From both energy and environmental points of view, it is highly desirable to produce organic compounds from greenhouse gas CO2. To reach such an attractive goal, high-performance catalysts are ...required. In this study, a new family of two-dimensional (2D) materials, transition-metal diboride (MB2), are theoretically designed. With intrinsic transition-metal-terminated surfaces, MB2 monolayers exhibit a high catalytic activity for the conversion of CO2 selectively to CH4. In particular, the OsB2 monolayer has an ultralow limiting potential of −0.4 V for CH4 production. Non-noble-metal-based FeB2 and MnB2 also have a low limiting potential, and they are thus very promising for practical applications. Atomistic mechanisms of the catalyzed CO2 conversion are understood based on the first-principles calculations. Oxygen binding energy is found to be a good descriptor for the catalytic performance, and the activity “volcano” plot suggests that, in the OsB2 case, it is very close to the optimal value of 6.4 eV. The outstanding catalytic performance of this new type of 2D materials makes them especially attractive for CO2 utilization.
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•The adsorbate-induced surface charge perturbation becomes more local as Cu size increases.•For two-electron products, Cu147 appears near the top in the volcano plots.•The ...under-coordinated sites are more active than low-index surfaces.
Electrochemical conversion of CO2 into useful chemicals represents a promising approach to mitigate our pressing environment and energy problems. To date, only Cu electrodes, of all metals examined experimentally, have been shown to be capable of producing significant quantities of hydrocarbons with adequate Faradaic efficiency from CO2 electroreduction. In this work, we use density functional theory calculations to study size-dependent changes on the adsorption of reaction intermediates and reaction free energy for CO2 reduction on Cu nanoparticles ranging from 13 to 561 atoms. We found that the adsorbate-induced surface charge perturbation on Cu nanoparticles becomes more local as the Cu nanoparticles size increases, and the extent of charge perturbations on 309 atom Cu appears to be very similar in Cu(1 1 1) surface. For two-electron products (CO, HCOOH and H2), Cu147 appears near the top in the volcano plots, implying that Cu147 has a near optimal binding energy of the key intermediates to produce two-electron products. To identify the active sites for the CO2 reduction, we compared the activity of different reaction sites, namely, facet, edge and corner sites of Cu nanoparticles, Cu(1 1 1), Cu(1 0 0), Cu(2 1 1) and hexagonal Cu nanowire. We find that the under-coordinated sites are more active than the low-index surfaces. The presented size-activity and structure-activity relationships will provide useful insight for the design better nanostructured Cu catalysts for CO2 electroreduction.
Abstract
Dominica, one of the most magmatically active islands of the Lesser Antilles through its four active volcanoes, is likely host under its central part, below Morne Trois Pitons–Micotrin, to a ...well-established transcrustal mush system. Pre-eruptive spatiotemporal magma dynamics are examined for five, explosive, pumiceous eruptions of this volcano in the last 24 kyrs through a combined Crystal System Analysis and intracrystalline Fe–Mg interdiffusion timescales modelling approaches. Before all eruptions, two magmatic environments of close compositions have interacted. These interactions began ~ 10–30 years prior to the four smaller of these eruptions, with more sustained mixing in the last decade, accelerated in the last 2 years. This contrasts with the largest pumiceous eruption, involving deeper magmas, with magma interaction starting over roughly a century but with various patterns. This suggests a possibility that increasing reactivation signals could be registered at the surface some years before future eruptions, having significant implications for volcanic risk mitigation.
Although chemoselective hydrogenation of unsaturated aldehydes is the major route to highly valuable industrially demanded unsaturated alcohols, it is still challenging, as the production of ...saturated aldehydes is more favorable over unsaturated alcohols from the view of thermodynamics. By combining the structural features of porous nanowires (NWs) and metal‐organic frameworks (MOFs), a unique class of porous Pt‐Ni NWs in situ encapsuled by MOFs (Pt‐Ni NWs@Ni/Fex‐MOFs) is designed to enhance the unsaturated alcohols selectivity in the cinnamaldehyde (CAL) hydrogenation. A detailed catalytic study shows that the porous Pt‐Ni NWs@Ni/Fex‐MOFs exhibit volcano‐type activity and selectivity in CAL hydrogenation as a function of Fe content. The optimized porous PtNi2.20 NWs@Ni/Fe4‐MOF is highly active and selective with 99.5% CAL conversion and 83.3% cinnamyl alcohol selectivity due to the confinement effect, appropriate thickness of MOF and its optimized electronic structure, and excellent durability with negligible activity and selectivity loss after five runs.
Porous Pt‐Ni nanowires (NWs) within metal‐organic frameworks (MOFs) are successfully constructed by using organic ligands to in situ coordinate with the dissolved Ni2+ during the dealloying process. The porous Pt‐Ni NWs@Ni/Fex‐MOFs exhibit volcano‐type activity and selectivity in cinnamaldehyde hydrogenation as a function of Fe content. The optimized porous PtNi2.20 NWs@Ni/Fe4‐MOF shows 99.5% cinnamaldehyde conversion and 83.3% cinnamyl alcohol selectivity.
The electrocatalytic nitrogen reduction reaction (NRR) is a most attractive approach to ammonia synthesis, and the development of catalysts with excellent activity, high NRR selectivity, and ...long‐term durability is crucial but remains a great challenge. Herein, by means of density functional theory calculations, the stability and catalytic performance of anchored bimetals was systematically investigated by pairing different transition‐metal atoms (Mo, Cr, Ti, V, Ru, and W) on graphene with different coordination atoms (C, N, O, P, and S) for N2 fixation. By screening the stability, limiting potential, and selectivity of 105 candidates, carbon was found to be the optimal coordination atom for bimetallic pairs, whereas the other four coordination atoms were unsatisfactory owing to either thermodynamically unstable anchor sites for bimetallic pairs (O, P, and S atoms) or relatively low catalytic activity (N atom). Notably, the bimetallic compound of Mo and Ti supported on C‐coordinated graphene (MoTi‐CG) and TiV‐CG were predicted as effective NRR catalysts with the attractive limiting potentials of −0.34 and −0.30 V. Furthermore, the volcano curve between the limiting potential and the adsorption free energy of NH2* ΔG(NH2*) was revealed, in which a moderate ΔG(NH2*) was required for high‐activity NRR catalysts. This study not only provides a theoretical basis for the rational design of bimetallic compounds anchored on graphene as effective NRR catalysts under ambient conditions but also opens up a new way to accelerate the screening of NRR catalysts.
Bi and large: Carbon is predicted to be the optimal coordination atom for bimetallic pairs supported on graphene to achieve high stability, excellent activity, and outstanding selectivity for nitrogen fixation through the electrocatalytic nitrogen reduction reaction.
Abstract
Interaction between magma and crustal carbonate at active arc volcanoes has recently been proposed as a source of atmospheric CO
2
, in addition to CO
2
released from the mantle and ...subducted oceanic crust. However, quantitative constraints on efficiency and timing of these processes are poorly established. Here, we present the first
in situ
carbon and oxygen isotope data of texturally distinct calcite in calc-silicate xenoliths from arc volcanics in a case study from Merapi volcano (Indonesia). Textures and C-O isotopic data provide unique evidence for decarbonation, magma-fluid interaction, and the generation of carbonate melts. We report extremely light δ
13
C
PDB
values down to −29.3‰ which are among the lowest reported in magmatic systems so far. Combined with the general paucity of relict calcite, these extremely low values demonstrate highly efficient remobilisation of crustal CO
2
over geologically short timescales of thousands of years or less. This rapid release of large volumes of crustal CO
2
may impact global carbon cycling.
Volcanic eruptions differ enormously in their size and impacts, ranging from quiet lava flow effusions along the volcano flanks to colossal events with the potential to affect our entire ...civilization. Knowledge of the time and size distribution of volcanic eruptions is of obvious relevance for understanding the dynamics and behavior of the Earth system, as well as for defining global volcanic risk. From the analysis of recent global databases of volcanic eruptions extending back to more than 2 million years, I show here that the return times of eruptions with similar magnitude follow an exponential distribution. The associated relative frequency of eruptions with different magnitude displays a power law, scale-invariant distribution over at least six orders of magnitude. These results suggest that similar mechanisms subtend to explosive eruptions from small to colossal, raising concerns on the theoretical possibility to predict the magnitude and impact of impending volcanic eruptions.
A new sequence of eruptions occurred at Mt. Etna volcano during the first half of 2017, after almost 8 months of quiescence. These episodes had low-to-mild intensity and markedly differ from the ...violent paroxysms occurred at the Voragine Crater (VOR) during December 2015 and May 2016. Despite the general weak explosive nature of the eruptions, the activity during 2017 revealed unusually complex dynamics of magma ascent and interaction. Detection and investigation of such dynamics required a multidisciplinary approach in which bulk rock compositions, crystal chemical zoning, diffusion chronometry and ground deformation data have been combined. Bulk rock major and trace elements suggest that the 2017 magmas followed a differentiation path similar to that experienced by magmas erupted at Mt. Etna during the 2015-16 eruptions at VOR. Olivine core compositions and zoning patterns indicate the presence of multiple magmatic environments at depth that strictly interacted each other through some episodes of intrusion and mixing before and during the 2017 eruptive events. Timescales retrieved from diffusion chronometry on olivine normal and reverse zoning correlate well with the ground deformation stages detected through geodetic data and associated models, thus allowing to track the evolution through time of the 2017 volcanic activity. Combination of all petrological and geodetic observations supports the idea that dynamics of magma transfer driving the eruptive episodes of 2017 have been a direct consequence of the violent eruptions occurred at VOR on May 2016, which boosted the ascent of new magma from depth and improved the efficiency of the plumbing system to transfer it upward to the surface. We propose a mechanism of self-feeding replenishment of the volcano plumbing system during 2017, where magma recharge from depth is triggered by sudden unloading of the magma column consequential to the violent paroxysmal activity occurred on May 2016 at VOR.
Mud volcanoes and the presence of PAHs Remizovschi, Alexei; Carpa, Rahela; Forray, Ferenc L ...
Scientific reports,
01/2020, Volume:
10, Issue:
1
Journal Article
Peer reviewed
Open access
A mud volcano (MV) is a naturally hydrocarbon-spiked environment, as indicated by the presence of various quantities of PAHs and aromatic isotopic shifts in its sediments. Recurrent expulsion of ...various hydrocarbons consolidates the growth of hydrocarbonoclastic bacterial communities in the areas around MVs. In addition to the widely-known availability of biologically malleable alkanes, MVs can represent hotbeds of polyaromatic hydrocarbons (PAHs), as well - an aspect that has not been previously explored. This study measured the availability of highly recalcitrant PAHs and the isotopic signature of MV sediments both by GC-MS and δ
C analyses. Subsequently, this study highlighted both the occurrence and distribution of putative PAH-degrading bacterial OTUs using a metabarcoding technique. The putative hydrocarbonoclastic taxa incidence are the following: Enterobacteriaceae (31.5%), Methylobacteriaceae (19.9%), Bradyrhizobiaceae (16.9%), Oxalobacteraceae (10.2%), Comamonadaceae (7.6%) and Sphingomonadaceae (5.5%). Cumulatively, the results of this study indicate that MVs represent polyaromatic hydrocarbonoclastic hotbeds, as defined by both natural PAH input and high incidence of putative PAH-degrading bacterial OTUs.
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