Stellar heating causes atmospheres of close-in exoplanets to expand and escape. These extended atmospheres are difficult to observe because their main spectral signature-neutral hydrogen at ...ultraviolet wavelengths-is strongly absorbed by interstellar medium. We report the detection of the near-infrared triplet of neutral helium in the transiting warm Neptune-mass exoplanet HAT-P-11b using ground-based, high-resolution observations. The helium feature is repeatable over two independent transits, with an average absorption depth of 1.08 ± 0.05%. Interpreting absorption spectra with 3D simulations of the planet's upper atmosphere suggests it extends beyond 5 planetary radii, with a large scale height and a helium mass loss rate ≲ 3×10
g‧s
A net blue-shift of the absorption might be explained by high-altitude winds flowing at 3 km‧s
from day to night-side.
Context. Ground-based telescopes equipped with state-of-the-art spectrographs are able to obtain high-resolution transmission and emission spectra of exoplanets that probe the structure and ...composition of their atmospheres. Various atomic and molecular species, such as Na, CO, H2O have been already detected in a number of hot Jupiters. Molecular species have been observed only in the near-infrared while atomic species have been observed in the visible. In particular, the detection and abundance determination of water vapor bring important constraints to the planet formation process. Aims. We aim to search for water vapor in the atmosphere of the exoplanet HD 189733b using a high-resolution transmission spectrum in the visible obtained with HARPS. Methods. We used the atmospheric transmission code Molecfit to correct for telluric absorption features. Then we computed the high-resolution transmission spectrum of the planet using three transit datasets. We finally searched for water vapor absorption in the water band around 6500 Å using a cross-correlation technique that combines the signal of 600–900 individual lines. Results. Telluric features are corrected to the noise level. We place a 5-σ upper limit of 100 ppm on the strength of the 6500 Å water vapor band. The 1-σ precision of 20 ppm on the transmission spectrum demonstrates that space-like sensitivity can be achieved from the ground, even for a molecule that is a strong telluric absorber. Conclusions. This approach opens new possibilites for the detection of various atomic and molecular species with future instruments such as ESPRESSO at the VLT. Extrapolating from our results, we show that only one transit with ESPRESSO would be sufficient to detect water vapor on HD 189733b-like hot Jupiter with a cloud-free atmosphere. Upcoming near-IR spectrographs will be even more efficient and sensitive to a wider range of molecular species. Moreover, the detection of the same molecular species in different bands (e.g., visible and IR) is key to constrain the structure and composition of the atmosphere, such as the presence of Rayleigh scattering or aerosols (cloud and/or hazes).
Context.
The atmosphere of exoplanets has been studied extensively in recent years, making use of numerical models to retrieve chemical composition, dynamical circulation, or temperature from the ...data. One of the best observational probes in transmission is the sodium doublet thanks to its extensive cross-section. However, modelling the shape of planetary sodium lines has proven to be challenging. Models with different assumptions regarding the atmosphere have been employed to fit the lines in the literature, yet statistically-sound, direct comparisons of different models are needed to paint a clear picture.
Aims.
We aim to compare different wind and temperature patterns, as well as to provide a tool to distinguish them based on their best fit for the sodium transmission spectrum of the hot Jupiter HD 189733b. We parametrise different possible wind patterns that have already been tested the in literature and introduce the new option of an upwards-driven vertical wind.
Methods.
We construct a forward model where the wind speed, wind geometry, and temperature are injected into the calculation of the transmission spectrum. We embed this forward model in a nested sampling retrieval code to rank the models via their Bayesian evidence.
Results.
We retrieve a best-fit to the HD 189733b data for vertical upward winds |
v
ver
(mean)| = 40 ± 4 km s
−1
at altitudes above 10
−6
bar. With the current data from HARPS, we cannot distinguish wind patterns for higher-pressure atmospheric layers.
Conclusions.
We show that vertical upwards winds in the upper atmosphere provide a possible explanation for the broad sodium signature in hot Jupiters. We highlight other influences on the width of the doublet and we explore strong magnetic fields acting on the lower atmosphere as one possible origin of the retrieved wind speed.
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•Both spiral wound membranes demonstrated a high metal and sulfate removal capacity.•No difference in rejections was observed at high pressures in both membranes.•Increase Reynolds ...number does not significantly affect the permeate flow.•VRF measurements provide important information for scaling up AMD treatment.•NF270 shows excellent performance until ten days of continuous operation.
The primary objective of this investigation was to evaluate the ability of two commercial spiral-wound membranes (NF90 and NF270) to remove metals and sulfate from acid mine drainage from an active copper mine. The structural and surface properties of the membranes, hydrodynamic conditions, polarization, and filtration resistance had a significant influence on the effectiveness of the treatment. The obtained results demonstrated a good removal capacity in both membranes (>94%) at a low operating pressure (15 bar). The increase in pressure had a strong impact on permeate flux, concentration polarization, and contaminant removal rate; however, the increase in the value of the Reynolds number exhibited had no significant effects. The NF270 membrane was selected to perform concentration and long-term tests as it demonstrated a high treatment capacity, high rejections, low resistance, and low polarization at moderate pressures. The permeate flux in the concentration and continuous operation tests decreased by ∼45% and ∼12%, respectively, due to the increases in resistance of ∼63% and ∼13%, respectively, while rejection exhibited a slight increase in both tests. The model parameters successfully identified the convective and diffusive contributions to ions transport in all experiments.
We present the analysis of TESS optical photometry of WASP-121b, which reveals the phase curve of this transiting ultra-hot Jupiter. Its hotspot is located at the sub-stellar point, showing ...inefficient heat transport from the dayside (2870 ± 50 K) to the nightside (<2500 K at 3
σ
) at the altitudes probed by TESS. The TESS eclipse depth, measured at the shortest wavelength to date for WASP-121b, confirms the strong deviation from blackbody planetary emission. Our atmospheric retrieval on the complete emission spectrum supports the presence of a temperature inversion, which can be explained by the presence of VO and possibly TiO and FeH. The strong planetary emission at short wavelengths could arise from an H
−
continuum.
The production of hydrogen via steam reforming (SR) of simulated bio-oil (glycerol, syringol, n-butanol, m-xylene, m-cresol, and furfural) was investigated over Ni/CeO2-Al2O3 and Me-Ni/CeO2-Al2O3 ...(Me = Rh, Ru) catalysts. Monometallic (Ni) and bimetallic (Rh-Ni and Ru-Ni) catalysts were prepared by the wetness impregnation technique of the CeO2-Al2O3 support previously synthesized by the surfactant-assisted co-precipitation method. The as-prepared powders were systematically characterized by N2-physisorption, XRD, H2-TPR, and TEM measurements to analyze their structure, morphology, and reducibility properties. Experiments were performed in a continuous fixed-bed reactor at atmospheric pressure, temperature of 800 °C, steam to carbon (S/C) ratio of 5, and WHSV of 21.15 h−1. Then, the temperature was decreased to 700 °C and increased afterwards to 800 °C. After the experiments TPO and TEM analysis were performed on the spent catalysts to check any evidence of catalyst deactivation. The results showed that the incorporation of noble metal (Ru or Rh) promoter positively affected the activity of the Ni/CeO2-Al2O3 catalysts by enhancing the reducibility of Ni2+ species. Ni-based catalyst deactivated under the studied conditions, whereas Ru- and mainly Rh-promoted systems showed increased resistance to carbon deposition by favouring the gasification of adsorbed carbon species. Between all tested catalysts, the Rh-Ni/CeO2-Al2O3 provided the highest H2 yield and coking-resistance in SR of simulated bio-oil.
•SR of simulated bio-oil over CeO2-Al2O3 supported Ni and Me-Ni (Me = Rh, Ru) catalysts.•Promoting effect of Rh and Ru due to increased reducibility of Ni2+ species.•Increased coking-resistance of bimetallic systems due to gasification of carbon deposits.•High and stable H2 yield over Rh-Ni/CeO2-Al2O3 catalyst.
In this work, monometallic (1 wt% of Ru or 5 wt% of Ni) and bimetallic catalysts (1 wt% Ru-5 wt.% Ni) deposited on alumina (Al2O3), magnesium aluminate spinel (MgAl2O4), and yttria-stabilized ...zirconia (YSZ) were prepared by wet impregnation. The synthesis method of MgAl2O4 was optimized and a well crystallized phase with high specific surface area was obtained by using wet impregnation, as a simple and low cost route, at 800 °C for 2 h.
The catalytic activity was compared at atmospheric pressure and 750 °C toward methane dry reforming (DRM) reaction with a molar ratio CH4/CO2 = 1/1 and a Weight Hourly Space Velocity (WHSV) of 60.000 mL g−1.h−1.
Catalytic activity classification was obtained as the following: Ni/MgAl2O4 > Ru-Ni/Al2O3 > Ru-Ni/MgAl2O4 > Ru-Ni/YSZ > Ni/Al2O3 > Ni/YSZ > Ru/Al2O3 > Ru/YSZ » Ru/MgAl2O4. Between the different catalysts, 5 wt% Ni/MgAl2O4 catalyst exhibited excellent catalytic activity for DRM. Furthermore, this catalyst was found to be very stable without any deactivation after 50 h under reacting mixture with a low carbon formation rate (3.58 mgC/gcat/h). Such superior activity and stability of MgAl2O4 supported Ni catalyst is consistent with characterization results from BET, XRD, TPR, CO-pulse chemisorption and CHNS analysis. It can be due to a strong interaction between Ni and MgAl2O4 leading to the incorporation of Ni into the spinel lattice and the formation of oxygen vacancies offering a benefit for DRM reaction.
Furthermore, it seems that the addition of ruthenium onto Ni/MgAl2O4 decreases the interaction between Ni and the spinel leading to a decrease in the catalyst performance. On the other side, the addition of ruthenium on Ni/Al2O3 leads to an increase in the catalyst stability and efficiency by inhibiting the formation of poorly active phase NiAl2O4 already observed in TPR.
•5 wt% Ni/MgAl2O4 exhibits highest performance in DRM.•Strong Ni/MgAl2O4 interaction leads to incorporation of Ni into spinel lattice.•Ru addition has positive effect on Ni/Al2O3for DRM contrary to Ni/MgAl2O4 and Ni/YSZ.•5 wt% Ni/MgAl2O4: high stability without deactivation after 50 h in reacting mixture.
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•Synthesis of Ni/CeO2 and Ni–Rh/CeO2 nanopowders by solution combustion method.•Deposition on monolith and foam by support dip-coating into acid-free catalyst dispersion.•Catalytic ...activity towards steam reforming and oxy-steam reforming of biogas.•Slightly higher performance of NiRh-based catalyst compared to Ni-based sample.•Higher activity of foam systems compared to honeycomb structured catalysts.
Ni(7.5wt.%)/CeO2 and Ni(7.5wt.%)-Rh(0.5wt.%)/CeO2 powders (previously prepared by solution combustion synthesis) were washcoated on cordierite monolith and alumina open-cell foam by means of support dip-coating into acid-free catalyst dispersion. Catalytic performances toward the steam reforming (SR) and the oxy-steam reforming (OSR) of biogas were investigated and compared at different temperatures (700–800°C) and weight space velocities (WSV=70,000–350,000Nmlgcat−1h−1). Coating load was controlled by multiple depositions; homogeneous and well adherent layers were found. Catalytic tests demonstrated superior performances of the bimetallic samples (Ni–Rh/CeO2) compared to the monometallic one (Ni/CeO2), especially at high space velocity. At the same time, foam showed better performances with respect to the monolithic support toward the SR and OSR processes.
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