Support effects on properties of Ce-Zr mixed oxide-supported gold catalysts in oxidation of methanol

Ce-Zr oxide-supported nano-sized Au catalysts Au/Ce1-xZrxO2 (x = 0, 0.2, 0.4, 0.6, 0.8) were prepared by a deposition-precipitation method. Their catalytic properties were examined in both the combustion of methanol and the selective oxidation of methanol to methyl formate. The composition and structure of the catalysts were characterized by complementary methods including nitrogen physisorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. Their acidity and basicity were probed by CO2 and NH3 temperature-programmed desorption and also Fourier transform infrared spectroscopy for CO adsorption. The characterization results showed that the catalysts possessed similar particle size and phase of the Ce1-xZrxO2 supports, and their Au nanoparticles were of around 3.0 nm mainly in the state of Au-0. In the CH3OH combustion reaction (1% CH3OH + 14% O-2), the activity of the Au/Ce1-xZrxO2 catalysts decreased with decreasing the Ce contents in the Ce1-xZrxO2 supports. Similar change was also found in the methanol selective oxidation (6% CH3OH + 3% O-2), while the selectivity to methyl formate increased with decreasing the Ce contents. Such changes in the catalytic activity of the Au/Ce1-xZrxO2 catalysts were in positive parallel with their oxygen storage capacity values, which reflect the number of the lattice oxygen atoms active for the methanol oxidation. The support effects on the selectivity for methyl formate were clear not due to effects of the supports on the acid-base properties of the catalysts but to the effects on the active lattice oxygen atoms on catalyst surfaces and consequently their reducibility. Such understanding on the support effects provides useful information for design of oxide-supported Au catalysts with improved activity or selectivity for the targeted oxidation reactions.