Density functional theory was used to investigate the electrocatalytic activity of graphitic, edge, and in-plane defects in pyridinic-N doped on single-layer graphene (SLG) and bilayer graphene (BLG) ...for the oxygen reduction reaction (ORR) in alkaline media. The N-doped BLG exhibited better ORR activity than the N-doped SLG. Graphitic-N-doped multilayer graphene promoted the 4e– associative ORR mechanism, where OOH* formation was the rate-determining step. The intermediate species of the ORR (OOH*, O*, and OH*) were more strongly bound to the N-doped Bernal BLG structures than to N-doped SLG because of the interlayer covalent π–π bonding between the graphene layers in the former. Bernal stacking of the BLG can improve the stability and ORR activity of graphitic, edge, and in-plane N-defects, where the rate-determining step of the ORR is the same as that in the N-doped graphene monolayer. The overpotential of the BLG with pyridinic-N doped on the edge was 0.570 V, which is nearly identical to that of Pt(111) in alkaline sodium. Therefore, the edge pyridinic-N-doped Bernal BLG may be a promising electrocatalyst for the ORR in polymer electrolyte membrane fuel cells.
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The electrochemical synthesis of NH3 and NO3 – by the N2 reduction reaction (NRR) and the N2 oxidation reaction (NOR) under ambient conditions utilizing H2O as the hydrogen and oxygen source has ...aroused great attention. Here, we report the fabrication of oxygen-coordinated molybdenum (Mo) single atoms anchored on carbon (Mo–O–C) using bacterial cellulose (BC) as the impregnation regulator and carbon source. As a result, the as-synthesized Mo–O–C as an electrocatalyst exhibits superior bifunctional NRR and NOR activities with high stability. A superb NH3 yield rate of 248.6 ± 12.9 μg h–1 mgcat. –1 and a faradaic efficiency (FE) of 43.8 ± 2.3% can be obtained at −0.20 V (vs RHE) by the Mo–O–C-catalyzed NRR, and Mo–O–C can also afford a NO3 – yield rate of 217.1 ± 13.5 μg h–1 mgcat. –1 with a FE of 7.8 ± 0.5% at 2.35 V (vs RHE) for the NOR. The synchrotron-based X-ray absorption spectra and theoretical calculation results unveil that the O-coordinated molybdenum configuration of Mo–(O–C2)4 anchored on carbon is the most stable single-atom structure as the catalytic active sites for N2 adsorption, activation, and bifunctional hydrogenation/oxidation reactions.
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The development of inexpensive and efficient Co-based heterogeneous catalysts for hydroformylation reactions remains an enormous challenge. In this paper, N-doped carbon supported CoFe bimetallic ...catalysts (CoFe/NC) are successfully synthesized through a simple thermal decomposition of a mixture of Co(acac)2 and Fe(acac)3, and melamine with activated carbon in N2 atmosphere. With the CoFe/NC-800 as the catalyst, hydroformylation of diisobutene proceeded smoothly in THF under 4 MPa syngas at 130 °C to obtain 92% conversion of diisobutene and 79.6% selectivity to isononyl aldehydes. Detailed studies revealed that the N-doped carbon supported FeCo alloy may be the active species in which nitrogen might act as ligand played an important role in improvement of catalytic performance of hydroformylation reactions. The present study provided meaningful insights into tuning the catalytic performance of non-noble metal heterogeneous catalysts for carbonylation reaction.
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RILEM TC 267-TRM is studying tests for the reactivity supplementary cementitious materials (SCMs). In the first phase, the lime reactivity (LR) test, which is standardised in Indian standard ...(IS)-1727, gave promising correlations with 90-days cement mortar strength. In Phase 2, working group 1 has looked at further optimisation and robustness study of the LR test. A parameter screening approach for improving the mix design to use fixed mass proportions targeting enhanced reproducibility and robustness was focused. The parameters studied include mixture properties such as the effects of lime (hydrated lime/calcium hydroxide-CH) to SCM ratio, water to binder (binder = CH + SCM) ratio (w/b), activators, curing temperature, and testing age as well as the impact of factors from different national standards (IS and European Committee for Standardisation-EN) such as mould size, shape & type of sand. The modified mixture recommended by the TC uses a fixed CH to SCM mass ratio of 1:1 and the addition of activators. Also, a higher curing temperature of 50 °C in comparison to the 27 °C specified in IS 1727, for the first 2 days is proposed to accelerate the early hydration especially for slowly reacting SCMs. It is also recommended that, the minimum purity and fineness of the CH need to be specified to obtain reproducible results.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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•Soot reactivity of diesel engine fueled with methanol-diesel blends was investigated.•Methanol addition leads to a higher oxidative reactivity of diesel soot.•Effects of methanol ...addition on soot structure and chemistry were assessed.•Methanol blend yields soot with less compactness and more disordered structure.•Methanol addition increases content of aliphatic C-H groups on diesel-soot surface.
This paper compared the soot reactivity and its primarily related factors including soot structure, graphitization degree and surface functional groups, when using mineral diesel fuel (DF) and methanol blended fuel (MBF) at two typical low and high engine loads. Results showed that the soot reactivity increases with increasing methanol concentration in the MBF. Additionally, with the constant methanol blend ratio of methanol, the reactivity of MBF soot degrades as the engine load increases. Correspondingly, the MBF soots had lower aggregate compactness, smaller primary particle size, more disordered structure and more active aliphatic C-H groups in comparison with the DF soot, providing higher concentration and accessibility of active sites for oxidation reactions. The addition of methanol creates variations in combustion kinetics and fuel formulation, which exerts reverse effects on the soot structure and chemistry. Therefore, the factors related to these properties show non-monotonic variations when alter the methanol blend ratio and engine operating mode. Especially, when the methanol blend ratio increases from 10% to 15%, the soot structure and chemistry transform onto the features that are reluctant for soot oxidation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Although a lot of effort has been directed toward individual utilization of CO2 and CH4, simultaneous transformation of CH4 and CO2 to acetic acid provides a green route for greenhouse gas ...utilization. However, the chemical inertness of both CH4 and CO2 hinders this process, and hence there is a need to design an effective catalyst that can easily facilitate this transformation. In this study, we have used a defective Fe2M (M = Mn, Fe, Co, Ni, Cu, Zn) metal–organic framework (MOF) node to computationally investigate the possibility of acetic acid synthesis from CH4 and CO2. Our study suggests that the presence of missing linker defects makes MIL-127 suitable for acetic acid synthesis, which otherwise was impossible in the pristine MOF. Again, heterometal substitution has an influence on the energetics of the reaction. Our study suggests that a heterometal, which simultaneously lowers the LUMO energy of the catalyst and increases the spin density on the hydrogen abstracting atom (H-AA), eases the process of C–H bond scission. A higher HOMO value of the intermediate formed after C–H bond dissociation has been found to enhance the CO2 insertion process. Detailed analysis predicts that Fe2Cu is an efficient catalyst for acetic acid synthesis. Since desorption of acetic acid is one of the important factors affecting the catalyst design, coadsorption of water molecules to Fe2Cu has been shown to enhance the acetic acid desorption process by a factor of about 14 with a desorption energy of 1.62 kcal/mol.
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Realizing the extraordinary potential of unactivated sp³ C-H bond oxidation in organic synthesis requires the discovery of catalysts that are both highly reactive and predictably selective. We report ...an iron (Fe)-based small molecule catalyst that uses hydrogen peroxide (H₂O₂) to oxidize a broad range of substrates. Predictable selectivity is achieved solely on the basis of the electronic and steric properties of the C-H bonds, without the need for directing groups. Additionally, carboxylate directing groups may be used to furnish five-membered ring lactone products. We demonstrate that these three modes of selectivity enable the predictable oxidation of complex natural products and their derivatives at specific C-H bonds with preparatively useful yields. This type of general and predictable reactivity stands to enable aliphatic C-H oxidation as a method for streamlining complex molecule synthesis.
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A new theory for the study of the reactivity in Organic Chemistry, named Molecular Electron Density Theory (MEDT), is proposed herein. MEDT is based on the idea that while the electron density ...distribution at the ground state is responsible for physical and chemical molecular properties, as proposed by the Density Functional Theory (DFT), the capability for changes in electron density is responsible for molecular reactivity. Within MEDT, the reactivity in Organic Chemistry is studied through a rigorous quantum chemical analysis of the changes of the electron density as well as the energies associated with these changes along the reaction path in order to understand experimental outcomes. Studies performed using MEDT allow establishing a modern rationalisation and to gain insight into molecular mechanisms and reactivity in Organic Chemistry.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Bastnäsite ((Ce,La)FCO3) is the primary mineral source of light rare earth elements, but its surface structure is not well understood. This presents a major challenge in improving beneficiation ...strategies. In this work, a synergistic combination of X-ray scattering and ab initio molecular dynamics (AIMD) was used to gain atomistic insight into the interfacial structure of bastnäsite. Surface X-ray scattering was used to measure crystal truncation rods (CTRs) of the bastnäsite (001) surface, a significant crystal face with a previously unknown termination. The best-fit atomic-scale model of the CTR data features a carbonate layer at the surface, which is stabilized by the relaxation of carbonate groups from their bulk structural positions. AIMD simulations predict similar surface relaxations, which are shown to be influenced by the protonation of oxygen atoms at the surface. Evidence of ordered water at the interface is also observed in the best-fit model and AIMD simulations. The presence of a carbonate layer at this dominant crystal surface is significant for improving separation technologies because most commonly used ligands utilize anionic functional groups to chelate metal cations at particle surfaces. Without modification, anionic ligands are expected to have poor affinity for the carbonate-terminated (001) surface.
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The study addresses the question of what type of political content can trigger reactions from electoral candidates' followers on Facebook. Citizens' reactivity is increasingly important in ...contemporary political communication. The politicians' posts can reach the wider public through the citizens' public reactions. While we have extended knowledge about mass media reactivity, citizens' political reactivity on social media is highly underexplored. This study is intended to fill this gap by examining what type of political content can trigger reaction from followers on politicians' Facebook pages. The data contain 7048 Facebook posts by 183 single-member district candidates posted during the Hungarian general election campaign in 2014. The unit of analysis is the individual Facebook post, and the dependent variables are the numbers of likes, comments, and shares. The independent variables are the structural (text, picture, video, etc.) and substantial (content, emotional tone, etc.) characteristics of each post, after controlling for, inter alia, a general follower-activity score on politicians' Facebook pages. Results showed that citizens are highly reactive to negative emotion-filled, text-using, personal, and activity-demanding posts. Virality is especially facilitated by memes, videos, negative contents and mobilizing posts, and posts containing a call for sharing.
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