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

Abstract

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, 2h) 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 2h aging. While the 27Al NMR spectra of 2 and 10h 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 2h 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.