Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous ...composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica-alumina shell further reduces the mass transport to the active sites within the composite.Catalyst deactivation in fluid catalytic cracking processes is unavoidably associated with structural changes. Here, the authors visualize the deactivation of zeolite catalysts by ptychography and other imaging techniques, showing pronounced amorphization of the outer layer of the catalyst particles.
Oxygen storage materials such as ceria are used in many catalytic applications because they can reversibly bind and release oxygen. Tools are needed to observe and quantify this activity which ...involves a change in the cerium oxidation state and to understand the involvement of cerium in catalytic processes. To prove that cerium changes its oxidation state in the catalytic cycle the transient rates of Ce
3+
formation and decay should be compared to the overall reaction rate. For such mechanistic studies the time resolution is essential as the quantification of the Ce
3+
species should be faster than the reaction rate. However, it is challenging to follow the dynamic changes of the cerium oxidation state under reaction conditions, especially when the concentration of cerium atoms involved in the reaction cycle is low. In this paper, we evaluate the sensitivity of high-resolution X-ray emission-based methods for the
in situ
time-resolved quantification of small concentrations of Ce
3+
in ceria-based materials. We demonstrate that resonant X-ray emission spectroscopy (RXES) at optimal excitation energy is more sensitive than high energy resolution off-resonant spectroscopy (HEROS) and non-resonant X-ray emission spectroscopy (non-resonant XES) and that it can track the reactivity of less than 0.3% of cerium atoms in a 1% Pt/CeO
2
catalyst in a plug-flow reactor with sub-second time resolution. These results demonstrate that X-ray emission-based methods can be used as very sensitive tools and provide new insights into dynamic changes of the oxidation state in reducible oxides in a variety of applications.
High sensitivity of X-ray emission spectroscopy based methods for
in situ
time-resolved quantification of Ce
3+
in ceria-based catalysts and related materials.
Aims
The Multidisciplinary Approach to the Study of Chronic Pelvic Pain (MAPP) Research Network initiated a second observational cohort study—the Symptom Patterns Study (SPS)—to further investigate ...the underlying pathophysiology of Urologic Chronic Pelvic Pain Syndrome (UCPPS) and to discover factors associated with longitudinal symptom changes and responses to treatments.
Methods
This multisite cohort study of males and females with UCPPS features a run‐in period of four weekly web‐based symptom assessments before a baseline visit, followed by quarterly assessments up to 36 months. Controls were also recruited and assessed at baseline and 6 months. Extensive clinical data assessing urological symptoms, nonurological pain, chronic overlapping pain syndromes, and psychosocial factors were collected. Diverse biospecimens for biomarker and microbiome studies, quantitative sensory testing (QST) data under multiple stimuli, and structural and functional neuroimaging scans were obtained under a standardized protocol.
Results
Recruitment was initiated (July 2015) and completed (February 2019) at six discovery sites. A total of 620 males and females with UCPPS and 73 Controls were enrolled, including 83 UCPPS participants who re‐enrolled from the first MAPP Network cohort study (2009‐2012). Baseline neuroimaging scans, QST measures, and biospecimens were obtained on 578 UCPPS participants. The longitudinal follow‐up of the cohort is ongoing.
Conclusions
This comprehensive characterization of a large UCPPS cohort with extended follow‐up greatly expands upon earlier MAPP Network studies and provides unprecedented opportunities to increase our understanding of UCPPS pathophysiology, factors associated with symptom change, clinically relevant patient phenotypes, and novel targets for future interventions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A series of well-defined catalysts based on platinum nanoparticles supported on amorphous silica–alumina with varying composition was prepared by incipient wetness impregnation. Quantitative ...structural characterization of alumina and aluminosilicate domains by
27Al (3Q) MAS NMR spectroscopy showed that the concentration of Brønsted acid sites determined by pyridine adsorption is related solely to the concentration of the aluminosilicate domain. However, only a very small fraction of the tetrahedrally coordinated aluminum led to the formation of Brønsted acid sites, because the negative charge on most of the tetrahedral Al–O was balanced by cationic aluminum oxide clusters. The preparation method led to small, uniform (0.6–0.8 nm) Pt particles on all aluminum-containing supports.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The molecular mechanisms that promote excitatory synapse development have been extensively studied. However, the molecular events preventing precocious excitatory synapse development so that synapses ...form at the correct time and place are less well understood. Here, we report the functional characterization of ARHGAP12, a previously uncharacterized Rho GTPase-activating protein (RhoGAP) in the brain. ARHGAP12 is specifically expressed in the CA1 region of the hippocampus, where it localizes to the postsynaptic compartment of excitatory synapses. ARHGAP12 negatively controls spine size via its RhoGAP activity and promotes, by interacting with CIP4, postsynaptic AMPA receptor endocytosis. Arhgap12 knockdown results in precocious maturation of excitatory synapses, as indicated by a reduction in the proportion of silent synapses. Collectively, our data show that ARHGAP12 is a synaptic RhoGAP that regulates excitatory synaptic structure and function during development.
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•ARHGAP12 functions at excitatory synapses of CA1 hippocampal neurons•ARHGAP12 promotes postsynaptic AMPA receptor endocytosis•ARHGAP12 restricts synaptic maturation by limiting silent synapse unsilencing
Ba et al. find that the Rac1 GAP, ARHGAP12, coordinates dendritic spine morphology and synaptic strength via its GAP activity and interaction with CIP4, respectively. ARHGAP12 limits synapse maturation by restricting silent synapses converting to functional synapses in the developing hippocampus.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
X-ray absorption near-edge structure (XANES) spectra are the fingerprint of the local atomic and electronic structures around the absorbing atom. However, the quantitative analysis of these ...spectra is not straightforward. Even with the most recent advances in this area, for a given spectrum, it is not clear a priori which structural parameters can be refined and how uncertainties should be estimated. Here, we present an alternative concept for the analysis of XANES spectra, which is based on machine learning algorithms and establishes the relationship between intuitive descriptors of spectra, such as edge position, intensities, positions, and curvatures of minima and maxima on the one hand, and those related to the local atomic and electronic structure which are the coordination numbers, bond distances and angles and oxidation state on the other hand. This approach overcoms the problem of the systematic difference between theoretical and experimental spectra. Furthermore, the numerical relations can be expressed in analytical formulas providing a simple and fast tool to extract structural parameters based on the spectral shape. The methodology was successfully applied to experimental data for the multicomponent Fe:SiO
2
system and reference iron compounds, demonstrating the high prediction quality for both the theoretical validation sets and experimental data.
Phosphine metal-organic frameworks (P-MOFs) are crystalline porous coordination polymers that contain phosphorus functional groups within their pores. We present the use of X-ray absorption ...spectroscopy (XAS) at the P K-edge to determine the phosphine to phosphine oxide ratio in two P-MOFs with MIL-101 topology. The phosphorus oxidation state is of particular interest as it strongly influences the coordination affinity of these materials for transition metals. This method can determine the oxidation state of phosphorus even when the material contains paramagnetic nuclei, differently from NMR spectroscopy. We observed that phosphine in LSK-15 accounts for 72 ± 4% of the total phosphorus groups and that LSK-12 contains only phosphine oxide.
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