Conversion of NO_x over Aluminosilicate Cu-CHA Zeolite Catalysts Synthesized Free of Organic Structure-Directing Agents

Featured Application: Catalytic NOx emission control. Cu-CHA zeolites have proven to be effective for NO_x reduction, but a drawback in using CHA zeolites is the cost associated with using expensive organic structure-directing agents. To overcome this drawback, we are reporting here the synthesis of Cu-CHA zeolite catalysts in both their NH₄-form as well as K-form that do not require the use of organic structure-directing agents. After comprehensive characterization by XRF, XRD, ²⁷Al NMR spectroscopy, FE-SEM, SEM/EDS, N₂-adsorption/desorption, NH₃-TPD, H₂-TPR, and XPS, the zeolite catalysts were tested for NO_x conversion by NH₃-selective catalytic reduction (NH₃-SCR). Cu-NH₄-CHA zeolite catalysts exhibited remarkable activity and thermal stability over a wide temperature window, outperforming their counterpart K-forms. Among the NH₄-forms of CHA zeolite catalysts, the 0.1 M Cu-NH₄-CHA showed the best catalytic performance, achieving 50% NO_x conversion at a temperature as low as 192 °C, and reaching full conversion of NO_x at 261 °C. These Cu-based CHA zeolite catalysts are promising thanks to their environmentally friendly synthesis and offer the opportunity of maximizing DeNO_x strategies in applications for NO_x pollution abatement.