## 2 Materials and Methods  
### Catalyst Synthesis  
Monometallic Au (2 wt.%) and Pd (1 wt.%) and bimetallic Pd (1 wt.%)-Au (2 wt.%) catalysts were prepared over alumina-supported ceria (30 wt.%) and alumina-supported Y-doped ceria (1 wt.% Y\({}_{2}\)O\({}_{3}\) in respect to the amount of ceria). Impregnation (IM) and mechanochemical mixing (MM) were used for synthesis of CeO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) and Y-CeO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\). The wet impregnation of alumina (Sasol) was carried out with aqueous solution of Ce(NO\({}_{3}\))\({}_{3}\)\(\cdot\)6H\({}_{2}\)O by stirring at room temperature for 4 h. The water was removed in a rotary evaporator at 70 \({}^{\circ}\)C. Then mixed oxides were calcined in air at 400 \({}^{\circ}\)C for 2 h. In order to study the effect of doping with yttrium, the procedure was repeated using aqueous solution of Y(NO\({}_{3}\))\({}_{3}\)\(\cdot\)6H\({}_{2}\)O. The MM route involved: (i) well mixing of alumina and the calculated amount of cerium hydroxide (prepared by precipitation of Ce(NO\({}_{3}\))\({}_{3}\)\(\cdot\)6H\({}_{2}\)O with K\({}_{2}\)CO\({}_{3}\)) and fully grinding for 30 min in agate mortar; (ii) calcination at 400 \({}^{\circ}\)C for 2 h. Alumina-supported Y-doped ceria solids were prepared by the same way with addition of 1 wt.% commercial Y\({}_{2}\)O\({}_{3}\) (Sigma-Aldrich).  
Gold-based catalysts were prepared by deposition-precipitation on supports, preliminary subjected to ultrasound treatment in water. The interaction between HAuCl\({}_{4}\)\(\cdot\)3H\({}_{2}\)O and K\({}_{2}\)CO\({}_{3}\) was carried out at temperature = 60 \({}^{\circ}\)C, pH = 7, stirring speed = 250 rpm. After ageing at the same temperature within 1 h, the solids were filtered and washed until removal of chlorine ions. Thermal treatment was performed in air at 400 \({}^{\circ}\)C for 2 h. These samples were denoted as Au/CeAl and Au/CeAl IM (IM means method of support preparation), and respectively Au/YCeAl and Au/YCeAl IM for Y-modified supports. Gold-containing catalysts on ceria (Au/Ce) and on alumina (Au/AI) were prepared for comparative purposes. Bare ceria was prepared by precipitation of Ce(NO\({}_{3}\))\({}_{3}\)\(\cdot\)6H\({}_{2}\)O with K\({}_{2}\)CO\({}_{3}\) at constant pH 9 and temperature 60 \({}^{\circ}\)C, aging of the precipitate at the same temperature for 1 h and washing until removal of NO\({}_{3}\)\({}^{-}\) ions. Then, drying in vacuum at 80 \({}^{\circ}\)C and calcination in air at 400 \({}^{\circ}\)C for 2 h were carried out.  
Pd-containing samples were prepared following the same procedure, deposition-precipitation, as described for gold catalysts, using Pd(NO\({}_{3}\))\({}_{2}\)\(\cdot\)xH\({}_{2}\)O as precursor. Based on comparison of catalytic activity of gold-based catalysts (see below in Results), Pd-containing catalysts were synthesized only on supports prepared by MM method. Notation of the samples was Pd/CeAl and Pd/YCeAl. Samples on ceria and alumina were labeled Pd/Ce and Pd/AI, respectively.  
Bimetallic Pd-Au catalysts were prepared by sequential deposition-precipitation. Pd was deposited on the preliminary prepared and calcined Au/CeAl and Au/YCeAl (on MM-prepared oxides). Calcination in air at 400 \({}^{\circ}\)C for 2 h was repeated after Pd deposition. The samples were denoted as Pd-Au/CeAl, Pd-Au/YCeAl, Pd-Au/Ce and Pd-Au/Al.