The presence of iron(II) impurities hinders the leaching and purification of magnesium ores. The most viable technological solution is to oxidise Fe²⁺ to Fe³⁺, which then precipitates as goethite. However, this process requires the development of new catalysts for use in highly acidic media. This study demonstrates that the Pt^0.25/CeO₂⁵/TiO₂ catalyst is highly effective at oxidising Fe²⁺ in 0.3 M HNO₃, outperforming samples supported on pure titanium dioxide or cerium dioxide. The rate constant is 0.304 L/(mol·min) at room temperature. Notably, the activation energy is only 10.7 kJ/mol, which is over five times lower than that of the non-catalytic process. This result was achieved by selectively depositing platinum particles onto highly dispersed cerium dioxide particles (average size ~5 nm), synthesised using the sol–gel method, and then depositing them onto titanium dioxide. Using a hybrid mixed oxide support ensures a high density of oxygen vacancies at the interface between the platinum (Pt) and mixed cerium and titanium dioxide phases. The formation of abundant adsorbed oxygen species enhances the catalytic activity of the Pt^0.25/CeO₂⁵/TiO₂ catalyst. The catalyst Pt^0.25/CeO₂⁵/TiO₂ also reaches a plateau in terms of efficiency after a durability experiment, which is the highest among the other samples.