## 3 Results and Discussion
### Cu Loading to CHA Structure  
In this work, H\({}_{2}\)-TPR experiments were carried out on the NH\({}_{4}\)-form and K-form of Cu ion-exchanged CHA zeolite catalysts. Figure 8 presents the H\({}_{2}\)-TPR profiles of Cu-CHA catalysts under different conditions. The H\({}_{2}\)-TPR profile of the Cu-CHA ion exchanged catalyst over the NH\({}_{4}\)-form showed a broad low-temperature peak centered around 250 \({}^{\circ}\)C. The deconvolution of this peak into three peaks is shown in Figures S1-S3 (see the supporting information). The first peak is ascribed to the reduction of isolated Cu\({}^{2+}\) to Cu\({}^{+}\), while the second and third peaks are associated with the reduction of CuO to Cu\({}^{0}\) and Cu\({}^{+}\) to Cu\({}^{0}\), respectively [12; 41; 40; 42]. Therefore, the catalysts are characterized by the presence of Cu\({}^{0}\) and Cu\({}^{+}\) species independent of Cu loading. The intensities of each peak depend on the Cu concentration and the ion exchange temperature. The 0.1 MCu-NH\({}_{4}\)-CHA catalyst showed the highest peak intensity, followed by 0.05 Cu-NH\({}_{4}\)-CHA and 0.1 MCu-NH\({}_{4}\)-RT catalysts. However, two other peaks are visible at 650 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, belonging to the reduction of highly stable Cu\({}^{+}\), a characteristic of the CHA framework [43]. Accordingly, the main consideration is that the high-reduction peaks are denoted by the reduction of Cu\({}^{+}\) to Cu\({}^{0}\). The catalysts developed from the K-form of the CHA showed well-defined low-temperature peaks centered around 240 \({}^{\circ}\)C, which are ascribed to the reduction of the Cu\({}^{\text{II}}\)OH species [10; 44; 45]. Similarly, as seen from their H\({}_{2}\)-TPR, other well-defined peaks assigned to Cu\({}^{\text{II}}\) species [10; 44; 45] are apparent at about 364 \({}^{\circ}\)C.  
Figure 7: NH\({}_{3}\)-TPD profile CHA zeolite catalysts ion-exchanged at different conditions. Information about the oxidation or chemical state of Cu species on the different NH\({}_{4}\)-form CHA catalyst surfaces and their distribution was probed by XPS. It is worth mentioning that copper XPS analysis should be carried out carefully as copper is highly sensitive to radiation [45]. The exposure of X-ray radiation can lead to the reduction of Cu species to Cu\({}^{+}\). Therefore, for copper XPS analysis, sample freezing, minimizing exposure time, using a monochromatized X-ray source, or a low energy X-ray source are recommended. However, integration of H\({}_{2}\)-TPR and XPS analysis would conveniently explain the presence of the type of Cu species in a sample. Figure 9 shows the XPS spectra of Cu species before and after ion etching the samples for 30 s. All catalysts exhibited the presence of the same Cu species but with different peak intensities due to variations in Cu concentrations and ion exchange temperature. The XPS profile confirmed the presence of Cu 2p3/2 at lower binding energy ca. 932 and 933 eV belonging to Cu\({}^{+}\) and Cu\({}^{2+}\), respectively. Cu 2p1/2 was located at higher binding energy around 952 and 953 eV, features indicating that Cu existed primarily in the as-synthesized catalysts as Cu\({}^{+}\) and Cu\({}^{2+}\), respectively [46]. The Shakeup peaks, a property of the dispersed Cu\({}^{2+}\), were also observed at binding energies between 942 to 943 eV. Similarly, weak satellite features around 940 and 960 eV are generally assigned to Cu\({}^{2+}\) in the CuO phase [47; 48]. Figure 8: H\({}_{2}\)-TPR profile of CHA zeolite catalysts ion-exchanged under different conditions. Figure 9: The XPS spectra of Cu species before and after etching of the NH\({}_{4}\)-form of CHA zeolite catalysts with different Cu loading. Concerning ion-etched samples, it was observed that the intensities of all the satellite peaks that appeared in the as-synthesized zeolite catalysts were drastically reduced, and some even disappeared. Still, the Cu 2p1/2 and 2p3/2 peaks of 0.1 M Cu-NH4-CHA emerged sharply at their standard positions.