Ba Phase Research Articles

Benthic-pelagic coupling and isotopic fractionation of barium in Kiel Bight, SW Baltic Sea

Barium (Ba) isotopes are a promising new tracer for riverine freshwater input to the ocean and marine biogeochemical cycling. However, many processes that affect Ba cycling at continental margins have not yet been investigated with respect to Ba isotope fractionation. Here, we present a comprehensive data set of Ba concentration and isotope data for water column, pore water and sediment samples from Kiel Bight, a seasonally stratified and hypoxic fjord in the southwestern Baltic Sea. The surface water Ba concentration and Ba isotope inventory of the water column can generally be explained by mixing of riverine freshwater and Atlantic seawater. However, the deep-water below the seasonal pycnocline (10 - 15 m water depth) is characterized by a pronounced positive Ba concentration anomaly (up to 915 nM) that is accompanied by a δ138Ba of ~+0.25 ‰, which is lighter than expected from the seawater-freshwater mixing line (Ba: 77 nM, δ138Ba: +0.32 ‰ at a salinity of 18). Pore water profiles indicate a Ba flux across the sediment-water interface, which contributes to the enrichment in isotopically light Ba in the deep-water. Pore waters of surface sediments and deep-waters are oversaturated with respect to barite. Therefore, barite dissolution is unlikely to account for the benthic Ba flux. Water column Ba concentrations closely correlate with those of the nutrients phosphate and silica, which are removed from surface waters by biological processes and recycled from the sediment by diffusion across the sediment-water interface. As nutrient-to-Ba ratios differ among sites and from those observed in open-marine systems, we propose that Ba is removed from surface waters by adsorption onto biogenic particles (rather than assimilation) and regenerated within surface sediments upon organic matter degradation. Pore water data for subsurface sediments in Kiel Bight indicate preferential transfer of isotopically heavy Ba into an authigenic phase during early diagenesis. Quantifying the burial flux associated with this authigenic Ba phase along continental margins could potentially help to settle the isotopic imbalance between known Ba source and sink fluxes in the ocean.

Long-term safety and efficacy of bempedoic acid in patients at high risk of atherosclerotic cardiovascular disease: results from the CLEAR Harmony open-label extension study

Abstract Background Bempedoic acid (BA) is an oral first-in-class, ATP-citrate lyase inhibitor that lowers low-density lipoprotein cholesterol (LDL-C) levels in adults with hypercholesterolemia. In the phase 3 CLEAR Harmony study (NCT02666664, n=2230), BA 180 mg for 52 weeks significantly lowered LDL-C at week 12 compared with placebo and was maintained for 52 weeks in hypercholesterolemic patients with atherosclerotic cardiovascular disease (ASCVD) and/or heterozygous familial hypercholesterolemia (HeFH) on stable, maximally tolerated statins. Purpose To report long-term safety, tolerability, and efficacy of BA from the CLEAR Harmony open-label extension (OLE) study (NCT03067441). Methods After completing the 52-week placebo-controlled CLEAR Harmony study, patients immediately entered the OLE and received BA for 78 weeks, followed by a 4-week washout period; the potential cumulative exposure to BA was 2.5 years. The primary endpoint was long-term safety of BA in the OLE. Results A total of 1462 patients enrolled in the OLE (BA n=970; placebo n=492 from CLEAR Harmony). At OLE baseline, mean (SD) age was 66.9 (8.7) years, 73.9% were male, 96.3% had ASCVD, 3.7% had HeFH with or without ASCVD, and all were receiving statins (93.5% moderate or high intensity). At baseline of CLEAR Harmony, patients had mean (SD) LDL-C of 102.9 (29.9) mg/dL (BA) and 99.0 (24.2) mg/dL (placebo). The majority of OLE patients (86.2%, n=1260) completed 78 weeks of BA treatment. At week 12 and 78 of OLE treatment, respectively, mean LDL-C lowering from CLEAR Harmony baseline was –14.9% and –14.4%. A total of 1143 patients (78.2%) reported a treatment-emergent adverse event (TEAE), and 299 (20.5%) reported a serious TEAE. TEAEs of special interest, determined by the therapeutic area or prior observations in preclinical or early clinical studies, occurred at similar rates as CLEAR Harmony (creatine kinase elevations, 1.8%; gout, 2.6%; hepatic enzyme elevations, 2.0%; hypoglycemia, 1.2%; muscular disorders, 8.5%; neurocognitive disorders, 0.9%; new onset/worsening diabetes mellitus, 5.5%; renal disorders, 2.8%) with biochemical changes that were stable over the course of the study and approached baseline levels after treatment discontinuation. Overall, 114 patients (7.8%) reported a TEAE leading to discontinuation of BA (most common: myalgia [0.6%], muscle spasm [0.5%]). Conclusion Durable lipid lowering was observed through 78 weeks of BA treatment and patient adherence to BA therapy was high (86.2%). Overall safety during the OLE was similar to results reported in the 52-week-long CLEAR Harmony study and the overall BA phase 3 clinical program, with no new safety findings. Funding Acknowledgement Type of funding source: Private company. Main funding source(s): Esperion Therapeutics, Inc., funded the research for this study and provided writing support for this abstract. Medical writing assistance was provided by Agnella Izzo Matic, PhD, CMPP, and Kelly M Cameron, PhD, CMPP, of JB Ashtin.

Sol-gel synthesis of Ba-doped ZnO nanoparticles with enhanced photocatalytic activity in degrading Rhodamine B under UV-A irradiation

In this work, Ba-doped ZnO (Ba/ZnO) nanoparticles were synthesized through a facile sol-gel approach without the use of surfactants. The impacts of Ba content and calcination temperature on the performance of Ba/ZnO nanoparticles as photocatalyst in degrading Rhodamine B (RhB) under UV-A light irradiation were investigated. The results of the study indicated performance of Ba/ZnO nanoparticles than bare ZnO nanoparticles. Maximum photocatalytic activity was achieved at 0.1% Ba doped ZnO at 400°C calcination temperature. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX), nitrogen physisorption and Diffuse Reflectance Spectroscopy (DRS) techniques were used for investigating the structure and properties of Ba/ZnO nanoparticles. XRD pattern did not indicate any peaks regarding Ba phase in Ba/ZnO nanoparticles and a wurtzite crystal structure was observed. Also, mapping analysis revealed fair Ba distribution in ZnO lattice. Near spherical shape was observed in SEM image for Ba/ZnO nanoparticles and results of BET and BJH analysis indicated specific surface area of 109.81m2g−1 and pore volume of 0.424cm3g−1. DRS spectra indicated decrease in band-gap energy for 0.1% Ba doped ZnO in comparison with bare ZnO.

A pressure calibration method for a portable wide-access “panoramic” cell

A simple and convenient pressure calibration method is developed for a newly designed portable wide-access ‘panoramic’ cell. This cell is adapted to angle-dispersive-mode high-pressure in situ neutron diffraction of reactor neutron sources. This pressure calibration method has established a relationship between the cell pressure and the anvil displacement (gasket compression) based on the fixed-point calibration technique. By employing TiZr gasket with a thickness of 3 mm and WC anvil with a culet of 4 mm diameter, the average anvil displacements are 1.31 mm and 2.22 mm for Bi phase transitions (2.55 GPa and 7.7 GPa), and 1.85 mm for Ba phase transitions (5.5 GPa), respectively. In this pressure range, the pressure increases quickly with decreasing gasket thickness, and undergoes a linear increase with the anvil displacement. By extrapolating the calibration curve, the cell pressure will achieve 10 GPa when the anvil displacement is around 2.5 mm.

Novel Gas-assisted Three-liquid-phase Extraction System for Simultaneous Separation and Concentration of Anthraquinones in Herbal Extract

Gas-assisted three-liquid-phase extraction (GATE), which has the advantages of both three-liquid-phase extraction and solvent sublation, is a novel separation technique for separation and concentration of two organic compounds into different phases in one step. This highly effective and economically applicable method has been developed for separating emodin and rhein from herbal extract. In a GATE system composed of butyl acetate/PEG4000/ammonium sulfate aqueous solution, influence of various parameters including gas flow rate, flotation time, salt concentration, initial volume of PEG and butyl acetate was investigated. Within 50min of 30ml·min−1 nitrogen flow, removal ratio of emodin and rhein from aqueous phase could be over 99% and 97%, respectively. Mass fraction of emodin in the BA phase and rhein in the PEG phase could reach 97% and 95%, respectively. It is demonstrated that gas bubbling is effective for partitioning of emodin and rhein into butyl acetate and PEG phase respectively, and dispersed PEG and butyl acetate could be captured from the aqueous solution. Experimental results show that GATE could be an effective and economical technology for concentration and separation of co-existed products in medicinal plants.

First-principles investigations on Pb–Ba intermetallic compounds

To better clarify and understand the ground-state physical properties of Pb–Ba intermetallic compounds, phase stabilities, elastic properties and electronic structures of Pb–Ba intermetallic compounds have been investigated by using first-principles calculations within local density approximation. The formation enthalpies of these compounds indicate that they are thermodynamically stable. The bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio v were evaluated. The brittle and ductile properties were discussed by using B/G and Poisson’s ratio. The hardness was also estimated by using a semi-empirical equation. The mechanical anisotropy was characterized by calculating several different anisotropic indexes and the 3D figures of directional dependences of reciprocals of elastic moduli. Finally, the electronic structures were also discussed.

Effect of Sintering Temperature on Microstructure, Chemical Stability, and Electrical Properties of Transition Metal or Yb-Doped BaZr0.1Ce0.7Y0.1M0.1O3−δ (M = Fe, Ni, Co, and Yb)

Perovskite-type BaZr0.1Ce0.7Y0.1M0.1O3-δ (M = Fe, Ni, Co and Yb) (BZCY-M) oxides were synthesized using the conventional solid-state reaction method at 1350-1550 oC in air in order to investigate the effect of dopants on sintering, crystal structure, chemical stability under CO2 and H2S, and electrical transport properties. The formation of the single-phase perovskite-type structure with an orthorhombic space group Imam was confirmed by Rietveld refinement using powder X-ray diffraction (PXRD) for the Fe, Co, Ni and Yb-doped samples. The BZCY-Co and BZCY-Ni oxides show a total electrical conductivity of 0.01 and 8 × 10-3 Scm-1 at 600 oC in wet H2 with an activation energy of 0.36 and 0.41 eV, respectively. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX) revealed Ba and Co rich secondary phase at the grain-boundaries, which may explain the enhancement in the total conductivity of the BZCY-Co. However, ex-solution of Ni at higher sintering temperatures, especially at 1550 oC, decreases the total conductivity of the BZCY-Ni material. The Co and Ni dopants act as a sintering aid and form dense pellets at a lower sintering temperature of 1250 oC. The Fe, Co and Ni-doped BZCY-M samples synthesized at 1350 oC show stability in 30 ppm H2S/H2 at 800 oC, and increasing the firing temperature to 1550 oC, enhanced the chemical stability in CO2 / N2 (1: 2) at 25-900 oC. The BZCY-Co and Ni compounds with high conductivity in wet H2 could be considered as possible anodes for intermediate temperature solid oxide fuel cells (IT-SOFCs).

Comparison of the photoluminescence properties of Eu2+, Mn2+ co-doped M5(PO4)3Cl (M = Ca, Sr, Ba)

Eu2+ and Mn2+ singly doped or co-doped M5(PO4)3Cl (M=Ca, Sr and Ba) phosphors were synthesized by conventional solid state reactions and characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, PL decay curves, energy dispersive spectra (EDS) and Raman spectra. The results show that a better size match between the doped cation and the host cation allows a wider solid solution range (e.g. Ca2+/Mn2+) and a narrower emission band (e.g. Sr2+/Eu2+ and Ca2+/Mn2+). A lower phonon energy of the host (e.g. the Sr phase) reduces the non-radiation probability and enhances the PL efficiency. The PL performance of the Ba phase is exceptional possibly because of the large size difference between the doped cations and the host cations. The transfer efficiency (η) and the emission quantum efficiency (Q) were analyzed.In the studied phosphors, superficially Eu2+ efficiently transferred its absorbed energy to Mn2+ but the Q of the Mn2+ emission was not as high as expected. Two loss mechanisms are proposed: an “inverse bottleneck effect” and “charge transfer” between Eu2+ and Mn2+.

Effect of aging on NOx reduction in coupled LNT–SCR systems

The effect of simulated road aging on the NOx reduction performance of coupled Pt/Rh LNT and Cu-CHA SCR catalysts was studied using H2, CO and C3H6 as NOx reductants. Activity tests showed that the NOx reduction activity of the LNT was significantly decreased after aging, especially at low temperature. N2 physisorption, H2 chemisorption, elemental analysis and TEM results revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the aged LNT associated with the Ba phase was responsible for decreased NOx storage efficiency. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NOx storage and catalyst regeneration. The aged LNT showed higher NH3 selectivity than that of the fresh LNT in the temperature range 150–450°C, NH3 generated from the LNT being stored by the SCR catalyst which subsequently catalyzed its reaction with NOx slip from the LNT. Hence, the loss of NOx conversion over the LNT was partly compensated by the downstream SCR catalyst. N2O formation over the aged LNT was less than that over the fresh LNT and the N2O was partly mitigated by the downstream SCR catalyst. Microreactor tests further showed that in addition to NH3, the SCR catalyst was able to use slipped CO or C3H6 as NOx reductants. A comparison of the difference in NOx conversion for the aged LNT and LNT–SCR configurations for the three reductants used in this study showed that the greatest benefit was obtained when CO and C3H6 were the reductants. This is explained by the fact that the LNT catalyst was unable to utilize these reductants as efficiently as H2 due to their lower reactivity; hence, more NOx and reductant slip reached the SCR catalyst. The ability of the SCR catalyst to utilize these reductants therefore provides a significant advantage over the LNT-only configuration.

The different NOxtrap performance on ceria and barium/ceria containing LNT catalysts below 200 °C

The low-temperature NOx storage efficiency of Ce-containing lean NOx trap catalysts was investigated using temperature programmed adsorption. The incorporation of ceria either as a NOx storage phase or as the support for barium oxides improves the NOx storage capacity from 200 °C to 350 °C. However, as temperature increases from 100 °C to 150 °C, the rate of NOx storage slows down over the catalysts containing ceria as a storage phase, while this phenomenon is less obvious if ceria is used as the support for barium oxides. By investigating the individual components of catalysts using NO-TPD, we found that the NOx release was mainly from ceria. Based on the in situ DRIFT data, we conclude that nitrite species are formed on ceria during the NOx storage at low temperatures, and the nitrite species can be activated and transformed to nitrate species upon further oxidation, accompanied by NO release; on the other hand, NO release occurs weakly on barium/ceria as the nitrites are more stable on the more basic Ba phase than on the ceria. In addition, the dispersion of barium species on ceria is higher than that on γ-Al2O3, resulting in the formation of a larger amount of basic sites. The addition of barium onto ceria not only improves the stability of ad-NOx species but also positively impacts the amounts of NOx trapped.

Application of spaciMS to the study of ammonia formation in lean NOx trap catalysts

SpaciMS was employed to understand the factors influencing the selectivity of NOx reduction in two fully formulated LNT catalysts, both degreened and thermally aged. Both catalysts contained Pt, Rh, BaO and Al2O3, while one of them also contained La-stabilized CeO2. The amount of reductant required to fully regenerate each catalyst was first determined experimentally based on the OSC of the catalyst and the NOx storage capacity (NSC). In this way a correction was made for the change in catalyst OSC and NSC after aging, thereby eliminating these as factors which could affect catalyst selectivity to NH3. For both catalysts, aging resulted in an elongation of the NOx storage–reduction (NSR) zone due to a decrease in the concentration of NOx storage sites per unit catalyst length. In addition to decreased lean phase NOx storage efficiency, stretching of the NSR zone affected catalyst regeneration. Three main effects were identified, the first being an increase of the NOx “puff” that appeared during the onset of the rich front as it traversed the catalyst. Spatially, NOx release tracked the NSR zone, with the result that the NOx concentration peaked closer to the rear of the aged catalysts. Hence the probability that NOx could re-adsorb downstream of the reduction front and subsequently undergo reduction by NH3 (formed in the reduction front) was diminished, resulting in higher rich phase NOx slip. Second, the stretching of the NSR zone resulted in increased selectivity to NH3 due to the fact that less catalyst (corresponding to the OSC-only zone downstream of the NSR zone) was available to consume NH3 by either the NH3-NOx SCR reaction or the NH3-O2 reaction. Third, the loss of OSC and NOx storage sites, along with the decreased rate of NOx diffusion to Pt/Rh sites (as a result of Pt/Rh–Ba phase segregation), led to an increase in the rate of propagation of the reductant front after aging. This in turn resulted in increased H2:NOx ratios at the Pt/Rh sites and consequently increased selectivity to NH3.

NOx Reduction on Fully Formulated Lean NOx Trap Catalysts Subjected to Simulated Road Aging: Insights from Steady-State Experiments

Fully formulated lean NO x trap (LNT) catalysts of the type Pt/Rh/BaO/Al 2 O 3 were prepared with and without incorporation of CeO 2 -ZrO 2 in the washcoat, and their NO x reduction behavior was evaluated in steady-state, continuous flow experiments. In the fresh state, CeO 2 -ZrO 2 addition was found to exert little effect on NO x reduction activity using H 2 , CO, and NH 3 as the reductants. However, after simulated road aging, NO x reduction activity was significantly impaired for the CeO 2 -ZrO 2 -free catalyst, whereas the performance of the CeO 2 -ZrO 2 -containing analog was affected to only a minor degree. These differences are explained on the basis of high-resolution transmission electron microscopy measurements showing that Pt supported on CeO 2 -ZrO 2 remained highly dispersed after aging, whereas Pt supported on BaO/Al 2 O 3 underwent significant sintering. In addition, the Pt/CeO 2 -ZrO 2 component did not accumulate sulfur during aging, unlike Pt/BaO/Al 2 O 3 for which significant sulfation of the Ba phase occurred. For both catalysts, selectivity to NH 3 in NO and NO 2 reduction by H 2 increased after catalyst aging, indicative of a change in the relative surface coverages of N and H ad-atoms on the precious metal sites. The addition of CeO 2 -ZrO 2 to a Pt/Rh/BaO/Al 2 O 3 lean NO x trap catalyst affords significant benefits with respect to steady-state NO x reduction activity after catalyst aging. These benefits are explained on the basis of HRTEM analyses.

Effect of aging on the NOx storage and regeneration characteristics of fully formulated lean NOx trap catalysts

In order to elucidate the effect of washcoat composition on lean NOx trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NOx conversion as a consequence of impaired NOx storage and NOx reduction functions, while increased selectivity to NH3 was observed in the temperature range 250–450°C. Elemental analysis, H2 chemisorption and TEM data revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the catalysts, associated with the Ba phase, decreased catalyst NOx storage capacity. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NOx spillover from Pt to Ba during NOx adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NOx spillover during catalyst regeneration. For the aged catalysts, halving the Pt loading from 100 to 50g/ft3 was found to result in a significant decrease in overall NOx conversion, while for catalysts with the same 100g/ft3 Pt loading, increasing the relative amount of Pt on the NOx storage components (BaO and La-stabilized CeO2), as opposed to an Al2O3 support material (where it was co-located with Rh), was found to be beneficial. The effect of Rh loading on aged catalyst performance was found to be marginal within the range studied (10–20g/ft3), as was the effect of BaO loading in the range 30–45g/L.

Influence of Ba precursor on structural and catalytic properties of Pt–Ba/alumina NOx storage-reduction catalyst

The effect of the choice of barium precursor (nitrate or acetate), in the preparation of Pt–Ba/γ-Al2O3 NSR catalysts, on their structure and catalytic behavior has been investigated by means of X-ray diffraction (XRD), temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and catalytic tests. XRD patterns showed that the type of Ba precursor and repeated NSR cycles influence the crystallinity of Ba species. Depending on the Ba precursor, remarkable differences in Ba(NO3)2 crystallite sizes as well as availability of the Pt for hydrogen chemisorption were observed. TPD and TPR studies showed that the catalyst prepared using the Ba acetate-precursor route is more efficient in the decomposition and reduction of Ba nitrates at lower temperatures. The catalyst prepared by the Ba acetate-precursor route showed both enhanced NOx storage ability and selectivity toward nitrogen in the reduction process, which is attributed to the intimate contact of the small crystallites of the Ba-component and the Pt particles. Environmental transmission electron microscopy (ETEM) measurements revealed that introduction of H2O vapor induces morphological changes of the Ba phase leading to partial liquefaction as a result of the formation of hygroscopic barium hydroxides. The interplay of this liquid-like behavior of the Ba phase together with the chemical transformations occurring during NOx storage and reduction can lead to remarkable structural changes affecting the NSR performance.

Modeling the effect of Pt dispersion and temperature during anaerobic regeneration of a lean NO x trap catalyst

A crystallite-scale model is incorporated into a reactor-scale model to study the effect of Pt dispersion and temperature during the regeneration of a lean NO x trap (LNT) comprising a Pt/BaO catalyst. The current study is based on a recent experimental study [R.D. Clayton, M.P. Harold, V. Balakotaiah, C.Z. Wan, Appl. Catal. B 90 (2009) 662]. The model shows that an increase in the Pt dispersion for a fixed Pt loading increases the interfacial perimeter between Pt and Ba, and has a significant effect on the regeneration kinetics. The transient product distribution displayed by three catalysts having varied Pt dispersions (3.2%, 8% and 50%) is explained by the localized stored NO x gradients in the Ba phase. A rate determining process during the regeneration is found to be the diffusion of stored NO x within the Ba phase towards the Pt/Ba interface. Temperature-dependent NO x diffusivities in the Ba phase are used to predict the breakthrough profiles of H 2, N 2 and NH 3 over a range of catalyst temperatures. Finite gradients in the stored NO x concentration are predicted in the Ba phase, thus showing that the nitrate ions are not sufficiently mobile at lower temperatures for the low dispersion catalysts. The model predicts that the highest amount of NH 3 is produced by the low dispersion catalyst (3.2% dispersion) at high temperatures, by the high dispersion catalyst (50% dispersion) at low temperatures, and by the intermediate dispersion catalyst (8% dispersion) at intermediate temperatures, consistent with the experimental data. It is found that the net NH 3 generation is favored under conditions when NO x transport to the Pt/Ba interface is the rate determining process. The model considers the consumption of chemisorbed oxygen on Pt by H 2, which is used to predict the low effluent N 2 concentration for the 50% dispersion catalyst as compared to the 8% dispersion catalyst. Finally, a novel design is proposed to maximize the amount of NH 3 in the effluent of a LNT, which can be used as a feed to a selective catalytic reduction (SCR) unit placed downstream of the LNT.

Ba minerals in clinopyroxene rocks from the Myanmar jadeitite area: implications for Ba recycling in subduction zones

Barium (Ba) minerals identified in clinopyroxene rocks from the Myanmar jadeitite area include celsian, hyalophane, and hydrated barium aluminum silicate (an inferred barian zeolite). The hyalophane and hydrated barium aluminum silicate occur as interstitial phases and sometimes crosscut jadeite crystals, indicating they were formed at a later stage than jadeitite. The celsian has two modes of occurrence: (i) in association with jadeite in jadeitite; (ii) as a single-phase mineral forming part of multi-phase pseudomorphs in chromian omphacite rock (omphacitite). The latter rock type was formed predominantly during the same episode as the jadeitite under almost the same P-T conditions. Multi-phase pseudomorphs, mostly showing hexagonal form, contain celsian and kaolinite, with or without quartz, graphite and diaspore. The P-T condition constraints on celsian suggest that a precursor phase, probably cymrite, once existed under high-pressure conditions, and that celsian was formed by decomposition of the phase under decreasing pressure during uplift of the jadeitite. The frequent occurrence of Ba silicates in jadeitites worldwide reflects a Ba-enriched environment for the formation of jadeitite, which is inferred to be related to subducted barite-bearing slab sediments. Therefore, the jadeitite records metasomatism and metamorphism, as well as fluid interactions and phase changes in the BaO-Al 2 O 3 -SiO 2 -H 2 O system. In this way, jadeitite provides information on Ba phase transformations and Ba recycling within the subduction zone. Taken together with previous results, this study further suggests that jadeite-forming fluids are derived from the dehydration of the altered oceanic slab containing deep-sea sediments.

The Si–Sr and Si–Ba phase diagrams over the Si-rich composition range

For the first time, Si–Sr and Si–Ba phase diagrams have been investigated over the Si-rich composition range. The solid solubilities of Sr and Ba impurity getters in silicon were measured in the temperature range from 1173 to 1573 K by analytical methods, including microhardness and instrumental neutron activation analysis. The liquidus curves for the primary crystallization of silicon were determined by differential thermal and activation analyses. The alloys were prepared from pure components using induction heating with subsequent quenching. The samples were subjected to isochronous homogenization annealing at different temperatures for 100 h. The elements Sr and Ba exhibit retrograde solubility in silicon. The maximum equilibrium solubility of Sr in Si is 1.15 at.% at 1573 K, while the Ba solubility limit is 0.98 at the same temperature. The thermodynamic description of the experimental liquidus curves for the primary crystallization of Si indicates that the Si–Sr and Si–Ba liquid alloys do not inherently have a regular nature. We expect that the clathrate structure can exist in the Si-rich melts of the Si–Sr and Si–Ba systems.

NOx storage and reduction in model lean NOx trap catalysts studied by in situ DRIFTS

NOx storage and reduction on a model Pt/BaO/Al2O3 catalyst was studied by means of in situ DRIFTS measurements. To examine the effect of ceria addition, experiments were also conducted using Pt/BaO/Al2O3 to which Pt/CeO2 was added as a physical mixture in a 74:26 weight ratio. For the former catalyst, DRIFT spectra acquired during NO/O2 and NO2/O2 storage indicated the formation of nitrite at 200°C during the initial stages of adsorption, while increasing the adsorption temperature appeared to facilitate the oxidation of nitrite to nitrate. The ceria-containing catalyst afforded similar DRIFT spectra under these conditions, although the presence of cerium nitrates was observed at 200 and 300°C, consistent with NOx storage on the ceria phase. DRIFT spectra acquired during NOx reduction in CO and CO/H2 showed that Ba nitrate species remained on the surface of both catalysts at 450°C, whereas the use of H2-only resulted in complete removal of stored NOx. The observation of Ba carbonates when CO was present suggests that the inferior reduction efficiency of CO may arise from the formation of a crust of BaCO3 on the Ba phase, which inhibits further NOx reduction. DRIFT spectra acquired during lean-rich cycling (6.5min lean, 1.0min rich) with CO/H2 as the rich phase reductants revealed that a significant concentration of nitrates remained on the catalysts at the end of the rich phase. This implies that a large fraction of nitrate is not decomposed during cycling and thus cannot participate in NOx abatement through storage and regeneration.

Effect of Ceria on the Sulfation and Desulfation Characteristics of a Model Lean NO x Trap Catalyst

The effect of ceria addition on the sulfation and desulfation characteristics of a model Ba-based lean NO x trap (LNT) catalyst was studied. According to DRIFTS and NO x storage capacity measurements, ceria is able to store sulfur during catalyst exposure to SO2, thereby helping to limit sulfation of the main (Ba) NO x storage phase and maintain NO x storage capacity. Temperature programmed desulfation experiments revealed that desulfation of a model ceria-containing catalyst occurred in two stages, corresponding to sulfur elimination from the ceria phase at ~450 °C, followed by sulfur loss from the Ba phase at ~650 °C. Significantly, the ceria-containing catalyst displayed relatively lower sulfur evolution from the Ba phase than its non-ceria analog, confirming that the presence of ceria lessened the degree of sulfur accumulation on the Ba phase.

Kinetic Modeling of NOx Storage/Reduction on Pt/BaO/Al2O3 Monolith Catalysts

A balance of the complexity of the reactor model and the chemical reaction mechanism has to be made in order to predict the dynamic nature of NOx storage/reduction processes in real time. In this work, a one-dimensional, two-phase model is used to simulate the transient behavior of a monolithic Pt/BaO/Al2O3 catalyst for NOx storage/reduction. The following aspects of the process are discussed: (i) kinetics of NO and NO2 adsorption on BaO sites, (ii) effects of CO2 and H2O on NO/NO2 adsorption, and (iii) reduction of surface nitrates using H2. NOx adsorption with excess oxygen involves two kinetic routes, namely, NO2 disproportionation and direct NO adsorption, both of which form nitrates on the catalyst at 300 °C. A model with two time scales was found to be necessary to describe NO2 adsorption on the 20 wt % BaO catalyst. The model and parameters required to fit the NOx breakthrough curves suggest that CO2 and H2O in the feed reduce the number of sites for NO adsorption by changing the surface morphology of the Ba phase. The rate constants for both fast and slow NO2 uptake are decreased in the presence of CO2 and H2O, but the total capacity remains the same. Under reaction conditions, H2 reduction of surface NOx is limited by the supply of the reductant; that is, the rate of surface NOx removal is limited by the flux of inlet H2. NH3 serves as the reducing intermediate/H carrier during the H2 reduction process. The confined reduction front moving along the channel localizes the heat generation, thus leading to a surface temperature in the reduction front about 35 °C higher than the inlet gas temperature for our reaction conditions.