## 4 Conclusions  
Room- and low-temperature Cu ion-exchanged NH\({}_{4}\)-forms and K-forms of CHA zeolite catalysts were synthesized with Cu loadings of 0.05 and 0.1 M. All as-synthesized Cu-NH\({}_{4}\)-CHA zeolite catalysts showed higher catalytic NOx conversion than the Cu-K-CHA catalysts. The XRD profile revealed that all the as-synthesized CHA zeolites featured diffractograms identical to the well-known XRD patterns of the CHA framework. The \({}^{27}\)Al NMR spectroscopic results indicated that the NH\({}_{4}\)-CHA possessed tetrahedral and octahedral aluminum coordination within the zeolite framework. At the same time, the K-CHA form was dominated by the tetrahedral coordination of aluminum. This signifies that NH\({}_{4}\)-CHA zeolite catalysts possessed more Al coordination in the extraframework position than in the K-CHA forms. Morphologically, the NH\({}_{4}\)-CHA type formed more bundles of well-interconnected cuboids than the other zeolite-type catalysts, beneficial for keeping them structurally intact and perhaps advantageous to their thermal stability. In terms of textural properties, considering the surface area and pore volume of the as-synthesized zeolite catalysts, it can be inferred that their textural properties are similar to those of the conventional SAPO-34 and SSZ-13 zeolites. Thus, the synthesis procedure adopted is promising. The Cu  
Figure 11: NOx conversion by the K-CHA zeolite catalyst ion-exchanged at different concentrations and temperatures. Catalyst loading: 50 mg (40–80 mesh) mixed with 50 mg silica gel. Reaction conditions: 500 ppm NO + 500 ppm NH\({}_{3}\) + 14% O\({}_{2}\)/N\({}_{2}\) + 5% CO\({}_{2}\) + 5% H\({}_{2}\)O + N\({}_{2}\). Total gas flow rate: 200 mL/min. Space velocity 240 L/h-g. Temperature ramp: 2.5 \({}^{\circ}\)C/min. Total reaction time: 172 min. ion-exchanged CHA forms of zeolites typically have three commonly known acid sites: Lewis sites, Cu-sites, and Brensted sites. In this context, the prepared Cu ion-exchanged NH\({}_{4}\)-form of CHA zeolites showed mainly two acid sites characterized by Lewis and Cu-sites. In contrast, the K-Form of Cu-CHA zeolite catalysts were characterized by only Cu-sites and, thus, supported the notion that their NH\({}_{3}\)-SCR activity for NO\({}_{\rm x}\) conversion is undoubtedly dissimilar. The H\({}_{2}\)-TPR profile of the Cu-NH\({}_{4}\)-CHA proved that the Cu species distribution over the catalysts was dominated by a mixture of Cu\({}^{+}\) and Cu\({}^{2+}\) species, while in the other CHA zeolite catalysts, the predominant Cu species were mainly Cu in the form of Cu\({}^{\rm II}\)OH. The XPS spectra of Cu-NH\({}_{4}\)-CHA further supported this: that Cu existed primarily in the catalysts as Cu\({}^{+}\) and Cu\({}^{2+}\). To reveal this study's most important finding, the as-synthesized Cu-NH\({}_{4}\)-CHA zeolite catalysts, particularly 0.1 M Cu-NH\({}_{4}\)-CHA, achieved superior performance in the NH\({}_{3}\)-SCR reaction with 100% NO\({}_{\rm x}\) conversion within the temperature window between 192 and 261 \({}^{\circ}\)C. This seems to be one of the lowest temperature windows compared to the windows of NH\({}_{3}\)-SCR reaction for NO\({}_{\rm x}\) conversions by Cu-zeolites-based catalysts reported in the literature. In contrast to the Cu-NH\({}_{4}\)-CHA, the as-synthesized Cu-K-CHA zeolite catalysts suffered significantly from the potassium (K) poisoning effect, causing notable deactivation accompanied by the rapid loss of NH\({}_{3}\)-SCR catalytic activity. Finally, this work shows that Cu-based CHA zeolite, particularly the NH\({}_{4}\)-CHA forms, can be synthesized successfully without using an organic structure-directing agent (OSDA) with desired morphology; texture; and framework Al coordination, which are key factors for determining the structure-activity relationship in zeolite catalytic reactions. Thus, this synthesis technique can be directed towards actual application for their synthesis and utilization in DeNO\({}_{\rm X}\) catalytic strategies.