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Characterization of supported Nb catalysts by ToF‐SIMS
Author(s) -
Bukallah Saeed B.,
Houalla Marwan,
Hercules David M.
Publication year - 2000
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/1096-9918(200012)29:12<818::aid-sia931>3.0.co;2-4
Subject(s) - characterization (materials science) , catalysis , materials science , chemistry , nanotechnology , organic chemistry
A series of Nb 2 O 5 /TiO 2 catalysts were prepared by incipient wetness impregnation of TiO 2 with aqueous solutions of niobium oxalate/oxalic acid. Eight different catalysts with Nb loadings of 0.48–8.5 wt.% Nb were prepared. Analysis of the time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) spectra of Nb 2 O 5 /TiO 2 catalysts shows the presence of monomeric, dimeric and trimeric Nb x O y clusters at all loadings. This indicates that polymeric Nb oxide species are present even at loadings well below that corresponding to monolayer coverage (∼4.5 wt.% Nb). Moreover, it was found that the degree of aggregation of the niobia active phase increases with Nb loading. The tetrameric Nb oxide cluster was the largest fragment detected for amorphous Nb 2 O 5 . For Nb 2 O 5 /TiO 2 catalysts the tetrameric Nb cluster was first detected in the 2.8 wt.% Nb catalyst. It is concluded that bulk‐like Nb 2 O 5 is present in catalysts containing ≥2.8 wt.% Nb (i.e. ≥60% theoretical coverage). Copyright © 2000 John Wiley & Sons, Ltd.