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Operando and Postreaction Diffraction Imaging of the La–Sr/CaO Catalyst in the Oxidative Coupling of Methane Reaction

Operando and Postreaction Diffraction Imaging figureOur paper on Operando and Postreaction Diffraction Imaging of the La–Sr/CaO Catalyst in the Oxidative Coupling of Methane Reaction has been published online by The Journal of Physical Chemistry.

A La–Sr/CaO catalyst was studied operando during the oxidative coupling of methane (OCM) reaction using the X-ray diffraction computed tomography technique. Full-pattern Rietveld analysis was performed in order to track the evolving solid-state chemistry during the temperature ramp, OCM reaction, as well as after cooling to room temperature. We observed a uniform distribution of the catalyst main components: La2O3, CaO–SrO mixed oxide, and the high-temperature rhombohedral polymorph of SrCO3. These were stable initially in the reaction; however, doubling the gas hourly space velocity resulted in the decomposition of SrCO3 to SrO, which subsequently led to the formation of a second CaO–SrO mixed oxide. These two mixed CaO–SrO oxides differed in terms of the extent of Sr incorporation into their unit cell. By applying Vegard’s law during the Rietveld refinement, it was possible to create maps showing the spatial variation of Sr occupancy in the mixed CaO–SrO oxides. The formation of the Sr-doped CaO species is expected to have an important role in this system through the enhancement of the lattice oxygen diffusion as well as increased catalyst basicity.

Read the full article at https://pubs.acs.org/doi/10.1021/acs.jpcc.8b09018

Prof. Andrew Beale discusses our recently published paper on 5D diffraction imaging in his Behind the Paper article – Chemistry in multiple dimensions

3D image for chemistry in multiple dimensionsSolid catalysts are used in almost every field of the chemical industry, ranging from pharmaceuticals to petrochemicals as well as the automotive industry, to produce the desired products. These catalytic solids usually comprise complex 3D structures which can be inhomogeneous. In recent years, it has been realised that it is crucial to investigate these materials using characterisation techniques that provide spatially-resolved information as these heterogeneities can play a crucial role in the catalyst performance.

In our recent paper in Nature Communications we show that synchrotron X-ray diffraction computed tomography (XRD-CT) can be used to study the evolution in solid-state composition in complex materials in 3D under real process conditions and as a function of time; specifically a complex multi-component Ni-Pd/CeO2-ZrO2/Al2O3 solid catalyst under operating conditions.

Read the full article at https://chemistrycommunity.nature.com/channels/1465-behind-the-paper/posts/40955-5d-chemical-imaging