Possible origin of improved high temperature performance of hydrothermally aged Cu/beta zeolite catalysts

The hydrothermal stability of Cu/beta NH3 SCR catalysts are explored here. In particular, this paper focuses on the interesting ability of this catalyst to maintain and even enhance high-temperature performance for the “standard” SCR reaction after modest (900 °C, 2 h) hydrothermal aging. Characterization of the fresh and aged catalysts was performed with an aim to identify possible catalytic phases responsible for the enhanced high temperature performance. XRD, TEM and 27Al NMR all showed that the hydrothermal aging conditions used here resulted in almost complete loss of the beta zeolite structure between 1 and 2 h aging. While the 27Al NMR spectra of 2 and 10 h hydrothermally aged catalysts showed significant loss of a peak associated with tetrahedrally coordinated Al species, no new spectral features were evident. Two model catalysts, suggested by these characterization data as possible mimics of the catalytic phase formed during hydrothermal aging of Cu/beta, were prepared and tested for their performance in the “standard” SCR and NH3 oxidation reactions. The similarity in their reactivity compared to the 2 h hydrothermally aged Cu/beta catalyst suggests possible routes for preparing multi-component catalysts that may have wider temperature windows for optimum performance than those provided by current Cu/zeolite catalysts.

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► Moderate hydrothermal treatment of a Cu/beta zeolite ammonia SCR catalyst leads to loss of low temperature activity.
► However, maintenance and even enhancement of high temperature performance is realized by this treatment.
► Catalyst characterization provides clues to the possible structure of the hydrothermally treated catalyst.
► Model catalysts were prepared based on the insights from the characterization data.
► These model catalysts displayed high temperature performance for ammonia SCR, suggesting possible practical solutions.