Zr（Ⅳ） surface sites determine CH3OH formation rate on Cu/ZrO2/SiO2-CO2 hydrogenation catalysts

Cu/ZrO2/SiO2 are efficient catalysts for the selective hydrogenation of CO2 to CH3OH. In order to understand the role of ZrO2 in these mixed-oxides based catalysts, in situ X-ray absorption spectroscopy has been carried out on the Cu and Zr K-edge. Under reaction conditions, Cu remains metallic, while Zr is present in three types of coordination environment associated with 1) bulk ZrO2, 2) coordinatively saturated and 3) unsaturated Zr(Ⅳ) surface sites. The amount of coordinatively unsaturated Zr surface sites can be quantified by linear combination fit of reference X-Ray absorption near edge structure (XANES) spectra and its amount correlates with CH3OH formation rates, thus indicating the importance of Zr(Ⅳ) Lewis acid surface sites in driving the selectivity toward CH3OH. This finding is consistent with the proposed mechanism, where CO2 is hydrogenated at the interface between the Cu nanoparticles that split H2 and Zr(Ⅳ) surface sites that stabilizes reaction intermediates.

Ceria in halogen chemistry

Halogen chemistry constitutes an essential part in the industrial production of polymers and gains increasing attention as an attractive strategy to activate light alkanes that constitute natural gas. CeO2-based catalysts offer an exciting potential for advances in hydrogen halide recovery that enables a high efficiency of halogen-based processes for activation of small molecules. This review provides an overview of recently developed ceria-based catalysts in the context of polymer industry(polyvinyl chloride, polyurethanes, and polycarbonates) and activation of light hydrocarbons for natural gas upgrading. In addition, mechanistic insight and the challenges of ceria catalysts are provided, aiding the design of future catalytic materials and applications.

Lighting up aggregate emission of perylene diimide by leveraging polymerization-mediated through-space charge transfer and π-π stacking

The molecular engineering of fluorescent organic/polymeric materials,specifically those emitting in the deep red to near-infrared spectrum,is vital for advancements in optoelectronics and biomedicine.Perylene diimide(PDI),a well-known fluorescent scaffold,offers high thermal and photophysical stability but suffers from fluorescence quenching in solid or aggregate states due to intenseπ-πinteractions.To mitigate this,simple and versatile methods for strong PDI aggregate emission without extensive synthetic demands are highly desirable but still lacking.Here,we report a straightforward strategy to enhance the solid-state emission of PDI by introducing certain degree of through-space charge transfer(TSCT)via controlled radical polymerization,which can efficiently distort the typical face-to-face PDI stacking,enabling greatly enhanced deep red emission.This is achieved by growing electron-donating star-shape styrenic(co)polymers from a multidirectional electron-accepting PDI initiator.The incorporation of polycyclic aromatic monomers further shifted the emission into the near-infrared region,albeit with a reduced intensity.Overall,the emission of the PDI-based TSCT polymers can be systematically manipulated by leveraging the balance between PDI stacking and the TSCT degree,as confirmed by both experimental study and theoretical calculations.Our approach circumvents complex synthetic procedures,offering highly emissive materials with large Stokes shifts and showing broad potential for optoelectronic technology.

Superb cryogenic strength of equiatomic CrCoNi derived from gradient hierarchical microstructure

This work demonstrates the effectiveness of a cryogenic torsional pre-straining for significantly improving the cryogenic strength of an equiatomic CrCoNi alloy. The origin of this phenomenon is elucidated by various microstructural characterization tools, which shows that the sequential torsion and tension tests lead to the observed hierarchical microstructure through the activation of different twinning systems and stacking faults. This gives rise to the significant increase in the yield strength from 600 MPa to 1215 MPa,while the fracture strain changes from 68% to 48%. The current study reveals that the incorporation of nanotwins architecture by shear deformation may constitute a viable strategy to tune the mechanical performance and, in particular, to dramatically increase the strength while keeping a good ductility.

Vascularization mediated by mesenchymalstem cells from bone marrow and adiposetissue: a comparison

Tissue-engineered constructs are promising to overcome shortage of organ donors and to reconstruct at least partsof injured or diseased tissues or organs. However, oxygen and nutrient supply are limiting factors in many tissues,especially after implantation into the host. Therefore, the development of a vascular system prior to implantationappears crucial. To develop a functional vascular system, different cell types that interact with each other need tobe co-cultured to simulate a physiological environment in vitro. This review provides an overview and a comparison ofthe current knowledge of co-cultures of human endothelial cells (ECs) with human adipose tissue-derived stem/stromal cells (ASCs) or bone marrow-mesenchymal stem cells (BMSCs) in three dimensional (3D) hydrogel matrices.Mesenchymal stem cells (MSCs), BMSCs or ASCs, have been shown to enhance vascular tube formation of ECs and toprovide a stabilizing function in addition to growth factor delivery and permeability control for ECs. Althoughphenotypically similar, MSCs from different tissues promote tubulogenesis through distinct mechanisms. In this report,we describe differences and similarities regarding molecular interactions in order to investigate which of these two celltypes displays more favorable characteristics to be used in clinical applications. Our comparative study shows that ASCsas well as BMSCs are both promising cell types to induce vascularization with ECs in vitro and consequently arepromising candidates to support in vivo vascularization.

Scalable, ultra-resistant structural colors based on network metamaterials

Structural colors have drawn wide attention for their potential as a future printing technology for various applications,ranging from biomimetic tissues to adaptive camouflage materials.However,an efficient approach to realize robust colors with a scalable fabrication technique is still lacking,hampering the realization of practical applications with this platform.Here,we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless,ultra-thin dielectric coatings.By using theory and experiments,we show how subwavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network,generating the formation of saturated structural colors that cover a wide portion of the spectrum.Ellipsometry measurements support the efficient observation of these colors,even at angles of 70°.The network-like architecture of these nanomaterials allows for high mechanical resistance,which is quantified in a series of nano-scratch tests.With such remarkable properties,these metastructures represent a robust design technology for real-world,large-scale commercial applications.

In situ frequency gating and beam splitting of vacuum- and extreme-ultraviolet pulses

Monochromatization of high-harmonic sources has opened fascinating perspectives regarding time-resolved photoemission from all phases of matter.Such studies have invariably involved the use of spectral filters or spectrally dispersive optical components that are inherently lossy and technically complex.Here we present a new technique for the spectral selection of near-threshold harmonics and their spatial separation from the driving beams without any optical elements.We discover the existence of a narrow phase-matching gate resulting from the combination of the non-collinear generation geometry in an extended medium,atomic resonances and absorption.Our technique offers a filter contrast of up to 104 for the selected harmonics against the adjacent ones and offers multiple temporally synchronized beamlets in a single unified scheme.We demonstrate the selective generation of 133,80 or 56 nm femtosecond pulses from a 400-nm driver,which is specific to the target gas.These results open new pathways towards phase-sensitive multi-pulse spectroscopy in the vacuum-and extreme-ultraviolet,and frequencyselective output coupling from enhancement cavities.

Understanding X-ray absorption spectra by means of descriptors and machine learning algorithms

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.