## 3 Results
However, it is obvious that the (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al showed the largest specific surface area and had the largest pore size of about 4.6 nm, consistent with the results of SEM images and N\({}_{2}\) adsorption-desorption isotherm analysis above. Figure 3: The surface and cross-section SEM images and pore diagram distribution diagram of supports with different acid pore-widening treatments. The surface SEM images: (**a**) \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**b**) (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**c**) (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**d**) (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al; the cross-section SEM images: (**e**) \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**f**) (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**g**) (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**h**) (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al; the pore diagram distribution diagram: (**i**) \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**j**) (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**k**) (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, (**l**) (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al. In this study, Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalyst was produced by active metal Pd impregnation. Figure 5a-d show that the surface of Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al was obviously covered with Pd particle. These small Pd metal particles were uniformly dispersed on the surface of the catalyst, and the catalyst surface exhibited a dense and ordered porous structure. The Pd particles on the surface of the Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al without acid pore-widening treatment had larger particle diameter and agglomeration, attributed to the small pore size of the support without acid pore-widening treatment, which was not favorable for the diffusion and attachment of metal particles. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Support** & **S\({}_{\textbf{BET}}\)** & **Vp** & **Dp** \\  & **(m\({}^{2}\)/g)** & **(\(\mu\)L/g)** & **(nm)** \\ \hline \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 70 & 97.1 & 3.7 \\ (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 72 & 99.9 & 3.8 \\ (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 75 & 105.1 & 4.0 \\ (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 80 & 116.1 & 4.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Textural properties of different acid pore-widening treatment \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports. Figure 4: N\({}_{2}\) adsorption–desorption isotherms of differently acid pore-widening treatment \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports. Figure 6a-d show the metal particle size distribution of Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalysts after different acid pore expansion modifications. The results showed a significant reduction in the particle size of metal particles on the surface of catalysts with different acid pore-widening treatments compared with the untreated Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, indicating that with the increasing pore size of the acid pore-widening treated supports, the active metal particles could be more easily dispersed and adhered during the loading process [29]. Remarkably, given the largest pore size of the (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al support compared to (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al and (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports, the surface of Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al support exhibited the smallest average Pd metal particle size, namely 41 nm.