur Dioxide \((SO_2)\):  Sulfur dioxide is typically obtained by burning sulfur (\( \text{S} \)) or by roasting metal sulfide ores.

Catalytic Oxidation to Sulfur Trioxide \((SO_3)\):

Sulfur dioxide (\( \text{SO}_2 \)) reacts with oxygen (\( \text{O}_2 \)) in the presence of a catalyst to form sulfur trioxide (\( \text{SO}_3 \)):

\(2 \text{SO}_2 + \text{O}_2\overset{\text{catalyst}}{\longrightarrow} 2 \text{SO}_3 \)

The catalyst used in this step is vanadium pentoxide (\( \text{V}_2\text{O}_5 \)). Vanadium pentoxide acts as a heterogeneous catalyst, meaning it exists in a different phase from the reactants (solid catalyst with gaseous reactants). It helps lower the activation energy for the reaction, thus speeding up the conversion of \( \text{SO}_2 \) to \( \text{SO}_3 \).

Absorption of Sulfur Trioxide in Water:

The \( \text{SO}_3 \) produced in the oxidation step is then absorbed in concentrated sulfuric acid to form oleum (\( \text{H}_2\text{SO}_4 + \text{SO}_3 \)), which is subsequently diluted with water to produce sulfuric acid:

\(\text{SO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{S}_2\text{O}_7 \)

\(\text{H}_2\text{S}_2\text{O}_7 + \text{H}_2\text{O} \rightarrow 2 \text{H}_2\text{SO}_4\)

\(V_2O_5\) as the Catalyst:

High Catalytic Activity: Vanadium pentoxide (\( \text{V}_2\text{O}_5 \)) is chosen as the catalyst because it has a high catalytic activity for the oxidation of \( \text{SO}_2 \) to \( \text{SO}_3 \). It promotes the reaction by providing a surface where \( \text{SO}_2 \) and \( \text{O}_2 \) molecules can adsorb and react more easily.

Stability and Efficiency: \( \text{V}_2\text{O}_5 \) is stable under the reaction conditions of the Contact process and does not undergo significant decomposition or poisoning. This ensures that the catalyst remains effective over extended periods of operation.

Industrial Practicality: The choice of \( \text{V}_2\text{O}_5 \) is also practical from an industrial standpoint, balancing cost, efficiency, and durability in large-scale sulfuric acid production.

In summary, \(V_2O_5\) is the catalyst of choice in the Contact process due to its ability to facilitate the oxidation of sulfur dioxide to sulfur trioxide efficiently and reliably under industrial conditions.