NMR studies of Cu/zeolite SCR catalysts hydrothermally aged with urea

The effects of hydrothermal aging of Cu/zeolite urea-selective catalytic reduction (SCR) catalysts on their reactivity and material properties were assessed by performance tests and multiple characterization techniques that included 27Al nuclear magnetic resonance (NMR) and X-ray diffraction (XRD). Three aging protocols were used that consisted of varying temperature during hydrothermal aging with or without exposure to aqueous urea solution. Differences in behavior were even found for samples hydrothermally aged immediately following exposure to the urea solution or if the sample was dried overnight before hydrothermal aging. The combination of urea and high-temperature exposure increased the deactivation of Cu/zeolite SCR catalysts beyond that observed by hydrothermal aging alone, with an immediate high-temperature exposure following wetting of the catalyst core with aqueous urea causing the most significant deterioration in performance. The impact of urea on SCR catalyst durability was also found to increase with the aging temperature. NMR analysis suggested that aging with urea resulted in relatively more dealumination of the zeolite for the SCR catalysts in this study.