In-depth insights into N2O formation over Rh-and Pt-based LNT catalysts

L. Castoldi, R. Matarrese, L. Kubiak, M. Daturi, N. Artioli, S. Pompa, L. Lietti

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6 Citations (Scopus)

Abstract

In this paper mechanistic aspects involved in the formation of N2O over model Pt-Ba/Al2O3and Rh-Ba/Al2O3LNT catalysts are discussed. The reactivity of both gaseous NO and of stored NOx(nitrates) has been studied,with simultaneous surface characterization by operando FT-IR spectroscopy, using different reductants (i.e. H2,CO, CO + H2,CO+H2O) both under isothermal conditions and temperature programming. The results showthat N2O formation may occur during both the lean/rich and rich/lean switches (primary and secondary N2O,respectively). In particular: i) primary N2O formation involves the presence of gas-phase NO and partially re-duced metal sites; ii) N2O formation increases in the presence of CO because the reduction of the metal sites isslower, thus favoring N2O formation upon the lean/rich transition; iii) residual reducing species onto the surface(i.e. NCO−, CO) can react with NO giving the secondary N2O peak. A reaction pathway for N2O formation issuggested where metal sites (Pt or Rh) catalyse the NO dissociation reaction into N- and O-adatoms; N-speciesfurther interact with undissociated NO molecules leading to the formation of N2O (primary N2O). In additions,isocyanates formed during the NOxreduction in the presence of CO may participate in the N2O formation uponreaction with NO during the lean phase (secondary N2O).Pt- and Rh-based catalysts show similar behavior even if Rh-based catalyst is less reactive than Pt-basedsample likely due to the lower dispersion of the noble metal
Original languageEnglish
JournalCatalysis Today
DOIs
Publication statusPublished - 04 Feb 2018

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