In situ X-ray diffraction computed tomography studies examining the thermal and chemical stabilities of working Ba0.5Sr0.5Co0.8Fe0.2O3-δ membranes during oxidative coupling of methane

Mapping of lithium ion concentrations in 3D structures through development of in situ correlative imaging of X-ray Compton scattering-computed tomography

Understanding the correlation between chemical and microstructural properties is critical for unraveling the fundamental relationship between materials chemistry and physical structures that can benefit materials science and engineering. Here, we demonstrate novel in situ correlative imaging of the X-ray Compton scattering computed tomography (XCS-CT) technique for studying this fundamental relationship. XCS-CT can image light elements that do not usually exhibit strong signals using other X-ray characterization techniques. This paper describes the XCS-CT setup and data analysis method for calculating the valence electron momentum density and lithium-ion concentration, and provides two examples of spatially and temporally resolved chemical properties inside batteries in 3D. XCS-CT was applied to study two types of rechargeable lithium batteries in standard coin cell casings: (1) a lithium-ion battery containing a cathode of bespoke microstructure and liquid electrolyte, and (2) a solid-state battery containing a solid-polymer electrolyte. The XCS-CT technique is beneficial to a wide variety of materials and systems to map chemical composition changes in 3D structures.

Recent developments in X-ray diffraction/scattering computed tomography for materials science

X-ray diffraction/scattering computed tomography (XDS-CT) methods are a non-destructive class of chemical imaging techniques that have the capacity to provide reconstructions of sample cross-sections with spatially resolved chemical information. While X-ray diffraction CT (XRD-CT) is the most well-established method, recent advances in instrumentation and data reconstruction have seen greater use of related techniques like small angle X-ray scattering CT and pair distribution function CT. Additionally, the adoption of machine learning techniques for tomographic reconstruction and data analysis are fundamentally disrupting how XDS-CT data is processed. The following narrative review highlights recent developments and applications of XDS-CT with a focus on studies in the last five years. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Kinetics of Strontium Carbonate Formation on a Ce-Doped SrFeO3 Perovskite

Some perovskites exhibit catalytic activity in the abatement of organic pollutants in water. However, their performance decreases over time, possibly due to forms of poisoning, such as carbonate formation. Here, we present the kinetics of carbonate formation on a Ce-doped SrFeO3 perovskite with formula Sr0.85Ce0.15FeO3−δ (SCF), which can act as a thermocatalyst for the degradation of organic pollutants. The carbonate formation was studied in air, in deionized water, and during degradation of bisphenol A. The formation of SrCO3 occurred for perovskites in aqueous environments, i.e., when dispersed in water or used as catalysts in the degradation of bisphenol A, while no SrCO3 was detected for samples stored in air for up to 195 days. SrCO3 formation was detected using both XRD and ATR-FT-IR, and from the XRD, the crystallite size was found to decrease when carbonates formed. The samples containing SrCO3 showed an increasing mass loss at >610 °C with increasing time used as catalysts or dispersed in water, showing that SCF reduces its own efficiency during catalytic use. The kinetics of carbonate formation based on the TGA measurements showed that SrCO3 forms approximately three times faster during the degradation of organic compounds in water compared to SCF dispersed in water. The formation of SrCO3 in SCF is thermally reversible; thus, the catalyst can resume its activity after heat treatment at 900 °C for 1 h.

Direct Conversion of Methane to C2 Hydrocarbons in Solid-State Membrane Reactors at High Temperatures

Direct conversion of methane to C₂ compounds by oxidative and nonoxidative coupling reactions has been intensively studied in the past four decades; however, because these reactions have intrinsic severe thermodynamic constraints, they have not become viable industrially. Recently, with the increasing availability of inexpensive "green electrons" coming from renewable sources, electrochemical technologies are gaining momentum for reactions that have been challenging for more conventional catalysis. Using solid-state membranes to control the reacting species and separate products in a single step is a crucial advantage. Devices using ionic or mixed ionic-electronic conductors can be explored for methane coupling reactions with great potential to increase selectivity. Although these technologies are still in the early scaling stages, they offer a sustainable path for the utilization of methane and benefit from the advances in both solid oxide fuel cells and electrolyzers. This review identifies promising developments for solid-state methane conversion reactors by assessing multifunctional layers with microstructural control; combining solid electrolytes (proton and oxygen ion conductors) with active and selective electrodes/catalysts; applying more efficient reactor designs; understanding the reaction/degradation mechanisms; defining standards for performance evaluation; and carrying techno-economic analysis.

Multi-Scale Studies of 3D Printed Mn–Na–W/SiO2 Catalyst for Oxidative Coupling of Methane

This work presents multi-scale approaches to investigate 3D printed structured Mn–Na–W/SiO2 catalysts used for the oxidative coupling of methane (OCM) reaction. The performance of the 3D printed catalysts has been compared to their conventional analogues, packed beds of pellets and powder. The physicochemical properties of the 3D printed catalysts were investigated using scanning electron microscopy, nitrogen adsorption and X-ray diffraction (XRD). Performance and durability tests of the 3D printed catalysts were conducted in the laboratory and in a miniplant under real reaction conditions. In addition, synchrotron-based X-ray diffraction computed tomography technique (XRD-CT) was employed to obtain cross sectional maps at three different positions selected within the 3D printed catalyst body during the OCM reaction. The maps revealed the evolution of catalyst active phases and silica support on spatial and temporal scales within the interiors of the 3D printed catalyst under operating conditions. These results were accompanied with SEM-EDS analysis that indicated a homogeneous distribution of the active catalyst particles across the silica support.

DLSR: a solution to the parallax artefact in X-ray diffraction computed tomography data

A new tomographic reconstruction algorithm is presented, termed direct least-squares reconstruction (DLSR), which solves the well known parallax problem in X-ray-scattering-based experiments. The parallax artefact arises from relatively large samples where X-rays, scattered from a scattering angle 2θ, arrive at multiple detector elements. This phenomenon leads to loss of physico-chemical information associated with diffraction peak shape and position (i.e. altering the calculated crystallite size and lattice parameter values, respectively) and is currently the major barrier to investigating samples and devices at the centimetre level (scale-up problem). The accuracy of the DLSR algorithm has been tested against simulated and experimental X-ray diffraction computed tomography data using the TOPAS software.