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Monitoring the spontaneous reconstruction of the surface of metal oxides under electrocatalytic reaction conditions is critical to identifying the active sites and establishing structure-activity relationships. Here, we report on a self-terminated surface reconstruction of Ruddlesden-Popper lanthanum nickel oxide (La 2 NiO 4+δ ) that occurs spontaneously during reaction with alkaline electrolyte species. Using a combination of high-resolution scanning transmission electron microscopy (HR-STEM), surface-sensitive X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (sXAS), as well as electrochemical techniques, we identify the structure of the reconstructed surface layer as an amorphous (oxy)hydroxide phase that features abundant under-coordinated nickel sites. No further amorphization of the crystalline oxide lattice (beyond the ∼2 nm thick layer formed) was observed during oxygen evolution reaction (OER) cycling experiments. Notably, the formation of the reconstructed surface layer increases the material's oxygen evolution reaction (OER) activity by a factor of 45 when compared to that of the pristine crystalline surface. In contrast, a related perovskite phase, i.e. , LaNiO 3 , did not show noticeable surface reconstruction, and also no increase in its OER activity was observed. This work provides detailed insight into a surface reconstruction behavior dictated by the crystal structure of the parent oxide and highlights the importance of surface dynamics under reaction conditions.

The reversible phase transitions in phase-change memory devices can switch on the order of nanoseconds, suggesting a close structural resemblance between the amorphous and crystalline phases. Despite this, the link between crystalline and amorphous tellurides is not fully understood nor quantified. Here we use in-situ high-temperature x-ray absorption spectroscopy (XAS) and theoretical calculations to quantify the amorphous structure of bulk and nanoscale GeTe. Based on XAS experiments, we develop a theoretical model of the amorphous GeTe structure, consisting of a disordered fcc-type Te sublattice and randomly arranged chains of Ge atoms in a tetrahedral coordination. Strikingly, our intuitive and scalable model provides an accurate description of the structural dynamics in phase-change memory materials, observed experimentally. Specifically, we present a detailed crystallization mechanism through the formation of an intermediate, partially stable 'ideal glass' state and demonstrate differences between bulk and nanoscale GeTe leading to size-dependent crystallization temperature., (© 2024. The Author(s).)

Supported, bimetallic catalysts have shown great promise for the selective hydrogenation of CO 2 to methanol. In this study, we decipher the catalytically active structure of Ni-Ga-based catalysts. To this end, model Ni-Ga-based catalysts, with varying Ni:Ga ratios, were prepared by a surface organometallic chemistry approach. In situ differential pair distribution function (d-PDF) analysis revealed that catalyst activation in H 2 leads to the formation of nanoparticles based on a Ni-Ga face-centered cubic (fcc) alloy along with a small quantity of GaO x . Structure refinements of the d-PDF data enabled us to determine the amount of both alloyed Ga and GaO x species. In situ X-ray absorption spectroscopy experiments confirmed the presence of alloyed Ga and GaO x and indicated that alloying with Ga affects the electronic structure of metallic Ni (viz., Ni δ- ). Both the Ni:Ga ratio in the alloy and the quantity of GaO x are found to minimize methanation and to determine the methanol formation rate and the resulting methanol selectivity. The highest formation rate and methanol selectivity are found for a Ni-Ga alloy having a Ni:Ga ratio of ∼75:25 along with a small quantity of oxidized Ga species (0.14 mol Ni -1 ). Furthermore, operando infrared spectroscopy experiments indicate that GaO x species play a role in the stabilization of formate surface intermediates, which are subsequently further hydrogenated to methoxy species and ultimately to methanol. Notably, operando XAS shows that alloying between Ni and Ga is maintained under reaction conditions and is key to attaining a high methanol selectivity (by minimizing CO and CH 4 formation), while oxidized Ga species enhance the methanol formation rate., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

This work provides insight into the local structure of Na in MgO-based CO 2 sorbents that are promoted with NaNO 3 . To this end, we use X-ray absorption spectroscopy (XAS) at the Na K-edge to interrogate the local structure of Na during the CO 2 capture (MgO + CO 2 ↔ MgCO 3 ). The analysis of Na K-edge XAS data shows that the local environment of Na is altered upon MgO carbonation when compared to that of NaNO 3 in the as-prepared sorbent. We attribute the changes observed in the carbonated sorbent to an alteration in the local structure of Na at the NaNO 3 /MgCO 3 interfaces and/or in the vicinity of [Mg 2+ ···CO 3 2- ] ionic pairs that are trapped in the cooled NaNO 3 melt. The changes observed are reversible, i.e., the local environment of NaNO 3 was restored after a regeneration treatment to decompose MgCO 3 to MgO. The ex situ Na K-edge XAS experiments were complemented by ex situ magic-angle spinning 23 Na nuclear magnetic resonance (MAS 23 Na NMR), Mg K-edge XAS and X-ray powder diffraction (XRD). These additional experiments support our interpretation of the Na K-edge XAS data. Furthermore, we develop in situ Na (and Mg) K-edge XAS experiments during the carbonation of the sorbent (NaNO 3 is molten under the conditions of the in situ experiments). These in situ Na K-edge XANES spectra of molten NaNO 3 open new opportunities to investigate the atomic scale structure of CO 2 sorbents modified with Na-based molten salts by using XAS., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Gallia-based shells with a thickness varying from a submonolayer to ca. 2.5 nm were prepared by atomic layer deposition (ALD) using trimethylgallium, ozone, and partially dehydroxylated silica, followed by calcination at 500 °C. Insight into the atomic-scale structure of these shells was obtained by high-field 71 Ga solid-state nuclear magnetic resonance (NMR) experiments and the modeling of X-ray differential pair distribution function data, complemented by Ga K-edge X-ray absorption spectroscopy and 29 Si dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) studies. When applying one ALD cycle, the grown submonolayer contains mostly tetracoordinate Ga sites with Si atoms in the second coordination sphere ( [4] Ga (Si) ) and, according to 15 N DNP SENS using pyridine as the probe molecule, both strong Lewis acid sites (LAS) and strong Brønsted acid sites (BAS), consistent with the formation of gallosilicate Ga-O-Si and Ga-μ 2 -OH-Si species. The shells obtained using five and ten ALD cycles display characteristics of amorphous gallia (GaO x ), i.e., an increased relative fraction of pentacoordinate sites ( [5] Ga (Ga) ), the presence of mild LAS, and a decreased relative abundance of strong BAS. The prepared Ga1-, Ga5-, and Ga10-SiO 2-500 materials catalyze the dehydrogenation of isobutane to isobutene, and their catalytic performance correlates with the relative abundance and strength of LAS and BAS, viz., Ga1-SiO 2-500 , a material with a higher relative fraction of strong LAS, is more active and stable compared to Ga5- and Ga10-SiO 2-500 . In contrast, related ALD-derived Al1-, Al5-, and Al10-SiO 2-500 materials do not catalyze the dehydrogenation of isobutane and this correlates with the lack of strong LAS in these materials that instead feature abundant strong BAS formed via the atomic-scale mixing of Al sites with silica, leading to Al-μ 2 -OH-Si sites. Our results suggest that [4] Ga (Si) sites provide strong Lewis acidity and drive the dehydrogenation activity, while the appearance of [5] Ga (Ga) sites with mild Lewis activity is associated with catalyst deactivation through coking. Overall, the atomic-level insights into the structure of the GaO x -based materials prepared in this work provide a guide to design active Ga-based catalysts by a rational tailoring of Lewis and Brønsted acidity (nature, strength, and abundance)., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The development of effective CO 2 sorbents is vital to achieving net-zero CO 2 emission targets. MgO promoted with molten salts is an emerging class of CO 2 sorbents. However, the structural features that govern their performance remain elusive. Using in situ time-resolved powder x-ray diffraction, we follow the structural dynamics of a model NaNO 3 -promoted, MgO-based CO 2 sorbent. During the first few cycles of CO 2 capture and release, the sorbent deactivates owing to an increase in the sizes of the MgO crystallites, reducing in turn the abundance of available nucleation points, i.e., MgO surface defects, for MgCO 3 growth. After the third cycle, the sorbent shows a continuous reactivation, which is linked to the in situ formation of Na 2 Mg(CO 3 ) 2 crystallites that act effectively as seeds for MgCO 3 nucleation and growth. Na 2 Mg(CO 3 ) 2 forms due to the partial decomposition of NaNO 3 during regeneration at T ≥ 450°C followed by carbonation in CO 2 .

We elucidate the underlying cause of a commonly observed increase in the rate of oxygen release of an oxygen carrier with redox cycling (here specifically for the perovskite Sr 0.8 Ca 0.2 FeO 3- δ ) in chemical looping applications. This phenomenon is often referred to as activation. To this end we probe the evolution of the structure and surface elemental composition of the oxygen carrier with redox cycling by both textural and morphological characterization techniques (N 2 physisorption, microscopy, X-ray powder diffraction and X-ray absorption spectroscopy). We observe no appreciable changes in the surface area, pore volume and morphology of the sample during the activation period. X-ray powder diffraction and X-ray absorption spectroscopy analysis (at the Fe and Sr K -edges) of the material before and after redox cycles do not show significant differences, implying that the bulk (average and local) structure of the perovskite is largely unaltered upon cycling. The analysis of the surface of the perovskite via X-ray photoelectron and in situ Raman spectroscopy indicates the presence of surface carbonate species in the as-synthesized sample (due to its exposure to air). Yet, such surface carbonates are absent in the activated material, pointing to the removal of carbonates during cycling (in a CO 2 -free atmosphere) as the underlying cause behind activation. Importantly, after activation and a re-exposure to CO 2 , surface carbonates re-form and yield a deactivation of the perovskite oxygen carrier, which is often overlooked when using such materials at relatively low temperature (≤500 °C) in chemical looping., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Establishing generic catalyst design principles by identifying structural features of materials that influence their performance will advance the rational engineering of new catalytic materials. In this study, by investigating metal-substituted manganese oxide (spinel) nanoparticles, Mn 3 O 4 :M (M=Sr, Ca, Mg, Zn, Cu), we rationalize the dependence of the activity of Mn 3 O 4 :M for the electrocatalytic oxygen reduction reaction (ORR) on the enthalpy of formation of the binary MO oxide, Δ f H°(MO), and the Lewis acidity of the M 2+ substituent. Incorporation of elements M with low Δ f H°(MO) enhances the oxygen binding strength in Mn 3 O 4 :M, which affects its activity in ORR due to the established correlation between ORR activity and the binding energy of *O/*OH/*OOH species. Our work provides a perspective on the design of new compositions for oxygen electrocatalysis relying on the rational substitution/doping by redox-inactive elements., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

MgO-based CO 2 sorbents promoted with molten alkali metal nitrates (e.g., NaNO 3 ) have emerged as promising materials for CO 2 capture and storage technologies due to their low cost and high theoretical CO 2 uptake capacities. Yet, the mechanism by which molten alkali metal nitrates promote the carbonation of MgO (CO 2 capture reaction) remains debated and poorly understood. Here, we utilize 18 O isotope labeling experiments to provide new insights into the carbonation mechanism of NaNO 3 -promoted MgO sorbents, a system in which the promoter is molten under operation conditions and hence inherently challenging to characterize. To conduct the 18 O isotope labeling experiments, we report a facile and large-scale synthesis procedure to obtain labeled MgO with a high 18 O isotope content. We use Raman spectroscopy and in situ thermogravimetric analysis in combination with mass spectrometry to track the 18 O label in the solid (MgCO 3 ), molten (NaNO 3 ), and gas (CO 2 ) phases during the CO 2 capture (carbonation) and regeneration (decarbonation) reactions. We discovered a rapid oxygen exchange between CO 2 and MgO through the reversible formation of surface carbonates, independent of the presence of the promoter NaNO 3 . On the other hand, no oxygen exchange was observed between NaNO 3 and CO 2 or NaNO 3 and MgO. Combining the results of the 18 O labeling experiments, with insights gained from atomistic calculations, we propose a carbonation mechanism that, in the first stage, proceeds through a fast, surface-limited carbonation of MgO. These surface carbonates are subsequently dissolved as [Mg 2+ ···CO 3 2- ] ionic pairs in the molten NaNO 3 promoter. Upon reaching the solubility limit, MgCO 3 crystallizes at the MgO/NaNO 3 interface., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Catalysts with well-defined isolated Ni(ii) surface sites have been prepared on three silica-based supports. The outer shells of the support were comprised either of an amorphous aluminosilicate or amorphous alumina (AlO x ) layer - associated with a high and low density of strong Brønsted acid sites (BAS), respectively. When tested for ethene-to-propene conversion, Ni catalysts with a higher density of strong BAS demonstrate a higher initial activity and productivity to propene. On all three catalysts, the propene productivity correlates closely with the concentration of C 8 aromatics, suggesting that propene may form via a carbon-pool mechanism. While all three catalysts deactivate with time on stream, the deactivation of catalysts with Ni(ii) sites on AlO x , i.e. , containing surface Ni aluminate sites, is shown to be reversible by calcination (coke removal), in contrast to the deactivation of surface Ni silicate or aluminosilicate sites, which deactivate irreversibly by forming Ni nanoparticles., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The thermal carburization of MoO 3 nanobelts (nb) and SiO 2 -supported MoO 3 nanosheets under a 1 : 4 mixture of CH 4  : H 2 yields Mo 2 C-nb and Mo 2 C/SiO 2 . Following this process by in situ Mo K-edge X-ray absorption spectroscopy (XAS) reveals different carburization pathways for unsupported and supported MoO 3 . In particular, the carburization of α-MoO 3 -nb proceeds via MoO 2 , and that of MoO 3 /SiO 2 via the formation of highly dispersed MoO x species. Both Mo 2 C-nb and Mo 2 C/SiO 2 catalyze the dry reforming of methane (DRM, 800 °C, 8 bar) but their catalytic stability differs. Mo 2 C-nb shows a stable performance when using a CH 4 -rich feed (CH 4  : CO 2 = 4 : 2), however deactivation due to the formation of MoO 2 occurs for higher CO 2 concentrations (CH 4  : CO 2 = 4 : 3). In contrast, Mo 2 C/SiO 2 is notably more stable than Mo 2 C-nb under the CH 4  : CO 2 = 4 : 3 feed. The influence of the morphology of Mo 2 C and its dispersion on silica on the structural evolution of the catalysts under DRM is further studied by in situ Mo K-edge XAS. It is found that Mo 2 C/SiO 2 features a higher resistance to oxidation under DRM than the highly crystalline unsupported Mo 2 C-nb and this correlates with an improved catalytic stability. Lastly, the oxidation of Mo in both Mo 2 C-nb and Mo 2 C/SiO 2 under DRM conditions in the in situ XAS experiments leads to an increased activity of the competing reverse water gas shift reaction., Competing Interests: The authors declare that there is no conflict of interest regarding the publication of this article., (This journal is © The Royal Society of Chemistry.)

This work explores how H 2 pretreatment at 550 °C induces structural transformation of two gallia-based propane dehydrogenation (PDH) catalysts, viz. nanocrystalline γ/β-Ga 2 O 3 and amorphous Ga 2 O 3 (GaO x ) supported on silica (γ-Ga 2 O 3 /SiO 2 and Ga/SiO 2 , respectively) and how it affects their activity, propene selectivity and stability with time on stream (TOS). Ga/SiO 2 -H 2 shows poor activity and propene selectivity, no coking and no deactivation with TOS, similar to Ga/SiO 2 . In contrast, the high initial activity and propene selectivity of γ-Ga 2 O 3 /SiO 2 -H 2 decline with TOS but to a lesser extent than in calcined γ-Ga 2 O 3 /SiO 2 . In addition, γ-Ga 2 O 3 /SiO 2 -H 2 cokes less than γ-Ga 2 O 3 /SiO 2 . Ga K-edge X-ray absorption spectroscopy suggests an increased disorder of the nanocrystalline γ/β-Ga 2 O 3 phases in γ-Ga 2 O 3 /SiO 2 -H 2 and the emergence of additional tetrahedral Ga sites (Ga IV ). Such Ga IV sites are strong Lewis acid sites (LAS) according to studies using adsorbed pyridine and CO probe molecules, i.e. , the abundance of strong LAS is higher in γ-Ga 2 O 3 /SiO 2 -H 2 compared to γ-Ga 2 O 3 /SiO 2 but lower than in Ga/SiO 2 and Ga/SiO 2 -H 2 . Dissociation of H 2 on the Ga-O linkages in γ-Ga 2 O 3 /SiO 2 -H 2 yields high-frequency Ga-H bands that are observed in Ga/SiO 2 and Ga/SiO 2 -H 2 but not detected in γ-Ga 2 O 3 /SiO 2 . We attribute the increased amount of Ga IV sites in γ-Ga 2 O 3 /SiO 2 -H 2 mostly to an increased disorder in γ/β-Ga 2 O 3 . X-ray photoelectron spectroscopy detects the formation of Ga + and Ga 0 species in both Ga/SiO 2 -H 2 and γ-Ga 2 O 3 /SiO 2 -H 2 . Therefore, it is likely that a minor amount of Ga IV sites also forms through the interaction of Ga + (such as Ga 2 O) and/or Ga 0 with silanol groups of SiO 2 ., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Chemical looping is an emerging technology to produce high purity hydrogen from fossil fuels or biomass with the simultaneous capture of the CO 2 produced at the distributed scale. This process requires the availability of stable Fe 2 O 3 -based oxygen carriers. Fe 2 O 3 -Al 2 O 3 based oxygen carriers exhibit a decay in the H 2 yield with cycle number, due to the formation of FeAl 2 O 4 that possesses a very low capacity for water splitting at typical operating conditions of conventional chemical looping schemes (700-1000 °C). In this study, the addition of sodium ( via a sodium salt) in the synthesis of Fe 2 O 3 -Al 2 O 3 oxygen carriers was assessed as a means to counteract the cyclic deactivation of the oxygen carrier. Detailed insight into the oxygen carrier's structure was gained by combined X-ray powder diffraction (XRD), X-ray absorption spectroscopy (XAS) at the Al, Na and Fe K-edges and scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDX) analyses. The addition of sodium prevented the formation of FeAl 2 O 4 and stabilized the oxygen carrier via the formation of a layered structure, Na-β-Al 2 O 3 phase. The material, i.e. Na-β-Al 2 O 3 stabilized Fe 2 O 3 , showed a stable H 2 yield of ca. 13.3 mmol g -1 over 15 cycles., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Gallia-alumina (Ga,Al) 2 O 3( x  :  y ) spinel-type solid solution nanoparticle catalysts for propane dehydrogenation (PDH) were prepared with four nominal Ga : Al atomic ratios (1 : 6, 1 : 3, 3 : 1, 1 : 0) using a colloidal synthesis approach. The structure, coordination environment and distribution of Ga and Al sites in these materials were investigated by X-ray diffraction, X-ray absorption spectroscopy (Ga K-edge) as well as 27 Al and 71 Ga solid state nuclear magnetic resonance. The surface acidity (Lewis or Brønsted) was probed using infrared spectroscopy with pyridine and 2,6-dimethylpyridine probe molecules, complemented by element-specific insights (Ga or Al) from dynamic nuclear polarization surface enhanced cross-polarization magic angle spinning 15 N{ 27 Al} and 15 N{ 71 Ga} J coupling mediated heteronuclear multiple quantum correlation NMR experiments using 15 N-labelled pyridine as a probe molecule. The latter approach provides unique insights into the nature and relative strength of the surface acid sites as it allows to distinguish contributions from Al and Ga sites to the overall surface acidity of mixed (Ga,Al) 2 O 3 oxides. Notably, we demonstrate that (Ga,Al) 2 O 3 catalysts with a high Al content show a greater relative abundance of four-coordinated Ga sites and a greater relative fraction of weak/medium Ga-based surface Lewis acid sites, which correlates with superior propene selectivity, Ga-based activity, and stability in PDH (due to lower coking). In contrast, (Ga,Al) 2 O 3 catalysts with a lower Al content feature a higher fraction of six-coordinated Ga sites, as well as more abundant Ga-based strong surface Lewis acid sites, which deactivate through coking. Overall, the results show that the relative abundance and strength of Ga-based surface Lewis acid sites can be tuned by optimizing the bulk Ga : Al atomic ratio, thus providing an effective measure for a rational control of the catalyst performance., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The development of stable Ni-based dry reforming of methane (DRM) catalysts is a key challenge owing to the high operating temperatures of the process and the propensity of Ni for promoting carbon deposition. In this work, Al 2 O 3 -coated Ni/SiO 2 catalysts have been developed by employing atomic layer deposition (ALD). The structure of the catalyst at each individual preparation step was characterized in detail through a combination of in situ XAS-XRD, ex situ 27 Al NMR and Raman spectroscopy. Specifically, in the calcination step, the ALD-grown Al 2 O 3 layer reacts with the SiO 2 support and Ni, forming aluminosilicate and NiAl 2 O 4 . The Al 2 O 3 -coated Ni/SiO 2 catalyst exhibits an improved stability for DRM when compared to the benchmark Ni/SiO 2 and Ni/Al 2 O 3 catalysts. In situ XAS-XRD during DRM together with ex situ Raman spectroscopy and TEM of the spent catalysts confirm that the ALD-grown Al 2 O 3 layer suppresses the sintering of Ni, in turn reducing also coke formation significantly. In addition, the formation of an amorphous aluminosilicate phase by the reaction of the ALD-grown Al 2 O 3 layer with the SiO 2 support inhibited catalysts deactivation via NiAl 2 O 4 formation, in contrast to the reference Ni/Al 2 O 3 system. The in-depth structural characterization of the catalysts provided an insight into the structural dynamics of the ALD-grown Al 2 O 3 layer, which reacts both with the support and the active metal, allowing to rationalize the high stability of the catalyst under the harsh DRM conditions., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Early transitional metal carbides are promising catalysts for hydrogenation of CO 2 . Here, a two-dimensional (2D) multilayered 2D-Mo 2 C material is prepared from Mo 2 CT x of the MXene family. Surface termination groups T x (O, OH, and F) are reductively de-functionalized in Mo 2 CT x (500 °C, pure H 2 ) avoiding the formation of a 3D carbide structure. CO 2 hydrogenation studies show that the activity and product selectivity (CO, CH 4 , C 2 -C 5 alkanes, methanol, and dimethyl ether) of Mo 2 CT x and 2D-Mo 2 C are controlled by the surface coverage of T x groups that are tunable by the H 2 pretreatment conditions. 2D-Mo 2 C contains no T x groups and outperforms Mo 2 CT x , β-Mo 2 C, or the industrial Cu-ZnO-Al 2 O 3 catalyst in CO 2 hydrogenation (evaluated by CO weight time yield at 430 °C and 1 bar). We show that the lack of surface termination groups drives the selectivity and activity of Mo-terminated carbidic surfaces in CO 2 hydrogenation., (© 2021. The Author(s).)

Since the discovery of charge disproportionation in the FeO_{2} square-lattice compound Sr_{3}Fe_{2}O_{7} by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained "hidden" to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO_{2} planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on "hidden order" in other materials.

The addition of molten alkali metal salts drastically accelerates the kinetics of CO 2 capture by MgO through the formation of MgCO 3 However, the growth mechanism, the nature of MgCO 3 formation, and the exact role of the molten alkali metal salts on the CO 2 capture process remain elusive, holding back the development of more-effective MgO-based CO 2 sorbents. Here, we unveil the growth mechanism of MgCO 3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO 3 The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO 2 , a noncrystalline surface carbonate layer of ca. 7-Å thickness forms. In contrast, when MgO(100) is coated with NaNO 3 , MgCO 3 crystals nucleate and grow. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO 3 MgCO 3 grows epitaxially with respect to MgO(100), and the lattice mismatch between MgCO 3 and MgO is relaxed through lattice misfit dislocations. Pyramid-shaped pits on the surface of MgO, in proximity to and below the MgCO 3 crystals, point to the etching of surface MgO, providing dissolved [Mg 2+ …O 2- ] ionic pairs for MgCO 3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions., Competing Interests: The authors declare no competing interest.

Background: Recent research shows AKI increases the risk of incident CKD. We hypothesized that perioperative AKI may confer increased risk of subsequent CKD compared to nonperioperative AKI., Methods: A MEDLINE search was performed for "AKI, CKD, chronic renal insufficiency, surgery, and perioperative" and related terms yielded 5209 articles. One thousand sixty-five relevant studies were reviewed. One thousand six were excluded because they were review, animal, or pediatric studies. Fifty-nine studies underwent full manuscript review by two independent evaluators. Seventeen met all inclusion criteria and underwent analysis. Two-by-two tables were constructed from AKI +/- and CKD +/- data. The R package metafor was employed to determine odds ratio (OR), and a random-effects model was used to calculate weighted ORs. Leave-1-out, funnel analysis, and structured analysis were used to estimate effects of study heterogeneity and bias., Results: Nonperioperative studies included studies of oncology, percutaneous coronary intervention, and myocardial infarction patients. Perioperative studies comprised patients from cardiac surgery, vascular surgery, and burns. There was significant heterogeneity, but risk of bias was overall assessed as low. The OR for AKI versus non-AKI patients developing CKD in all studies was 4.31 (95% CI 3.01-6.17; p < 0.01). Nonperioperative subjects demonstrated OR 3.32 for developing CKD compared to non-AKI patients (95% CI 2.06-5.34; p < 0.01) while perioperative patients demonstrated OR 5.20 (95% CI 3.12-8.66; p < 0.01) for the same event., Conclusions: We conclude that studies conducted in perioperative and nonperioperative patient populations suggest similar risk of development of CKD after AKI.

This work critically assesses the electrocatalytic activity, stability, and nature of the active phase of a two-dimensional molybdenum carbide (MXene) with single-atomic iron sites, Mo 2 C T x :Fe ( T x are surface terminating groups O, OH, and F), in the catalysis of the oxygen reduction reaction (ORR). X-ray absorption spectroscopy unequivocally confirmed that the iron single sites were incorporated into the Mo 2 C T x structure by substituting Mo atoms in the molybdenum carbide lattice with no other detectable Fe-containing phases. Mo 2 C T x :Fe, the first two-dimensional carbide with isolated iron sites, demonstrates a high catalytic activity and selectivity in the oxygen reduction to hydrogen peroxide. However, an analysis of the electrode material after the catalytic tests revealed that Mo 2 C T x :Fe transformed in situ into a graphitic carbon framework with dispersed iron oxyhydroxide (ferrihydrite, Fh) species (Fh/C), which are the actual active species. This experimental observation and the results obtained for the titanium and vanadium 2D carbides challenge previous studies that discuss the activity of the native MXene phases in oxygen electrocatalysis. Our work showcases the role of 2D metal carbides as precursors for active carbon-based (electro)catalysts and, more fundamentally, highlights the intrinsic evolution pathways of MXenes in electrocatalysis.

Synthesizing high-quality two-dimensional nanomaterials of nonlayered metal oxide is a challenge, especially when long-range single-crystallinity and clean high-energy surfaces are required. Reported here is the synthesis of single-crystalline MgO(111) nanosheets by a two-step process involving the formation of ultrathin Mg(OH) 2 nanosheets as a precursor, and their selective topotactic conversion upon heating under dynamic vacuum. The defect-rich surface displays terminal -OH groups, three-coordinated O 2- sites and low-coordinated Mg 2+ sites, as well as single electrons trapped at oxygen vacancies, which render the MgO nanosheets highly reactive, as evidenced by the activation of CO molecules at low temperatures and pressures with formation of strongly adsorbed red-shifted CO and coupling of CO molecules into C 2 species., (© 2020 Wiley-VCH GmbH.)

Carbon dioxide capture and storage technologies are short to mid-term solutions to reduce anthropogenic CO 2 emissions. CaO-based sorbents have emerged as a viable class of cost-efficient CO 2 sorbents for high temperature applications. Yet, CaO-based sorbents are prone to deactivation over repeated CO 2 capture and regeneration cycles. Various strategies have been proposed to improve their cyclic stability and rate of CO 2 uptake including the addition of promoters and stabilizers (e. g., alkali metal salts and metal oxides), as well as nano-structuring approaches. However, our fundamental understanding of the underlying mechanisms through which promoters or stabilizers affect the performance of the sorbents is limited. With the recent application of advanced characterization techniques, new insight into the structural and morphological changes that occur during CO 2 uptake and regeneration has been obtained. This review summarizes recent advances that have improved our mechanistic understanding of CaO-based CO 2 sorbents with and without the addition of stabilizers and/or promoters, with a specific emphasis on the application of advanced characterization techniques., (© 2020 Wiley-VCH GmbH.)

Calcium looping (CaL) is a CO2 capture technique based on the reversible carbonation/calcination of CaO that is considered promising to reduce anthropogenic CO2 emissions. However, the rapid decay of the CO2 uptake of CaO over repeated cycles of carbonation and calcination due to sintering limits its implementation at the industrial scale. Thus, the development of material design strategies to stabilize the CO2 uptake capacity of CaO is paramount. The addition of alkali metal salts to CaO has been proposed as a strategy to mitigate the rapid loss of its cyclic CO2 uptake capacity. However, there are conflicting results concerning the effect of the addition of alkali metal carbonates on the structure and CO2 capacity of CaO. In this work, we aim at understanding the effect of the addition of Na2CO3 to CaO on the sorbent's structure and its CO2 uptake capacity. We demonstrate that under industrially-relevant conditions the addition of as little as 1 wt% of Na2CO3 reduces severely the CO2 uptake of CaO. Combining TGA, XAS and FIB-SEM analysis allowed us to attribute the performance degradation to the formation of the double salt Na2Ca(CO3)2 that induces strong sintering leading to a significant loss in the sorbent's pore volume. In addition, during the carbonation step the formation of a dense layer of Na2Ca(CO3)2 that covers unreacted CaO prevents its full carbonation to CaCO3.

The two-dimensional morphology of molybdenum oxycarbide (2D-Mo 2 CO x ) nanosheets dispersed on silica is found vital for imparting high stability and catalytic activity in the dry reforming of methane. Here we report that owing to the maximized metal utilization, the specific activity of 2D-Mo 2 CO x /SiO 2 exceeds that of other Mo 2 C catalysts by ca. 3 orders of magnitude. 2D-Mo 2 CO x is activated by CO 2 , yielding a surface oxygen coverage that is optimal for its catalytic performance and a Mo oxidation state of ca. +4. According to ab initio calculations, the DRM proceeds on Mo sites of the oxycarbide nanosheet with an oxygen coverage of 0.67 monolayer. Methane activation is the rate-limiting step, while the activation of CO 2 and the C-O coupling to form CO are low energy steps. The deactivation of 2D-Mo 2 CO x /SiO 2 under DRM conditions can be avoided by tuning the contact time, thereby preventing unfavourable oxygen surface coverages.

The effect of NaNO 3 and its physical state on the thermal decomposition pathways of hydrated magnesium hydroxycarbonate (hydromagnesite, HM) towards MgO was examined by in situ total scattering. Pair distribution function (PDF) analysis of these data allowed us to probe the structural evolution of pristine and NaNO 3 -promoted HM. A multivariate curve resolution alternating least squares (MCR-ALS) analysis identified the intermediate phases and their evolution upon the decomposition of both precursors to MgO. The total scattering results are discussed in relation with thermogravimetric measurements coupled with off-gas analysis. MgO is obtained from pristine HM (N 2 , 10 °C min -1 ) through an amorphous magnesium carbonate intermediate (AMC), formed after the partial removal of water of crystallization from HM. The decomposition continues via a gradual release of water (due to dehydration and dehydroxylation) and, in the last step, via decarbonation, leading to crystalline MgO. The presence of molten NaNO 3 alters the decomposition pathways of HM, proceeding now through AMC and crystalline MgCO 3 . These results demonstrate that molten NaNO 3 facilitates the release of water (from both water of crystallization and through dehydroxylation) and decarbonation, and promotes the crystallization of MgCO 3 and MgO in comparison to pristine HM. MgO formed from the pristine HM precursor shows a smaller average crystallite size than NaNO 3 -promoted HM and preserves the initial nano-plate-like morphology of HM. NaNO 3 -promoted HM was decomposed to MgO that is characterized by a larger average crystallite size and irregular morphology. Additionally, in situ SEM allowed visualization of the morphological evolution of HM promoted with NaNO 3 at a micrometre scale.

Molybdenum carbide (β-Mo 2 C) supported on carbon spheres was prepared via a carbothermal hydrogen reduction (CHR) method from delaminated nanosheets of molybdenum(vi) oxide (d-MoO 3 /C). The carburization process was followed by combined in situ XANES/XRD analysis revealing the formation of molybdenum oxycarbide Mo 2 C x O y as an intermediate phase during the transformation of d-MoO 3 /C to β-Mo 2 C/C. It was found that Mo 2 C x O y could not be completely carburized to β-Mo 2 C under a He atmosphere at 750 °C, instead a reduction in H 2 is required. The β-Mo 2 C/C obtained showed activity and stability for the dry reforming of methane at 800 °C and 8 bar. In situ XANES/XRD evaluation of the catalyst under DRM reaction conditions combined with high resolution TEM analysis revealed the evolution of β-Mo 2 C/C to Mo 2 C x O y /C. Notably, the gradual oxidation of β-Mo 2 C/C to Mo 2 C x O y /C correlates directly with the increased activity of the competing reverse water gas shift reaction.

Ruthenium pyrochlores, that is, oxides of composition A 2 Ru 2 O 7-δ , have emerged recently as state-of-the-art catalysts for the oxygen evolution reaction (OER) in acidic conditions. Here, we demonstrate that the A-site substituent in yttrium ruthenium pyrochlores Y 1.8 M 0.2 Ru 2 O 7-δ (M = Cu, Co, Ni, Fe, Y) controls the concentration of surface oxygen vacancies (V O ) in these materials whereby an increased concentration of V O sites correlates with a superior OER activity. DFT calculations rationalize these experimental trends demonstrating that the higher OER activity and V O surface density originate from a weakened strength of the M-O bond, scaling with the formation enthalpy of the respective MO x phases and the coupling between the M d states and O 2 p states. Our work introduces a novel catalyst with improved OER performance, Y 1.8 Cu 0.2 Ru 2 O 7-δ , and provides general guidelines for the design of active electrocatalysts.

Two-dimensional (2D) carbides, nitrides, and carbonitrides known as MXenes are emerging materials with a wealth of useful applications. However, the range of metals capable of forming stable MXenes is limited mostly to early transition metals of groups 3-6, making the exploration of properties inherent to mid or late transition metal MXenes very challenging. To circumvent the inaccessibility of MXene phases derived from mid-to-late transition metals, we have developed a synthetic strategy that allows the incorporation of such transition metal sites into a host MXene matrix. Here, we report the structural characterization of a Mo 2 C T x :Co phase (where T x are O, OH, and F surface terminations) that is obtained from a cobalt-substituted bulk molybdenum carbide (β-Mo 2 C:Co)  through a two-step synthesis: first an intercalation of gallium yielding Mo 2 Ga 2 C:Co followed by removal of Ga via HF treatment. Extended X-ray absorption fine structure (EXAFS) analysis confirms that Co atoms occupy Mo positions in the Mo 2 C T x lattice, providing isolated Co centers without any detectable formation of other cobalt-containing phases. The beneficial effect of cobalt substitution on the redox properties of Mo 2 C T x :Co is manifested in a substantially improved hydrogen evolution reaction (HER) activity, as compared to the unsubstituted Mo 2 C T x catalyst. Density functional theory (DFT) calculations attribute the enhanced HER kinetics of Mo 2 C T x :Co to the favorable binding of hydrogen on the oxygen terminated MXene surface that is strongly influenced by the substitution of Mo by Co in the Mo 2 C T x lattice. In addition to the remarkable HER activity, Mo 2 C T x :Co features excellent operational and structural stability, on par with the best performing non-noble metal-based HER catalysts. Overall, our work expands the compositional space of the MXene family by introducing a material with site-isolated cobalt centers embedded in the stable matrix of Mo 2 C T x . The synthetic approach presented here illustrates that tailoring the properties of MXenes for a specific application can be achieved via substitution of the host metal sites by mid or late transition metals.

We report an operando examination of a model nanocrystalline In 2 O 3 catalyst for methanol synthesis via CO 2 hydrogenation (300 °C, 20 bar) by combining X-ray absorption spectroscopy (XAS), X-ray powder diffraction (XRD), and in situ transmission electron microscopy (TEM). Three distinct catalytic regimes are identified during CO 2 hydrogenation: activation, stable performance, and deactivation. The structural evolution of In 2 O 3 nanoparticles (NPs) with time on stream (TOS) followed by XANES-EXAFS-XRD associates the activation stage with a minor decrease of the In-O coordination number and a partial reduction of In 2 O 3 due to the formation of oxygen vacancy sites (i.e., In 2 O 3- x ). As the reaction proceeds, a reductive amorphization of In 2 O 3 NPs takes place, characterized by decreasing In-O and In-In coordination numbers and intensities of the In 2 O 3 Bragg peaks. A multivariate analysis of the XANES data confirms the formation of In 2 O 3- x and, with TOS, metallic In. Notably, the appearance of molten In 0 coincides with the onset of catalyst deactivation. This phase transition is also visualized by in situ TEM, acquired under reactive conditions at 800 mbar pressure. In situ TEM revealed an electron beam assisted transformation of In 2 O 3 nanoparticles into a dynamic structure in which crystalline and amorphous phases coexist and continuously interconvert. The regeneration of the deactivated In 0 /In 2 O 3- x catalyst by reoxidation was critically assessed revealing that the spent catalyst can be reoxidized only partially in a CO 2 atmosphere or air yielding an average crystallite size of the resultant In 2 O 3 that is approximately an order of magnitude larger than the initial one.

Hydrogen (H 2 ) is a clean energy carrier and a major industrial feedstock, e.g., to produce ammonia and methanol. High-purity H 2 can be produced efficiently from methane (CH 4 ) using chemical looping-based approaches. In this work, we report on the development of a calcium-iron-based oxygen carrier (Ca 2 Fe 2 O 5 ) doped with Ni or Cu and investigate its redox performance for H 2 production when CH 4 is used as the fuel. The experimental results suggest that the rapid formation of metallic Ni or Cu through exsolution promotes the reducibility of Ca 2 Fe 2 O 5 with CH 4 . It was found that the reversible exsolution of Ni or Cu nanoparticles and their reincorporation in the Ca 2 Fe 2 O 5 structure is key to avoid particle sintering and deactivation. Having the potential of converting a larger fraction of steam to H 2 than pure iron oxide in addition to its higher reactivity with CH 4 , the doped calcium-iron-based oxygen carrier is a promising material for chemical looping H 2 production.

A rapid electrochemical deposition protocol is reported to synthesize highly porous Cu foams serving as model oxygen carriers for chemical looping, a promising technology to reduce anthropogenic CO 2 emission. To overcome the sintering-induced decay in the oxygen carrying capacity of unsupported Cu foams, Al 2 O 3 films of different thicknesses (0.1-25 nm) are deposited onto the Cu foams via atomic layer deposition (ALD). An ALD-grown Al 2 O 3 overcoat of 20 nm thickness (∼4 wt % Al 2 O 3 ) is shown to be sufficient to ensure excellent redox cyclic stability. Al 2 O 3 -coated Cu foams exhibit a capacity retention of 96% over 10 redox cycles, outperforming their coprecipitated counterpart (equal Al 2 O 3 content). The structural evolution of the stabilized foams is probed in detail and compared to benchmark materials to elucidate the stabilizing role of the Al 2 O 3 overcoat. Upon heat treatment, the initially conformal Al 2 O 3 overcoat induces a fragmentation of large Cu(O) branches into small particles. After multiple redox cycles, the Al 2 O 3 overcoat transforms into sub-micrometer-sized grains of aluminum-containing phases (δ-Al 2 O 3 , CuAl 2 O 4 , and CuAlO 2 ) that are dispersed homogeneously within the CuO matrix. Finally, the diffusion of Cu through an Al 2 O 3 layer upon heat treatment in an oxidizing atmosphere is probed in model thin films.

The production of high purity hydrogen with the simultaneous capture of CO2, can be achieved through a chemical looping (CL) cycle relying on an iron oxide-based oxygen carrier. Indeed, the availability of active and cyclically stable oxygen carriers is a key criterion for the practical implementation of this technology. In this regard, improving our understanding of the reduction pathway(s) of iron-based oxygen carriers and the development of concepts to increase the reduction kinetics are important aspects. The aim of this work is to evaluate the effect of the addition of copper on the redox behaviour of iron oxide based oxygen carriers stabilized on ZrO2. In situ pulsed-H2 XANES (Fe K-edge) experiments allowed for the determination of the reduction pathways in these materials, viz. the reduction of both Fe2O3 and CuFe2O4 proceeded via a Fe2+ intermediate: Fe2O3 (CuFe2O4) → Fe3O4 (Cu0) → FeO (Cu0) → Fe0 (Cu0). In the first step CuFe2O4 is reduced to Cu0 and Fe3O4, whereby Cu0 promotes the further reduction of iron oxide, increasing their rate of formation. In particular, the rate of reduction of FeO → Fe0 is accelerated most dramatically by Cu0. This is an encouraging result as the FeO → Fe0 transition is the slowest reduction reaction.

The dry reforming of methane (DRM), i.e., the reaction of methane and CO 2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a Mg x Al y O z matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m 2 /g cat ), pore volume (0.51-0.66 cm 3 /g cat ), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni 4 Fe 1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Adequate cerebral perfusion is necessary to maintain consciousness in upright humans. Following maximal anaerobic exercise, cerebral perfusion can become compromised and result in syncope. It is unknown whether post-exercise reductions in cerebral perfusion can lead to visual-cognitive deficits prior to the onset of syncope, which would be of concern for emergency workers and warfighters, where critical decision making and intense physical activity are combined. Therefore, the purpose of this experiment was to determine if reductions in cerebral blood velocity, induced by maximal anaerobic exercise and head-up tilt, result in visual-cognitive deficits prior to the onset of syncope. Nineteen sedentary to recreationally active volunteers completed a symptom-limited 60° head-up tilt for 16 min before and up to 16 min after a 60 sec Wingate test. Blood velocity of the middle cerebral artery was measured using transcranial Doppler ultrasound and a visual decision-reaction time test was assessed, with independent analysis of peripheral and central visual field responses. Cerebral blood velocity was 12.7 ± 4.0% lower (mean ± SE; P < 0.05) after exercise compared to pre-exercise. This was associated with a 63 ± 29% increase (P < 0.05) in error rate for responses to cues provided to the peripheral visual field, without affecting central visual field error rates (P = 0.46) or decision-reaction times for either visual field. These data suggest that the reduction in cerebral blood velocity following maximal anaerobic exercise contributes to visual-cognitive deficits in the peripheral visual field without an apparent affect to the central visual field., (© 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.)

The dependence of the lattice parameter on dopant concentration in Ce1-xMxO2 (M = Sn and Ti) solid solutions is not linear. A change towards a steeper slope is observed around x ∼ 0.35, though the fluorite structure (space group Fm3m) is preserved up to x = 0.5. This phenomenon has not been observed for Ce1-xZrxO2 solid solutions showing a perfectly linear decrease of the lattice parameter up to x = 0.5. In order to understand this behavior, the oxidation state of the metal ions, the disorder in the oxygen substructure and the nature of metal-oxygen bonds have been analyzed by XPS, (119)Sn Mössbauer spectroscopy and X-ray absorption spectroscopy. It is observed that the first Sn-O coordination shell in Ce1-xSnxO2 is more compact and less flexible than that of Ce-O. The Sn coordination remains symmetric with eight equivalent, shorter Sn-O bonds, while Ce-O coordination gradually splits into a range of eight non-equivalent bonds compensating for the difference in the ionic radii of Ce(4+) and Sn(4+). Thus, a long-range effect of Sn doping is hardly extended throughout the lattice in Ce1-xSnxO2. In contrast, for Ce1-xZrxO2 solid solutions, both Ce and Zr have similar local coordination creating similar rearrangement of the oxygen substructure and showing a linear lattice parameter decrease up to 50% Zr substitution. We suggest that the localized effect of Sn substitution due to its higher electronegativity may be responsible for the deviation from Vegard's law in Ce1-xSnxO2 solid solutions.

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are emerging CO2 capture technologies that could reduce appreciably the costs associated with the capture of CO2. In CLC and CLOU, the oxygen required to combust a hydrocarbon is provided by a solid oxygen carrier. Among the transition metal oxides typically considered for CLC and CLOU, copper oxide (CuO) stands out owing to its high oxygen carrying capacity, exothermic reduction reactions and fast reduction kinetics. However, the low Tammann (sintering) temperature of CuO is a serious drawback. In this context, it has been proposed to support CuO on high Tammann temperature and low cost alumina (Al2O3), thus, reducing the morphological changes occurring over multiple CLC or CLOU redox cycles and stabilizing, in turn, the high activity of CuO. However, in CuO-Al2O3 systems, phase stabilization and avoiding the formation of the CuAl2O4 spinel is key to obtaining a material with a high redox stability and activity. Here, we report a Na(+) doping strategy to phase stabilize Al2O3-supported CuO, yielding in turn an inexpensive material with a high redox stability and CO2 capture efficiency. We also demonstrate that doping CuO-Al2O3 with Na(+) improves the oxygen uncoupling characteristics and coke resistance of the oxygen carriers. Utilizing in situ and ex situ X-ray absorption spectroscopy (XAS), the local structure of Cu and the reduction pathways of CuO were determined as a function of the Na(+) content and cycle number. Finally, using 4-point conductivity measurements, we confirm that doping of Al2O3-supported CuO with Na(+) lowers the activation energy for charge transport explaining conclusively the improved redox characteristics of the new oxygen carriers developed.

The quaternary gold(I) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(III) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10](10+) layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(I)3(As2)4](10-) layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1-As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by (197)Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(I), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie-Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K.

Sustained postexercise vasodilation, which may be mediated at both a neural and vascular level, is seen in previously active skeletal muscle vascular beds following both large and small muscle-mass exercise. Blunted sympathetic vascular transduction and a downward resetting of the arterial baroreflex contribute to this vasodilation after cycling (large muscle-mass exercise), but it is unknown if these responses also contribute to sustained vasodilation following small muscle-mass exercise. This study aimed to determine if baroreflex sensitivity is altered, the baroreflex is reset, or if sympathetic vascular transduction is blunted following small muscle-mass exercise. Eleven healthy, college-aged subjects (five males, six females) completed one-leg dynamic knee-extension exercise for 1 h at 60% of peak power output. While cardiovagal baroreflex sensitivity was increased ~23% postexercise relative to preexercise (P < 0.05), vascular and integrated baroreflex sensitivity were not altered following exercise (P = 0.31 and P = 0.48). The baroreflex did not exhibit resetting (P > 0.69), and there was no evidence of changes in vascular transduction following exercise (P = 0.73). In conclusion, and in contrast to large muscle-mass exercise, it appears that small muscle-mass exercise produces a sustained postexercise vasodilation that is largely independent of central changes in the baroreflex., (© 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.)