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Model NO x Storage Materials at Realistic NO 2 Pressures
Author(s) -
Desikusumastuti Aine,
Schernich Stefan,
Happel Markus,
Sobota Marek,
Laurin Mathias,
Libuda Jörg
Publication year - 2009
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.200900137
Subject(s) - barium , decomposition , chemistry , absorption spectroscopy , spectral line , infrared spectroscopy , nanoparticle , analytical chemistry (journal) , materials science , inorganic chemistry , nanotechnology , physics , organic chemistry , chromatography , quantum mechanics , astronomy
The interaction of NO 2 with single‐crystal‐based model NO x storage materials, consisting of barium aluminate nanoparticles on Al 2 O 3 /NiAl(110), are investigated by time‐resolved infrared reflection absorption spectroscopy (TR‐IRAS) at realistic NO 2 partial pressures up to 1.75 mbar. The data is compared to spectra obtained under ultrahigh vacuum (UHV) conditions on the same model system. At 300 K, the NO 2 uptake at pressures around 1 mbar proceeds through rapid initial formation of surface nitrites and nitrates, similar to that under UHV conditions. The vibrational spectra of the surface species formed at realistic NO 2 pressures are comparable to those for species formed under UHV conditions. Beyond the formation of surface species, the formation of bulk nitrates occurs, but is kinetically strongly hindered. At a very low rate, the formation of a disordered barium bulk nitrate is detected. At 500 K, this kinetic hindrance is overcome and the available Ba 2+ is quantitatively converted to bulk Ba(NO 3 ) 2 . The IRAS spectrum of these Ba(NO 3 ) 2 particles differs characteristically from those obtained for nitrate multilayers formed upon incomplete conversion under UHV conditions. In addition to the formation of bulk Ba(NO 3 ) 2 , a more weakly bound disordered nitrate species is formed. This species gives rise to a dynamic NO 2 uptake and release well below the decomposition temperature of bulk Ba(NO 3 ) 2 . The experiments show that model studies under UHV conditions mainly provide information on the initial reaction mechanism, whereas the observation of actual bulk NO x storage phases requires experiments at realistic temperatures and pressures.