Deep CO Research Articles

Innovative Charge-Tuning for Highly Dispersed Pt Catalysts: Achieving Deep CO Removal in Industrial H2 Purification for Fuel Cells.

Proton exchange membrane fuel cells have strict requirements for the CO concentration in H2-rich fuel gas. Here, from the perspective of industrial practicability, a highly dispersed Pt catalyst (2-4 nm) supported on activated carbon (AC), which was modified by electronic promoters (K+) and structural promoters (isopropanol), is studied in detail. Compared with traditional metal oxide supports, the K-Pt/AC catalysts, which benefit from the tuned charge distribution, achieve a significant reduction of CO (from 1% to <0.1 ppb) under H2-rich conditions and show potential for used in large-scale industrial hydrogen purification. Experimental results and theoretical calculations reveal that the K atom, with its lower electronegativity, contributes to the shift of surface Pt2+ to a lower binding energy due to the presence of oxygen species on the AC surface. This facilitates oxygen activation and accelerates desorption of the CO2 product, thereby accelerating the reaction process and enabling the deep removal of CO in a hydrogen-rich atmosphere.

Ionized and Cold Gas Components in Low Surface Brightness Galaxy AGC 102004

Abstract We present the integral field spectroscopic observations of ionized gas (Hα and [N II]) using the PCWI, along with deep CO(2–1) observations by the ‵ U ¯ ‵ u ¯ receiver on JCMT for AGC 102004. The velocity field of Hα shows an anomalous distribution in the northwestern (NW) disk. The Hα spectrum is well-fitted by two Gaussian components, and the weak Gaussian component is dominated by the anomalous Hα in the NW disk. The Gaussian fit center of Hα emission is offset by +24.2 km s−1 from the systemic velocity obtained from the H i emission. We derive the gas-phase metallicity, 12+log(O/H), using [N II]λ6583/Hα ratio as a proxy. The mean value of 12+log(O/H) is 8.30 ± 0.19 over the whole galaxy. The metallicity in the outer disk is lower than the detection limit of 7.72, indicating the metallicity gradient exists in AGC 102004. We speculate a minor/mini-merger event could have happened to the NW disk. CO(2–1) emission has nondetection in AGC 102004, reaching a noise level of 0.33 mK smoothed to 30 km s−1. The upper limit of molecular gas mass in AGC 102004 is 2.1 × 107 M ⊙ with X CO = 3.02 × 1020 cm−2 (K km s−1)−1. The M H 2 /M H I corr of AGC 102004 is lower than 0.0037 and lower than that of normal galaxies.

RuNi/MMO Catalysts Derived from a NiAl-NO3-LDH Precursor for CO Selective Methanation in H2-Rich Gases

CO selective methanation (CO-SMET) is a promising method for deep CO removal from H2-rich gases. In this study, a series of RuNi/MMO catalysts are prepared using the support MMO-N derived from NiAl-NO3-LDHs, which was prepared from NiAl-CO3-LDHs via an acid–alcohol ion-exchange reaction. The prepared catalysts were characterized by XRD, SEM, TEM, XPS, H2-TPR, CO-TPD, CO2-TPD, NH3-TPD, and TG. The RuNi/MMO-N catalyst demonstrated excellent CO-SMET performance, successfully reducing the CO to less than 10 ppm with a selectivity greater than 50% in a reaction temperature window ranging from 180 °C to 260 °C. Compared with similar catalysts derived from NiAl-CO3-LDHs, the exceptional CO-SMET capability of the RuNi/MMO-N catalyst is suggested to be associated with a more effective hydrogen spillover, a larger number of electron-rich Ni sites, and a higher density of acid sites on the surface of RuNi/MMO-N, which are conducive to CO adsorption and the inhibition of CO2 methanation.

Cost and Life Cycle Analysis for Deep CO2 Emissions Reduction for Steel Making: Direct Reduced Iron Technologies

Among heavy industrial sectors worldwide, the steel industry ranks first in carbon dioxide (CO2) emissions. Technologies that produce direct reduced iron (DRI) enable the industry to reduce emissions or even approach net‐zero CO2 emissions for steel production. Herein, comprehensive cradle‐to‐gate (CTG) life cycle analysis (LCA) and techno‐economic analysis (TEA) are used to evaluate the CO2 emissions of three DRI technologies. Compared to the baseline of blast furnace and basic oxygen furnace (BF–BOF) technology for steel making, using natural gas (NG) to produce DRI has the potential to reduce CTG CO2 emissions by 33%. When 83% or 100% renewable H2 is used for DRI production, DRI technologies can potentially reduce CO2 emissions by 57% and 67%, respectively, compared to baseline BF–BOF technology. However, the renewable H2 application for DRI increases the levelized cost of steel (LCOS). When renewable natural gas (RNG) and clean electricity are used for steel production, the CTG CO2 emissions of all the DRI technologies can potentially be reduced by more than 90% compared to the baseline BF–BOF technology, although the LCOS depends largely on the cost of RNG and clean electricity.

Experimental optimization analysis on operating conditions of CO removal process from hydrogen-rich reformate

The catalytic effects of CO preferential oxidation and methanation catalysts for deep CO removal under different operating conditions (temperature, space velocity, water content, etc.) are systematically studied from the aspects of CO content, CO selectivity, and hydrogen loss index. Results indicate that the 3 wt% Ru/Al2O3 preferential oxidation catalysts reduce CO content to below 10 ppm with a high hydrogen consumption of 11.6–15.7%. And methanation catalysts with 0.7 wt% Ru/Al2O3 also exhibit excellent CO removal performance at 220–240 °C without hydrogen loss. Besides, NiClx/CeO2 methanation catalysts possess the characteristics of high space velocity, high activity, and high water-gas resistance, and can maintain the CO content at close to 20 ppm. Based on these experimental results, the coupling scheme of combining NiClx/CeO2 methanation catalysts (low cost and high reaction space velocity) with 0.7 wt% Ru/Al2O3 methanation catalysts (high activity) to reduce CO content to below10 ppm is proposed.

The Extremely Buried Nucleus of IRAS 17208–0014 Observed at Submillimeter and Near-infrared Wavelengths

Abstract The ultraluminous infrared galaxy IRAS 17208−0014 is a late-stage merger that hosts a buried active galactic nucleus (AGN). To investigate its nuclear structure, we performed high-spatial-resolution ( ∼ 0.″04 ∼ 32 pc) Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 9 (∼450 μm or ∼660 GHz), along with near-infrared AKARI spectroscopy in 2.5–5.0 μm. The Band 9 dust continuum peaks at the AGN location, and toward this position CO(J = 6 − 5) and CS(J = 14 − 13) are detected in absorption. Comparison with nonlocal thermal equilibrium calculations indicates that, within the central beam (r ∼ 20 pc), there exists a concentrated component that is dense (107 cm−3) and warm (&gt;200 K) and has a large column density ( N H 2 &gt; 10 23 cm − 2 ). The AKARI spectrum shows deep and broad CO rovibrational absorption at 4.67 μm. Its band profile is well reproduced with a similarly dense and large column but hotter (∼1000 K) gas. The region observed through absorption in the near-infrared is highly likely in the nuclear direction, as in the submillimeter, but with a narrower beam including a region closer to the nucleus. The central component is considered to possess a hot structure where vibrationally excited HCN emission originates. The most plausible heating source for the gas is X-rays from the AGN. The AKARI spectrum does not show other AGN signs in 2.5–4 μm, but this absence may be usual for AGNs buried in a hot mid-infrared core. Further, based on our ALMA observations, we relate the various nuclear structures of IRAS 17208−0014 that have been proposed in the literature.

A Massive AGB Donor in Scutum X-1: Identification of the First Mira Variable in an X-Ray Binary

Abstract The symbiotic X-ray binary Sct X-1 was suggested to be the first known neutron star accreting from a red supergiant companion. Although known for nearly 50 yr, detailed characterization of the donor remains lacking, particularly due to the extremely high reddening toward the source (A V ≳ 25 mag). Here, we present (i) improved localization of the counterpart using Gaia and Chandra observations, (ii) the first broadband infrared spectrum (≈1–5 μm; R ≈ 2000) obtained with SpeX on the NASA Infrared Telescope Facility, and (iii) the J-band light curve from the Palomar Gattini-IR survey. The infrared spectrum is characterized by (i) deep water absorption features (H2O index ≈ 40%), (ii) strong TiO, VO, and CO features, and (iii) weak/absent CN lines. We show that these features are inconsistent with known red supergiants but suggest an M8-9 III–type O-rich Mira donor star. We report the discovery of large-amplitude (ΔJ ≈ 3.5 mag) periodic photometric variability, suggesting a pulsation period of 621 ± 36 (systematic) ± 8 (statistical) days, which we use to constrain the donor to be a relatively luminous Mira (M K = −8.6 ± 0.3 mag) at a distance of 3.6 − 0.7 + 0.8 kpc. Comparing these characteristics to recent models, we find the donor to be consistent with a ≈3–5 M ⊙ star at an age of ≈0.1–0.3 Gyr. Together, we show that Sct X-1 was previously misclassified as an evolved high-mass X-ray binary; instead, it is an intermediate-mass system with the first confirmed Mira donor in an X-ray binary. We discuss the implications of Mira donors in symbiotic X-ray binaries and highlight the potential of wide-field infrared time-domain surveys and broadband infrared spectroscopy to unveil their demographics.

Effect of SiO2 on the CO Selective Methanation over SiO2/Ni‐ZrO2 Catalysts

AbstractCO selective methanation is a reliable and efficient method for deep CO removal from H2‐rich reformate gases in proton exchange membrane fuel cell (PEMFC). In this study, a series of SiO2/Ni‐ZrO2 catalysts with different mass fractions of SiO2 was prepared for CO selective methanation, and the structures and surface chemical properties of Ni‐ZrO2 could be controlled by SiO2. It was found that SiO2 greatly increased the specific surface areas of the catalyst and the dispersion of supported metallic Ni, which endowed the catalyst with higher active Ni surface area and then increased the adsorption quantity of CO, which improved the conversion of CO at low temperature. More importantly, the SiO2 weakened the surface basicity over the Ni‐ZrO2 catalyst, and thus decreased the strength and quantity of CO2 adsorption, which greatly inhibited the methanation of CO2, leading to the higher selectivity for CO methanation. However, the strength of CO adsorption was found to be more related to the methanation of CO, which would be weakened by SiO2 in the catalysts. Meanwhile, the SiO2 increased the strength of H2 adsorption over Ni surface. Therefore, excess SiO2 added into Ni‐ZrO2 enhanced the competitive adsorption between CO and H2 molecules over Ni surface, which weakened CO adsorption, resulting in the increase of CO outlet concentration.

Changes in rock matrix compressibility during deep CO2 storage

AbstractGeologic carbon storage projects aim to permanently trap large volumes of CO2 in reservoir rock sealed with low permeability layers. As high‐pressure supercritical or liquid CO2 is injected, hydromechanical and chemical processes caused by the reaction between the rock and acidic mixture of brine and CO2 are initiated. The compressibility of reservoir rock needs to be properly characterized in order to assess the deformation and stability of the host formations, and there are a number of factors to be considered, including the matrix structure, solid, pores, and fluid. This study triggers from a fundamental question whether CO2 treatment affects the compressibility of the rock matrix and its dominant composing solid minerals. Three different reservoir representatives are selected: Berea sandstone for silica‐rich rock, and Apulian limestone and Indiana limestone for calcite‐rich rock. Quartz and calcite are the main composing minerals of the reservoir rock, and their crystals are separately examined. Experimental methods are introduced for high‐pressure CO2 treatment of water‐saturated materials, and measurements of the unjacketed and solid compressibilities are conducted. No change in the solid compressibility of the sandstone and quartz after CO2 treatment is observed, whereas it increases by 18–21% for the limestones and by 15% for calcite. The latter observation is inconsistent with the ultrasonic wave velocities measurements and is believed to be due to the local dissolution of the calcite crystal surface. The results show that only the solid matrix of the limestones becomes more compressible after CO2 treatment. Consequent microimaging and mercury intrusion porosimetry analyses allowed observations of dissolution and precipitation of calcite, and creation of new connected and non‐connected pores. Finally, the changes in limestone solid compressibilities and pore structure could significantly affect the rock properties and behavior during and after CO2 injection and should be accounted for in the reservoir models. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Deep Observations of CO and Free–Free Emission in Ultraluminous Infrared QSO IRAS F07599+6508

Abstract Infrared quasi-stellar objects (IR QSOs) are a rare subpopulation selected from ultraluminous infrared galaxies (ULIRGs) and have been regarded as promising candidates of ULIRG-to-optical QSO transition objects. Here we present NOEMA observations of the CO (1−0) line and 3 mm continuum emission in IR QSO IRAS F07599+6508 at z = 0.1486, which has many properties in common with Mrk 231. The CO emission is found to be resolved with a major axis of ∼6.1 kpc that is larger than the size of ∼4.0 kpc derived for 3 mm continuum. We identify two faint CO features located at a projected distance of ∼11.4 and 19.1 kpc from the galaxy nucleus, both of which are found to have counterparts in the optical and radio bands and may have a merger origin. A systematic velocity gradient is found in the CO main component, suggesting that the bulk of molecular gas is likely rotationally supported. Based on the radio-to-millimeter spectral energy distribution and IR data, we estimate that about 30% of the flux at 3 mm arises from free–free emission and infer a free–free-derived star formation rate of 77 M ⊙ yr−1, close to the IR estimate corrected for the AGN contribution. We find a high-velocity CO emission feature at the velocity range of about −1300 to −2000 km s−1. Additional deep CO observations are needed to confirm the presence of a possible very high velocity CO extension of the OH outflow in this IR QSO.

SYNTHESIS, CHARACTERISTIC AND ACTIVITY OF NANOSIZED Cu–Me (Me–Co, Zn, Ni) OXIDE SYSTEMS IN CO OXIDATION IN THE PRESENCE OF H2

Nanooxides of Cu–Me composition (Me–Co, Zn, Ni) were synthesized by hydrothermal reduction of metal salts with subsequent calcination and the influence of their properties (size, morphology, structure) on catalytic activity of deep CO oxidation reaction in the presence of H2 was considered. The nanooxides have been characterized by XRD and SEM methods. It was revealed that particles of Cu–Co–O are nanoplates (30–35 nm), and Cu–Zn–O (12.5–20 nm) are nanorods. The SEM method revealed a higher structural organization of the Cu–Сo–O particles than Cu–Zn–O; the growth of nanocrystals is shown by varying the magnification of the scale grid of images. The highest activity of the Cu–Co–O system was found among the mentioned and corresponding individual oxides. The effect of metal (Cu/Co) ratio on the dispersibility and morphology of nanoparticles and their activity has been studied. The non-additive increase in activity is explained by the redox properties of cobalt oxides and the contribution of copper to electronic state of this element. The variation of composition, as well as high dispersibility (30–35 nm) make it possible to reduce the temperature of oxidation beginning (T50%) of CO to less than 1150C

Low Dose Soft X-Ray Remotely Triggered Lanthanide Nanovaccine for Deep Tissue CO Gas Release and Activation of Systemic Anti-Tumor Immunoresponse.

Gas‐based therapy has emerged as a new green therapy strategy for anti‐tumor treatment. However, the therapeutic efficacy is still restricted by the deep tissue controlled release, poor lymphocytic infiltration, and inherent immunosuppressive tumor microenvironment (TME). Herein, a new type of nanovaccine is designed by integrating low dose soft X‐ray‐triggered CO releasing lanthanide scintillator nanoparticles (ScNPs: NaLuF4:Gd,Tb@NaLuF4) with photo‐responsive CO releasing moiety (PhotoCORM) for synergistic CO gas/immuno‐therapy of tumors. The designed nanovaccine presents significantly boosted radioluminescence and enables deep tissue CO generation at unprecedented tissue depths of 5 cm under soft X‐ray irradiation. Intriguingly, CO as a superior immunogenic cell death (ICD) inducer further reverses the deep tissue immunosuppressive TME and concurrently activates adaptive anti‐tumor immunity through efficient reactive oxygen species (ROS) generation. More importantly, the designed nanovaccine presents efficient growth inhibition of both local and distant tumors via a soft X‐ray activated systemic anti‐tumor immunoresponse. This work provides a new strategy of designing anti‐tumor nanovaccines for synergistic deep tissue gas‐therapy and remote soft X‐ray photoactivation of the immune response.

Landscape modification due to agricultural irrigation: Carbonate tufa formation on Tenerife, Canary Islands, Spain

The use of irrigation water on Tenerife has modified the hydrogeological system resulting in the formation of an anthropogenic carbonate tufa . The processes involved in its formation are: 1) infiltration of rainwater and mixing with groundwater rich in volcanic carbon dioxide (CO 2 ), 2) weathering of volcanic rocks increasing the ion content of the water, 3) extraction of this water from subterranean galleries and channels and spilling it onto the Lomo Morin slope, 4) mechanical CO 2 degassing and photosynthetic activity driving calcite precipitation. The tufa consists of boundstones of algae and coated stems of reeds, along with laminated microbial crusts. Textures range from microspar to coarse mosaics to fibrous-radial calcite, all containing biogenic features. The presence of the green macroalga Blidingia is noticeable. Carbon stable isotope ratio ( δ 13 C) varies between -3.58 and +1.03‰ VPDB (Vienna Pee Dee Belemnite) and oxygen stable isotope ratio ( δ 18 O) between -6.77 and -5.00‰ VPDB, highlighting the largely meteoric origin of the water with some addition of deep CO 2 . A strontium isotope ratio ( 87 Sr/ 86 Sr) of 0.7030 confirms the weathering of volcanic rocks as the source of calcium. The Lomo Morin tufa provides a scale model of how water use contributes to rapid landscape change through alterations in the hydrogeological system. It also provides a good example of a CO 2 sink in a continental setting, and is comparable to the global carbon cycle, which mostly involves marine limestones. Although anthropogenic processes are commonly viewed negatively, the human modification of the hydrogeological system reported in this study has produced changes to geological and ecological conditions that have increased the geo - and biodiversity of the island.

SUPER

Feedback from active galactic nuclei (AGN) is thought to be key in shaping the life cycle of their host galaxies by regulating star-formation activity. Therefore, to understand the impact of AGN on star formation, it is essential to trace the molecular gas out of which stars form. In this paper we present the first systematic study of the CO properties of AGN hosts at z ≈ 2 for a sample of 27 X-ray selected AGN spanning two orders of magnitude in AGN bolometric luminosity (log Lbol / erg s−1 = 44.7 − 46.9) by using ALMA Band 3 observations of the CO(3-2) transition (∼1″ angular resolution). To search for evidence of AGN feedback on the CO properties of the host galaxies, we compared our AGN with a sample of inactive (i.e., non-AGN) galaxies from the PHIBSS survey with similar redshift, stellar masses, and star-formation rates (SFRs). We used the same CO transition as a consistent proxy for the gas mass for the two samples in order to avoid systematics involved when assuming conversion factors (e.g., excitation corrections and αCO). By adopting a Bayesian approach to take upper limits into account, we analyzed CO luminosities as a function of stellar masses and SFRs, as well as the ratio LCO(3–2)′/M∗ (a proxy for the gas fraction). The two samples show statistically consistent trends in the LCO(3–2)′−LFIR and LCO(3–2)′−M∗ planes. However, there are indications that AGN feature lower CO(3-2) luminosities (0.4–0.7 dex) than inactive galaxies at the 2–3σ level when we focus on the subset of parameters where the results are better constrained (i.e., LFIR ≈ 1012.2 L⊙ and M* &gt; 1011 M⊙) and on the distribution of the mean log(LCO(3–2)′/M∗). Therefore, even by conservatively assuming the same excitation factor r31, we would find lower molecular gas masses in AGN, and assuming higher r31 would exacerbate this difference. We interpret our result as a hint of the potential effect of AGN activity (such as radiation and outflows), which may be able to heat, excite, dissociate, and/or deplete the gas reservoir of the host galaxies. Better SFR measurements and deeper CO observations for AGN as well as larger and more uniformly selected samples of both AGN and inactive galaxies are required to confirm whether there is a true difference between the two populations.

AGN feedback in a galaxy merger: multi-phase, galaxy-scale outflows with a fast molecular gas blob ∼6 kpc away from IRAS F08572+3915

To understand the role that active galactic nuclei (AGN) feedback plays in galaxy evolution, we need in-depth studies of the multi-phase structure and energetics of galaxy-wide outflows. In this work, we present new, deep (∼50 h) NOEMA CO(1-0) line observations of the molecular gas in the powerful outflow driven by the AGN in the ultra-luminous infrared galaxy IRAS F08572+3915. We spatially resolve the outflow, finding that its most likely configuration is a wide-angle bicone aligned with the kinematic major axis of the rotation disk. The molecular gas in the wind reaches velocities up to approximately ±1200 km s−1and transports nearly 20% of the molecular gas mass in the system. We detect a second outflow component located ∼6 kpc northwest from the galaxy moving away at ∼900 km s−1, which could be the result of a previous episode of AGN activity. The total mass and energetics of the outflow, which includes contributions from the ionized, neutral, and warm and cold molecular gas phases, is strongly dominated by the cold molecular gas. In fact, the molecular mass outflow rate is higher than the star formation rate, even if we only consider the gas in the outflow that is fast enough to escape the galaxy, which accounts for ∼40% of the total mass of the outflow. This results in an outflow depletion time for the molecular gas in the central ∼1.5 kpc region of only ∼3 Myr, a factor of ∼2 shorter than the depletion time by star formation activity.

Cloud–cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center

AbstractRecent large-area, deep CO surveys in the Galactic disk have revealed the formation of ~50 high-mass stars or clusters triggered by cloud–cloud collisions (CCCs). Although the Galactic Center (GC)—which contains the highest volume density of molecular gas—is the most favorable place for cloud collisions, systematic studies of CCCs in that region are still untouched. Here we report for the first time evidence of CCCs in the common foot point of molecular loops 1 and 2 in the GC. We have investigated the distribution of molecular gas toward the foot point by using a methodology for identifying CCCs, and we have discovered clear signatures of CCCs. Using the estimated displacements and relative velocities of the clouds, we find the elapsed time since the beginnings of the collisions to be 105–106yr. We consider possible origins for previously reported peculiar velocity features in the foot point and discuss star formation triggered by CCCs in the GC.

Kinematic Detections of Protoplanets: A Doppler Flip in the Disk of HD 100546

Abstract Protoplanets and circumplanetary disks are rather elusive in their thermal IR emission. Yet they are cornerstones to the most popular interpretations for the protoplanetary disk structures observed in the gas and dust density fields, even though alternative theories exist. The gaseous velocity field should also bear the imprint of planet–disk interactions, with non-Keplerian fine structure in the molecular-line channel maps. Such kinks or wiggles are affected by the optical depth structure and synthesis imaging limitations, but their detail could in principle be connected to the perturber by comparison with hydrodynamical simulations. These predictions appear to have been observed in HD 163296 and HD 97048, where the most conspicuous wiggles are interpreted in terms of embedded planets. The velocity centroid maps may allow for more robust indirect detections of embedded planets. The non-Keplerian velocity along the planetary wakes undergoes an abrupt sign reversal across the protoplanet. After subtraction of the disk rotation curve, the location of the perturber should be identifiable as a Doppler flip in velocity centroid maps. Here we improve our rotation curves in an extension to disks with intermediate inclinations, which we apply to deep and fine angular resolution CO isotopologue data sets. Trials in HD 163296 and in HD 97048 yield nondetections. However, in HD 100546 we pick up a conspicuous Doppler flip, an important part of which is likely due to radial flows. Its coincidence with a fine ridge crossing an annular groove inside the continuum ring suggests a complex dynamical scenario, in which the putative protoplanet might have recently undergone pebble accretion.

Low Star Formation Efficiency in Typical Galaxies at z = 5–6

Abstract Using the Very Large Array and ALMA, we have obtained CO(2–1), [C ii], and [N ii] line emission and multiple dust continuum measurements in a sample of “normal” galaxies at z = 5–6. We report the highest-redshift detection of low-J CO emission from a Lyman break galaxy, at z ∼ 5.7. The CO line luminosity implies a massive molecular gas reservoir of (1.3 ± 0.3)(α CO/4.5 M ⊙ (K km s−1 pc2)−1) × 1011 M ⊙, suggesting low star formation efficiency with a gas depletion timescale of order ∼1 Gyr. This efficiency is much lower than traditionally observed in z ≳ 5 starbursts, indicating that star-forming conditions in main-sequence galaxies at z ∼ 6 may be comparable to those of normal galaxies probed up to z ∼ 3 to date but with rising gas fractions across the entire redshift range. We also obtain a deep CO upper limit for a main-sequence galaxy at z ∼ 5.3 with an approximately three times lower star formation rate, perhaps implying a high α CO conversion factor, as typically found in low-metallicity galaxies. For a sample including both CO targets, we also find faint [N ii] 205 μm emission relative to [C ii] in all but the most IR-luminous “normal” galaxies at z = 5–6, implying more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties suggest that low metallicity may be common in typical ∼1010 M ⊙ galaxies at z = 5–6. While a fraction of main-sequence star formation in the first billion yr may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.

Deep and narrow CO absorption revealing molecular clouds in the Hydra-A brightest cluster galaxy

Active galactic nuclei play a crucial role in the accretion and ejection of gas in galaxies. Although their outflows are well studied, finding direct evidence of accretion has proved very difficult and has so far been done for very few sources. A promising way to study the significance of cold accretion is by observing the absorption of an active galactic nucleus's extremely bright radio emission by the cold gas lying along the line-of-sight. As such, we present ALMA CO(1-0) and CO(2-1) observations of the Hydra-A brightest cluster galaxy (z=0.054) which reveal the existence of cold, molecular gas clouds along the line-of-sight to the galaxy's extremely bright and compact mm-continuum source. They have apparent motions relative to the central supermassive black hole of between -43 and -4 km s$^{-1}$ and are most likely moving along stable, low ellipticity orbits. The identified clouds form part of a $\sim$$10^{9}$ $\text{M}_{\odot}$, approximately edge-on disc of cold molecular gas. With peak CO(2-1) optical depths of $\tau$=0.88 $^{+0.06}_{-0.06}$, they include the narrowest and by far the deepest absorption of this type which has been observed to date in a brightest cluster galaxy. By comparing the relative strengths of the lines for the most strongly absorbing region, we are able to estimate a gas temperature of $42^{+25}_{-11}$ K and line-of-sight column densities of $N_{CO}=2^{+3}_{-1}\times 10 ^{17} cm^{-2}$ and $N_{ H_{2} }=7^{+10}_{-4}\times 10 ^{20} cm^{-2}$.

The influence of CO, CO2 and H2O on selective CO methanation over Ni(Cl)/CeO2 catalyst: On the way to formic acid derived CO-free hydrogen

For the first time the influence of CO, CO2 and H2O content on the performance of chlorinated NiCeO2 catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO2 increases with the increasing H2 concentration, is independent of CO2 concentration and decreases with increasing CO and H2O concentrations; the rate of CO2 methanation is weakly sensitive to H2 and CO2 concentrations and decreases with increasing CO and H2O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO2 hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO2 was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO2 (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO2-η-Al2O3/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.