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Methodology for the structural characterisation of V x O y species supported on silica under reaction conditions by means of in situ O K‐edge X‐ray absorption spectroscopy
Author(s) -
Hävecker Michael,
Cavalleri Matteo,
Herbert Rita,
Follath Rolf,
KnopGericke Axel,
Hess Christian,
Hermann Klaus,
Schlögl Robert
Publication year - 2009
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.200945067
Subject(s) - xanes , x ray absorption spectroscopy , extended x ray absorption fine structure , vanadium , auger electron spectroscopy , chemistry , density functional theory , catalysis , absorption spectroscopy , spectroscopy , absorption (acoustics) , x ray absorption fine structure , oxidation state , vanadium oxide , k edge , analytical chemistry (journal) , crystallography , materials science , inorganic chemistry , computational chemistry , physics , organic chemistry , quantum mechanics , nuclear physics , composite material
A methodology and its application to silica supported vanadia are presented that allows for a detailed analysis of structural peculiarities of the vanadia species on the surface. We introduce in situ oxygen K‐edge X‐ray absorption spectroscopy (XAS) based on the Auger electron yield (AEY) technique as a characterisation tool to assist vibrational spectroscopy that has been applied extensively in earlier work on this system. The analysis of the O K‐near edge X‐ray absorption fine structure (NEXAFS) allows a clear distinction between separate vanadia, silica and interface contribution in contrast to vibrational spectroscopy with strongly overlapping contributions due to vibrational coupling. Differently coordinated oxygen can be identified in the O K‐NEXAFS spectrum by comparison with theoretical spectra obtained by state of the art density‐functional theory (DFT) calculation. A study of catalysts with different V loadings (0 wt% V, 2.7 wt% V, and 10.8 wt% V) shows that the contributions of silica to the NEXAFS appear in an energy region well separated from the spectral signature of oxygen bound to vanadium. Dehydrated catalysts with high (10.8 wt% V) and low (2.7 wt% V) vanadium loading on silica SBA‐15 show identical NEXAFS under in situ conditions. This finding indicates that independent of the loading a distribution of vanadia species with a very similar molecular structure, including non‐monomeric as well as possibly monomeric configurations and different from crystalline V 2 O 5 , is present on this model catalyst. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)