Active site localization of methane oxidation on Pt nanocrystals

Abstract

High catalytic efficiency in metal nanocatalysts is attributed to large surface area to volume ratios and an abundance of under-coordinated atoms that can decrease kinetic barriers. Although overall shape or size changes of nanocatalysts have been observed as a result of catalytic processes, structural changes at low-coordination sites such as edges, remain poorly understood. Here, we report high-lattice distortion at edges of Pt nanocrystals during heterogeneous catalytic methane oxidation based on in situ 3D Bragg coherent X-ray diffraction imaging. We directly observe contraction at edges owing to adsorption of oxygen. This strain increases during methane oxidation and it returns to the original state after completing the reaction process. The results are in good agreement with finite element models that incorporate forces, as determined by reactive molecular dynamics simulations. Reaction mechanisms obtained from in situ strain imaging thus provide important insights for improving catalysts and designing future nanostructured catalytic materials.

In situ three-dimensional imaging of strain in gold nanocrystals during catalytic oxidation

“…The availability of coherent hard X-rays from synchrotron light sources opens new opportunities for imaging studies of nanomaterials, 13,14 where Bragg coherent Xray diffraction imaging (Bragg CDI) can reveal the strain distribution of single micro-and nano-sized objects in three dimensions and under operando conditions. [15][16][17][18][19][20][21] Here, we investigate a model gold sample under CO oxidation reaction conditions at ambient pressure. Besides oen being considered as a prototypical reaction to study the fundamental concepts of heterogeneous catalysis, this reaction is also of high environmental and societal importance.…”

Bragg coherent imaging of nanoprecipitates: role of superstructure reflections

“…The good spatial resolution and extremely high strain sensitivity of BCDI make it the only technique suitable to image the 3D field of nanoprecipitates in the size range where they are still in perfect coherence with the matrix. More importantly, the technique is particularly adapted for in situ and operando experiments (Dupraz et al, 2017;Kim et al, 2018), and we foresee the possibility of imaging the evolution of the shape and strain fields in real time during ageing at HT. Such knowledge would help in understanding how to design stable microstructures that retain excellent mechanical properties at HT.…”

Structure of a single palladium nanoparticle and its dynamics during the hydride phase transformation

“…The possibility of using reactive environments during the measurement makes BCDI an ideal technique to probe dynamic changes and observe the evolution of defects' distribution. In recent years, in situ BCDI has revealed the dynamics occurring during catalytic processes [15][16][17] , strain mapping and nucleation dislocation during ionic diffusion in Lithium-ion batteries [18][19][20][21][22] , as well as the defect evolution during the hydriding phase transformation of palladium nanocrystals [23][24][25] . In ref.…”