The properties of supports (such as oxygen vacancies, oxygen species properties, etc.) significantly impact the anti-carbon ability due to their promotional effect on the activation of COsub.2 in dry ...reforming of methane (DRM). Herein, pyrochlore-type Lasub.2Cesub.2Osub.7 compounds prepared using co-precipitation (CP), glycine nitrate combustion (GNC) and sol–gel (S-G) methods, which have highly thermal stability and unique oxygen mobility, are applied as supports to prepare Ni-based catalysts for DRM. The effect of the calcining temperature (500, 600 and 700 °C) on Lasub.2Cesub.2Osub.7(CP) has also been investigated. Based on multi-technique characterizations, it is found that the synthesis method and calcination temperature can influence the particle size of the Lasub.2Cesub.2Osub.7 support. Changes in particle size strongly modulate the pore volume, specific surface area and numbers of surface oxygen vacancies of the Lasub.2Cesub.2Osub.7 support. As a result, the distribution of supported Ni components is affected due to the different metal–support interaction, thereby altering the activity of the catalysts for cracking CHsub.4. Moreover, the supports’ abilities to adsorb and activate COsub.2 are also adjusted accordingly, accelerating the removal of the carbon deposited on the catalysts. Finally, Lasub.2Cesub.2Osub.7(CP 600) with an appropriate particle size exhibits the best catalytic activity and stability in DRM.
Carbon Dioxide-Enhanced Coalbed Methane (COsub.2-ECBM), a progressive technique for extracting coalbed methane, substantially boosts gas recovery and simultaneously reduces greenhouse gas emissions. ...In this process, the dynamics of coalbed fractures, crucial for COsub.2 and methane migration, significantly affect carbon storage and methane retrieval. However, the extent to which fracture roughness, under the coupled thermal-hydro-mechanic effects, impacts engineering efficiency remains ambiguous. Addressing this, our study introduces a pioneering, cross-disciplinary mathematical model. This model innovatively quantifies fracture roughness, incorporating it with gas flow dynamics under multifaceted field conditions in coalbeds. This comprehensive approach examines the synergistic impact of COsub.2 and methane adsorption/desorption, their pressure changes, adsorption-induced coalbed stress, ambient stress, temperature variations, deformation, and fracture roughness. Finite element analysis of the model demonstrates its alignment with real-world data, precisely depicting fracture roughness in coalbed networks. The application of finite element analysis to the proposed mathematical model reveals that (1) fracture roughness ξ markedly influences residual coalbed methane and injected COsub.2 pressures; (2) coalbed permeability and porosity are inversely proportional to ξ; and (3) adsorption/desorption reactions are highly sensitive to ξ. This research offers novel insights into fracture behavior quantification in coalbed methane extraction engineering.
The present work aims to analyse the influence of present-day burial depths of coal seams on the sorption properties towards CHsub.4 and COsub.2, respectively. For medium-rank coals located in the ...southwestern area of the Upper Silesian Coal Basin (USCB), the gravimetric sorption measurements were carried out with pure gases at a temperature of 30 °C. The variability of COsub.2/CHsub.4 exchange sorption and diffusivity ratios was determined. It was revealed that in coal seams located at a depth above 700 m, for which the sorption exchange ratio was the greatest, the process of COsub.2 injection for permanent storage was more beneficial. In the coal seams lying deeper than 700 m with a lower COsub.2/CHsub.4 sorption ratio, the CHsub.4 displacement induced by the injection of COsub.2 (COsub.2-ECBM recovery) became more favourable.
Using the colloidal solution combustion approach, a three-dimensional mesoporous 5%Ni-CeOsub.2-M catalyst was developed, with Ni incorporated into the pores, and applied in the dry reforming of ...methane. Comprehensive characterization revealed that the 5%Ni-CeOsub.2-M catalyst had a large specific surface area and a three-dimensional mesoporous structure. A rich Ni-CeOsub.2 interface was formed by closely spaced tiny CeOsub.2 and NiO nanoparticles within the spherical pore wall. With very little carbon deposition over a 100 h period at 700 °C, the catalyst showed excellent activity and stability. The tiny Ni nanoparticles, along with the substantial Ni-CeOsub.2 interfaces that make up this three-dimensional in-form mesoporous catalyst, are responsible for the outstanding effectiveness of this 5%Ni-CeOsub.2-M catalyst.
The tetrafluoroborate salt of the cationic Cu(I) complex Cu(CHpzsub.3)(PPhsub.3)sup.+, where CHpzsub.3 is the tridentate N-donor ligand tris(pyrazol-1-yl)methane and PPhsub.3 is triphenylphosphine, ...was synthesized through a displacement reaction on the acetonitrile complex Cu(NCCHsub.3)sub.4BFsub.4. The compound crystallizes in the monoclinic P2sub.1/c space group. The single-crystal X-ray diffraction revealed that the copper(I) centre is tetracoordinated, with a disposition of the donor atoms surrounding the metal centre quite far from the ideal tetrahedral geometry, as confirmed by continuous shape measures and by the τsub.4 parameter. The intermolecular interactions at the solid state were investigated through the Hirshfeld surface analysis, which highlighted the presence of several non-classical hydrogen bonds involving the tetrafluoroborate anion. The electronic structure of the crystal was modelled using plane-wave DFT methods. The computed band gap is around 2.8 eV and separates a metal-centred valence band from a ligand-centred conduction band. NMR spectroscopy indicated the fluxional behaviour of the complex in CDClsub.3 solution. The geometry of the compound in the presence of chloroform as implicit solvent was simulated by means of DFT calculations, together with possible mechanisms related to the fluxionality. The reversible dissociation of one of the pyrazole rings from the Cu(I) coordination sphere resulted in an accessible process.
The reaction of bis(pentafluorophenyl)mercury with the ligands bis(diphenylphosphano) methane P,P’-dioxide ({Phsub.2P(O)}sub.2CHsub.2) (1), bis{2-(N,N,N’N’-tetraethyldiaminophosphano) imidazol-1-yl} ...methane P,P’-dioxide ({2-PO(NEtsub.2)sub.2Csub.3Nsub.2Hsub.2}sub.2CHsub.2) (2) and bis (2-diphenylphosphanophenyl) ether P,P’-dioxide ({2-PPhsub.2(O)Csub.6Hsub.4}sub.2O) (3) afforded crystalline σ-donor complexes {Hg(Csub.6Fsub.5)sub.2}sub.2{Phsub.2P(O)}sub.2CHsub.2 (1Hg), Hg(Csub.6Fsub.5)sub.2{2-PO(NEtsub.2)sub.2Csub.3Nsub.2Hsub.2}sub.2CHsub.2sub.n (2Hg) and Hg(Csub.6Fsub.5)sub.2{2-PPhsub.2(O)Csub.6Hsub.4}sub.2O (3Hg), respectively. The molecular structures of 1Hg, 2Hg and 3Hg show considerable differences. In complex 1Hg, a single bridging bidentate ligand connects two three-coordinate T-shape mercury atoms with a near linear C-Hg-C atom array. Complex 2Hg is a one-dimensional coordination polymer in which adjacent four-coordinate mercury atoms with a linear C-Hg-C atom array are linked by bridging bidentate O,O’- ligands, whilst in complex 3Hg a T-shape three-coordinate mercury atom is ligated by (3) in a monodentate fashion. The Hg-O bond lengths of complexes 1Hg, 2Hg and 3Hg differ substantially (range 2.5373(14)-2.966(3) Å) owing to structural and bonding differences.
Atmospheric methane grew very rapidly in 2014 (12.7 ± 0.5 ppb/year), 2015 (10.1 ± 0.7 ppb/year), 2016 (7.0 ± 0.7 ppb/year), and 2017 (7.7 ± 0.7 ppb/year), at rates not observed since the 1980s. The ...increase in the methane burden began in 2007, with the mean global mole fraction in remote surface background air rising from about 1,775 ppb in 2006 to 1,850 ppb in 2017. Simultaneously the 13C/12C isotopic ratio (expressed as δ13CCH4) has shifted, now trending negative for more than a decade. The causes of methane's recent mole fraction increase are therefore either a change in the relative proportions (and totals) of emissions from biogenic and thermogenic and pyrogenic sources, especially in the tropics and subtropics, or a decline in the atmospheric sink of methane, or both. Unfortunately, with limited measurement data sets, it is not currently possible to be more definitive. The climate warming impact of the observed methane increase over the past decade, if continued at >5 ppb/year in the coming decades, is sufficient to challenge the Paris Agreement, which requires sharp cuts in the atmospheric methane burden. However, anthropogenic methane emissions are relatively very large and thus offer attractive targets for rapid reduction, which are essential if the Paris Agreement aims are to be attained.
Plain Language Summary
The rise in atmospheric methane (CH4), which began in 2007, accelerated in the past 4 years. The growth has been worldwide, especially in the tropics and northern midlatitudes. With the rise has come a shift in the carbon isotope ratio of the methane. The causes of the rise are not fully understood, and may include increased emissions and perhaps a decline in the destruction of methane in the air. Methane's increase since 2007 was not expected in future greenhouse gas scenarios compliant with the targets of the Paris Agreement, and if the increase continues at the same rates it may become very difficult to meet the Paris goals. There is now urgent need to reduce methane emissions, especially from the fossil fuel industry.
Key Points
Atmospheric methane is rising; its carbon isotopic ratio has become more depleted in C‐13
The possible causes of the change include an increase in emissions, with changing relative proportions of source inputs, or a decline in methane destruction, or both
If this rise continues, there are significant consequences for the UN Paris Agreement
MnNaW/SiO.sub.2 oxide system based on a mesoporous silica matrix synthesized using tetraethoxysilane and cetyltrimethylammonium bromide as precursors were prepared and characterized by SEM/EDS, XRD, ...EPR, N.sub.2 adsorption-desorption measurements and studied in the oxidative conversion of methane (OCM). It is shown that MnNaW/SiO.sub.2 catalyst consists of MnO.sub.x, Na.sub.2WO.sub.4, MnWO.sub.4, and SiO.sub.2 phases. At the reaction temperature of 750-850°C the molten Na.sub.2WO.sub.4 phase covers the surface of crystalline SiO.sub.2, and the interaction of MnO.sub.x, Na.sub.2WO.sub.4 and SiO.sub.2 matrix forms "liquid glass". It is assumed that Na.sub.1-yMnO.sub.x particles formed as a result of the interaction of the system components during catalyst formation and characterized by the presence of ion-radical lattice oxygen are catalytically active sites in the OCM process.
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