ZrO
2-O and ZrO
2-N were prepared from ZrCl
4 following a preparation route of UiO-66 [
33], the resulting UiO-66 was calcined in air or NH
3 at 600 ℃ for 3 h to obtain ZrO
2-O (air) or ZrO
2-N (NH
3). The traditional zirconia (ZrO
2) was obtained by decomposing of ZrO
2 sol–gel solution [
34]. Ru was introduced by incipient wetness impregnation of zirconia with ruthenium(Ⅲ) nitrosyl nitrate solution. The diffraction peaks of tetragonal zirconia at 2
θ = 30.3, 34.6, 35.3, 50.3, 50.7, 59.4, 60.2, 62.9, 74.6 and 81.8° can be found in the XRD patterns of Ru/ZrO
2 and Ru/ZrO
2-O (
Fig. 1). However, besides the peaks of tetragonal zirconia, the new diffraction peaks at about 24.5, 28.2 and 31.6°, which are assigned to the monoclinic zirconia (PDF #81–1314) [
35-
37], can be found in the XRD patterns of Ru/ZrO
2-N. It can conclude that the tetragonal ZrO
2 is dominant phase in Ru/ZrO
2 and Ru/ZrO
2-O, while there are the mixed-phases of tetragonal and monoclinic ZrO
2 in Ru/ZrO
2-N. A similar conclusion on the difference in zirconia phases could be drawn from Rietveld analysis based on the as-prepared ZrO
2 supports (Fig. S1 in Supporting information). On the other hand, no characteristic diffraction peaks corresponding to Ru metal or Ru oxide are found, indicating that Ru species is well dispersed on support material. This result is in line with the observations of EDS mappings and TEM images (Figs. S2 and S3 in Supporting information). The results of temperature-programmed oxidation study of ZrO
2-O and ZrO
2-N show that there is a larger amount of carbon species on ZrO
2-O than that on ZrO
2-N (Fig. S4 in Supporting information). However, the differences in the amount of carbon species between Ru catalysts are slight because most unstable carbon would be removed during the heat treatment of Ru catalysts. As a consequence, elemental analysis shows that the carbon contents of Ru/ZrO
2-O and Ru/ZrO
2-N are 3.67 and 3.50 wt%, respectively (Table S1). A similar amount of carbon species remained on Ru/ZrO
2-O and Ru/ZrO
2-N is also confirmed by the result of Raman spectra (Fig. S5 in Supporting information), and two bands at 1345 (D band) and 1595 cm
−1 (G band), which are characteristic peaks of carbon [
38-
41], can be found in Raman spectra of Ru catalysts. The presence of carbon species leads to enhancement of the surface area for Ru catalysts, but no significant difference in the surface area can be found between Ru/ZrO
2-O and Ru/ZrO
2-N catalysts (Table S1 in Supporting information). Moreover, the Ru loadings are 5.55, 5.28 and 5.37 wt% for Ru/ZrO
2, Ru/ZrO
2-O and Ru/ZrO
2-H (Table S1), indicating that the variation in catalytic performances of Ru catalysts cannot be fully attributed to the change in Ru content.