Size of Au-Nanoparticles Supported on Mesostructural Cellular Foams Studied by the Pair Distribution Function Technique

Mesostructural cellular foam (MCF) materials that were modified by Zr, Nb, and Mo incorporation, followed by APTMS (3-aminopropyl-trimethoxysilane) grafting and gold loading were studied using the pair distribution function (PDF) technique. Measurements were focused on changes in gold crystallite sizes and on local geometry changes in the supports. Initially, ex situ prepared samples were investigated at different stages of synthesis and after catalytic oxidation of carbon monoxide. The crystallization and agglomeration of gold species as well as carbon monoxide oxidation were then tracked by in situ high energy diffraction measurements. The influence of metal type (Nb or Mo) and incorporation method in the MCF material on the agglomeration of metallic gold particles during increasing calcination temperature was determined. The structure of MCF materials was preserved during calcination and oxidation of CO and local symmetry of gold particles is not changed under CO oxidation conditions. In samples oxidized in the laboratory flow reactor, the interaction of gold particles with the reagents (CO and O₂) leads to slight decrease in gold particle size

Additional file 1: of Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms

Data S1. A table listing all parameters, but those listed in Table 1, which were refined during PDF data analysis

Arsenate and Selenate Scavenging by Basaluminite: Insights into the Reactivity of Aluminum Phases in Acid Mine Drainage

Basaluminite precipitation may play an important role in the behavior of trace elements in water and sediments affected by acid mine drainage and acid sulfate soils. In this study, the affinity of basaluminite and schwertmannite for arsenate and selenate is compared, and the coordination geometries of these oxyanions in both structures are reported. Batch isotherm experiments were conducted to examine the sorption capacity of synthetic schwertmannite and basaluminite and the potential competitive effect of sulfate. In addition, synchrotron-based techniques such as differential pair distribution function (d-PDF) analysis and extended X-ray absorption fine structure (EXAFS) were used to determine the local structure of As­(V) and Se­(VI) complexes. The results show that oxyanion exchange with structural sulfate was the main mechanism for removal of selenate, whereas arsenate was removed by a combination of surface complexes and oxyanion exchange. The arsenate adsorption capacity of basaluminite was 2 times higher than that of schwertmannite and 3 times higher than that of selenate in both phases. The sulfate:arsenate and sulfate:selenate exchange ratios were 1:2 and 1:1, respectively. High sulfate concentrations in the solutions did not show a competitive effect on arsenate sorption capacity but had a strong impact on selenate uptake, suggesting some kind of specific interaction for arsenate. Both d-PDF and EXAFS results indicated that the bidentate binuclear inner sphere was the most probable type of ligand for arsenate on both phases and for selenate on schwertmannite, whereas selenate forms outer-sphere complexes in the aluminum octahedral interlayer of basaluminite. Overall, these results show a strong affinity of poorly crystalline aluminum phases such as basaluminite for As­(V) and Se­(VI) oxyanions, with adsorption capacities on the same order of magnitude as those of iron oxides. The results obtained in this study are relevant to the understanding of trace element behavior in environments affected by acid water, potentially opening new research lines focused on remediation by natural attenuation processes or engineered water treatment systems

Additional file 2: of Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms

Data S2. The sensitivity of calculated XRD patterns to the number of TCMn3+

Real-Time <i>Operando</i> Diffraction Imaging of La–Sr/CaO During the Oxidative Coupling of Methane

An La–Sr/CaO catalyst has been chemically imaged during activation and under <i>operando</i> conditions during the oxidative coupling of methane reaction (OCM) at high temperature using X-ray diffraction computed tomography (XRD-CT) in combination with full pattern Rietveld refinement. At room temperature the main components of the catalyst were present as carbonates and hydroxides. During the activation stage (temperature ramp) they decomposed, forming La₂O₃, SrO, and mixed CaO–SrO oxides. Under the OCM reaction conditions, the predominant phases present were (∼20% wt) La₂O₃ and CaO-SrO (∼45% wt), and these remained stable throughout the entire reaction, whereas SrO, formed during activation, reacted with produced CO₂ leading to formation of SrCO₃ (∼35% wt). Two polymorphs of SrCO₃, orthorhombic and rhombohedral, were found to be stable under reaction conditions although the extent to which these phases were observed varied spatially and temporally with reactant gas composition. The presence of the high temperature rhombohedral polymorph can be associated with higher combustion activity, and since the Rietveld analysis is performed on a pixel-by-pixel basis, it is possible to observe, for the first time, domains of differing activity within the reactor