A Single Source Precursor Route to Group 13 Homo- and Heterometallic Oxides as Highly Active Supports for Gold-Catalyzed Aerobic Epoxidation of trans-Stilbene

A new Mitsubishi-type of star-shaped homoleptic derivative of indium(III), In4(mdea)6 (2, mdeaH2 = N-methyldiethanolamine), was synthesized by the chloro–aminoalkoxo exchange reaction of a heteroleptic complex In6Cl6(mdea)6 (1) and used as a facile single source molecular precursor for the sol–gel preparation of high surface area indium oxide. Successful deposition of gold nanoparticles (1 wt.-%) of average size 3.3 nm on the above metal oxide by using HAuCl4·3H2O afforded a highly efficient Au/In2O3 catalyst for the aerobic epoxidation of trans-stilbene at low temperature. The above single source precursor approach was further extended to obtain other group 13 homo- and heterometallic oxides, namely, α-Ga2O3, β-Ga2O3 and Al4Ga2O9, as highly active supports for gold catalysts. The obtained Au/M2O3 (M = Ga, In) and Au/Al4Ga2O9 catalysts were thoroughly characterized by using several physicochemical techniques such as XRD, high resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). A comparative study of the above catalysts for the model aerobic oxidation of stilbene in methylcyclohexane was undertaken.