## 3 Results and Discussion  
### Characterization  
To detect the surface properties of the as-prepared catalysts, X-ray photoelectron spectroscopy (XPS) was employed to examine the content and types of Au species. The results of Au contents of all prepared samples were simultaneously measured by ICP, as shown in Table 1 (and Figure S1 in Supporting Information). It can be seen that Au exists in the form of Au\({}^{0}\) and Au\({}^{x+}\) oxidation states with the relative intensities of Au\({}^{0}\) and Au\({}^{x+}\) being 41% and 59% respectively. Probably because the reduction at 150 \({}^{\circ}\)C is not so strong to reduce all the gold in the oxidized states, the gold is present also as Au\({}^{x+}\) in a larger amount. We found that this value of actual gold content examined by ICP is much higher than the surface gold content examined by XPS. It indicates that most of the Au nanoparticles moved into the interlayers of the clay. The actual gold contents of the Au-Ti/Na-ABen and Au-Ti-Ce/Na-ABen catalysts are much higher than that of Au/Ti-Na-ABen. This could be attributed to the surface gold content of Au/Ti-Na-ABen being higher than Au-Ti/Na-ABen and Au-Ti-Ce/Na-ABen. The results show that the Ti cross-linking compound could result in the gold moving into the interlayer space of bentonite and improving the actual gold content of the sample. Figure 1 shows the powder X-ray diffraction pattern of the catalyst. XRD was used to determine the crystalline phases of catalyst. The 20 angles at about 19.88\({}^{\circ}\) and 26.78\({}^{\circ}\) belong to kaolinite and SiO\({}_{2}\), respectively. The peak at 38.2\({}^{\circ}\) show that Au phase formed in the Au-Ti/Na-ABen and Au-Ti-Ce/Na-ABen catalysts, since the catalyst produced by compound cross-linking can improve the load of gold, while no Au reflection peak was observed for the Au/Ti-Na-ABen catalyst. This is because the gold in the Au/Ti-Na-ABen catalyst was highly dispersed fine nano-particles on the surface [59], and the actual Au content in this sample was not high. The reflection peak of CeO\({}_{2}\) was not observed since CeO\({}_{2}\) was highly dispersed in the interlayer space of bentonite. The broad peaks of the TiO\({}_{2}\) phase are found in the Au-Ti-Ce/Na-ABen catalyst. The probable reason is that a solid solution may be formed due to the Ce\({}^{4+}\) species in the TiO\({}_{2}\) lattice. Table 2 shows the 20 and d(001) spacing of the prepared samples. It shows that the original d(001) spacing of Ca-bentonite is 12.73 A. After the Na ion exchange and activation process, the d(001) spacing of Na-ABen became 14.91 A. While, the introduction of Au to the Na-ABen resulted in the reduction of the d(001) spacing of Au/Na-ABen to 12.08 A, while, the cross-linking agent could obviously increase the d(001) spacing of the bentonite. Ti-Na-ABen, Au/Ti-Na-ABen, Au-Ti/Na-ABen, and Au-Ti-Ce/Na-ABen show d(001) spacings of 15.12, 15.27, 15.82, and 16.30 A, respectively. The shifting of the 20 value from 5.840\({}^{\circ}\) to 5.410\({}^{\circ}\), clearly demonstrates the expansion of the interlayers of bentonite during the pillaring process. The BET surface area, average pore volume, and average pore diameter for all prepared samples are shown in Table 3. The surface area of Ben increased from 35.5 to 134.3 m\({}^{2}\)/g after Na ion exchange and the activation process. This is because the inorganic salt and metal oxide in the interlayer of bentonite were removed, which makes the pores of the clay dredged. The cross-linking agent pillared catalysts show an even higher surface area, since the components of crosslinking went into the interlayer of bentonite and forced the layers of clay apart [60]. However, the surface area of Na-ABen and Ti-Na-ABen decreased from 134.3 and 210.6 m\({}^{2}\)/g to 112.9 and 191.8 m\({}^{2}\)/g, respectively, after the loading of Au (Au/Na-ABen and Au/Ti-Na-ABen) This could be mainly ascribed to the Au nanoparticles going into the pores of the support, which did not function as a pillar, and blocked some of the pores.