Alkali Metal Nitrates Research Articles

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption cycles, retaining over 85 % of its initial adsorption capacity. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Preparation of molten salt promoted MgO for efficient CO2 capture by microwave method: Performance evaluation and mechanism exploration

MgO’s great potential for capturing CO2 has drawn a lot of attention, but the limited O2– sites prevents its further development. This work proposed a microwave-induced method (microwave hydrothermal and microwave sintering) to produce high-performance MgO CO2 adsorbent and was further modified using carbonates (K2CO3) and nitrates of alkali metals (NaNO3, KNO3). The outcomes demonstrated that the small particle size MgO nanocrystals (6.20 nm) with a CO2 uptake of 1.8 mmol·g−1 could be produced by a unique method of microwave heating from the inside out. Among the modified samples, addition of 20 mol% NaNO3 on the surface of MgO exhibited the highest CO2 uptake (11.91 mmol·g−1), and the uptake was still 7.9 mmol·g−1 after 10 cycles. The addition of molten salt changed the adsorbent’s active sites, resulting in an increase in O2– alkaline sites and the activation of MgO lattice defects, both of which improved the sample’s CO2 adsorption performance. This work could offer a new idea for creating affordable and effective CO2 solid adsorbents to capture CO2.

Mesoporous carbon with extremely low micropore content synthesized from graphene oxide modified with alkali metal nitrates

High-temperature thermal exfoliation is a simple, rapid, and cost-efficient method for transforming graphene oxide (GO) materials into reduced graphene oxide (rGO) materials. In this study, GO materials were dispersed with alkali metal nitrates (MNO3), leading to the preparation of porous rGO materials characterized by high specific surface area (SSA) and pore volume via high-temperature thermal exfoliation. Experimental data indicate that the metal cations of MNO3 tend to react directly with the oxygen functional groups (OFG) of GO, modulating the OFG content. Simultaneously, nitrate anions have preferential interaction with alkali metal ions and adhere to the surface of the GO. The presence of MNO3 on the surface of GO facilitates the thermal exfoliation process and leads to the formation of structures with an extremely high proportion of mesoporous content. The isothermal gas adsorption results show that the exfoliation efficiency of the samples activated with different nitrate salts decreases in the order rGO-KNO3 > rGO-NaNO3 > rGO-LiNO3. Among these samples, rGO modified with KNO3 exhibited the greatest exfoliation efficiency, with a mesopore-to-micropore volume ratio of 22.4, more than 1.7 times that of rGO. Its SSA and pore volume were 359 m2 g−1 and 1.26 cm3 g−1, respectively. These values significantly surpass those of rGO. Our research findings demonstrate that activation with MNO3 significantly increases the SSA and pore volume of the GO material after high-temperature annealing.

Nitrate-promoted gas–solid reactions of H2 and CaCO3 for mid-temperature integrated CO2 capture and methanation

Integrated CO2 capture and methanation (ICCM) technology has attracted increasing attention for Carbon Neutrality. However, in the mid-temperature ICCM studies dominated by MgO, which involves the gas–gas catalytic pathway, the problems of high CO2 escape and low CH4 yield are common. Replacing MgO with CaO reduced CO2 escape because the reaction proceeded via the gas–solid pathway. However, the lower CaCO3 conversion rate limits its further applications. Here, we present an ICCM process with efficient CaCO3 conversion using alkali metal nitrates (KNO3, LiNO3, and (Li-K)NO3) to promote Ru/CeO2-CaO. The results showed that the doping of nitrates led to a decrease in the specific surface area of CaO, thus losing part of the CO2 capture performance. On the other hand, forming the molten liquid layer facilitated the gas–solid reaction between CaCO3 and H2, which improved the CaCO3 conversion. Compared with the Ru/CeO2-Neat CaO without nitrate promotion, the CaCO3 conversion of Ru/CeO2-KNO3/CaO was increased by 42% and CH4 yield by 52% after five ICCM cycles. Furthermore, kinetic analysis and in situ DRIFTS experiments demonstrated that molten KNO3 facilitated mass transfer in the diffusion-controlled stage of direct CaCO3 hydrogenation.

Preparation and Application of Slag‐Based Catalyst for Steelmaking

This study focuses on utilizing ground granulated blast furnace slag (GGBS) from a steel plant as the main raw material, with water and calcium‐based montmorillonite as binders, with manganese and alkali metal nitrates (Na, K, Mg, Ca). A series of supported denitration catalysts are prepared using the equal volume impregnation method. These catalysts are then employed in the selective catalytic reduction process to investigate their impact on denitration effectiveness. Furthermore, the mechanism of low‐temperature denitration in selective catalytic reduction is analyzed by combining catalyst activity tests and characterization techniques. The activity of catalysts is assessed through Fourier transform infrared spectrometer (FT‐IR), X‐Ray diffraction (XRD), and search engine marketing (SEM) characterization tests, along with examining its denitration and sulfur resistance capabilities to determine the denitration mechanism. Experimental results indicate that Mn–Mg/GGBS exhibit the most efficient low‐temperature denitrification effect, and it demonstrates certain sulfur resistance with a 5% Mn loading and a 3% second active component. Introducing Ce as the third active component further enhances the sulfur resistance of Mn–Mg–Ce/GGBS when loaded at 1%.

Effect of alkali metal nitrates on palladium dissolution in nitric acid solutions

Hydrometallurgical unit operations are typically used to recover palladium (Pd) from its ores and secondary resources with high selectivity owing to their low energy consumption, cost effectiveness, and volume flexibility. Herein, diluted HNO3 solutions with added nitrate salts were used to dissolve Pd powders. Moreover, solutions of nitrates with same valency cations (such as HNO3, LiNO3, NaNO3, KNO3, CsNO3, and NH4NO3) and same period cations (such as NaNO3, Mg(NO3)2, and Al(NO3)3) were used to reveal the involved beneficial effects of the nitrates on the Pd dissolution in an environment friendly way with low acidity of the solutions. Among all added alkali metal nitrates, LiNO3 resulted in the highest Pd dissolution efficiency, which was attributed to the higher dissociation constant of LiNO3, resulting in a higher concentration of free nitrate and hence a higher oxidation potential of the overall system. The dissolution process was systematically investigated to determine the optimal temperature (353 K), LiNO3 and HNO3 concentrations (6 and 1 mol L−1, respectively), stirring speed (500 rpm), and reaction time (5 h). These optimal conditions yielded a dissolution efficiency of 99.6%. Notably, as the reaction proceeded, the Pd powder surfaces corroded to form numerous holes, indicating that internal diffusion control also affected Pd dissolution.

Effects of alkali-metal nitrate salts on hydrotalcite-based sorbents for enhanced cyclic CO2 capture at high temperatures

CO2 capture using solid-based adsorbents at high temperatures has been in the spotlight as a CO2 capture and storage (CCS) technology for solving global warming and climate change problems. Hydrotalcite is an anionic clay that is widely used as a CO2 sorbent at temperatures of 200–400 °C. In various methods to improve the relatively low CO2 uptake of hydrotalcite, the hydrotalcites with a high Mg/Al molar ratio achieved significantly increased CO2 sorption uptake. This was because the preparation method allowed incorporation of NaNO3 in the hydrotalcite structure; the maximum CO2 sorption uptake was measured as 28.4 wt% when the Mg/Al molar ratio was 30. The different degrees of NaNO3 melting, depending on the sorption temperature, led to different CO2 sorption kinetics and uptakes at 250, 275, and 300 °C. Over the repeated sorption-desorption cycles, the CO2 cyclic capacity continuously decreased under sorption at 250 and 275 °C, whereas it increased at 300 °C, regardless of the Mg/Al molar ratio. The partial melting of NaNO3 at 250 and 275 °C, below its melting temperature, provided insufficient rearrangement of molten NaNO3. This further caused sintering of the MgO structure, which also increased its crystallite size. Conversely, the accelerated rearrangement of molten NaNO3 at 300 °C, near its melting temperature, and the low CO2 uptake at the initial step inhibited sintering. Different changes in the strength of CO2 sorption on the hydrotalcite-based sorbents also appeared as the cycle number increased.

Molten salts for efficient removal of radioactive contaminants from stainless steel surface: Mechanisms and applications

Here, we have demonstrated an innovative decontamination strategy using molten salts as a solvent to clean stubborn uranium contaminants on stainless steel surfaces. The aim of this work was to investigate the evolutionary path of contaminants in molten salts to reveal the decontamination mechanism, thus providing a basis for the practical application of the method. Thermodynamic analysis revealed that alkali metal hydroxides, carbonates, chlorides and nitrates can react with uranium oxides (UO3 and U3O8) to form various uranates. Notably, the decontamination mechanism was elucidated by analyzing the chemical composition of the contaminants in the molten salts and the surface morphology of the specimens considering NaOH–Na2CO3–NaCl melt as the decontaminant. The decontamination process involved two stages: a rapid decontamination stage dominated by the thermal effect of molten salt, and a stable decontamination stage governed by the chemical reactions and diffusion of molten salt. Subsequently, a multiple decontamination strategy was implemented to achieve high decontamination rates and low residual radioactivity. Within the actual cleaning time of 30 min, the decontamination efficiency (DE) of UO3-contaminated specimens reached 97.8% and 93.0% for U3O8-contaminated specimens. Simultaneously, the radioactivity levels of all specimens were reduced to below the control level for reuse in the nuclear domain. Particularly, the actual radioactive waste from the nuclear industry reached a reusable level of radioactivity after decontamination. The NaOH–Na2CO3–NaCl melt outperforms conventional chemical solvents and may be one of the most rapid and efficient decontaminants for stubborn uranium contamination of metal surfaces, which provides insights in regard to handling nuclear waste.

НИЗКОТЕМПЕРАТУРНЫЕ ФАЗОВЫЕ РАВНОВЕСИЯ В БИНАРНЫХ СИСТЕМАХ И ПОЛУЧЕНИЕ ФУНКЦИОНАЛЬНЫХ МАТЕРИАЛОВ

The problems of studying low-temperature phase formation in systems, which are the basis for obtaining functional materials, are selected. The use of salt fluxes (alkali metal nitrates and sulfates) is an effective method of accelerating the achievement of equilibrium in fluoride and oxide systems. Extrapolation of phase equilibria to absolute zero temperature, taking into account the requirements of the third law of thermodynamics, is a powerful method for obtaining relevant information. Summary phase diagrams of the ZrO2-Sc2O3 and albite — anorthite systems are proposed.

KRb2(NO3)2Cl: a new birefringent crystal exhibiting a perovskite-related framework and a short cutoff edge.

The combination of π-conjugated groups [NO3] and Cl-centered polyhedra generates a new birefringent crystal with a perovskite-related framework, KRb2(NO3)2Cl, which is the first alkali metal nitrate chloride synthesized by a mild hydrothermal method. It crystallizes in the orthorhombic space group pbam (no. 55). In addition, KRb2(NO3)2Cl crystals with dimensions up to 7 × 1.5 × 1 mm3 were grown. Notably, KRb2(NO3)2Cl has a short UV cut-off edge (below 228 nm) and a significantly enhanced birefringence (Δn = 0.084 at 1064 nm). Theoretical calculations indicate that the birefringence enhancement mainly derives from π-conjugated [NO3] plane triangles.

Uncovering the CO2 Capture Mechanism of NaNO3-Promoted MgO by 18O Isotope Labeling.

MgO-based CO2 sorbents promoted with molten alkali metal nitrates (e.g., NaNO3) have emerged as promising materials for CO2 capture and storage technologies due to their low cost and high theoretical CO2 uptake capacities. Yet, the mechanism by which molten alkali metal nitrates promote the carbonation of MgO (CO2 capture reaction) remains debated and poorly understood. Here, we utilize 18O isotope labeling experiments to provide new insights into the carbonation mechanism of NaNO3-promoted MgO sorbents, a system in which the promoter is molten under operation conditions and hence inherently challenging to characterize. To conduct the 18O isotope labeling experiments, we report a facile and large-scale synthesis procedure to obtain labeled MgO with a high 18O isotope content. We use Raman spectroscopy and in situ thermogravimetric analysis in combination with mass spectrometry to track the 18O label in the solid (MgCO3), molten (NaNO3), and gas (CO2) phases during the CO2 capture (carbonation) and regeneration (decarbonation) reactions. We discovered a rapid oxygen exchange between CO2 and MgO through the reversible formation of surface carbonates, independent of the presence of the promoter NaNO3. On the other hand, no oxygen exchange was observed between NaNO3 and CO2 or NaNO3 and MgO. Combining the results of the 18O labeling experiments, with insights gained from atomistic calculations, we propose a carbonation mechanism that, in the first stage, proceeds through a fast, surface-limited carbonation of MgO. These surface carbonates are subsequently dissolved as [Mg2+···CO3 2-] ionic pairs in the molten NaNO3 promoter. Upon reaching the solubility limit, MgCO3 crystallizes at the MgO/NaNO3 interface.

Promoting effect of alkali metal on the catalytic performance of hierarchical Pt/Beta in the aromatization of n-heptane

Previous research showed that hierarchical Beta zeolite supported Pt was an effective catalyst for the aromatization of alkanes and the modification with K could further enhance its catalytic performance; however, the intrinsic effect of alkali metal on the alkanes aromatization over Pt/Beta was still rather obscure. In this work, a series of hierarchical Pt/Beta-Me catalysts were prepared by modifying the Beta zeolite with different alkali metal nitrates (MeNO3, Me = Li, Na, K and Rb) through ion-exchange and used in the aromatization of n-heptane; the effect of alkali metal on the catalytic performance of Pt/Beta-Me was then systematically investigated. The results indicate that the alkali metals used to modify the Pt/Beta-Me catalysts can not only passivate the strong Brønsted acid sites of Beta zeolite, but also enhance the Pt dispersion and induce an electron-rich chemical environment for the supported Pt species. Accordingly, the modification with alkali metal can effectively suppress the cracking reactions and carbonaceous deposition and meanwhile promote the dehydroaromatization of alkanes, in favor of enhancing the catalytic stability and aromatization selectivity of Pt/Beta-Me. The extent of promoting effect of various alkali metals follows the order of Rb > K > Na > Li. In particular, the Pt/Beta-Rb catalyst exhibits excellent performance in the aromatization of n-heptane, with a much higher selectivity to aromatics (78.2%) and larger turnover number of aromatic products (Pt-based TON, 19.4 × 103) than the unmodified Pt/Beta-H one (27.7% and 4.8 × 103, respectively). These results help to clarify the role of alkali metal played in the catalysis of Pt/Beta-Me for n-heptane aromatization and pave the way for designing more efficient catalysts in the aromatization of alkanes.

Understanding the Anion-Templated, OSDA-Free, Interzeolite Conversion Synthesis of High Silica Zeolite ZK-5.

High silica zeolite ZK-5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework - alkali metal cation - nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.

Novel molten phase route for composite CO2 separation membranes

Alkali metal nitrates were successfully used as starting chemicals in the production of composite CO2 separation membranes. The easy conversion of nitrates into carbonates after high temperature annealing in CO2 is confirmed using techniques like FTIR (Fourier transform infrared) or selective NO3− electrodes. This conversion shows a step like increase at temperatures in the order of 600 °C, consistent with target utilization temperatures for these membranes. A second but equally relevant consequence of this novel route is the formation of significant concentrations of oxide ions in the molten phase, able to boost the membrane performance, where the ceramic phase modest oxide ion conductivity is rate determining. At 650 °C, a CO2 separation flux enhancement in the order of 60% was reached using nitrates as starting chemicals. A deep analysis of the oxide ion content in molten phases using a variety of analytical techniques, confirmed the specific features of the nitrates as starting chemicals but also showed that even when carbonates are used as precursors, the role of oxide ions in the molten phase can increase significantly the membrane performance.

Viscosities and Densities of Mixed Aqueous Alkali Metal Nitrate Solutions at T = (293.15–333.15) K

Viscosities and Densities of Mixed Aqueous Alkali Metal Nitrate Solutions at <i>T</i> = (293.15–333.15) K

A transferable force-field for alkali metal nitrates

We present a new rigid-ion force-field for the alkali metal nitrates that is suitable for simulating solution chemistry, crystallisation and polymorphism. We show that it gives a good representation of the crystal structures, lattice energies, elastic and dielectric properties of these compounds over a wide range of temperatures. Since all the alkali metal nitrates are fitted together using a common model for the nitrate anion, the force-field is also suitable for simulating solid solutions. We use the popular Joung and Cheatham model for the interactions of the alkali metal cations with water and obtain the interaction of the nitrate ion with water by fitting to a hydrate.

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Nitrates in the Millimeter Spectral Range

Radio Brightness Contrasts of Aqueous Solutions of Alkali Metal Nitrates in the Millimeter Spectral Range

Niobium oxide promoted with alkali metal nitrates for soot particulate combustion: elucidating the vital role of active surface nitrate groups.

With the target of developing efficient base metal oxide catalysts for soot particulate combustion, Nb2O5 catalysts promoted using different alkali metal nitrates have been prepared via an impregnation method. The activity of all the modified catalysts is better than that of the pure Nb2O5, and follows the sequence of CsNb1-9 > KNb1-9 > NaNb1-9 > LiNb1-9 > Nb2O5. It has been discovered that the original LiNO3 and NaNO3 precursors were decomposed into inert Li2O and Na2O on LiNb1-9 and NaNb1-9 during the calcination process. However, the KNO3 and CsNO3 precursors were intact on KNb1-9 and CsNb1-9 due to the strong stabilization effect of the K+ and Cs+ cations. As confirmed using different means, surface nitrates are the predominant active centers that contribute to the soot oxidation activity, through the redox cycles between nitrate (NO3-) and nitrite (NO2-) groups. Due to the existence of a large quantity of active surface NO3- groups, KNb1-9 and CsNb1-9 thus exhibit a much better reaction performance than LiNb1-9 and NaNb1-9.

Promotion of Alkali Metal Nitrate for the Dissolution of Pd

Promotion of Alkali Metal Nitrate for the Dissolution of Pd

Insights into Nickel-Based Dual Function Materials for CO2 Sorption and Methanation: Effect of Reduction Temperature

Ni-MgO dual function materials (DFMs) show promise for integrated CO2 sorption and methanation. To improve CO2 sorption capacity, Ni-MgO DFMs are promoted with alkali metal nitrates. However, the h...