Pt and Pt-Au nanoparticles supported on reduced graphene oxide (rGO) were synthesized by reverse microemulsion method with metal loading of 20 wt% and 10: 10 wt%, respectively. The nanomaterials were ...characterized by Raman, X-ray diffraction, thermogravimetric analysis and transmission electronic microscope. The obtained materials were evaluated as electrocatalysts for Oxygen Reduction Reaction (ORR), obtaining the highest catalytic activity with Pt-Au/rGO compared to Pt/rGO; besides, the stability of the catalyst is determined until 50,000 cycles. Pt-Au/rGO was used to prepare membrane electrode assembly (MEA), in order to study the performance of this nanomaterial in the proton exchange membrane fuel cell (PEMFC). The maximum power density is 20 mW cm−2 and 70 mW cm−2 for Pt/rGO and Pt-Au/rGO, respectively, those values increased up to 365 mW cm−2, when Pt-Au nanoparticles supported on multiwall carbon nanotubes (CNT) was used as spacer.
•Pt-Au/rGO were synthesized by reverse microemulsion, obtaining particle size below 3 nm.•Pt-Au/rGO exhibited better performance for ORR catalytic activity than Pt/rGO.•The stability of the Pt-Au/rGO was remarkable compared to other reported catalysts.•Pt-Au/rGO was used to prepare MEAs and fuel cell evaluation was performed.•The power density at fuel cell increases up to 5.2 times when a spacer is added.
Technological approaches which enable the effective utilization of CO2 for manufacturing value-added chemicals and fuels can help to solve environmental problems derived from large CO2 emissions ...associated with the use of fossil fuels. One of the most interesting products that can be synthesized from CO2 is methanol, since it is an industrial commodity used in several chemical products and also an efficient transportation fuel. In this review, we highlight the recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO2 to methanol. The main efforts focused on the improvement of conventional Cu/ZnO based catalysts and the development of new catalytic systems targeting the specific needs for CO2 to methanol reactions (unfavourable thermodynamics, production of high amount of water and high methanol selectivity under high or full CO2 conversion). Major studies on the development of active and selective catalysts based on thermodynamics, mechanisms, nano-synthesis and catalyst design (active phase, promoters, supports, etc.) are highlighted in this review. Finally, a summary concerning future perspectives on the research and development of efficient heterogeneous catalysts for methanol synthesis from CO2 will be presented.
This paper addresses the options developed over the past two decades for the conversion of methane into valuable chemicals and fuels while avoiding the high energy requirements of the steam reforming ...process for producing H
2/CO mixtures. Several aspects of the approaches undertaken accordingly are briefly examined here. Each option has its own set of limitations. Nonetheless, the cost-effective separation of useful products is a common denominator across the board in these processes, with the other most important issue being the separation of oxygen from air, requiring C–H bond activation by oxygen. The widespread use of methane for producing fuels and chemicals appears to be within reach, but current economic uncertainties limit both the amount of research activity and the implementation of emerging technologies, although the extensive use of methane for the production of fuels and chemicals is expected to become a reality very soon.
Nuclear star clusters (NSCs) are the densest stellar systems in the Universe and are found in the centres of all types of galaxies. They are thought to form via mergers of star clusters such as ...ancient globular clusters (GCs) that spiral to the centre as a result of dynamical friction or through in situ star formation directly at the galaxy centre. There is evidence that both paths occur, but the relative contribution of either channel and their correlation with galaxy properties are not yet constrained observationally. Our aim was to derive the dominant NSC formation channel for a sample of 25 nucleated galaxies, mostly in the Fornax galaxy cluster, with stellar masses between
M
gal
∼ 10
8
and 10
10.5
M
⊙
and NSC masses between
M
NSC
∼ 10
5
and 10
8.5
M
⊙
. Using Multi-Unit Spectroscopic Explorer data from the Fornax 3D survey and the ESO archive, we derived star formation histories, mean ages, and metallicities of NSCs, and compared them to the host galaxies. In many low-mass galaxies, the NSCs are significantly more metal poor than their hosts, with properties similar to GCs. In contrast, in the massive galaxies we find diverse star formation histories and cases of ongoing or recent in situ star formation. Massive NSCs (> 10
7
M
⊙
) occupy a different region in the mass–metallicity diagram than lower-mass NSCs and GCs, indicating a different enrichment history. We find a clear transition of the dominant NSC formation channel with both galaxy and NSC mass. We hypothesise that while GC accretion forms the NSCs of the dwarf galaxies, central star formation is responsible for the efficient mass build up in the most massive NSCs in our sample. At intermediate masses both channels can contribute. The transition between these formation channels seems to occur at galaxy masses
M
gal
∼ 10
9
M
⊙
and NSC masses
M
NSC
∼ 10
7
M
⊙
.
Hand stencils are a remarkable graphic expression in Prehistoric rock art, dating back to 42 ka BP. Although these stencils provide direct impressions of the artists' hands, the characterization of ...their biological profile (i.e., biological sex and age) is very challenging. Previous studies have attempted this analysis with traditional morphometrics (TM), whereas little research has been undertaken using Geometric Morphometrics (GM), a method widely used in other disciplines but only tentatively employed in rock art studies. However, the large variation in relative finger position in archaeological hands poses the question of whether these representations can be examined through GM, or, in contrast, if this creates an unmanageable error in the results. To address this issue, a 2D hand scans sample of 70 living individuals (F = 35; M = 35) has been collected in three standardized positions (n = 210) and digitized with 32 2D conventional landmarks. Results show that the intra-individual distance (mean Procrustes distance between Pos. 1-2 = 0.132; 2-3 = 0.191; 1-3 = 0.292) is larger than the inter-individual distance (mean in 1 = 0.122; 2 = 0.142; 3 = 0.165). Finally, it has been demonstrated that the relative finger positions, as well as the inclusion of all hand parts in the analysis, have an overshadowing effect on other variables potentially involved in the morphometric variability of the hand, such as biological sex.
The 31 brightest galaxies (mB ≤ 15 mag) inside the virial radius of the Fornax cluster were observed from the centres to the outskirts with the Multi Unit Spectroscopic Explorer on the Very Large ...Telescope. These observations provide detailed high-resolution maps of the line-of-sight kinematics, line strengths of the stars, ionised gas reaching 2–3 Re for 21 early-type galaxies, and 1–2 Re for 10 late-type galaxies. The majority of the galaxies are regular rotators, with eight hosting a kinematically distinct core. Only two galaxies are slow rotators. The mean age, total metallicity, and Mg/Fe abundance ratio in the bright central region inside 0.5 Re and in the galaxy outskirts are presented. Extended emission-line gas is detected in 13 galaxies, most of them are late-type objects with wide-spread star formation. The measured structural properties are analysed in relation to the galaxies’ position in the projected phase space of the cluster. This shows that the Fornax cluster appears to consist of three main groups of galaxies inside the virial radius: the old core; a clump of galaxies, which is aligned with the local large-scale structure and was accreted soon after the formation of the core; and a group of galaxies that fell in more recently.
Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the ...red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour–metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with a high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at (
g
−
z
) ∼ 1.1 mag. The less massive galaxies in our sample (
M
*
< 10
10
M
⊙
) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies (
M
*
≥ 10
11
M
⊙
). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (10
10
≤
M
*
< 10
11
M
⊙
) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.
Ni-based catalysts are very effective and largely used for the steam reforming of heavy hydrocarbons (tars) generated from biomass gasification, even if Ni suffers from deactivation issues mainly due ...to carbon deposition, sintering and sulphur poisoning. Mayenite (Ca12Al14O33), as support for Ni, has been previously studied and has shown excellent oxidation properties that increase the resistance of the catalyst to carbon deposits. Nevertheless Ni/Mayenite catalyst still suffers from sulphur poisoning. Ceria (CeO2) is well known to be an effective promoter that can bring several advantages to catalysts, such as enhancing the resistance to carbon deposits and increasing the sulphur tolerance of nickel. Here CeO2 is added to Ni/Mayenite catalysts to evaluate its promoting features and resistance to deactivation. In this study Ni/Mayenite and Ce/Ni/Mayenite catalysts were synthesized, characterized and tested in the steam reforming of tar model compounds. The catalytic tests were carried out under different operating parameters (temperature, space velocity and nature of tar compounds) and in the presence of sulphur, and the used samples were characterized to identify the reasons of deactivation.
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