Unraveling the mysterious failure of Cu/SAPO-34 selective catalytic reduction catalysts

Abstract

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.

Deactivation of Cu‐Exchanged Automotive‐Emission NH3‐SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X‐ray Microscopy

“…The square‐planar Cu II in Cu Clus4 (Figure d) implied the formation of Cu x O y nanoparticles, which are regarded as an inactive species in NH 3 ‐SCR . To investigate their spatial distribution more closely, pixels with an asymmetric Cu II L‐edge peak, such as the one shown in Figure d, that is, Cu II present in multiple geometric structures, were selected and divided into four groups that varied in their fraction of square‐planar Cu II .…”

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

“…However, Cu/SAPO-34 was proven to lack durability at low temperatures (<100 • C) in the presence of moisture [19,20]. Due to the destructive effect of H 2 O on the SAPO-34 framework, H 2 O in air could destroy Cu/SAPO-34 zeolite even at room temperature [21], which would lead to the loss of activity for Cu/SAPO-34 in NH 3 -SCR. Therefore, it is of great significance to develop novel Cu-based zeolite catalysts with both high activity and good hydrothermal stability in a wide temperature window.…”

Water‐Induced Structural Dynamic Process in Molecular Sieves under Mild Hydrothermal Conditions: Ship‐in‐a‐Bottle Strategy for Acidity Identification and Catalyst Modification

“…In the catalytic petroleum refining, the zeolite catalysts, such as Pt/MOR, ZSM‐5, ZSM‐22 and Y, are exposed in a harsh hydrothermal environment since steam is commonly used as the driving gas in the hydroisomerization, hydrocracking and FCC operations [24, 34] . Additionally, SAPO‐34 molecular sieve with CHA topology that featured as narrow 8‐MR window (3.8 Å×3.8 Å) and super‐cage structure (Scheme 1 b), has been successfully applied in industrial methanol‐to‐olefins (MTO) and selective‐catalytic‐reduction (SCR) of nitrogen oxides (NO x ) processes in which water is co‐fed and co‐produced substance [35–38] . However, at the temperature range for catalytic processes, due to the lack of suitable research techniques that reflect the attack from water on the zeolite/SAPO‐catalysts, the effects of hydrothermal conditions on the molecular‐sieve framework, which are critical for a deeply understanding of the functions of water during catalytic reaction, have not yet been studied.…”