## 3 Results and Discussion
### Properties of Platinum  
In addition to study the acid properties of the carrier, the noble metal Pt has an important effect on the hydroxomerization of the alkane. Pt with a content of 0.5 wt. % was loaded on all the samples.  
Figure 9 exhibits the TEM images of Pt dispersed on ZSM-23 zeolites, the Pt sizes shown here represent the size of most Pt particles over different samples, respectively. Pt/H-ZS-2 shows a maximum Pt particle size of about 2.5 nm, which may be due to its minimum external area and smooth external surface (Table 2). While the Pt particle size of about 1.9 nm of the Pt/H-ZN-1 can be attributed to the high B acid content and the rough outer surface of the sample (Table 1). The average size of Pt particle calculated by CO pulse adsorption is shown in Table 1. We can see that the particle size of Pt calculated is close to that observed by TEM. The order of B acid content on the outer surface of the zeolites is Pt/H-ZN-1 \(>\) Pt/H-ZS-1 \(>\) Pt/H-ZS-2, and the Pt particle size decreases in the order  
Figure 8: IR spectra of 2,6-di-tert-butylpyridine adsorbed on different zeolites at 150 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Acidity Types (\(\mu\)mol/g)**} \\ \cline{2-5}
**Samples** & \multicolumn{2}{c}{**Bronsted**} & \multicolumn{2}{c}{**Lewis**} \\ \cline{2-5}  & **150 \({}^{\circ}\)C** & **350 \({}^{\circ}\)C** & **150 \({}^{\circ}\)C** & **350 \({}^{\circ}\)C** \\ \hline H-ZS-1 & 131 & 99 & 26 & 18 \\ H-ZS-2 & 136 & 100 & 15 & 11 \\ H-ZN-1 & 182 & 137 & 30 & 24 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Acidities of the zeolites determined by Py-IR.  
of Pt/H-ZN-1 > Pt/H-ZS-1 > Pt/H-ZS-2. Therefore, the dispersion and the size of Pt particles mainly depend on the B acid amount on the outer surface of the zeolites.  
In order to further study the effect of the surface properties of different zeolites on the properties of Pt particle, the reducibility of Pt over different catalysts was characterized by H\({}_{2}\)-TPR. As shown in Figure 10, all the catalysts have two H\({}_{2}\) reduction peaks in the temperature range of 150 to 350 \({}^{\circ}\)C and one broad peak at 400-500 \({}^{\circ}\)C. The hydrogen reduction peaks at 200 \({}^{\circ}\)C of the catalysts are attributed to the reduction of PtO and PtO\({}_{2}\) species coordinated with the outer surface of zeolites [26]. And the broad peak at 400-500 \({}^{\circ}\)C is generally considered to be the Pt species that is difficult to be reduced over the catalyst because of the strong metal-support interaction [27]. Pt/H-ZS-1 and Pt/H-ZS-2 have similar hydrogen reduction peaks of Pt. However, the Pt/H-ZN-1 has a large reduction peak at a higher temperature of 275 \({}^{\circ}\)C due to its higher acid density and acid strength. The results show that the catalyst with aluminum sulfate is easy to be reduced. The results show that the catalyst with aluminum sulfate as aluminum source is easier to be reduced due to the weakening interaction between the metal and the zeolite.  
Figure 10: H\({}_{2}\)-TPR curves of different samples.  
Figure 9: TEM images of Pt loaded zeolites (**a**) Pt/H-ZS-1; (**b**) Pt/H-ZS-2; (**c**) Pt/H-ZN-1.