## 3 Results
The binding energies at 335 eV and 340.3 eV were, respectively, assigned to Pd 3d\({}_{5/2}\) and Pd 3d\({}_{3/2}\) of Pd\({}^{0}\) particles in the catalysts prepared with different acid pore-widening treatments, indicating the presence of metallic Pd\({}^{0}\) loaded onto the \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports. The second pair of Pd signals appearing at 336.3 eV and 341.9 eV was attributed to Pd atoms with lower charge density (Pd\({}^{2+}\)) [34]. To visually observe the amount of Pd in different valence states on different catalysts, we conducted further investigation. Table 3 summarizes the relative contents of Pd in different valence states on different catalysts, which were calculated from the curve fitting in XPS spectra. The data show that the Pd\({}^{0}\) content of catalysts with different acid pore-widening treatments was higher than that of untreated catalysts, indicating that a larger pore size facilitates the full access of reducing substances to the interior of the microscopic pore structures, thus realizing more complete reduction. Specifically, we noticed that the Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al had the largest content of Pd\({}^{0}\), indicating that the Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al was most fully reduced. Figure 10 shows the conversion of nitrobenzene and the yield of aniline over granular and structured mesh-type Pd/Al\({}_{2}\)O\({}_{3}\)/Al catalysts as well as different acid pore-widening treatment structured mesh-type Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalysts at different liquid flow rates. The results show that the conversion of nitrobenzene increased with smaller liquid flow rate and the aniline yield increased with larger liquid flow rate under the experimental conditions (liquid flow rate 0.1 mL/min-0.5 mL/min). At the same liquid flow rate, the \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Catalyst**} & \multicolumn{2}{c}{**Pd (\%)**} \\ \cline{2-3}  & **Pd\({}^{0}\)** & **Pd\({}^{2+}\)** \\ \hline Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 52 & 48 \\ Pd/(H\({}_{2}\)C\({}_{0}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 54 & 46 \\ Pd/(H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 56 & 44 \\ Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al & 59 & 41 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical compositions of different Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalyst surfaces obtained by XPS calculations. Figure 9: XPS diagrams of different Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalysts. nitrobenzene conversion and the aniline yield of the structured mesh-type catalyst was higher than the granular catalyst, attributed to the fact that the structured mesh-type catalyst had a lower pressure drop compared to the granular catalyst, resulting in a thinner liquid film on the catalyst surface. The thinner liquid film facilitated diffusion of the H\({}_{2}\) from nitrobenzene solution to the catalyst surface active site [35], leading to a higher catalytic activity. As the liquid flow rate increased, the catalytic activity gap between the structured mesh-type catalyst and the granular catalyst became wider. Figure 10 also shows the conversion of nitrobenzene and the yield of aniline over different acid pore-widening treatment Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalysts at different liquid flow rates. The result shows that the activities of Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al catalysts with different acid pore-widening treatments were improved compared with untreated Pd/Al\({}_{2}\)O\({}_{3}\)/Al catalyst, due to the higher active metal loading, smaller active metal particle sizes, and increased Pd\({}^{0}\) content after the acid pore-widening treatments.