## 3 Results
Notably, the Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al exhibited the highest catalytic activity compared with Pd/(H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al and Pd/(H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, owing to the largest active metal loading, the smallest active metal particle size, as well as the largest Pd\({}^{0}\) content of the Pd/(HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al. In order to further investigate the reason for different catalytic activity between granular and structured mesh-type catalysts, the pressure drop across the granular catalyst bed and structured mesh-type catalyst bed was measured and calculated. The specific surface area of the granular and structured mesh-type catalysts can be calculated by the following Equation (4):  
\[a=\frac{s}{v} \tag{4}\]  
where \(a\) denotes the specific surface area of the catalyst, \(s\) denotes the surface area of the catalyst, \(v\) denotes the catalyst volume. The void ratio of the granular and structured mesh-type catalysts can be calculated by the following Equation (5):  
\[\varepsilon=\frac{V_{b}-V_{c}}{V_{b}} \tag{5}\]  
where \(\varepsilon\) denotes the void ratio of the catalyst, \(V_{b}\) denotes the bed volume of the catalyst, \(V_{c}\) denotes the volume of the catalyst deposition. The bed Reynolds number \(Re^{\prime}\) can be calculated by the following Equation (6):  
\[Re^{\prime}=\frac{\rho u}{a(1-\varepsilon)\mu} \tag{6}\]  
Figure 10: Nitrobenzene liquid-phase hydrogenation performance over granular and structured mesh-type Pd/Al\({}_{2}\)O\({}_{3}\)/Al as well as different acid pore-widening treatment Pd/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al structured mesh-type catalysts: (**a**) nitrobenzene conversion and (**b**) aniline yield. where \(\rho\) denotes the density of the nitrobenzene solution, whose value is 0.86 g/cm\({}^{3}\), \(u\) denotes the nitrobenzene solution flow rate of the fluid in the thin tub, and \(\mu\) denotes the viscosity factor of the nitrobenzene solution, whose value is 2.037 \(\times\) 10\({}^{-3}\) Pa-s. When \(Re^{\prime}<2\), the pressure drop can be calculated by the Kozeny Equation (7):  
\[\frac{\Delta p}{L}=K^{\prime}\frac{a^{2}\big{(}1-\varepsilon\big{)}^{2}}{ \varepsilon^{3}}\,\mu u \tag{7}\]  
where \(\Delta p\) denotes the pressure drop, \(L\) denotes the bed height, whose value is 100 mm, and \(K^{\prime}\) denotes the Kozeny coefficient, whose value is 5.0 (\(Re^{\prime}<2\)). For example, with nitrobenzene solution flow rate of 0.5 mL/min (the value of \(u\) is 7.37 \(\times\) 10\({}^{-3}\) cm/s), the bed pressure drop across the structured mesh-type catalyst and bed granular catalyst bed was calculated based on the above equations, as shown in Table 4.  
Based on Table 4, it was found that the bed pressure drop of the structured mesh-type catalyst bed was 1/72 of the granular catalyst bed. Figure 11 shows that when the bed pressure drop became smaller, the pressure of liquid on the surface of structured catalysts was greater than that of granular catalysts at the same bed height. When the pressure of nitrobenzene solution on the surface of structured catalysts became greater (P\({}_{1}>\) P\({}_{3}\), P\({}_{2}>\) P\({}_{4}\)), the nitrobenzene solution liquid film on the surface of structured catalysts became thinner, leading to the H\({}_{2}\) reaching the catalyst surface increasing and leading to an increase in the conversion rate of the reaction. Taken together, based on the above calculations, it was demonstrated that the structured mesh-type catalyst enabled more effective diffusion of the H\({}_{2}\) across from nitrobenzene solution to the active sites on the surface of the catalysts, thus increasing the catalytic activity.