Catalytic site requirements for N2O decomposition on Cu-, Co-, and Fe-SSZ-13 zeolites

Fan Lin, Tahrizi Andana, Yiqing Wu, János Szanyi, Yong Wang, Feng Gao

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

N2O decomposition is investigated on Cu, Co and Fe-exchanged SSZ-13 zeolite catalysts at relatively low metal loadings. The catalysts are synthesized by solution ion exchange, and subjected to X-ray diffraction (XRD), temperature-programed-reduction by H2 (H2-TPR), temperature-programed-reaction of N2O (N2O-TPR) coupled with in-situ transmission FTIR, and finally steady-state flow reaction tests. At low N2O pressures (<0.05 kPa), all catalysts display pseudo first-order kinetics. From Arrhenius analysis, Cu and Fe-SSZ-13 display very different apparent activation energies but similar pre-exponential factors, suggesting their similar reaction mechanisms. N2O decomposition follows a dual-site mechanism, occurring on dimeric M-O-M sites in these catalysts, and O2 is formed by the combination of two O ad-atoms from two vicinal metal sites. Under low N2O pressure (0.05 kPa) and first-order kinetic regime, the reaction is limited by N-O cleavage on bare metal active sites. In comparison to Cu-SSZ-13, the much higher N2O decomposition rate over Fe-SSZ-13 is attributed to the much lower activation barriers for the N-O cleavage step. N2O decomposition occurs on isolated Co2+ ions in Co-SSZ-13. The rate-limiting step is N-O cleavage on an O-occupied Co site in the low-pressure first order kinetic regime. This single-site mechanism leads to much higher pre-exponential factors as compared to the dual-site mechanism. This beneficial factor for reaction rate enhancement, however, is compromised by the much higher activation barriers over this catalyst.

Original languageEnglish
Pages (from-to)70-80
Number of pages11
JournalJournal of Catalysis
Volume401
DOIs
StatePublished - Sep 2021
Externally publishedYes

Keywords

  • Co
  • Cu
  • Fe
  • Ion-exchanged zeolite catalyst
  • NO decomposition
  • Reaction kinetics
  • Reaction mechanism

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