Role Of Alkali Research Articles

Cover Feature: The Role of Alkalis in Orchestrating Uranyl‐Peroxide Reactivity Leading to Direct Air Capture of Carbon Dioxide (Chem. Eur. J. 27/2024)

Cover Feature: The Role of Alkalis in Orchestrating Uranyl‐Peroxide Reactivity Leading to Direct Air Capture of Carbon Dioxide (Chem. Eur. J. 27/2024)

A green route for hydrogen production from alkaline thermal treatment (ATT) of biomass with carbon storage

Hydrogen, a green energy carrier, is one of the most promising energy sources. However, it is currently mainly produced from depleting fossil fuels with high carbon emissions, which has serious negative effects on the economy and environment. To address this issue, sustainable hydrogen production from bio-energy with carbon capture and storage (HyBECCS) is an ideal technology to reduce global carbon emissions while meeting energy demand. This review presents an overview of the latest progress in alkaline thermal treatment (ATT) of biomass for hydrogen production with carbon storage, especially focusing on the technical characteristics and related challenges from an industrial application perspective. Additionally, the roles of alkali and catalyst in the ATT process are critically discussed, and several aspects that have great influences on the ATT process, such as biomass types, reaction parameters, and reactors, are expounded. Finally, the potential solutions to the general challenges and obstacles to the future industrial-scale application of ATT of biomass for hydrogen production are proposed.

Role of alkalis on the incorporation of iodine in simple borosilicate glasses

To understand the influence of alkali elements on the incorporation mechanisms and incorporation limit of iodine in borosilicate glasses used for nuclear waste immobilization, series of model glasses with different alkali contents (22 or 35 mol% Na2O, or 22 mol% of a mixture of alkalis: Na substituted by Li, K and Cs) were loaded with iodine (from 1 000 to 10 000 ppm at. under the form of iodide) at 1100 °C. When the incorporation limit of iodine was reached, alkali iodide crystals were observed (e.g., NaI). For oversaturated samples containing two alkalis, iodide crystals were analyzed and it was found that crystals are enriched in the heavier one of the two relative to bulk composition. Crystal-free glasses were studied by Electron Probe Micro-Analysis to measure the incorporation limit of iodine. A complex variation of incorporation limit was found. Initial substitution of Na by other alkalis (<50%) leads to a decrease in I incorporation limit, this decrease being smallest for Li and largest for Cs. For substitution >50%, only the potassium-bearing system could be studied. In this case, the incorporation limit was non-linear and passed through a minimum for a substitution of ∼75%. Glass structure was determined by X-Ray absorption spectroscopy and Nuclear Magnetic Resonance, providing evidence for local I environments rich in alkalis. It is concluded that high alkali content and high concentrations of Na2O are particularly favorable for iodine incorporation.

Role of Alkalis in Natural Pozzolans on Alkali-Silica Reaction

Role of Alkalis in Natural Pozzolans on Alkali-Silica Reaction

Structural changes in aluminosilicate glasses up to 164 GPa and the role of alkali, alkaline earth cations and alumina in the densification mechanism

Pressure induced structural changes in silicate melts have a great impact on their physico-chemical properties and hence on their behaviour in the deep Earth's interior. In order to gain a deeper understanding we have studied the densification mechanism in multicomponent aluminosilicate glasses (albitic and albit-diopside composition) by means of extended X-ray absorption fine structure spectroscopy coupled to a diamond anvil cell up to 164 GPa. We have monitored the structural modifications from the network-former Ge as well as the network-modifier Sr. Notably, we tracked the evolution of Ge-O and Sr-O bond lengths (RGe-O, RSr-O) and their coordination number with pressure. We show that RGe-O increases strongly up to about 32 GPa, whereas RSr-O increases only slightly up to ~26 GPa. We assign these extensions to the increase of the coordination number from 4 to 6 (Ge) and from ~6 to at least 9 (Sr). Upon further compression RGe-O and RSr-O exhibit a continuous decrease to the highest probed pressure. These bond contractions, notably of RGe-O, that are continuous and exceed the one observed in pure SiO2 and GeO2, reflect a higher structural flexibility of multi-component glasses compared to those simple systems. Particularly, the high fraction of non-bridging oxygen atoms due to the presence of Na, Sr, Ca, Mg in the studied glasses, favours the simple compression of the highly-coordinated polyhedra of Si and Ge at pressure greater than 30 GPa. This is in strong contrast to pure oxides where cation polyhedral distortions govern the densification mechanism of the glass. The results of this study demonstrate that low field-strength alkali and alkaline earth cations, ubiquitous in deep Earth's melts, have a profound influence on the densification mechanism of glasses. Our results provide important constrains for interpreting the observed low velocity anomalies at the Earth's core-mantle boundary that have been, beyond others, referred to the presence of high-density melts. The hypothesis that non-buoyant melts at the Earth's core-mantle boundary can be formed by peculiar structural transformations in melts leading to higher coordination numbers compared to their crystalline equivalents is not supported from the present observations. The present results rather suggest that if velocity anomalies are to be explained by melts, these likely have considerable differences in chemical composition to the surrounding crystalline phase assemblage.

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

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.

Role of Alkali or Alkaline Earth Metals as Additives to Co/Al2O3 in Suppressing Carbon Formation during CO2 Reforming of CH4

Effect of alkali or alkaline earth metals (Li, Na, K, Mg, Ca, and Sr) as additives to Co/Al2O3 on CH4–CO2 reforming and carbon formation was examined. It was shown that the alkali metals decreased the reforming rate, whereas the rate was scarcely influenced by the alkaline earth ones. Carbon deposition was also more markedly retarded by the alkali metals than the alkaline earth ones. It was revealed that one of the essential roles of the basic additives was to reduce the ability of cobalt for methane decomposition through a partial covering of the active sites. Another effect was to modify acid-base properties of the catalyst surface toward higher basicity thus increasing adsorption of acidic CO2. Abundance of adsorbed CO2 on the catalyst should be an unfavorable condition for decomposition of methane and consequently, carbon formation was further suppressed. It was also suggested that carbon gasification rate was not significantly influenced by the additives.

The Role of Alkalis in Hydraulic Mixtures

Alkali substances are present in cements used as a binder in concrete only in a minimum content. The most known process that alkali causes is the alkali-silica reaction. In this reaction, the alkali contained in the cement or supplied from the outside with an inappropriately selected aggregate containing amorphous SiO2. This reaction results in the development of hydration products, resulting in an increase in the volume of the original components, which can cause a breakage of the concrete structure and subsequent disintegration. The range of alkali-silica reaction can be reduced by the use of a suitable aggregate or the use of Type II admixtures which are characterized by pozzolanic or latently hydraulic activity. These admixtures react with alkali and then no longer react with the amorphous SiO2 contained in the aggregate. Alkalis also affect other properties of concrete such as basic physical-mechanical properties, frost resistance and pH.In the experimental part the pH values were compared between mixtures of Portland cement and alkaline activated blast furnace slag using slag aggregate from the heap Koněv.

Efflorescence of Alkali-Activated Cements (Geopolymers) and the Impacts on Material Structures: A Critical Analysis

Even with the rapid development of the alkali-activated cement (AAC) technology in the past few years, some phenomena still needs to be better understood, that may alter the durability of the material. In many industrial uses and laboratory researches the formation of the salts on the surface alkali-activated type cements was observed, which was identified as efflorescence. This occurs due to the presence of an alkali transported in contact with the humidity and CO2 environment. It may present externally from the formation of salts on the surface and internally with the carbonation of the alkalis in capillary pores. The effects of efflorescence on the material in use, as well as all factors that can influence its formation are not yet fully understood or reported. The search for papers was conducted using the search words efflorescence and geopolymer/alkali-activated, combined in the electronic data base. Due to the limited quantity of papers published related to efflorescence in geopolymers, the review was complemented using papers that discuss this behavior in Portland cement (PC) and based on the main properties that can influence the formation of efflorescence. In this paper, to understand the nature of efflorescence, upon which proper methods of minimizing of this issue can be based, the following aspects are discussed and re-examined: (1) the development of efflorescence's in PC concrete, (2) the role of alkalis in AACs, (3) efflorescence in AACs, and (4) effect from a physical and microstructural point of view of efflorescence's on the ACCs. This paper highlights that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control efflorescence rate and changes in mechanical behavior. However, the stability of the alkalis and their relationship with the formed gel, which are determining factors in the formation of efflorescence, remain not completely understood. In the same way, the effect of efflorescence in tensile strength and shrinkage needs to be evaluated.

Negative Thermal Expansion Properties and the Role of Guest Alkali Atoms in LnFe(CN)6 (Ln = Y, La) from ab Initio Calculations

Using the ab initio calculations within density functional theory combined with the quasi-harmonic approximation (QHA), we have investigated the negative thermal expansion (NTE) properties of LnFe(CN)6 (Ln = Y, La) systems and the role of alkali as guest atoms being inserted in LnFe(CN)6. We have found that both the antiprism mode originated from the torsional vibration of N atoms in LnN6 units and the transverse vibration of CN ligand mainly contribute to the magnitude of NTE in LnFe(CN)6, and the largest coefficients of negative thermal expansion (CNTE) are found to be approximately −39.3 × 10–6 K–1 at 180 K for YFe(CN)6 and −50 × 10–6 K–1 at 110 K for LaFe(CN)6, respectively. The transverse vibration modes of CN ligand are significantly enhanced when Y atoms are substituted by their La counterparts, which results a larger CNTE of LaFe(CN)6 than that of YFe(CN)6. Such NTE can be tuned to be smaller, up to zero, or even to positive expansion by inserting one or more gust alkali ions in the vacancy of LaF...

Melting phlogopite-rich MARID: Lamproites and the role of alkalis in olivine-liquid Ni-partitioning

In this study, we show how veined lithospheric mantle is involved in the genesis of ultrapotassic magmatism in cratonic settings. We conducted high pressure experiments to simulate vein+wall rock melting within the Earth's lithospheric mantle by reacting assemblages of harzburgite and phlogopite-rich hydrous mantle xenoliths. These comprised a mica-, amphibole-, rutile-, ilmenite-, diopside (MARID) assemblage at 3–5GPa and 1325–1450°C. Melting of the MARID assemblages results in infiltration of melt through the harzburgite, leading to its chemical alteration. At 3 and 4GPa, melts are high in K2O (>9wt%) with K2O/Na2O>>2 comparable to anorogenic lamproites. Higher pressures and temperatures (5GPa/1450°C) lead to increasing MgO contents of the melt and to some extent lower K2O contents (5–7wt%) at equally high K2O/Na2O ratios. Our experiments provide insights into the role of alkalis in nickel-partitioning (DNi) between olivine and ultrapotassic melt. We observe that the high contents of Na, K, and Al are indicative of high DNi values, implying that the melt polymerization is the dominant factor influencing the olivine/melt nickel partitioning. The change of DNi as a function of melt composition results in a pressure independent, empirical geothermometer:T°C=−88.14·lnliq(Na2O+K2O·liq1+SiO2TiO2·liqAl2O3liqMgO+FeO·DNi+1906.2Element oxides represent the composition of the glass (in wt%), and DNi is the liquid/olivine Ni-partitioning coefficient. We propose that this geothermometer is applicable to all natural silicate melts that crystallized olivine in a temperature interval between 1000 and 1600°C. Application to glass-olivine pairs from calc-alkaline settings (Mexico), MORB (East Pacific Rise), and OIB (Hawaii) yielded reasonable values of 996–1199°C, 1265°C, and 1330°C, respectively.

Activity and deactivation of Pd/Al2O3 catalysts in hydrogen and oxygen recombination reaction; a role of alkali (Li, Cs) dopant

Activity and deactivation of alkali (Li, Cs) doped 2%Pd/Al2O3 catalyst in the exothermic H2 and O2 reaction have been studied in view of potential application in the passive autocatalytic recombiners (PAR), the safety devices applied in the nuclear plant containments to lower the explosion risk associated with hydrogen release. The catalysts have been prepared with impregnation method and characterized by BET, XPS, TEM and STEM techniques. The role of humidity in the H2/O2 recombination reaction has been studied in a flow laboratory reactor using water saturated reaction mixture (0.5 vol% H2). The time-on-stream behavior of catalyst in contact with reaction mixture of high H2 concentration (7.2 vol%) has been studied using Microscal gas-flow through microcalorimeter. The thermal effects accompanying the H2 conversion during slow deactivation of catalysts have been monitored. The pattern of changes in both the heat evolution and the H2 conversion in the Pd-catalyzed H2/O2 recombination reaction seem to reflect the inhibiting effect of humidity present in the reaction mixture and water molecules formed in the reaction. The presence of both Li and Cs enhanced deactivation of Pd/Al2O3 catalyst and Cs-dopant displayed more pronounced effect. On the other hand, the alkali dopants do not essentially affect the amount of heat evolved during the recombination process ranging from 187 to 220 kJ/mol H2, e.g. being lower than the heat of water formation (246 kJ/mol). The detrimental effect of Li,Cs dopant has been attributed to higher affinity to water, promoting retention of water molecules/films on the catalyst surface and blockage of active sites due to enhanced adsorption of surface species, like H2O/OH.

Mineralogical Aspects of Durable Geocement Matrix Formation - Role of Alkali

Less than half a century ago just an idea of presence of free alkalis in a ceramic matrix was considered by ordinary Portland cement people as an absurd one and this was a basic postulate accepted in chemistry of cements. In 1957 a scientist from Ukraine (USSR) Viktor Glukhovsky put forward an assumption which was taken as a base for development and bringing into practice of construction a principally new class of cementitious materials which first appeared in the field under a name of alkaline (now also known under a general name of alkali-activated) cementitious materials. A validity of these ideas was confirmed by more than 50 years of evolutional development and vast experience collected on practical use of new materials in different applications. The paper covers theoretical views on role played by alkali in the formation of an alkali-activated cement matrix with high durability. Examples of compositional build-up of the alkali-activated cementitious materials vs. quantity of added alkali and type of aluminosilicate component are reported together with results of 50-year experience obtained from observation of concrete structures made from these cements.

Improvements of Mixed-surfactants in Alkaline/Surfactant/Polymer Solutions

The authors present a comprehensive evaluation of phase behaviors of alkaline/surfactant/polymer (ASP) systems. The experimental results proved that the phase behavior of mixed-surfactant solutions (single- and double-tail anionic surfactants) would be better than the one of single surfactant. These mixtures were also more compatible with polymer, and adjusted optimum salinity to the reservoir brine. They next examined the role of alkalis in ASP process. Three types of alkalis were tested to select the optimum one for high-temperature reservoir. This study showed that sodium metaborate is the best choice.

Effect of surfactant composition on reservoir wettability and scale inhibitor squeeze lifetime in oil wet carbonate reservoir

Abstract In the oil industry, scale inhibitor (SI) squeeze treatment is an established method to prevent deposition of inorganic scales in the wellbore and near wellbore formation. Most scale inhibitor chemicals are water soluble and therefore typically deployed as an aqueous solution. However, most carbonate reservoirs being preferentially oil-wet, SI squeeze treatment could be short lived, because of the competition for adsorption surface between the native oil and the SI. Although several authors studied surfactant activities on reservoir rock and fluid properties in relation to enhanced oil recovery, the literature lacks information on the effect of surfactant based preflush treatment on rock characteristics in relation to SI squeeze lifetime. It is obvious that a proper design of preflush, based on a detailed understanding of rock–fluid properties, could be as important as designing the main treatment (SI) itself. The objective of this study was to develop an understanding of surfactant composition and pH in altering carbonate rock wettability, and its impact on scale inhibitor squeeze performance. A set of carbonate core plugs with oil wet characteristics, crude oil and treatment chemicals (anionic surfactant and SI) were collected from an offshore oilfield. Surfactant preflush compositions with and without alkalis were evaluated for their ability to minimize oil–brine IFT and the extent of rock wettability alteration. A series of coreflood studies were conducted with selected preflush compositions and SI, followed by injecting incompatible brines. SI squeeze lifetimes were determined through observation of core permeability damage. The scale inhibitor and strontium return profile analyzed through ICP-MS studies also validated the onset of permeability damage. The study clearly established a correlation between rock wettability and scale inhibitor lifecycle. Extended SI lifecycle is evidenced in the core with a strongly water wet core and vice versa. The importance of proper preflush design based on rock–fluid characteristics and the role of alkali in changing wettability characteristics, surfactant adsorption and inhibitor lifecycle are discussed with experimental evidence.

Plagioclase and apatite from exsolution structures in minerals from mantle xenoliths

483 Chlorine and alkali bearing minerals unusual for the kimberlitic matrix from nonserpentinized kimber lite of the Udachnaya pipe (Yakutia) with an anoma lously low concentration of water [1] were described in the groundmass [2], as chloride–carbonate nodules [3], and in melt inclusions in olivines from this kim berlite [4]. Phlogopite, apatite, calcite, djerfisherite [5], and sodalite [5, 6] were observed in xenoliths of deformed lherzolites from the Udachnaya pipe; tetra ferriphlogopite, halite, sylvite, alkaline carbonates, and sulfates were registered in melt inclusions from all primary minerals of these xenoliths [5]. Graphite bearing megacrystalline garnet orthopyroxenite con tained three generations of phlogopite, sylvite between orthopyroxene and phlogopite, apatite, sodalite, and potassic feldspar among the minerals of the rim around garnet, calcite in an orthopyroxene inclusion in garnet, and tetraferriphlogopite in a microfracture with djerfisherite and rusvumite, which was not previ ously reported in xenoliths [7]. Extremely nonequili brated ilmenite ultrabasic rock contained several gen erations of phlogopite, sodalite, apatite, calcium car bonate, and djerfisherite [8]. The presence of these minerals in deep xenoliths of mantle rocks is explained either by the interaction with the kimberlitic melt [5] or by metasomatic alteration of rock before it was cap tured by kimberlite [6–8]. In any case we deal with the mantle (probably multistage) process with a signifi cant role of alkalis and chlorine. The depth of this pro cess is confirmed by the finds of phlogopite, apatite, carbonate, and K sulfide inclusions in diamond [9]; the multistage nature, by quite a wide range of PT conditions of equilibrium in mantle rocks, in which alkali and chlorine bearing minerals were registered, as well as by the presence of several generations of phl ogopite in xenoliths and combination of water soluble sylvite and water bearing phlogopite in the same xenolith [7].

Au/activated-carbon catalysts for selective oxidation of alcohols with molecular oxygen under atmospheric pressure: Role of basicity

Abstract Addition of alkali (NaOH) increases significantly the activity of carbon supported gold catalyst for selective oxidation of alcohols with molecular oxygen carried out in non-aqueous medium (toluene) under mild conditions (1 atm. and 80 °C). The role of alkali in the reaction was investigated and it was found that the significant improvement of activity might be ascribed to the formation of Au–OH − sites where H-abstraction from alcohol takes place. The re-used catalyst completed four cycles without any appreciable loss of activity or selectivity under the given reaction conditions.

Influence of alkali and alkaline earth ions on the O-alkylation of the lower rim phenolic-OH groups of p-tert-butyl-calix[4]arene to result in amide-pendants: Template action of K+ and the structure of K+ bound tetra-amide derivative crystallized with a p-tert-butyl-calix[4]arene anion

Role of alkali and alkaline earth ions on the formation of calix[4]arene-amide derivatives through O-alkylation of the lower rim phenolic-OH groups in general and template action of K+ in particular have been explored. Na+ and K+ ions among alkali, and Ca2+ and Sr2+ ions among alkaline earth have shown tetra-amide derivatives bound to metal ion species. Among all these, potassium salts act as template and yields a K+ bound tetra-amide derivative where the charge is counter balanced by a calix[4] arene-monoanion and the product is crystallographically characterized. Change in the amide precursor used in these O-alkylation reactions has no effect on the type of the amide derivative formed. Also demonstrated is a direct one-step reaction for the preparation of 1,3-di-amide derivative in high yield and low reaction period using CsHCO3.

Effect of Alkali Doping on a V2O5/TiO2Catalyst from Periodic DFT Calculations

The role of alkali (Li, Na, K) and H in a vanadia/titania catalyst model is discussed in terms of geometry, electronic structure, and reactivity. Neutral alkali interact with several oxygen sites involving active phase and support. The vanadyl VO groups are affected by the presence of such dopants and elongate with respect to the undoped systems. Neutral alkali adsorption takes place through an electron transfer from the adatom to the surface vanadium atoms, pushing the Fermi level to higher energies. Alkali-doped slabs show a state in the gap lying 0.25 eV below the conduction band. This state appears for H, Li, and K only after using the GGA+U method. Undoped slabs are more active (higher adsorption energies) than the doped ones for electrostatic (methanol adsorption) and redox (hydrogenation) processes. Methanol adsorbs dissociatively, and the adsorption energy becomes less exothermic in the series H−Li−Na−K which corresponds to an increase in the basicity of the slabs and to a decrease of the hardness of the alkali dopant. Hydrogenation takes place by electron transfer to the vanadium sites and becomes less exothermic in the series H−Li−Na−K. Bridging V−O−Ti sites are preferred to vanadyl VO sites in both methanol and hydrogen adsorption final structures.

Fates and roles of alkali and alkaline earth metals during the pyrolysis of a Victorian brown coal

H-, Na- and Ca-form coal samples were prepared from a sample of Loy Yang brown coal and pyrolysed in a wire-mesh reactor. The tars were characterised with UV-absorption and UV-fluorescence spectroscopies. Increases in heating rate (1 to 2000Ks−1) and temperature (up to 700°C) were found to facilitate the release of larger (“equivalently” larger than naphthalene) aromatic ring systems from coal during pyrolysis. The presence of alkali and alkaline earth metallic (AAEM) species in the coal samples greatly hindered the release of the larger aromatic ring systems during pyrolysis. The AAEM species also reduced the effects of heating rate on the release on aromatic ring systems at lower temperatures. However, the hindering effect was not proportional to the contents of AAEM species in the coal. In addition, the ion-exchange processes caused irreversible changes to coal structure. Significant proportions of the AAEM species in the coal samples were volatilised during pyrolysis even at temperatures as low as 300°C. The volatilisation of AAEM species was not sensitive to changes in heating rate but was intensified with increasing temperature. The monovalent species (Na) was always volatilised to a much larger extent that the divalent species (Mg and Ca) under similar pyrolysis conditions. At high temperatures (900–1200°C), the drastic volatilisation of Na (up to 80%) and of Ca (up to 40%) was accompanied by the increases in tar yield during the pyrolysis of the Na-form and Ca-form samples. The fates and roles of the AAEM species during pyrolysis are thought to be related to their transformation during pyrolysis. The AAEM species might have been involved in a repeated bond-forming and bond-breaking process between the AAEM species and the coal/char matrix. During this process, tar precursors were repeatedly linked to the coal/char matrix and were thermally cracked. Some of the more aliphatic components and/or smaller aromatic ring systems in a tar precursor were cracked to gas and some of the larger aromatic ring systems were charred.