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A combination of several in situ techniques (XRD, XAS, AP-XPS, and E-TEM) was used to explore links between the structural and chemical properties of a Cu@TiOx catalyst under CO2 hydrogenation conditions. The active phase of the catalyst involved an inverse oxide/metal configuration, but the initial core@shell motif was disrupted during the pretreatment in H2. As a consequence of strong metal–support interactions, the titania shell cracked, and Cu particles migrated from the core to on top of the oxide with the simultaneous formation of a Cu–Ti–Ox phase. The generated Cu particles had a diameter of 20–40 nm and were decorated by small clusters of TiOx (<5 nm in size). Results of in situ XAS and XRD and images of E-TEM showed a very dynamic system, where the inverse oxide/metal configuration promoted the reactivity of the system toward CO2 and H2. At room temperature, CO2 oxidized the Cu nanoparticles (CO2,gas → COgas + Ooxide) inducing a redistribution of the TiOx clusters and big modifications in catalyst surface morphology. The generated oxide overlayer disappeared at elevated temperatures (>180 °C) upon exposure to H2, producing a transient surface that was very active for the reverse water–gas shift reaction (CO2 + H2 → CO + H2O) but was not stable at 200–350 °C. When oxidation and reduction occurred at the same time, under a mixture of CO2 and H2, the surface structure evolved toward a dynamic equilibrium that strongly depended on the temperature. Neither CO2 nor H2 can be considered as passive reactants. In the Cu@TiOx system, morphological changes were linked to variations in the composition of metal-oxide interfaces which were reversible with temperature or chemical environment and affected the catalytic activity of the system. The present study illustrates the dynamic nature of phenomena associated with the trapping and conversion of CO2. 

This study introduces a novel iterative Bragg peak removal with automatic intensity correction (IBR-AIC) methodology for X-ray absorption spectroscopy (XAS), specifically addressing the challenge of Bragg peak interference in the analysis of crystalline materials. The approach integrates experimental adjustments and sophisticated post-processing, including an iterative algorithm for robust calculation of the scaling factor of the absorption coefficients and efficient elimination of the Bragg peaks, a common obstacle in accurately interpreting XAS data, particularly in crystalline samples. The method was thoroughly evaluated on dilute catalysts and thin films, with fluorescence mode and large-angle rotation. The results underscore the technique's effectiveness, adaptability and substantial potential in improving the precision of XAS data analysis. While demonstrating significant promise, the method does have limitations related to signal-to-noise ratio sensitivity and the necessity for meticulous angle selection during experimentation. Overall, IBR-AIC represents a significant advancement in XAS, offering a pragmatic solution to Bragg peak contamination challenges, thereby expanding the applications of XAS in understanding complex materials under diverse experimental conditions.

 

In the context of developing novel fuel cell catalysts, we have successfully synthesized in high yields not only ultrathin nanowires with compositions of Pt1Ru1 and Pt3Ru1 but also more complex spoke-like dendritic clusters of Pt1Ru1 and Pt1Ru9 in ambient pressure under relatively straightforward, solution-based reaction conditions, mediated by either CTAB (cetyltrimethylammonium bromide) or oleylamine (OAm), respectively. EXAFS analysis allowed us to determine the homogeneity of as-prepared samples. Based on this analysis, only the Pt3Ru1 sample was found to be relatively homogeneous. All of the other samples yielded results, suggestive of a tendency for the elements to segregate into clusters of ‘like’ atoms. We have also collected complementary HRTEM EDS mapping data, which support the idea of a segregation of elements consistent with the EXAFS results. We attribute the differences in the observed morphologies and elemental distributions within as-prepared samples to the presence of varying surfactants and heating environments, employed in these reactions. Methanol oxidation reaction (MOR) measurements indicated a correlation of specific activity (SA) values not only with intrinsic chemical composition and degree of alloying but also with the reaction process used to generate the nanoscale motifs in the first place. Specifically, the observed performance of samples tested decreased as a function of chemical composition (surfactant used in their synthesis), as follows: Pt3Ru1 (CTAB) > Pt1Ru1 (CTAB) > Pt1Ru1 (OAm) > Pt1Ru9 (OAm). 

This paper reports a robust strategy to catalyze in situ C–H oxidation by combining cobalt (Co) single-atom catalysts (SACs) and horseradish peroxidase (HRP). Co SACs were synthesized using the complex of Co phthalocyanine with 3-propanol pyridine at the two axial positions as the Co source to tune the coordination environment of Co by the stepwise removal of axial pyridine moieties under thermal annealing. These structural features of Co sites, as confirmed by infrared and X-ray absorption spectroscopy, were strongly correlated to their reactivity. All Co catalysts synthesized below 300 °C were inactive due to the full coordination of Co sites in octahedral geometry. Increasing the calcination temperature led to an improvement in catalytic activity for reducing O2, although molecular Co species with square planar coordination obtained below 600 °C were less selective to reduce O2 to H2O2 through the two-electron pathway. Co SACs obtained at 800 °C showed superior activity in producing H2O2 with a selectivity of 82–85% in a broad potential range. In situ production of H2O2 was further coupled with HRP to drive the selective C–H bond oxidation in 2-naphthol. Our strategy provides new insights into the design of highly effective, stable SACs for selective C–H bond activation when coupled with natural enzymes. 

Electrostrictors, materials developing mechanical strain proportional to the square of the applied electric field, present many advantages for mechanical actuation as they convert electrical energy into mechanical, but not vice versa. Both high relative permittivity and reliance on Pb as the key component in commercial electrostrictors pose serious practical and health problems. Here we describe a low relative permittivity (<250) ceramic, Zr_xCe_1-xO₂(x < 0.2), that displays electromechanical properties rivaling those of the best performing electrostrictors: longitudinal electrostriction strain coefficient ~10⁻¹⁶m²/V²; relaxation frequency ≈ a few kHz; and strain ≥0.02%. Combining X-ray absorption spectroscopy, atomic-level modeling and electromechanical measurements, here we show that electrostriction in Zr_xCe_1-xO₂is enabled by elastic dipoles produced by anharmonic motion of the smaller isovalent dopant (Zr). Unlike the elastic dipoles in aliovalent doped ceria, which are present even in the absence of an applied elastic or electric field, the elastic dipoles in Zr_xCe_1-xO₂are formed only under applied anisotropic field. The local descriptors of electrostrictive strain, namely, the cation size mismatch and dynamic anharmonicity, are sufficiently versatile to guide future searches in other polycrystalline solids.