## 3 Results  
Figure 2a shows the general appearance of the commercial Al mesh. Figure 2b shows the cross-sectional morphology of AAO which was observed by optical microscope. It can be seen that a porous and fluffy alumina film (the white section) with a thickness of 86.2 \(\upmu\)m grew vertically at the surface of the Al substrate (the blue section) after anodizing. Additionally, a 10 \(\upmu\)m dense layer between the Al layer and the alumina layer ensured the tight attachment of the catalyst layer to the substrate compared with the traditional aluminum oxide powder coating, which is more promising for application in gas-liquid reaction systems. Figure 2c,d shows the SEM images of AAO and \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) surfaces and the surface of AAO composed of a series of ordered pore structures was observed. Compared to AAO, the surface of \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\) after hot water combining treatment and calcination became rougher and the distribution of pores become disordered, consistent with the previous study [28]. Figure 2: (**a**) The photo of Al mesh; (**b**) the cross-sectional morphology of AAO/Al; the SEM images of the surface morphology of different supports: (**c**) AAO/Al, (**d**) \(\upgamma\)-Al\({}_{2}\)O\({}_{3}\)/Al. Figure 1: Flow chart of nitrobenzene liquid-phase catalytic hydrogenation reaction experimental device. Figure 3a-d show the surface of \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports with different acid pore-widening treatments. Notably, it was found that with short acid impregnation time, the rough surface and disordered distributed pores of the supports were not changed. Moreover, Figure 3e-h show the cross-section of different supports. Compared with untreated \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, the pore diameters of the cross-section in acid pore-widening treatment supports became larger, indicating that acid pore-widening treatment had a corrosive effect on the supports. Figure 3i-l show the diagram of the pore diagram distribution. The diagram of pore diameter distribution of different supports after the H\({}_{2}\)C\({}_{2}\)O\({}_{4}\) and H\({}_{2}\)SO\({}_{4}\) pore-widening treatment is similar to the untreated \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al, but the pore diameter distribution lines are slightly skewed to the right. Compared with the images of (H\({}_{2}\)SO\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al and (H\({}_{2}\)C\({}_{2}\)O\({}_{4}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports, there are more larger pore diameter distributions of support after the HNO\({}_{3}\) pore-widening treatment, exhibiting the most uniform surface and largest section of pores and indicating that HNO\({}_{3}\) had the most effective pore-designing effect on \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al support. The BET analysis was carried out to clarify the pore physical properties of the supports with different acid pore-widening treatments. Figure 4 shows the N\({}_{2}\) adsorption-desorption isotherms of different \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports. Firstly, the Type IV isotherms of both \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al and acid pore-widening treatment \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports had a hysteresis loop, indicating that the acid pore-widening treatments did not change their mesoporous nature. Moreover, the relative pressure of (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al hysteresis loop formation is higher compared to other supports, attributed to the fact that the (HNO\({}_{3}\))\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al has the largest pore diameter. Table 1 summarizes the textural properties of the different supports. Generally, the specific surface area and average pore size of \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)/Al supports increased after all kinds of acid pore-widening treatments. The pore diameters are uncertain below around 5 nm, where the BET and BJH methods are inaccurate.