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Coherent diffrAction foR a look Inside Nanostructures towards atomic rEsolution: catalysis and interface

Periodic Reporting for period 2 - CARINE (Coherent diffrAction foR a look Inside Nanostructures towards atomic rEsolution: catalysis and interface)

Reporting period: 2021-05-01 to 2022-10-31

To help optimising (electro- or photo-) catalyst and reactor operations simultaneously, it is important to develop tools for in situ characterisation of nanocatalysts under realistic reaction conditions to monitor the dynamics of catalysts with high spatial, temporal and energy resolutions. How a catalyst works is rather complex: molecules adsorb to surface of catalyst and onto support, catalyst sits on support; different molecules move on facets and interact; product molecule desorbs, ... Of particular interest for catalysis chemists is the simultaneous in situ characterization of the chemical, morphological and structural (strain, defects, …) dynamical evolution of individual nanoparticles at high resolution and (near) operational conditions. Among all the x-ray diffraction techniques, coherent x-ray diffraction (CDI) is one of the most promising. When applied under Bragg conditions, CDI has a unique sensitivity to atomic displacement and strain. The local symmetry of reciprocal space can be broken giving rise to a complex object in direct space, whose modulus represents the electron density of the object, and the phase, i.e. the displacements of these electron density portions relative to one another (with pm sensitivity), corresponding to strain. Progress in the catalytic issues requires the creation and development of new groundbreaking CDI methodology and techniques.

The CARINE project includes four important objectives:
1) the development of new in situ and operando environments (including temperature, gas and mass spectrometry analysis) compatible with nano-focused x-ray beams,
2) new coherent x-ray diffraction methodology for improved resolution and reproducibility in reconstructions.
3) the resolution of catalyst structures in situ and during operation
4) dynamic “real time” Bragg coherent diffraction imaging during catalysis

This research is aimed at implementing and developing new infrastructures and methodologies for state-of-the-art x-ray based in situ experiments to probe in 3D catalytic nanostructures, i.e. materials of next-generation nanometric devices for future sustainable energy supply as well as for eco-technology and “green” chemistry (case of water-splitting). The project will also impact other fields, e.g. nanoparticle synthesis / thermodynamic properties of alloyed nanoparticles / interface energies and Wulff shapes in different chemical environments.
We have developed the methodology around Bragg coherent x-ray diffraction as well as obtained major results in the field of structural imaging of model catalysts.

We have published a paper to give clues for a quantitative determination of strain in Bragg coherent x-ray diffraction imaging [J. Carnis, et al., Sci Rep 9, 1 (2019)].

In Ref. [N. Li et al., Sci Rep 10, 12760 (2020)], we have explored the use of continuous scanning during data acquisition for Bragg coherent diffraction imaging. Continuous scanning will allow to minimise sample instability under the beam and will become increasingly important at diffraction limited storage ring light sources.

We have also demonstrated the use of variable-wavelength quick scanning nano-focused x-ray microscopy for in situ strain and tilt mapping [M.-I. Richard, et al., Small 16, 1905990 (2020)].

We have applied Bragg coherent x-ray diffraction to map the evolution of structural defects along a nanowire [N. Li et al., ACS Nano 14, 10305 (2020)].

Studying model nanoparticles is one approach to better understand the structural evolution of a catalyst during reactions. A facet recognition algorithm has been applied to the image nanoparticles and provide facet-dependent structural information for all measured nanoparticles [J. Carnis, et al., Small 17, 2007702 (2021)].

Ordered phases are essential to enhance the magnetic or catalytic properties of alloyed nanoparticles. We have shown that a fully accurate strain distribution can be retrieved from both fundamental (in ordered and disordered phases) and superstructure (only in ordered phases) reflections [M. Dupraz, et al., J Appl Cryst 53, 5 (2020)].

For the first time, we have applied machine learning for defect classification from 3D coherent diffraction patterns [B. Lim et al., Npj Comput Mater 7, 1 (2021)]. We have demonstrated the use of a computational tool based on a 3D parametric atomistic model and a convolutional neural network to predict dislocations in a crystal from its 3D coherent diffraction pattern.

We have successfully demonstrated the possibility of measuring in 3D particles as small as 20 nm [M.-I. Richard et al., J. Appl. Crystallogr. 55, 621 (2022)] and of applying phase retrieval for the 3D diffraction patterns of these particles.

We have developed Gwaihir, a user-friendly and open-source tool to process and analyse Bragg coherent X-ray diffraction data. Its graphical interface, based on Jupyter Notebook widgets, combines an interactive approach for data analysis with a powerful environment destined to link large-scale facilities and scientists [D. Simonne et al., J. Appl. Crystallogr. accepted (2022)]. It is public for the community.

We have reported an unusual twin boundary migration process in a single platinum nanoparticle during CO oxidation using Bragg coherent diffraction imaging as the characterisation tool. Density functional theory calculations show that twin migration can be correlated with the relative change in the interfacial energies of the free surfaces exposed to CO [J. Carnis et al., Nat Commun 12, 5385 (2021)].

We have successfully measured in situ the catalytic structure-activity relationships of single Pt nanoparticles by nano-focused coherent Bragg imaging during CO oxidation [M. Dupraz et al., Nat Commun 13, 1 (2022)]. Density Functional Theory as well as atomistic simulations have been performed to link the structure (strain) to adsorption of atoms/molecules.
Our progress:
Demonstration of
- the feasibility of imaging the complex structure of very small particles in three dimensions. This paves the way towards the observation of realistic catalytic particles.
- continuous scanning for Bragg coherent x-ray imaging
- dynamic structural properties in catalysis during CO oxidation: twin migration, reshaping of nanoparticles and atomic/molecular adsorption depending on the type of crystallographic {hkl} facets of the nanoparticles
- the use of variable-wavelength quick scanning nano-focused x-ray microscopy
- the ability to identify defects from the diffraction pattern alone using machine learning to accelerate experiment design and execution.

Our expected results are:
- to gather essential knowledge to control the effects of both surface and interface at the nanometer scale for catalysis via advanced in situ and operando characterization methods
- to provide clues to control in situ and operando the surface/interface effects and new possibilities for tuning and optimizing the functional physical and chemical properties of nanomaterials
- to image deep inside matter in complex, active environments
- to enable strain-engineered catalysis
- to extract parameters to be incorporated into models to overcome the “cook and look” approach (i.e. to develop a predictive science)
- to deliver new breakthroughs and new models in the design of catalytic materials.
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