The manufacture of sulphuric acid by the contact process involves the catalyst (a) \(\mathrm{Ag}_{2} \mathrm{O}\) (b) \(\mathrm{CdO}\) (c) \(\mathrm{V}_{2} \mathrm{O}_{5}\) (d) Platinum coated graphite

The manufacture of sulphuric acid is a cornerstone of the chemical industry, given its numerous applications in the production of fertilizers, batteries, and various chemical processes. The Contact Process is the most widely used method for producing sulphuric acid on an industrial scale. It involves several steps, starting from the burning of sulphur or sulphide ores to produce sulphur dioxide (SO2).

The sulphur dioxide is then subjected to a two-stage oxidation to form sulphur trioxide (SO3). First, it is purified and dried, then it is passed over a catalyst at high temperatures to facilitate the oxidation. Synchronous with these chemical reactions, there are careful controls on temperature and pressure, as these conditions critically influence the process efficacy. The final stage involves the absorption of sulphur trioxide in water to produce concentrated sulphuric acid, a sequence that must be meticulously managed to avoid forming a hazardous mist of acid.

Sulphur dioxide oxidation is a pivotal step in the Contact Process where the gas is converted into sulphur trioxide (SO3), the direct precursor to sulphuric acid. For this oxidation to occur efficiently, it is performed at a temperature of about 450°C and a pressure close to atmospheric.

This carefully managed reaction is accomplished in a series of converter towers packed with a catalyst that promotes the oxidation without being consumed by the reaction. The catalyst's role is to lower the activation energy required for the chemical reaction to proceed, thereby making the process faster and more economically feasible. To maximize the conversion of SO2 to SO3, excess oxygen is often used, and the reaction may be conducted in multiple stages, allowing for intermediate cooling and removal of the formed SO3.

Vanadium(V) oxide (V2O5) serves a special role in the Contact Process as it is the catalyst that enables the oxidation of sulphur dioxide to sulphur trioxide. While platinum used to be the catalyst of choice due to its high efficiency, it has largely been replaced by V2O5 because of the cost implications; vanadium(V) oxide is considerably cheaper and also has a longer working life.

The catalyst, often in the form of pellets or a fine powder, is housed within the converter towers where the gas mixture flows through. Vanadium(V) oxide is particularly durable against poisoning by impurities, which ensures a steady catalytic action over extended periods. It exhibits this activity due to its ability to transfer oxygen atoms efficiently and revert to its original state, ready for further cycles of reaction. Furthermore, the catalyst can be regenerated if necessary, underscoring its economic and practical advantages in large-scale sulphuric acid production.