The XV
th Colloque Ray et Matière was held from November 21 to 24, 2023 in Bordeaux.
The aim of this biennial French-language symposium is to bring together all the communities that use and develop X-ray instrumentation for the study of matter, with the aim of covering all the fields of application that meet societal needs and challenges.
On this occasion, Michael Grimes presented a poster entitled "
Capturing catalyst strain dynamics during in situ CO oxidation".
The study of nanoparticle (NP) assisted chemical reactions is important for the development of efficient catalyst materials for a wide range of environmental and energy applications
[1]. Such studies are primarily focused on the role of surface sites - whether on particle facets or vertices. The rate and efficiency of heterogeneous catalysis is dependent on these distinct adsorption energies and turnover rates
[2]. In addition to facet-dependent catalytic activity, lattice strain is known to influence the reactivity of metal surfaces. One technique that can be used to probe lattice displacement with pm precision is Bragg Coherent Diffraction Imaging (BCDI) [3]. From the lattice displacement, the local strain of metal NPs can be examined in situ during catalyst-enhanced reactions. This has already been applied to Pt NP under CO reaction conditions in the steady state to compare the strain changes at different facets
[4].
In order to probe the kinetics of heterogeneous catalysis a dynamic probe of strain evolution in Pt NP is required. We demonstrate how BCDI can be carried out in real time and with pump-probe techniques at a synchrotron
[5]. The latter represents the first such demonstration of this technique during an in situ chemical reaction. The strain evolution of a Pt NP is observed during catalysis of the CO oxidation reaction. The propagation of strain during O2 adsorption and reaction conditions is observed. Based on the order of the gas introduction, we observe that the evolution of strain is dependent on which precursor gas is adsorbed on the Pt surface. This is evidence for the different mechanisms that occur during the catalytic oxidation of CO gas. The 3D strain profile shows that the surface and sub-surface regions undergo the greatest change during the reaction with small changes in the bulk of nanoparticles. Depending on the reaction mechanism, the strain changes along the
{111} direction can be further localised to specific facets, where we observe the rate of increase of tensile strain (τ = 7.0 s) at Pt {111} facets. With a benchmark figure of 0.25 s resolution, we observe oscillatory strain changes (T = 6.8 s) which can be related to site specific CO adsorption during the oxidation reaction.
[1] Hammer, B. & Norskov, J. K (1995).
Nature 376, 238–240.
[2] McEwen, J. S.
et al. (2003)
Surf. Sci. 545, 47–69.
[3] Marchesini, S.
et al. (2003).
Phys. Rev. B, 68, 140101.
[4] Dupraz, M.
et al. (2022).
Nat. Commun. 13, 1–10.
[5] Grimes, M.
et al. (2023). In preparation.