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S C I E N T I F I C H I G H L I G H T S
9 4 H I G H L I G H T S 2 0 2 1 I
The resulting multidimensional images revealed a series of phase changes and structural alterations (Figure 74b), exacerbated in the reactor hotspot zone. The changes include, for example, a heavily altered pellet exterior of changed porosity, increased amorphous solids and performance-impacting oxide content upon reactor use.
The occurrence of these changes and their apparent radial dependency suggest their origin to lie within local heat and mass transport limitations. This, in turn, points to a low degree of pore or active site utilisation, in other words, demonstrating an untapped catalyst pellet and process optimisation potential.
Fig. 74: Scanning X-ray diffraction of industrial vanadium phosphorus oxide (VPO) catalyst pellets. a) Schematic representation of a fixed-bed reactor utilised in the selective oxidation of n-butane to maleic acid and optical micrographs of the three examined Raschig ring-type VPO catalyst pellets with their approximate extraction location in the reactor. b) Compositional and microstructural maps of
the (i) pristine, (ii) used, and (iii) hotspot-extracted catalyst pellet. Shown are cross-sections of one pellet quadrant.
PRINCIPAL PUBLICATION AND AUTHORS
Evolution of Heterogeneity in Industrial Selective Oxidation Catalyst Pellets, J. Ihli (a), L. Bloch (b,c), S. Boecklein (d), P. Rzepka (a,b), M. Burghammer (c), J.C. da Silva (e), G. Mestl (d), J.A. van Bokhoven (a,b), ACS Catal. 11, 8274-8283 (2021); https:/doi.org/10.1021/acscatal.1c01744 (a) Paul Scherrer Institut, Villigen PSI 5232 (Switzerland) (b) ETH Zürich, Zürich (Switzerland) (c) ESRF (d) Clariant AG, Bruckmühl (Germany) (e) Institut Néel, Grenoble (France)
 S. Böcklein et al., Top. Catal. 60, 1682-1697 (2017).  Z. Gao et al., Sci. Adv. 7, 24 (2021).