Transmission Electron Microscopy Energy-dispersive X-ray Research Articles

Simulation of radiation damage via alpha decay in BFS:PC grouts using 4He2+ ion acceleration

The impact of alpha radiation on cements used to encapsulate intermediate-level waste (ILW) is not well understood. ILW wastes can contain high levels of alpha-emitting radionuclides, meaning that the grouts used to encapsulate them are exposed to significant ionising radiation. Thus, a damaged region could develop in the grout adjacent to the alpha-emitting species. This work attempted to recreate this behaviour through nonradioactive 4He2+ ion-accelerator experiments, which have not previously been applied to common encapsulation grouts. The influence of this irradiation on a slag-Portland cement was investigated at different ages via transmission electron microscopy energy-dispersive x-ray spectroscopy (TEM-EDX) and supporting techniques, to assess whether 4He2+ irradiation caused textural or chemical zonation. No significant changes in hydrate phases or textures were observed, other than minor variations associated with carbonation. This paper provides a proof of concept for using ion acceleration techniques on cements and furthers knowledge on their radiation response.

In-situ characterization of porcine fibroblasts in response to silver ions by Raman spectroscopy and liquid scanning transmission electron microscopy

Since silver ion is known for its antimicrobial function, most of the research has focused mainly on toxicity effects rather than the role of silver ion in general biology and the behind mechanism of actions of silver ion in mammalian cells. Moreover, a conventional in vitro approach to estimate the effects of silver ion on cells does not provide information about the biochemical changes and might accompany artifacts due to invasive and destructive sample preparation processes. In the present study, in-situ real time approaches were applied to evaluate the impact of silver ion (0.57, 1.34, 1.96, 2.33 mg/L) on fibroblast cells. Raman spectroscopy analysis showed that Raman peak intensities of proteins and nucleic acids significantly increased in the cells after exposure to silver ion for 21 h, especially at relatively higher levels 1.34, 1.96, and 2.33 mg/L. Raman peak at 1585 cm−1 and liquid scanning transmission electron microscopy energy-dispersive x-ray spectroscopy (STEM-EDS) analysis revealed the fate of silver ion that was taken up by the cell and reduced into metallic silver accumulating in the cell as silver nanoparticles. These results suggest cells were undergoing different activities such as enhanced metabolic activities rather than cell apoptosis or cell death. Additionally, Raman spectroscopy predicted the level of silver ion exposed to the cell at 2.11 ± 0.38 and 1.73 ± 0.26 mg/L by the PLS prediction model, compared with the results measured by inductively coupled plasma mass spectrometry (ICP-MS), 2.14 ± 0.07 and 1.87 ± 0.07 mg/L respectively, suggesting Raman spectroscopy can provide a new and fast approach to determine and measure the concentration of silver ion or probably other tested molecules treated to the cell for the future research.

Novel WC-Co-Ti3SiC2 cemented carbide with ultrafine WC grains and improved mechanical properties

New WC-Co-Ti3SiC2 cemented carbides with different fractions of Ti3SiC2 were prepared and characterised in this study. The composites were processed by hot isostatic pressing, and their microstructural characteristics and mechanical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) energy-dispersive X-ray (EDX) and indentation methods. The addition of Ti3SiC2 resulted in refined WC grains in the composites with uniform and narrow size distribution in the composites. Refinement was achieved by the decomposition of Ti3SiC2. The optimal composition of WC-Co-Ti3SiC2 was established to be 3.0 wt% of Ti3SiC2 when the hardness and indentation fracture toughness exhibited excellent values of 2076 kgf/mm2 and 10.1 MPa m1/2, respectively. The strengthening and toughening of WC-Co-Ti3SiC2 were attributed to the refinement of WC grains and to the intrinsic layered structure of Ti3SiC2, respectively.

Slow Synthesis Methodology-Directed Immiscible Octahedral Pdx Rh1-x Dual-Atom-Site Catalysts for Superior Three-Way Catalytic Activities over Rh.

This study provided an effective strategy to construct dual-atom sites by solid-solution alloying. A slow synthesis methodology was established for the solid-solution preparations as dual-atom-site catalysts. The atomic-level homogeneous Pdx Rh1-x dual-atom-site catalysts were successfully synthesized over the whole composition range, as evidenced by X-ray powder diffraction and scanning transmission electron microscope energy-dispersive X-ray spectroscopy mapping measurements. The challenging morphology formation in the immiscible alloys was achieved by an energy-controlling process as the octahedral Rh-rich alloys. The Pd0.3 Rh0.7 dual-atom-site catalyst had unique surface states to activate the key reactants of CO and NO in the complex three-way catalytic reactions, and it performed significantly better than pure Rh.

Deoxydehydration of Biomass-Derived Polyols Over Silver-Modified Ceria-Supported Rhenium Catalyst with Molecular Hydrogen.

Olefin production from polyols via deoxydehydration (DODH) was carried out over Ag-modified CeO2 -supported heterogeneous Re catalysts with H2 as a reducing agent. Both high DODH activity and low hydrogenation ability for C=C bonds were observed in the reaction of erythritol, giving a 1,3-butadiene yield of up to 90 % under "solvent-free" conditions. This catalyst is applicable to other substrates such as methyl glycosides (methyl α-fucopyranoside: 91 % yield of DODH product; methyl β-ribofuranoside: 88 % yield), which were difficult to be converted to the DODH products over the DODH catalysts reported previously. ReOx -Ag/CeO2 was reused 3 times without a decrease of activity or selectivity after calcination as regeneration. Although the transmission electron microscopy energy-dispersive X-ray spectroscopy and X-ray absorption fine structure analyses showed that Re species were highly dispersed and Ag was present as metal particles with various sizes from well-dispersed species (<1 nm) to around 5 nm particles, the catalysts prepared from size-controlled Ag nanoparticles showed similar performance, indicating that the catalytic performance is insensitive to the Ag particle size.

Carbonate accelerated transformation of ferrihydrite in the presence of phosphate

In soils and rhizospheres, iron (oxyhydr)oxides and oxyanions like carbonate and phosphate occur ubiquitously and their interaction have important implications for nutrients and metals cycling. An elevated activity of carbonate in soils and sediments (e.g., pCO2, ∼2%) above current atmospheric CO2 (∼0.04%) is observed. The level of agronomic soil test phosphorus (P) in intensively managed agricultural soils can be up to several hundred mg kg−1. Although it is known that the transformation of iron (oxyhydr)oxides is suppressed by phosphate adsorption, it is unclear how increasing carbonate activities exert the reaction process. Here, the effects of carbonate on the transformation of ferrihydrite were evaluated at pH 7.5 in the presence of phosphate using experimental geochemistry, Fe K-edge X-ray absorption spectroscopy, transmission electron microscopy-energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Our results, for the first time, showed that the inhibitory effect of phosphate on ferrihydrite transformation was retarded by carbonate, and it transformed into hematite. Under pCO2 = 408 ppm (0.213 mM carbonate), an increase in [phosphate]o from 0 to 0.5 mM decreased the transformation rate of ferrihydrite from 0.009 to 0.003 d−1. However, the suppression was drastically perturbed when carbonate was added to the phosphate-ferrihydrite system. When 11.42 mM carbonate (pCO2 = 20000 ppmv) was present, the rate increased from 0.009 to 0.033 d−1 without phosphate and from 0.003 to 0.018 d−1 with 0.5 mM of phosphate. Moreover, carbonate promoted the formation of more crystalline rhombic hematite particles, while phosphate modified the morphology of hematite from rhombic to ellipsoidal-like with rough surfaces. The distinctive difference of the influence of carbonate and phosphate on the transformation kinetics, products distribution, and morphologies come from the interaction between carbonate/phosphate and ferrihydrite. Although phosphate formed strong inner-sphere complexes on the ferrihydrite surface, which inhibited the direct contact and dissolution of ferrihydrite, co-adsorbed carbonate still promoted the olation reaction, facilitating the formation of hematite. These results suggest that as an important geochemical process, the increasing activity of carbonate or pCO2 can override the retarding impact of phosphate on the transformation of ferrihydrite and control the occurrence/crystallization of hematite in the subsurface soils under the scenario of climate change.

Segregation-driven exceptional twin-boundary strengthening in lean Mg–Zn–Ca alloys

Twinning-mediated plasticity in hexagonal close-packed crystal structures offers great potential for achieving lean Mg-based alloys with high strength and extended ductility. Micropillars from a lean MgZn1 Ca0.3 (ZX10, in wt%) alloy and pure Mg, each comprising one or more pre-existing {101¯2}<1¯011> extension twin boundaries and a parent orientation with its c-axis perpendicular to the loading direction, were subjected to in situ micropillar compression. By means of correlative characterization using transmission electron backscattered diffraction, transmission electron microscopy and nanoscale energy-dispersive X-ray spectroscopy, we assesed the effects of Zn and Ca solutes on micropillar deformation and on the response of pre-existing twin-boundaries to applied stress. In ZX10, both Zn and Ca solutes periodically segregate at the pre-existing extension twin boundaries, giving rise to a strengthening increment by about 300% compared to pure Mg, along with ductility enhancement. Due to segregation, the twin boundaries remain immobile throughout the deformation process, playing a critical role both in non-basal slip and twin-nucleation events. The former is facilitated by the formation of stable I1 stacking faults, while the latter is stimulated by active <c+a> slip across the pinned twin interface. In contrast, the pure Mg micropillars respond by massive twin growth followed by higher-order twinning events and profuse basal slip. In the absence of non-basal slip, pure Mg exhibits an earlier onset to failure due to shear incompatibility at the twin interface. The findings provide new insights into the role of solute Zn and Ca in stabilizing twinned microstructures for achieving synergistic strength-ductility enhancement in lean Mg alloys.

Development of Inorganic Impregnated Phase Change Material(PCM) in the Pores of Activated Carbon

Objectives : Recently, energy-related research has shifted from developing alternative energy to the efficient management technology of the produced energy. As an alternative, research on phase change materials (PCMs) capable of absorbing and releasing heat as an energy medium has been conducted. This study developed a more efficient heat storage medium using activated carbon as a medium for the phase change material. At the same time, we developed a method for efficiently impregnating the phase change material into the activated carbon pores.Methods : The activated carbon used in this experiment was charcoal powder activated carbon (250-350 mesh) and granular activated carbon. The inorganic phase change materials used in the experiment was manganese nitrate hexahydrate. The method for impregnating the phase change material was pressurization method and dilution method. The heat absorption / emission capacity of the developed material was examined within the range of 10℃ to 50℃.Results and Discussion : The Scanning electron microscope (SEM) and Transmission electron microscopy energy-dispersive X-ray spectroscopy (TEM-EDX) analysis showed that the phase change material was filled in the pore of activated carbon. When the phase change material is filled by the pressurized method, the material properties of manganese nitrate hexahydrate are reflected, resulting in absorption and release of heat at each phase change temperature. As a result of experiments for the selection of the optimum solvent in the phase change material filling study using the dilution method, when ethanol was used as the solvent, the heat absorption was clearly observed even after the phase change material was loaded. As a result of selecting the optimal dilution ratio, the ratio of ethanol was determined to be 1:1 as the dilution ratio with the lowest amount of floating activated carbon. The optimal solvent removal method experimental results show that the heat absorption/release section occurred when the ethanol was removed by evaporation at 85℃ temperature.Conclusions : 1) Both the pressurization method and the dilution method are filling methods in which inorganic phase change materials can be immobilized inside activated carbon, and heat absorption and release characteristics are maintained even after loading. 2) The heat absorption release was maintained for ethanol and the optimal dilution ratio was 1:1. 3) In case of the dilute solvent removal method, the heat absorption/release capacity was maintained when the solvent was removed using only the vaporization method.

Sequential microwave-ultrasound-assisted silver nanoparticles synthesis: A swift approach, their antioxidant, antimicrobial, and in-silico studies

The present research work unravels the novel optimization of microwave-ultrasound-assisted rapid synthesis of Olea europaea capped silver nanoparticles (O-AgNps) as a capping and stabilizing agent that is not previously studied. The synthesized O-AgNps were characterized using UV–Visible spectroscopy, Fourier transform infrared spectroscopy (ATR-FTIR), proton nuclear magnetic resonance (1H NMR), dynamic light scattering-zeta potential (DLS-Zeta potential), high-resolution transmission electron microscopy-energy dispersive X-ray spectroscopy (HR-TEM-EDAX), and atomic force microscopy (AFM) techniques. The HR-TEM-EDAX revealed that O-AgNps were ∼ 10 nm in diameter with a polydispersity index of 0.191 and were spherical to elliptical. The nanoparticles were analysed for the in-vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant, agar-well diffusion antibacterial assay, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) assays. The results were promising with a half-maximal inhibitory concentration (IC50) of 155.08 µg/mL for the antioxidant assay. The antimicrobial agar-well diffusion assay showed maximum zones of 24.9 ± 0.14 mm diameters at 8 mg/mL for Staphylococcus aureus (S. aureus) and 24.5 ± 0.7 mm at 8 mg/mL for Escherichia coli (E. coli). The MICs and MBCs were 156.25 µg/mL and 625 µg/mL for the antimicrobial assays againstS. aureusandE. coli. Additionally, the research throws limelight on the in-silico molecular docking analysis using AutoDock Vina software and arrives at a possible elucidation to support the experimental work.

Facile Material Design Concept for Co-Free Lithium Excess Nickel-Manganese Oxide as High-Capacity Positive Electrode Material

High-capacity Li1+x(Ni0.3Mn0.7)1-xO2, (0 < x < 1/3) samples were synthesized by the coprecipitation–calcination method. Both electrochemical cycle and high-rate performances were drastically improved by selecting an N2 atmosphere as final calcination. Scanning transmission electron microscopy—energy dispersive X-ray spectroscopy analysis showed that the sample calcined in an N2 atmosphere had a more homogeneous transition metal distribution into primary particles than that calcined in air. The solid-state 7Li nuclear magnetic resonance data showed that electrochemically inactive domains were only diminished for the sample calcined in an N2 atmosphere after electrochemical activation. X-ray Rietveld analysis revealed that the suitable transition metal distribution and content of the samples were different from those of typical layered rock-salt materials. Only that calcined in an N2 atmosphere had no spinel formation during charging and no oxide ion insertion reaction during discharging. No positive Co substitution effect was observed under the optimized preparation conditions. At the 100th cycle, the discharge capacity was 216 mAh g−1, which corresponds to 87% of the initial capacity (251 mAh g−1) at optimizing synthetic condition.

Rare earth elements (REEs) recovery from coal waste of the Western Kentucky No. 13 and Fire Clay Seams. Part I: Mineralogical characterization using SEM-EDS and TEM-EDS

The mineralogy of rare earth elements (REEs, including 15 lanthanides plus Sc and Y) in the Western Kentucky No. 13 and Fire Clay coal waste was studied based on elemental composition analyses using scanning electron microscopy- and transmission electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS and TEM-EDS). A total of 49 and 50 REE-bearing particles were found from the SEM-EDS specimens of the two materials, respectively. For both materials, light REEs were found in apatite, monazite, and crandallite-group minerals, while heavy REEs primarily existed in zircon and xenotime. Based on the number and REE contents of the REE-bearing particles, it was concluded that monazite, xenotime, and crandallite-group minerals were major contributors to the total REE contents in both materials. The number of crandallite-group mineral particles found from the Western Kentucky No. 13 material was more than that of monazite and xenotime particles. However, for the Fire Clay material, the number and size of crandallite-group mineral particles were close to those of monazite and xenotime particles. Since the monazite and xenotime particles contained more REEs relative to the crandallite-group mineral particles, it was inferred that the majority of the REEs, especially the light REEs, existing in the Fire Clay coal waste occurred as monazite and xenotime. In addition, comparing with the Western Kentucky No. 13 material, a larger portion of the heavy REEs in the Fire Clay material were comprised in zircon. SEM images of the REE-bearing particles indicated that both liberated particles and particles locked within dominant minerals (e.g., clays) existed in the two materials. A few of the particles found in the Western Kentucky No. 13 material were completely encapsulated within the dominant minerals. Findings from the current study will promote REE recovery from coal-related materials, particularly coal waste.

Nanoinclusions in zoned magnetite from the Sossego IOCG deposit, Carajás, Brazil: Implication for mineral zoning and magnetite origin discrimination

Compositional zoning is common in magnetite from different geological environments, but its formation mechanism remains controversial. Here, we characterize micron- to nano-scale textural and chemical variations in zoned magnetite from the Sossego iron oxide-copper–gold deposit (Carajás, Brazil) using electron probe microanalyzer (EPMA) and transmission electron microscopy (TEM). Lack of porosity and of a reaction front at both the micron and nanometer scales indicates that compositional zoning in magnetite is a pristine texture formed during crystal growth, rather than a secondary texture due to dissolution and reprecipitation reaction. TEM energy dispersive X-ray spectrometry analyses and mapping identify four types of nanoinclusions in zoned magnetite: 1) Mg-Fe-Al silicates, most likely amphibole, 2) Fe-Ti oxides, mainly ilmenite, 3) pyroxene, 4) Si-rich magnetite. The formation of ilmenite nanoinclusions in Sossego magnetite is possibly due to oxy-exsolution of ulvöspinel from Ti-rich magnetite, whereas nanoinclusions of other minerals likely formed by local supersaturation in the fluid boundary layer, followed by magnetite crystal entrapment. Compositional zoning in magnetite likely formed by a self-organization process where fluid composition fluctuations are feedback responses for an evolving fluid system far from equilibrium, rather than cyclic variations in external factors such as temperature and oxygen fugacity. Saturation of silicate minerals results in relative depletion of Si, Ca, and Al in boundary layer fluids, and formation of inclusion-poor zone depleted in these elements. Nanoinclusions in magnetite highlight the importance of textural characterization when using in situ chemical composition to discriminate the origin of magnetite. In addition, the assemblages of nanoinclusions in magnetite can be used to complement the discrimination of magnetite origins.

Fractionation of natural algal organic matter and its preservation on the surfaces of clay minerals

The sequestration of algal organic matter (AOM) in clays constitute important carbon sinks in lake sediments. The composition of AOM was proven recently to critically influence its preservation in sediments. Yet it remains unclear which AOM components and types of clay minerals contribute to AOM burial in lake sediments. Here we investigated the AOM fractionation in kaolinite and illite via their adsorption, to ascertain the distribution of AOM components on these clay surfaces. The results showed that the AOM adsorbed quantity was 2-fold higher for illite than kaolinite. The adsorption isotherm data of illite and kaolinite were well fitted by a Freundlich model. The three-dimensional excitation emission matrix fluorescence spectroscopy (3D EEM) with parallel factor analysis (PARAFAC) modeling identified the AOM component under fractionation. The AOM solution mainly consisted of humic acid-like, tyrosine-like, and tryptophan-like components. Notably, large amounts of the hydrophilic tyrosine-like components were adsorbed onto the surface of both kaolinite and illite, whereas the hydrophobic tryptophan-like components were seldom adsorbed onto neither of the clay materials, while humic acid-like components were only adsorbed onto illite. Therefore, illite is more suitable for the preservation of AOM. Both transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) and the X-ray photoelectron spectroscopy (XPS) analysis further confirmed the high adsorption of AOM on the surface of illite; i.e., the molar content of carbon in AOM adsorbed to illite was 22.04%, almost a double of that adsorbed to kaolinite (11.59%). Overall, our results demonstrate the selective preservation of AOM on clay surfaces and highlight the role of clay minerals as sequesters of organic matter in eutrophic lakes.

Effect of the addition mechanism of ZnO sintering aid on densification, microstructure and electrical properties of Ba(Zr,Y)O3-δ proton-conducting perovskite

We explore three different potential mechanisms to introduce 4 mol% ZnO sintering additive to the promising yttrium-doped barium zirconate (Ba(Zr,Y)O3-δ, BZY) proton conductor. The mechanisms involve Zn substitution for Y, Zr, or B-site cation excess. The addition of ZnO promotes high densification levels (up to 98% of the theoretical value) at 1300 °C, irrespective of the mechanism. However, scanning electron microscopy shows that the B-site cation excess mechanism leads to an impaired grain growth compared to the other mechanisms. Rietveld refinement of the lattice-parameters and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy indicates that Zn resides in both grains and grain boundaries in all cases. Determination of partial conductivities demonstrates that the Zr substitution mechanism provides slightly higher values of bulk protonic conductivity, as well as a higher hydration enthalpy. In contrast, the B-site excess mechanism provides the highest specific grain-boundary conductivity, as a result of greater Zn segregation to the grain boundary.

Tungsten Oxide-Modified SSZ-13 Zeolite as an Efficient Catalyst for Ethylene-To-Propylene Reaction

Among the zeolitic catalysts for the ethylene-to-propylene (ETP) reaction, the SSZ-13 zeolite shows the highest catalytic activity based on both its suitable pore architecture and tunable acidity. In this study, in order to improve the propylene selectivity further, the surface of the SSZ-13 zeolite was modified with various amounts of tungsten oxide ranging from 1 wt% to 15 wt% via a simple incipient wetness impregnation method. The prepared catalysts were characterized with several analysis techniques, specifically, powder X-ray diffraction (PXRD), Raman spectroscopy, temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and N2 sorption, and their catalytic activities were investigated in a fixed-bed reactor system. The tungsten oxide-modified SSZ-13 catalysts demonstrated significantly improved propylene selectivity and yield compared to the parent H-SSZ-13 catalyst. For the tungsten oxide loading, 10 wt% loading showed the highest propylene yield of 64.9 wt%, which was 6.5 wt% higher than the pristine H-SSZ-13 catalyst. This can be related to not only the milder and decreased strong acid sites but also the diffusion restriction of bulky byproducts, as supported by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) observation.

Characterizing electrical breakdowns upon reoxidation atmosphere for reliable multilayer ceramic capacitors

Electrical breakdowns of multilayer ceramic capacitors (MLCCs) manifest an increase in leakage current and are characterized as a function of atmospheric reoxidation. The atmospheric reoxidation is controlled with respect to the theoretical oxygen partial pressure for the oxidation of Ni internal electrodes. The breakdowns are characterized by a Maxwell–Wagner polarization technique, which dominantly exhibits space-charge-limited and Poole–Frenkel currents for all measured samples. The threshold voltage for the transition between these two conduction modes is suggested as an index for the robustness of the grain boundary resistance of BaTiO3; therefore, the breakdown voltage. The reoxidation atmosphere, which prevents the Ni oxidation, increases the threshold voltage, dramatically enhancing the breakdown voltage and insulation resistance. Impedance spectroscopy and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy reveal that the cation distribution throughout BaTiO3 grains and grain boundaries changes during the reoxidation, including Ni cations from the internal electrodes, which affects the grain boundary resistance and determines the breakdown voltage of MLCCs with Ni internal electrodes. These observations emphasize that the reoxidation should be concurrently optimized in terms of the cation redistribution and elimination of oxygen vacancies.

Heterostructural Mixed Oxides Prepared via ZnAlLa LDH or ex-ZnAl LDH Precursors-Effect of La Content and Its Incorporation Route.

The effect of La content and its incorporation route on physicochemical properties of ZnO/Zn(Al,La)2O4 or La2O3–ZnO/ZnAl2O4 mixed oxides with a spinel structure obtained from ZnAlLa Layered double hydroxides (LDHs) or ex-ZnAl LDH materials was investigated. The heterostructural nanocomposites with the similar Zn/Al molar ratio and varied La content were prepared by two techniques: via co-precipitation and thermal treatment of ZnAlLa LDHs at 500 °C or via incipient wetness impregnation of ex-ZnAl LDHs with aqueous solutions of lanthanum nitrate and subsequent thermal treatment. The obtained series of materials were characterized by the following techniques: X-ray fluorescence (XRF), N2 adsorption (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis with evolved gas analysis (TG/DTG/EGA), scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FFT). The evaluation of activity toward the high-temperature water gas shift (HT-WGS) within the temperature range of 350–420 °C was carried out on the basis of rate constant measurements in the kinetic mode using a differential reactor. The co-precipitation technique allowed for a better distribution of La in bulk and on the spinel surface than in case of lanthanum incorporation via impregnation. ZnO/Zn(Al,La)2O4 or La2O3–ZnO/ZnAl2O4 mixed oxides were characterized by moderate activity in the HT-WGS reaction. The results reveal that introduction of lanthanum oxide over 2.4–2.8 wt% induces the phase separation of the ZnAl2O4 spinel, forming ZnO on the ZnAl2O4 spinel surface.

Silica-Supported PdGa Nanoparticles: Metal Synergy for Highly Active and Selective CO2-to-CH3OH Hydrogenation.

The direct conversion of CO2 to CH3OH represents an appealing strategy for the mitigation of anthropogenic CO2 emissions. Here, we report that small, narrowly distributed alloyed PdGa nanoparticles, prepared via surface organometallic chemistry from silica-supported GaIII isolated sites, selectively catalyze the hydrogenation of CO2 to CH3OH. At 230 °C and 25 bar, high activity (22.3 molMeOH molPd–1 h–1) and selectivity for CH3OH/DME (81%) are observed, while the corresponding silica-supported Pd nanoparticles show low activity and selectivity. X-ray absorption spectroscopy (XAS), IR, NMR, and scanning transmission electron microscopy–energy-dispersive X-ray provide evidence for alloying in the as-synthesized material. In situ XAS reveals that there is a dynamic dealloying/realloying process, through Ga redox, while operando diffuse reflectance infrared Fourier transform spectroscopy demonstrates that, while both methoxy and formate species are observed in reaction conditions, the relative concentrations are inversely proportional, as the chemical potential of the gas phase is modulated. High CH3OH selectivities, across a broad range of conversions, are observed, showing that CO formation is suppressed for this catalyst, in contrast to reported Pd catalysts.

Control and Impact of Metal Loading Heterogeneities at the Nanoscale on the Performance of Pt/Zeolite Y Catalysts for Alkane Hydroconversion.

The preparation of zeolite-based bifunctional catalysts with low noble metal loadings while maintaining optimal performance has been studied. We have deposited 0.03 to 1.0 wt % Pt on zeolite H-USY (Si/Al ∼ 30 at./at.) using either platinum(II) tetraammine nitrate (PTA, Pt(NH3)4(NO3)2) or hexachloroplatinic(IV) acid (CPA, H2PtCl6·6H2O) and studied the nanoscale Pt loading heterogeneities and global hydroconversion performance of the resulting Pt/Y catalysts. Pt/Y samples prepared with PTA and a global Pt loading as low as 0.3 wt % Pt (nPt/nA = 0.08 mol/mol, where nPt is the number of Pt surface sites and nA is the number of acid sites) maintained catalytic performance during n-heptane (T = 210–350 °C, P = 10 bar) as well as n-hexadecane (T = 170–280 °C, P = 5 bar) hydroisomerization similar to a 1.0 wt % Pt sample. For Pt/Y catalysts prepared with CPA, a loading of 0.3 wt % Pt (nPt/nA = 0.08 mol/mol) sufficed for n-heptane hydroisomerization, whereas a detrimental effect on n-hexadecane hydroisomerization was observed, in particular undesired secondary cracking occurred to a significant extent. The differences between PTA and CPA are explained by differences in Pt loading per zeolite Y crystal (size ∼ 500 nm), shown from extensive transmission electron microscopy energy-dispersive X-ray spectroscopy experiments, whereby crystal-based nPt/nA ratios could be determined. From earlier studies, it is known that the Al content per crystal of USY varied tremendously and that PTA preferentially is deposited on crystals with higher Al content due to ion-exchange with zeolite protons. Here, we show that this preferential deposition of PTA on Al-rich crystals led to a more constant value of nPt/nA ratio from one zeolite crystal to another, which was beneficial for catalytic performance. Use of CPA led to a large variation of Pt loading independent of Al content, giving rise to larger variations of nPt/nA ratio from crystal to crystal that negatively affected the catalytic performance. This study thus shows the impact of local metal loading variations at the zeolite crystal scale (nanoscale) caused by different interactions of metal precursors with the zeolite, which are essential to design and synthesize optimal catalysts, in particular at low noble metal loadings.

Understanding up and down-conversion luminescence for Er3+/Yb3+ co-doped SiO2-SnO2 glass-ceramics

Er3+/Yb3+ co-doped SiO2-SnO2 glass-ceramics bulks were synthesized using the sol-gel method. High-resolution transmission electron microscopy images, x-ray diffraction, and energy-dispersive x-ray spectroscopy mapping confirm that 5 nm SnO2 crystals were homogeneously dispersed in the silica matrix. The incorporation of Er3+ and Yb3+ ions in SnO2 was also confirmed by X-ray photoelectron spectroscopy. This analysis shows Er3+ and Yb3+ ions locate in SnO2 nanocrystal and amorphous silica sites. Er3+/Yb3+ co-doped SiO2-SnO2 glass-ceramics behave as both down and up-conversion luminescent materials. Efficient energy transfers from Yb3+ ion sensitizers to Er3+ activators cause remarkable 5-fold Er3+ emission enhancement at 1.55 µm. We also propose a mechanism for down and up-conversion processes.