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

Abstract

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.