Gold supported on Cu-Mg-Al-mixed oxides: Strong enhancement of activity in aerobic alcohol oxidation by concerted effect of copper and magnesium

Gold nanoparticles were deposited on mixed oxides containing Cu, Mg, and Al in different ratios. The mixed-oxide supports were prepared by flame spray pyrolysis (FSP), resulting in agglomerated primary nanoparticles in the 10-15 nm range, onto which 6- to 9-nm gold particles were deposited by means of deposition-precipitation. The mixed-oxide-supported Au catalysts with noble metal loading of 0.6 +/- 0.17 wt% were investigated concerning their structural properties and tested in the aerobic liquid-phase oxidation of I-phenylethanol to phenyl-methyl ketone affording TOFs up to 1300 h(-1). The catalytic tests showed that the activity of these catalysts depends strongly on the composition of the support, with Cu and Mg being crucial components. Strongly enhanced catalytic activity was observed for gold supported on a ternary mixed oxide containing Cu, Mg, and Al at the molar ratio of 5:1:2. Extension of the catalytic tests to various structurally different alcohols indicated that the ternary mixed-oxide-supported gold catalyst has excellent catalytic properties in the aerobic oxidation of a broad range of structurally different alcohols, affording selectivities >= 98%. XANES revealed both reduced and oxidized Au species on the ternary mixed-oxide supports before and after the reaction. CO2 adsorption from the liquid phase combined with in situ ATR-IR and modulation excitation spectroscopy was applied to investigate differences in the basic surface properties of the mixed oxides. Monodentate and bidentate carbonates were identified, the former being dominant on ternary Cu-containing supports. (c) 2007 Elsevier Inc. All rights reserved.