## 3 Results and Discussion
### Morphology and Physical Properties  
Figure 4 reveals the morphology of the Cu-CHA catalysts prepared at different Cu concentrations and different temperatures. The FE-SEM images presented in Figure 4 have again confirmed the shape and particle size of the catalysts with reference to the OSDA-free CHA zeolite reported previously [25]. In principle, the particles are cuboids in shape and submicron in size. These cuboids were agglomerated and formed larger particles with sizes ranging from 5-8 \(\upmu\)m. It was observed that the modifications to the parent CHA zeolite did not alter the morphology of the Cu-CHA zeolite catalysts. The loading of Cu to the CHA structure was confirmed by the elemental distribution map (EDS/EDX), as presented in Figure 5 and Table 2.  
Figure 4: FE-SEM images of CHA zeolites catalysts ion-exchanged with Cu solution at different conditions. Figure 3: \({}^{27}\)Al NMR spectrum of CHA zeolite catalysts ion-exchanged with Cu at different conditions. The textural properties of as-synthesized catalysts were determined by the N\({}_{2}\) adsorption/desorption method. Figure 6 shows the N\({}_{2}\) adsorption/desorption isotherms of the Cu-exchanged zeolites and their corresponding pore width distributions against the differential volumes using the Horvath-Kawazoe model. The numerical treatment of N\({}_{2}\) isotherms provides surface area and pore volume presented in Table 2. Remarkably, the isotherms of the NH\({}_{4}\)-CHA zeolite type catalysts exhibited higher uptake of N\({}_{2}\) than the K-Form of zeolite catalysts. The poor N\({}_{2}\) uptake by the Cu-CHA catalysts prepared from the K-Form of CHA highlights the importance of pore openings of CHA, which were blocked by potassium ions prior to any modifications. The previous N\({}_{2}\) analysis showed no adsorption/desorption for the K-CHA [25]. However, an increase in ion exchange temperature from room temperature (RT) to 80 \({}^{\circ}\)C enhanced the degree of potassium exchange with Cu, as indicated by an increase in the BET surface area and pore volume, Table 2. The \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Surface Area (m\({}^{2}\)/g)**} & \multicolumn{3}{c}{**Pore Volume (cm\({}^{3}\)/g)**} & \multirow{2}{*}{**Cu/Al \({}^{*}\)**} \\ \cline{2-2} \cline{5-8}  & \(\mathbf{S_{ext}}\) & \(\mathbf{S_{micro}}\) & \(\mathbf{S_{tot.}}\) & & \(\mathbf{S_{L}}\) & \(\mathbf{V_{micro}}\) & \(\mathbf{V_{meso}}\) & \(\mathbf{V_{tot}}\) \\ \hline
0.05 M Cu-NH\({}_{4}\)-CHA & 20 & 409 & 429 & 465 & 0.150 & 0.024 & 0.174 & 0.72 \\
0.1 M Cu-NH\({}_{4}\)-CHA & 21 & 422 & 443 & 482 & 0.155 & 0.025 & 0.180 & 0.81 \\
0.1 M Cu-NH\({}_{4}\)-CHA-RT & 13 & 457 & 470 & 498 & 0.167 & 0.018 & 0.185 & 0.66 \\
0.05 M Cu-K-CHA & 29 & 158 & 186 & 240 & 0.060 & 0.037 & 0.098 & - \\
0.1 M Cu-K-CHA & 23 & 296 & 319 & 364 & 0.112 & 0.033 & 0.145 & - \\
0.1 M Cu-K-CHA-RT & 6 & 63 & 69 & 90 & 0.024 & 0.023 & 0.047 & - \\ \hline \hline \end{tabular} \({}^{*}\) Elemental analysis was conducted using EDX.  
\end{table} 
Table 2: Surface area and pore volume distribution of a series of Cu-CHA catalysts. Figure 5: Elemental distribution map (SEM/EDS) of Cu-CHA catalysts prepared from NH\({}_{4}\)-CHA. higher ion-exchange temperature facilitated the ion-exchange process even when the Cu concentration was 0.05 M.  
Noticeably, both the NH\({}_{4}\)-CHA and K-CHA forms of the zeolite synthesized catalysts exhibit a sharp increase in the relative pressure below 0.01, indicating the abundant presence of micropores [11]. However, as seen in Figure 6, all the K-CHA forms of zeolite samples exhibit a mixed type 1 and type IV isotherm with an H1 type hysteresis loop in the range of P/P\({}^{0}\) > 0.8, indicating the representation of dominant mesoporousity with only a small contribution from macroporosity [33].