EUROCAT oxide: an European V2O5–WO3/TiO2 SCR standard catalyst study: Characterisation by electron microscopies (SEM, HRTEM, EDX) and by atomic force microscopy

Abstract The morphology and the homogeneity in chemical compositions of fresh and used V 2 O 5 –WO 3 /TiO 2 EUROCAT SCR samples, in their original monolith form and after gentle grinding, have been investigated by means of electron microscopies and EDX analyses. It appears clearly that the monoliths were constituted of fibres rich in Si, Al and Ca embedded without preferential orientation in a nearly homogeneous oxide phase containing Ti, V, and W. This phase was in the form of small particles of homogeneous size of around 20–40 nm. The used catalyst was very similar to the fresh one, only the presence of S element and of more defects and more fibres were observed on the surface of the monolith. This observation was confirmed by a higher roughness detected using AFM technique. EDX–TEM studies on the powders obtained by gently grinding the monoliths have shown that W and V species were well distributed in TiO 2 support and that the repartition of the W species, very homogeneous in the fresh sample, became somewhat slightly more heterogeneous in the used sample. V species were not so well dispersed that W species and even, some particles rich in V were observed on the used sample. This may be due to the migration and agglomeration of some of the V species. More particles, very rich in Si, were also observed for the used sample suggesting that the coating of the fibres by the active phase was partly deteriorated during SCR reaction. This observation was supported by an AFM analysis which showed a higher surface roughness for the used sample. It was also observed by high resolution TEM that the first one or two atomic layers at the surface of all crystallites appear amorphous, while the further layers are well crystallised with the anatase structure. For the used sample this amorphous layer is slighly larger. This is an important feature for electrical conductivity (mainly at the surface) and catalytic properties.