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We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell ( Mytilus galloprovincialis ) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. Mg/Ca ratios of the inner surface of the outer shell layer, corresponding to the most recent date, show cyclic changes at 25–90 μm intervals, while no interpretable variations are observed in Sr/Ca and Ba/Ca ratios. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, therefore serving a proxy of the past tsunami. Following the tsunami, periodic peaks and troughs in Mg/Ca continued, perhaps due to a biological memory effect as an endogenous clock.

CO2 methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO2) to synthetic natural gas (CH4). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts and as adsorbent phases upon the combined capture and methanation of CO2. Their promotion effect during methanation of carbon dioxide mainly relies on their ability to generate new basic sites on the surface of metal oxide supports that favour CO2 chemisorption and activation. However, suppression of methanation activity can also occur under certain conditions. Regarding the combined CO2 capture and methanation process, the development of novel dual-function materials (DFMs) that incorporate both adsorption and methanation functions has opened a new pathway towards the utilization of carbon dioxide emitted from point sources. The sorption and catalytically active phases on these types of materials are crucial parameters influencing their performance and stability and thus, great efforts have been undertaken for their optimization. In this review, we present some of the most recent works on the development of alkali and alkaline earth metal promoted CO2 methanation catalysts, as well as DFMs for the combined capture and methanation of CO2.

Alkaline-earth metal oxides with the rocksalt structure, which are simple ionic solids, have attracted attention in attempts to gain fundamental insights into the properties of metal oxides. The surfaces of alkaline-earth metal oxides are considered promising catalysts for the oxidative coupling of methane (OCM); however, the development of such catalysts remains a central research topic. In this paper, we performed first-principles calculations to investigate the ability of four alkaline-earth metal oxides (MgO, CaO, SrO, and BaO) to catalyze the OCM. We adopted five types of surfaces of rocksalt phases as research targets: the (100), (110), stepped (100), oxygen-terminated octopolar (111), and metal-terminated octopolar (111) surfaces. We found that the formation energy of surface O vacancies is a good descriptor for the adsorption energy of a H atom and a methyl radical. The energies related to the OCM mechanism show that, compared with the most stable surface, the minor surfaces better promote the C - H bond cleavage of methane. However, as the trade-off for this advantage, the minor surfaces exhibit increased affinity for the methyl radical. On the basis of this trade-off relationship between properties, we identified several surfaces that we expect to be promising OCM catalysts. Our investigation of the temperature dependence of the Gibbs free energy indicated that, at higher temperatures, the step (100) surface exhibits properties that might benefit the OCM mechanism.

The catalytic pyrolysis of beech wood and corncob was experimentally investigated considering six additives containing alkali and alkaline earth metals (Na2CO3, NaOH, NaCl, KCl, CaCl2 and MgCl2). Thermogravimetric analyses (TGA) were carried out with raw feedstocks and samples impregnated with different concentrations of catalysts. In a bid to better interpret observed trends, measured data were analyzed using an integral kinetic modeling approach considering 14 different reaction models. As highlights, this work showed that cations (Na+, K+, Ca2+, and Mg2+) as well as anions (i.e., CO32−, OH−, and Cl−) influence pyrolysis in selective ways. Alkaline earth metals were proven to be more effective than alkali metals in fostering biomass decomposition, as evidenced by decreases in the characteristic pyrolysis temperatures and activation energies. Furthermore, the results obtained showed that the higher the basicity of the catalyst, the higher its efficiency as well. Increasing the quantities of calcium- and magnesium-based additives finally led to an enhancement of the decomposition process at low temperatures, although a saturation phenomenon was seen for high catalyst concentrations.

Thermal stability of macrocyclic complexes with alkaline earth metal salts is of crucial importance for their applicability as the components of new electrolytes, ionic liquids and precursors in chemical vapor deposition processes. The complexes of 18-crown-6 and stereoisomeric dicyclohexano-18-crown-6 with alkaline earth metal halides were synthesized and studied by the combination of simultaneous DSC/TGA and FTIR-spectroscopy. The stability of these compounds depended on the size of the cation and anion as follows: Ba 2+  < Sr 2+  < Ca 2+ and Cl −  < Br − ≈ I − . The two-stage mechanism of destruction was found for the complexes with CaCl 2 , SrBr 2 , SrI 2 . This implies, most probably, the coexistence of two conformationally nonequivalent forms of the macrocycles with different thermal stability rather than the destruction of the macrocycle at high temperatures. The revealed trends, in our opinion, were caused by changes in the interaction energy between macrocycle and metal cation.

The synthesis of molecules that feature main-group elements in unusual oxidation states and coordination environments is a primary pursuit of main-group chemistry. The p-block elements saw early success towards this goal, and dozens of compounds that contain subvalent p-block metals, semi-metals and non-metals are now known. The development of reliable syntheses for these compounds made it possible to study them in detail, which expanded our understanding of bonding and electronic structure and served as the foundation from which catalysis mediated by main-group elements has emerged. For the group 2 elements, isolating reduced compounds has been a synthetic challenge that has spurred exciting progress in the synthesis of reduced alkaline earth compounds. The past two decades has seen the isolation of stable Be(0), Be(I), Mg(0), Mg(I) and Ca(I) compounds, along with studies of their reactivity profiles. In this Review, we overview the chemistry of isolated low-valent species with a focus on comparing newly discovered chemical trends and features among the different elements in the group. Finally, we discuss future directions and challenges for the field.Alkaline earth elements are among the most abundant and cost-effective metals in the toolbox of synthetic chemists and investigations of their structures and bonding have led to fascinating discoveries. This Review discusses the emerging synthetic chemistry and unusual redox chemistry of low-oxidation-state Be, Mg and Ca complexes.

In the course of a routine water-quality survey in meso-oligotrophic lake Geneva (Switzerland), suspended matter was collected by filtration on 0.2 μm membranes in July and August 2012 at the depth of maximal chlorophyll a (Chl a) concentration (2 mg m–3). Examination by scanning electron microscopy revealed the presence of numerous dark and gelatinous patches occluding the pores of the membranes, containing high numbers of picoplanktonic cells and, in places, clusters of high-reflectance smooth microspheres (1-2 μm in diameter). Their chemical composition, determined by semi-quantitative, energy-dispersive X ray spectroscopy (EDS) showed magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba) (alkaline earth metals) to be the dominant cations. Among the anions, phosphorus (P) and carbon (C) were present, but only the latter is considered here (as carbonate). The microspheres were subdivided into four types represented in a Ca-Sr-Ba ternary space. All types are confined within a domain bound by Ca>45, Sr<10 and Ba<50 (in mole %). Type I, the most frequent, displays a broad variability in Ba/Ca, even within a given cluster. Types II and III are devoid of Ba, but may incorporate P. Type IV contains only Ca. The Type I composition resembles that of benstonite, a Group IIA carbonate that was recently found as intracellular granules in a cyanobacterium from alkaline lake Alchichica (Mexico).Lake Geneva microspheres are solid, featureless and embedded in a mucilage-looking substance in the vicinity of, but seemingly not inside, picoplanktonic cells morphologically similar to Chlorella and Synechococcus. In summer 2012, the macroscopic physico-chemical conditions in lake Geneva epilimnion were such as to allow precipitation of Ca but not of Sr and Ba carbonates. Favourable conditions did exist, though, in the micro-environment provided by the combination of active picoplankton and a mucilaginous envelope. Further studies are ongoing to investigate the vertical distribution of the microspheres, their internal structure and their exact mineralogical composition, as well as the taxonomy of the picoplankton and the nature of the mucilage, in order to gain a proper understanding of this intriguing process of alkaline-earth metals sequestration.

The present review devoted to the complete oxidation of CO using alkali- and alkaline-earth metal (AM/AEM)-modified ceria supported/mixed with noble metal and non-noble metal (NM). The AM/AEM-modified Ce supported/mixed with noble metal showed comparable CO oxidation with unmodified catalyst. However, AM/AEM-modified NM showed higher CO oxidation at lower temperature compared to the unmodified catalyst. The AM and AEM modifications were responsible for the formation of oxygen vacancies in Ce, which leads to the decrease in the CO and O 2 activation barrier. The dissociative oxygen adsorption on AM/AEM-modified Ce-supported/mixed with NM favours the CO oxidation at a lower temperature. However, AM/AEM-modified Ce-supported/mixed with noble metal showed CO adsorption with formation of superoxy and peroxy species, which leads to the comparable oxidation activity. The plausible mechanism for CO oxidation is explained in detail with correlation to the characterizations.

Complexation of alkaline earth metal cations with fluorescent tertiary-amide lower-rim calix[4]arene derivative bearing two phenanthridine moieties was studied experimentally (UV spectrophotometry, fluorimetry, isothermal microcalorimetry, NMR spectroscopy) and computationally (classical molecular dynamics and DFT calculations) at 25 °C. The complexation reactions were studied in acetonitrile, methanol, and ethanol, whereby the solvent effect on cation-binding processes was particularly addressed. The complex stability constants and standard reaction thermodynamic quantities (Gibbs energies, enthalpies, and entropies) were determined. The receptor exhibited particularly high affinity towards alkaline earth metal cations in acetonitrile, with peak affinity for Ca2+. The stability of all complexes was significantly lower in ethanol and methanol, where the most stable complex was formed with Sr2+. The decrease in cation-binding abilities was a consequence of the differences in solvation of the reactants and products of the complexation reactions (involving inclusion of the solvent molecule in the calixarene cone), cation charge density, as well as the cation–ligand binding site compatibility. The reactions were enthalpically controlled in acetonitrile, whereas in methanol and ethanol, the binding processes were endothermic and thus entropy driven. The results of 1H NMR measurements, MD simulations, and DFT calculations provided an insight into the structure of the complexes and the corresponding adducts with solvent molecules, as well as the structural aspects behind the differences in complexation thermodynamics. Due to the significant increase in its fluorescence upon cation binding, the studied calixarene derivative was proven to be a promising luminescent sensor for alkaline earth metal cations.

This study explores the use of alkaline earth metal carboxylates as sustainable alternatives to conventional ammonium-based lixiviants for the eco-friendly extraction of weathered crust elution-deposited rare earth ores. We investigated the impact of lixiviant concentration, pH, and leaching temperature on the extraction efficiency of rare earths and aluminum, utilizing magnesium acetate and calcium acetate alongside traditional ammonium salts. The results showed that a leaching rate exceeding 91% for rare earths was achieved, while aluminum leaching remained under 30% at 298 K, pH 6.5–7.0, and 0.20 mol/L concentration of carboxylates. Notably, magnesium acetate was particularly effective in extracting medium and heavy rare earths at lower concentrations. A double electric layer model was used to clarify the leaching mechanism, indicating that zeta potential and double electric layer thickness were significantly affected by the concentration and pH of the leaching agents. Overall, this method presents an efficient approach for low-impurity extraction, offering valuable insights for sustainable mineral resource development.