(762c) Remarkable Self-Degradation of Cu/SAPO-34 Selective Catalytic Reduction Catalysts during Storage at Ambient Conditions

 Remarkable self-degradation of Cu/SAPO-34 selective
catalytic reduction catalysts during storage at ambient conditions

Aiyong Wang,^a Ying Chen,^b Eric D. Walter,^b
Nancy M. Washton,^b Donghai Mei,^a Tamas Varga,^b
Yilin Wang,^a János Szanyi,^a
Yong Wang,^a Charles H.F. Peden,^a Feng Gao^a,*

^a Institute
for Integrated Catalysis, Pacific
Northwest National Laboratory, P.O. Box 999, Richland, WA 99354, United States

^b Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,
P.O. Box 999, Richland, WA 99354, United States

*corresponding author: feng.gao@pnnl.gov.

Abstract:

A model Cu/SAPO-34 SCR catalyst with all Cu species
maintain as isolated Cu(II) ions is synthesized.
Following lengthy storage on the shelf under ambient conditions, this catalyst
essentially completely and irreversibly deactivates. Via (1) continuous and pulsed wave EPR to quantify isolated
Cu(II) ions and to probe Cu-H and Cu-Al coupling; (2) ²⁷Al, ²⁹Si
and ³¹P solid-state NMR to probe SAPO-34 structural properties; (3)
additional detailed characterizations with surface area/pore
volume analysis, XRD, H₂-TPR, NH₃-TPD; and (4) density
functional theory calculations, it is concluded that over the course of
storage, Cu/SAPO-34 deactivates via the following 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.

Keywords:
SCR, ammonia, Cu-exchanged zeolite, SAPO-34, catalyst deactivation