S C

IE N

T IF

IC H

IG H

LI G

H T

S S

T R

U C

T U

R E

O F

M A

T E

R IA

L S

1 4 1 I H I G H L I G H T S 2 0 2 2

proposed that Ce does not improve the intrinsic catalytic properties of Mn at low reaction temperatures and that the effect of Ce is purely structural due to an increase in catalyst surface area. This provides a direction towards settling the ongoing debate about the role of Ce on the catalytic performance of Mn.

On the other hand, the addition of Ce has a positive effect on product selectivity. Figure 133b shows the

formation of undesired N2O as a function of the Mn surface density. The results show an exponential increase of the N2O formation with the Mn surface density, which suggests that Mn species in close proximity participate in the kinetic formation of N2O. Therefore, adding Ce in the formulation dilutes the MnOx active sites and suppresses subsequent oxidation steps that result in N2O, as illustrated in Figure 133c. This still makes Ce a promising selectivity promotor for catalyst formulations.

Fig. 133: a) Surface-specific activities for the NO reduction at 150°C plotted as a function of the Mn content on the catalysts. The blue dots correspond to the ternary MnCeTi catalysts. The red dots are from the binary MnTi and the individual Mn catalysts.

Red and blue trendlines were added to guide the eyes. b) Surface- specific N2O rates at 150°C as a function of the Mn surface density. The blue line is a guide to the eye suggesting an exponential-type trend. c) Artistic illustration of the N2O reaction

mechanism in MnTi binary and MnCeTi ternary catalysts.

PRINCIPAL PUBLICATION AND AUTHORS

Unraveling the structure and role of Mn and Ce for NOx reduction in application-relevant catalysts, L.E. Gevers (a), L.R. Enakonda (a), A. Shahid, (a), S. Ould-Chikh (a), C.I.Q. Silva (a), P.P. Paalanen (a), A. Aguilar-Tapia (b), J.-L. Hazemann (b,c), M.N. Hedhili (a), F. Wen (d), J. Ruiz-Martínez (a), Nat. Commun. 13, 2960 (2022); https:/doi.org/10.1038/s41467-022-30679-9 (a) King Abdullah University of Science and Technology, KAUST Catalysis Center (Saudi Arabia) (b) Institut de Chimie Moléculaire de Grenoble (France) (c) Institut Néel, Grenoble (France) (d) Umicore AG & Co. KG (Germany)

REFERENCES

[1] R. Zhang et al., Chem. Rev. 116, 3658-3721 (2016).