Abstract
In the presence of the Au/Al2O3, Au-MOx/Al2O3, and MOx/Al2O3 (M = Fe, Co, Ag, and Zr) catalysts, supercritical ethanol is converted to butan-1-ol in 3–4 times higher yields than the yields of conversion of gaseous ethanol. At 275 °C, the MOx/Al2O3 samples convert 4–6% of supercritical ethanol with 0.5–7% selectivity to butan-1-ol. The activity of Au/Al2O3 towards butan-1-ol formation in comparison with oxide samples is 100 times higher. This is explained by Au0-Al2O3 interfaces formed by supported (Au0)n particles. The sintering of (Au0)n particles during prolonged experiments results in a decreased content of Au0-Al2O3 interfaces and deactivation of the Au/Al2O3. Modification of Au/Al2O3 with MOx species stabilizes 3-nm Au0 phase, and the Au-MOx/Al2O3 samples demonstrate sustained activity during sequential runs. The electron transfer from gold to Fe, Co, and Ag oxides results in generation of Au+ species. The Au-FeOx/Al2O3, Au-CoOx/Al2O3, Au-Ag/Al2O3 samples possessing Au0-Au+-Al2O3 interfaces show better performance towards butan-1-ol formation than Au/Al2O3 and Au-ZrOx/Al2O3, which possess exclusively Au0-Al2O3 interfaces. The causes for the promotional effect of Au+ species are proposed and discussed. For the most promising 0.2%Au-0.06%FeOx/Al2O3 catalyst, 21% conversion of ethanol with 70% selectivity to butan-1-ol is observed at 275 °C. This performance is higher than the performance of Pt-Re/Al2O3, Pd/Al2O3, and Ni-Mo/Al2O3 reference catalysts.
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