What is the purpose of the${\mathbf{WO}}_{\mathbf{3}}$ and Cu in Figure 27-8?

• The loss of electrons by a molecule, atom, or ion during a reaction is referred to as oxidation.When the oxidation state of a molecule, atom, or ion increases, this is referred to as oxidation.
• Reduction is a half-reaction in which a chemical species reduces its oxidation number by gaining electrons. The other half of the reaction involves oxidation, which involves the loss of electrons.

The purpose of the ${\mathrm{WO}}_3$and Cu is explained below.

${\mathrm{WO}}_3$- oxidation catalyst

Catalyzes the combustion of carbon to carbon dioxide (oxidation) in the presence of excess oxygen in the atmosphere

Cu - reduction catalyst

Catalyzes the conversion of ${\mathrm{SO}}_3$to ${\mathrm{SO}}_2$ (reduction) and also removes the excess oxygen via the reactions below

$$\begin{gathered} \mathrm{Cu}+{\mathrm{SO}}_3\to {\mathrm{SO}}_2+\mathrm{CuO} \\ 2\mathrm{Cu}+{\mathrm{O}}_2\to 2\mathrm{CuO} \end{gathered}$$

Therefore the purpose of the ${\mathrm{WO}}_3$and is explained clearly.