The phase analyses of uranium oxides and supported gold catalysts were performed on a Shimadzu-6100 X-ray powder diffractometer with a monochromatic copper Kα radiation operated at 40 kV and 30 mA. The crystalline phase was identified according to the JCPDS pow- der diffraction file cards.
The textural property of each sample was measured by isothermal adsorption–desorption of nitrogen using a Quantachrome NOVA 3000e automated surface area and pore size analyzer. The specific sur- face area was determined by using nitrogen adsorption data from the relative equilibrium pressure interval of 0.03 b P/P0 b 0.3, where P is the equilibrium nitrogen pressure and P0 is the saturation nitrogen pressure, according to Brunauer–Emmett–Teller method. The average pore radius and the pore size distribution were calculated from the cor- responding nitrogen isotherm using Barret–Joyner–Halenda method.
The H2 TPR profiles of UO3, Au/UO3 and AuU3O8 samples were obtained in TP-5000 multifunction adsorption instrument. Prior to the reduction, 50 mg sample was baked at 60 °C for 2 h and then cooled down to room temperature in pure nitrogen and subsequently switched in the reducing gas of 10% hydrogen in argon at 20 mL/min. After the baseline became smooth, the temperature was linearly raised to800 °C at 10 °C/min. The 5A molecular sieve was mounted in the gas line to remove water formed during the reduction prior to going into the thermal conductivity detector.
XPS analyses of Au/UO3 and Au/U3O8 samples were finished on a VG ESCA 210 X-ray photoelectron spectrometer using Mg Kα radia- tion with an energy of 1253.6 eV and a residual gas pressure of 2.7 × 10− 6 Pa in the analysis chamber. The binding energy reference ofAu4f,U4f,andO1swastakenat285.0eVfortheC1speakarising from adventitious carbon. The analyzer was operated in constant an- alyzer energy mode. The surface gold atomic concentration of each sample was derived from corresponding peak area.