## 3 Results and Discussion
### Characterization
The surface areas of Au-Ti/Na-ABen and Au-Ti-Ce/Na-ABen are higher than those of Au/Na-ABen and Au/Ti-Na-ABen, since Au together with Ce and Ti cross-linking agent move into the interlayer of bentonite and lead to the increased layer spacing of bentonite. It was observed that the Au-Ti-Ce/Na-ABen catalyst has a larger surface area than Au-Ti/Na-ABen, this may be due to Ce\({}^{4+}\) and part of the Au species migrating into the interlayers by the synergistic effect. These results agreed well with those found by XRD measurement (Table 2). SEM images of Au/Na-ABen, Au/Ti-Na-ABen, Au-Ti/Na-ABen, and Au-Ti-Ce/Na-ABen catalysts are illustrated in Figure 2. It was found that the particles size was not uniform, and there were some large particles in the sample. This could be mainly attributable to the crosslinking agent precursors of organic volatiles moving out quickly during the calcination so that its frame has no time to contract evenly. In addition, some irregular frameworks emerged on the surface of bentonite dues to the pillared content increases. The morphologies of the supported Au catalysts are characterized by typical transmission electron microscopy (TEM). It is observed clearly from Figures 3a-c and 4d that both Au particles, Au-Ti pillaring species, and Au-Ti-Ce pillaring species appear as nanoparticles, and the mean diameters of them are about 12, 10, 8, and 6 nm, respectively. Au/Ti-ABen catalyst had the largest Au particle size, Furthermore, for the Au/Ti-ABen catalyst, Au particles dispersed unevenly and reunion. For the Au-Ti/ABen and Au-Ti-Ce/ABen catalysts, the pillaring species evenly dispersed on the surface of the bentonite and part of the pillaring species were dispersed to enter interlayers. Compared with other catalysts, Au/Na-ABen catalyst which had the largest Au particle size bring about the lower catalytic activity. For the Au-Ti/Na-ABen and Au-Ti-Ce/Na-ABen catalysts with special, pillaring species \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & **2\(\theta\)** & **d (\(\AA\))** \\ \hline Ben & 6.930 & 12.73 \\ Na-ABen & 5.924 & 14.91 \\ Au/Na-ABen & 7.313 & 12.08 \\ Ti-Na-ABen & 5.840 & 15.12 \\ Au/Ti-Na-ABen & 5.783 & 15.27 \\ Au-Ti/Na-ABen & 5.581 & 15.82 \\ Au-Ti-Ce/Na-ABen & 5.410 & 16.30 \\ \hline \end{tabular}
\end{table} 
Table 2: The 2\(\theta\) and d(001) spacing of the samples. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Average Pore Diameter (nm)** & **Pore Volume (cm\({}^{3}\)/g)** & **SBET (m\({}^{2}\)/g)** \\ \hline Au/TiO\({}_{2}\) & 7.95 & 0.123 & 62.0 \\ Ben & 6.68 & 0.059 & 35.5 \\ Na-ABen & 4.64 & 0.156 & 134.3 \\ Au/Na-ABen & 5.60 & 0.158 & 112.9 \\ Ti-Na-ABen & 5.48 & 0.289 & 210.6 \\ Au/Ti-Na-ABen & 5.90 & 0.283 & 191.8 \\ Au-Ti/Na-ABen & 9.91 & 0.621 & 250.7 \\ Au-Ti-Ce/Na-ABen & 9.64 & 0.677 & 281.0 \\ \hline \end{tabular}
\end{table} 
Table 3: Brunauer-Emmet-Teller (BET) surface area, pore volume, and average pore size of the samples. The thermal stability of the catalyst is very important for practical application. Thus it is necessary that the thermal stability of the as-prepared catalysts are also evaluated by thermogravimetric analysis (TGA). Figure 4 show the TGA carves of ABen, Au/Na-ABen, Au-Ti/ABen and Au/Ti-Na-ABen nanocomposite under an air atmosphere. The weight of ABen gradually decreased as the temperature was increased to 200 \({}^{\circ}\)C and the TGA profile of the others indicated that a significant weight loss was then observed at temperature ranging from 30 to 100 \({}^{\circ}\)C. This could be mainly assigned to the removal of adsorbed water molecules. There was not a significant weight loss obvious as the temperature was increased to 800 \({}^{\circ}\)C for the TGA curves of the as-prepared catalysts. The results indicate that the as-prepared catalysts modified by the cross-linking agent possess more a better thermal stability than the catalysts without modification by cross-linking agent.