## 3 Results and Discussion
### Impact of the Aluminum Source Type on the Precursor Morphology of the Aluminum Oxides  
Using eighteen-water aluminum sulfate, hexahydrate aluminum chloride, and nonahydrate aluminum nitrate as aluminum sources and ammonium bicarbonate as the precipitant, the impact of aluminum source types on the morphology of aluminum oxide was investigated. Initially, XRD and SEM analyses were performed on the precursor products obtained from the three aluminum sources. The test results are presented in Figure 6 and Figure 7, respectively. It is evident from Figure 6 that the precursors prepared from different aluminum sources exhibit a rod-like morphology. From Figure 7 and Table 1, it can be observed that aluminum oxide precursors prepared with aluminum sulfate and aluminum nitrate as the aluminum source result in pure-phase ammonium aluminate carbonate. The precursor prepared with aluminum chloride as the aluminum source primarily consists of ammonium aluminate carbonate, with minor amounts of boehmite. However, the precursor prepared from aluminum sulfate has a smaller particle size and severe aggregation. This is because, during the reaction process, some aluminum sulfate reacts with ammonium bicarbonate to form aluminum ammonium sulfate, as shown in the chemical reaction in Equation (9). The formation of aluminum ammonium sulfate, on the one hand, reduces the concentration of reactants, preventing the growth of crystal particles. On the other hand, as a coagulant, it promotes the aggregation of small particle crystals [23]. The precursors prepared from aluminum chloride and aluminum nitrate have similar particle sizes, and their surfaces  
Figure 5: N\({}_{2}\) adsorption–desorption isotherms and BJH pore size distribution plots of alumina prepared with different precipitants. (a) Sodium bicarbonate; (b) ammonium bicarbonate; (c) potassium bicarbonate. Figure 6: SEM images of alumina precursors prepared from different aluminum sources. (**a**) Aluminum sulfate; (**b**) aluminum chloride; (**c**) aluminum nitrate. appear rough, indicating that chloride ions and nitrate ions have no significant impact on the precursor morphology. \[2 Al_{2}(SO_{4})_{3}+3 NH_{4}HCO_{3}=3 NH_{4}Al(SO_{4})_{2}+Al(OH)_{3}\downarrow+3 CO_{2}\uparrow \tag{9}\]  
The precursor prepared with aluminum sulfate is sodium basic aluminum ammonium carbonate, with an average crystal grain size of 18.11 nm; the precursor prepared with aluminum chloride is sodium basic aluminum ammonium carbonate, with an average crystal grain size of 20.03 nm; the precursor prepared with aluminum nitrate is sodium basic aluminum ammonium carbonate, with an average crystal grain size of 15.26 nm. The average grain size of alumina precursors prepared from different aluminum sources is shown in Table 3.  
Since the aluminum oxide precursors prepared from the three different aluminum sources are mainly aluminum aluminate carbonate, their TG-DTG curves are similar. From Figure 8, it can be observed that the mass change before 259 \({}^{\circ}\)C, 279 \({}^{\circ}\)C, and 276 \({}^{\circ}\)C is attributed to the removal of adsorbed water and thermal decomposition. After 259 \({}^{\circ}\)C, 279 \({}^{\circ}\)C, and 276 \({}^{\circ}\)C, the mass change is caused by the removal of crystalline water from the aluminum oxide precursor. There is a mass loss of 68%, 63%, and 65%, respectively, on the TG curves, which corresponds to the theoretical mass loss of 63.3% when aluminum aluminate carbonate decomposes into aluminum oxide. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Aluminum Sources** & **Lattice Parameters (Å)** & **Average Crystalline Size, D (nm)** \\ \hline \multirow{4}{*}{(a)} & NH\({}_{4}\)Al (OH)\({}_{2}\)CO\({}_{3}\) (a = 6.6, b = 11.9, \(c\) = 5.7) & 18.11 \\  & \(\gamma\)-AlOOH (a = 3.7, b = 12.2, c = 2.8) & \\  & NH\({}_{4}\)Al (OH)\({}_{2}\)CO\({}_{3}\)(a = 6.6, b = 11.9, \(c\) = 5.7) & 20.03 \\  & NH\({}_{4}\)Al (OH)\({}_{2}\)CO\({}_{3}\) (a = 6.6, b = 11.9, \(c\) = 5.7) & 15.26 \\ \hline \hline \end{tabular}
\end{table}