Catalytic processes including adsorption and desorption of molecules affect atomic spacing near the surface and therefore it is important to study in operando and in-situ with a capability of determining local structure at the nanoscale. In particular, as materials for catalysis are beginning to be constructed in three dimensions from the bottom up, new tools to investigate them are desperately needed. In this work, we examine the strain distributions under different conditions of catalytic process and how the strain to modify the sorption energies of reactants and to reflect to surface catalytic activity. Coherent X-ray diffraction imaging (CXDI) allows determining the shape of the nanoparticles and the deformation field by mapping the phase through the crystal structure. Even though the spatial resolution of CXDI at current stage is yet ~10 nm, a resolution in the displacement retrieved from the phase is less than 0.1 nm. In this talk, we show the two examples of the evolution of in-situ local deformation field by CXDI. First, Pt nanoparticles are measured during the oxidation process of methane. Retrieved phases indicate changes above the activation temperature of methane oxidation. Because of the binding (or surface adsorption) energy of the gases, we observed the different magnitude of the deformation field distribution along the catalytic oxidation process. In addition, our simulation results show that the structural deformation is related to the interaction between the catalysts and the reactants and the adsorption of reactants can be varied with the crystal facets and edges. Second, Cu exchanged ZSM-5 zeolites are measured during the nitrogen oxide reduction catalysis using CXDI technique with the X-ray free electron laser. The use of additional hydrocarbon to activate the Cu ions at relatively low temperature, results in the observation of unusual strain during the catalytic process and is the signature of the inhomogeneous distribution of hydrocarbons adsorbed at particular areas of the zeolites. The strain is then released during the subsequent steps of the catalytic process of the reduction of the nitrogen oxides. The observed time dependence of the strain development during the catalytic process should therefore be considered as a major factor in the design of future catalytic materials.

Atomic scale strain field distribution of catalyst during the reaction process by coherent x-ray diffraction imaging

253rd National Meeting (2017)

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