Supercritical CO2 is used as an antisolvent to precipitate out nanostructured homogeneous mixtures of Cu2+ and Mn3+ with crystallites of 10–20 nm in diameter. Following calcination, this material forms a crystalline tetragonal spinel, CuMn2O4, with a branched chainlike structure with a length of 160–200 nm and diameters of approximately 40 nm. This new material is more than twice as active per unit surface area as the conventionally prepared hopcalite catalysts for the oxidation of carbon monoxide. This is the first time that homogeneous mixed oxides have been formed using this method.

A series of Pt-based catalysts were synthesised and investigated for ambient temperature CO oxidation with the aim to increase catalytic activity and improve moisture resistance through support modification. Initially, bimetallic PtPd catalysts supported on alumina were found to exhibit superior catalytic activity compared with their monometallic counterparts for the reaction. Following an investigation into the effect of Pt/Pd ratio, a composition of 0.1% Pt/0.4% Pd was selected for further studies. Following this, SnO2/Al2O3 supports were synthesised from a variety of tin oxide sources. Catalytic activity was improved using sodium stannate and tin oxalate precursors compared with a traditional tin oxide slurry. Catalytic activity versus tin concentration was found to vary significantly across the three precursors, which was subsequently investigated by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX).