Understanding the effect of thermal treatments on the structure of CuAu/SiO2 catalysts and their performance in propene oxidation

The synthesis and catalytic application of supported CuAu is discussed. Different thermal treatments of a dried precursor of copper nitrate and tetrachloroauric acid on silica lead to catalysts with significantly different structures and properties. Direct calcination gives a catalyst which contains very large gold ensembles with minimal interaction with the copper present. Hydrogen reduction of the dried precursor leads to the formation of copper-gold alloy nanoparticles. Subsequent high temperature calcination de-alloys the copper from the gold to a significant extent. The presence of gold stabilises the formation of Cu+ on this catalyst. The activity and selectivity observed in the oxidation of propene with molecular oxygen, with or without co-fed hydrogen, depends on the pre-treatment, reaction conditions and the ratio of copper to gold in the catalyst. A number of different catalytic active sites are identified and discussed.