Operando coherent X-ray diffraction: imaging in 3D dimensions nanoparticle catalysts

Abstract

Gold nanoparticles are highly active catalysts for CO oxidation, although bulk gold is considered quite inert even to reactive molecules, the nanometer-size gold particles are efficient catalysts. Several effects contribute to the catalytic properties of supported nanoparticles catalysts such as particle size, morphology, interaction with the support, low-coordinated atoms, strain effects and crystalline defects (dislocations, grain boundaries). During the reaction, nanoparticle surface goes under dynamic restructuration and expose different surface sites and defects with distinct reactivity. Understanding how the nanoparticles re-structure and catalyze the reactions is crucial and requires the study of active sites in situ and operando conditions. Coherent diffractive imaging (CDI) is a recent powerful X-ray imaging technique ideally suited for quantitative 3D characterization of materials at the nanoscale under operating conditions. CDI gives information about the nanoparticle 3D morphology (electron density distribution), the lattice distortion and defects (phase shift) and displacement of the material from an ideal lattice (strain). The defectives and strained regions have chemical and physical properties that are significantly different from those of unstrained surfaces and can affect the catalytic process. We intend to understand the mechanisms during the catalytic reaction and identify the active sites of supported gold catalysts as well as their strains and defects. The dynamic of gold nanoparticle surface restructuring process will be investigated in situ and operando by CDI during the CO oxidation reaction. The gold nanoparticles will be supported in metal oxides with different reactivity, TiO2, Al2O3 and CeO2. The influence of the support in the shape, strain, defects and stability of the gold nanoparticles will be investigated by advanced images techniques, CDI and electron microscopy. The experimental set up for CDI experiments will be compatible with electron microcopy which allows analyze the same sample before and after the reaction by both techniques and get complementary information. This study will contribute to the field of strain-engineered in catalysis and materials science optimizing the nanoparticles defects for a wide range of applications. (AU)