## 3 Results and Discussion  
### Effect of Heat Treatment of Carbon Black Supports on the Properties of Pd/C Catalysts  
The prepared Pd catalysts supported by the heat-treated carbon blacks (Pd/C\({}_{\text{v}}\) and Pd/C\({}_{\text{k}}\)) were characterized. Table 1 summarizes the BET surface area, pore volume based on the MP and BJH analyses, and crystallite size of the Pd catalysts determined by XRD. It can be seen from Table 1 that the BET surface area of the Pd/C catalysts increased when Pd was deposited onto heat-treated carbon support, irrespective of the kind of heat treatment and CB. This means that the BET surface area was increased by the heat treatment, which is consistent with the phenomena reported in the literature [11; 21]. Both the Pd/C\({}_{\text{k}}\) and Pd/C\({}_{\text{v}}\) that went through both carbonization and steam activation have the highest BET surface areas. This is due to the more porous construction caused by steam activation [22] which leads to a higher BET surface area. The BET surface areas of Ketjen and Vulcan proportionally increased with the intensity of the heat treatment, i.e., No \(<\) Carb \(<\) Act \(<\) All, due to the development of the micropore structure of the CBs. There is a big difference in the surface area between the Pd/C\({}_{\rm k}\)s and Pd/C\({}_{\rm v}\)s. This is due to the difference in the pore properties between the commercial Vulcan and Ketjen. Vulcan is a nonporous carbon material which has no or few micropores, and Ketjen is a porous carbon black which has a large fraction of micropores and broad pore size distribution [23]. Regarding the crystallite size of Pd, there is no particular trend in the heat treatment although Pd/C\({}_{\rm k}\) showed smaller crystallite sizes, i.e., 2.2-4.5 nm, than that of Pd/C\({}_{\rm v}\), i.e., 4.6-9.4 nm. On the basis of these results, heat treatment provides an enhancement of the total surface area, which is a trend similar to previous studies [13]. Figure 1 and Figure S1 shows the pore volume distribution, while Figure S2 shows nitrogen adsorption and desorption isotherms for Pd/C with the different CBs and heat treatments. The pore volume was classified according to the pore size: macroopre (>50 nm), mesopore (2-50 nm), and micropore (<2 nm) [11; 17]. Generally, the total pore volumes of the Pd/C\({}_{\rm k}\)s were significantly higher than those of Pd/C\({}_{\rm v}\) irrespective of the heat treatment type. For the Vulcan, the volume of the mesopore for Pd/C\({}_{\rm v}\)-carb was similar to that of Pd/C\({}_{\rm v}\)-no. Moreover, the volume of the macropore Pd/C\({}_{\rm v}\) increased from Pd/C\({}_{\rm v}\)-no resulting in the increased total pore volume. On the basis of these results, it is suggested that the mesopores would grow into macropores, and the small pores, such as the micro- or small mesopores, would be produced by the carbonization process. Referring to the effect of the steam activation, the total pore volumes of the Pd/C\({}_{\rm v}\)-act were much higher than those of Pd/C\({}_{\rm v}\)-no and Pd/C\({}_{\rm v}\)-carb. During the steam activation process, oxygen contained \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Heat Treatment on**} & \multicolumn{2}{c}{**BET Surface Area**} & \multicolumn{2}{c}{**Pore Volume**} & \multicolumn{2}{c}{**Pd Crystallite Size**} \\  & \multicolumn{2}{c}{**(m\({}^{2}\) g\({}^{-1}\))**} & \multicolumn{2}{c}{**(cm\({}^{3}\) g\({}^{-1}\))**} & \multicolumn{2}{c}{**(nm)**} \\ \cline{2-6}  & **Pd/C\({}_{\rm v}\)** & **Pd/C\({}_{\rm k}\)** & **Pd/C\({}_{\rm v}\)** & **Pd/C\({}_{\rm k}\)** & **Pd/C\({}_{\rm v}\)** & **Pd/C\({}_{\rm k}\)** \\ \hline No & 85 & 581 & 0.44 & 1.09 & 6.6 & 3.9 \\ Carbonization (Carb) & 166 & 609 & 0.47 & 1.13 & 7.7 & 4.4 \\ Steam activation (Act) & 221 & 714 & 0.59 & 1.29 & 9.4 & 2.2 \\ Carb and act (All) & 256 & 840 & 0.53 & 1.46 & 4.6 & 4.5 \\ \hline \hline \end{tabular}
\end{table}