Which catalyst converts sulfur dioxide into sulfur trioxide in the Contact process?

1. The Contact process starts by burning sulfur to give sulfur dioxide. 2. The sulfur dioxide is then oxidised with oxygen to sulfur trioxide. 3. That oxidation step uses a vanadium(V) oxide catalyst. 4. Treating the sulfur trioxide with water finally gives sulfuric acid. 5. Platinum is the catalyst of the Ostwald process, so it belongs to the making of nitric acid instead. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 14: The chemical industry_