Fe/SSZ-13 catalysts (Si/Al = 12, Fe loadings of 0.37% and 1.20%) were prepared via solution ion-exchange, and they were hydrothermally aged at 600, 700, and 800 °C. The fresh and aged catalysts were characterized with surface area/pore volume analysis, Mossbauer, solid-state MAS NMR, NO titration FTIR spectroscopies, and TEM and APT imaging. Hydrothermal aging causes dealumination of the catalysts and transformation of various Fe sites. The latter include conversion of free Fe 2+ ions to dimeric Fe(III) species, the agglomeration of isolated Fe-ions to Fe-oxide clusters, and incorporation of Al into the Fe-oxide species. These changes result in complex influences on standard SCR and NO/NH 3 oxidation reactions. In brief, mild aging causes catalyst performance enhancement for SCR, whereas harsh aging at 800 °C deteriorates SCR performance. In comparison to Fe/zeolites more prone to hydrothermal degradation, this study demonstrates that via the utilization of highly hydrothermally stable Fe/SSZ-13 catalysts, more accurate correlations between various Fe species and their roles in SCR related chemistries can be made.

Commercial Cu/SAPO-34 selective catalytic reduction (SCR) catalysts have experienced unexpected and quite perplexing failure. Understanding the causes at an atomic level is vital for the synthesis of more robust Cu/SAPO-34 catalysts. Here we show, via application of model catalysts with homogeneously dispersed isolated Cu ions, that Cu transformations resulting from low-temperature hydrothermal aging and ambient temperature storage can be semi-quantitatively probed with 2-dimensional pulsed electron paramagnetic resonance. Coupled with kinetics, additional material characterizations and DFT simulations, we propose the following catalyst deactivation steps: (1) detachment of Cu(II) ions from cationic positions in the form of Cu(OH) 2 ; (2) irreversible hydrolysis of the SAPO-34 framework forming terminal Al species; and (3) interaction between Cu(OH) 2 and terminal Al species forming SCR inactive, Cu-aluminate like species. Especially significant is that these reactions are greatly facilitated by condensed water molecules under wet ambient conditions, causing low temperature failure of the commercial Cu/SAPO-34 catalysts.

No abstract

No abstract

No abstract

No abstract

No abstract

No abstract