Mg-Al Hydrotalcite Research Articles

MgAl hydrotalcite supported ultrafine PdNi bimetallic catalyst for the dehydrogenation of dodecahydro-N-ethylcarbazole

Liquid organic hydrogen storage is a promising way of storing hydrogen. The development of efficient and low-cost dehydrogenation catalysts is still required to advance the commercialization of N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/H12-NEC) hydrogen storage and transport system.In this paper, PdNi bimetallic catalyst (Pd3Ni1/LDHs) supported on MgAl hydrotalcite was prepared by NaBH4 and ultrasound-assisted stepwise reduction. Ultrasonic cavitation could excite the hydroxyl hydrogen of hydrotalcite in the form of hydrogen radicals to reduce PdCl42− to Pd nanoparticles (NPs), and also promoted the formation of PdNi alloys as well as the dispersion of NPs. In the Pd3Ni1/LDHs catalyst, the average particle size of NPs was 1.98 nm, suggesting an excellent dispersion of Pd, Ni, and PdNi NPs. The electronic effects of Ni and Pd significantly improved the catalytic efficiency of Pd3Ni1/LDHs in H12-NEC dehydrogenation, resulting in a hydrogen release rate of 98.4 % after 6 h at 180 °C, surpassing that of Pd/LDHs. It can be considered that the dehydrogenation performance of Pd3Ni1/LDHs for H12-NEC is related to the alloy phase, electronic structure and NPs size.

An application of hierarchical MgAl hydrotalcite in the highly efficient treatment of oilfield macromolecular contaminants.

In this work, salicylic acid (SA) was used to induce the self-assembly of octadecyl trimethyl ammonium chloride (OTAC), a cationic surfactant, into three-dimensional wormlike micelle aggregates. These aggregates act as a soft template for hierarchical MgAl hydrotalcite (LDH) to create a multi-level pore structure adsorption material. Scanning electron microscopy characterization showed that the surface of the hierarchical hydrotalcite exhibited a dense layered structure, unlike the monolayer structure of ordinary hydrotalcite. Furthermore, the hierarchical MgAl-LDH possesses a significantly larger specific surface area (113.94 m2/g) and wide pore size distribution ranging more extensively from 2 to 80nm, which significantly has an impressive adsorption effect on sulfonated lignite (SL), with a maximum adsorption capacity of 192.7mg/g at pH = 7. Extensive research has been conducted on the adsorption mechanism of hierarchical MgAl-LDH, attributing it to surface adsorption due to the unique multi-level structure of the adsorbent. After two cycles of regeneration experiments, the adsorption capacity of the adsorbent remained at a high level of 179.1mg/g, demonstrating the excellent renewability of hierarchical MgAl-LDH. Moreover, the hierarchical hydrotalcite showed high adsorption capacity in the adsorption of sulfonated lignite, which was attributed to its larger specific surface area and superior pore structure to expose more active sites.

Improving the carbonation performance of sulfate-activated material cured waste sediments by calcined Mg-Al hydrotalcite: Influence of CLDH dosages, carbonation concentrations and cycles

A method was proposed to strengthen the carbonation resistance of the waste sludge matrix by replacing part of cement with industrial by-products such as ground-granulated blast-furnace slag (GGBFS) and fly ash (FA) via the structural recrystallization and anion exchangeability of calcined Mg-Al hydrotalcite in a humid carbon dioxide environment. The mechanical and workability results showed that although the addition of CLDH weakened the flow extension of the mixture samples, they accelerated the solidification and hardening of the samples and increased the development of compressive strength in a slightly carbonized environment (e.g., C5T3L0.3 and C5T3L0.6). Furthermore, XRD, TG, BSE, and MIP techniques were used to analyze the composition of the hydration products and the distribution of the pore structure of the CLDHs-containing samples at different carbonation times and carbonation concentrations. The results indicated that CLDHs had good carbon sequestration capability. The addition of CLDH helped to refine the pores, and a slightly carbonized product like calcium carbonate could enhance the strength development by filling the pores, but too much had side effects. The outcomes of the study also provided an alternative way of thinking about the anti-carbonation behavior of cement pastes.

Investigation of pore structure and high-temperature fracture behavior of lamellar hydrates bonded alumina-spinel castables

Lamellar hydrates of CAC were designed with the introduction of Mg-Al hydrotalcite (M-A-H), and the effects on the early setting behavior, demolding strength, pore structures, mechanical properties, and fracture behavior of alumina-spinel castables were investigated. The results showed that Mg-Al hydrotalcite stimulated rapidly the hydration of CAC and the formation of lamellar C2AH8 and C4AcH11 when curing at 25 and 40 °C. In comparison, CAH10 and C2AH8 were detected without M-A-H and were transformed completely into C3AH6 at 40 °C. The formation of lamellar C2AH8 and C4AcH11 would contribute to a more complicated pore structure, especially in the range of 1–10 µm. Meanwhile, the incorporation of MgO from M-A-H also regulates the distribution of CA6 and spinel (pre-formed and in-situ). Consequently, the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks, thus facilitating the consumption of fracture energy when testing at 1400 °C.

The influence of additive MgO and its content on the carbonation resistance of alkali-activated slag concrete with different activators

The influence of additive MgO and its content on both the compressive strength and carbonation depth of alkali-activated slag concrete (AASC) was investigated under an accelerated carbonation environment. Furthermore, the modification mechanism of MgO on the carbonation resistance of AASC was explored by multiple analytical techniques. Results showed that the incorporation of MgO effectively enhanced the post-carbonation compressive strength and diminished the carbonation depth of concrete. As the MgO content increased, there was a gradual reduction in carbonation depth. The incorporation of MgO promotes the hydration of slag, altering the Al environment, and promoting the formation of C-S-H and Mg-Al hydrotalcite phases. Moreover, the addition of MgO resulted in the emergence of magnesium carbonate and calcium magnesium carbonate in the carbonation products, which filled the pores and prevented the further diffusion of CO2 into the interior. In addition, the improvement effects are more pronounced in the water glass system compared to the NaOH system.

Environmentally benign synthesis of hydrotalcite-like materials for enhanced efficiency of aldol condensation reactions

MgAl hydrotalcites (HTCs) are promising catalysts for biomass valorization applications. However, their production suffers from excessive wastewater generation while their application is limited by insufficient accessibility of active sites. Here, we change the paradigm of hydrotalcite synthesis by replacing the traditional co-precipitation by MgO impregnation with aluminum isopropoxide followed by calcination and (re)hydration. This synthesis affords surface HTC phase ensuring excellent accessibility to Brønsted basic sites. HTC supported on MgO surface (bulk Mg/Al = 20) exhibited same conversion and selectivity in aldol condensation of furfural with acetone as conventional HTC (Mg/Al = 3). Besides maximized efficiency of aluminum use to generate accessible Brønsted basic sites, the catalyst was stable in several consecutive catalytic experiments, if optimal rehydration conditions were applied. Moreover, the use of large quantities of water required for the co-precipitation-based method was avoided. This makes the new method superior also from green synthesis and sustainability point of view.

Effect of interlayer anions on the catalytic activity of Mg-Al layered double hydroxides for furfural and acetone aldol condensation reaction

The aldol condensation reaction between furfural (F) and acetone (A), which typically produces 4-(2-Furyl)-3-buten-2-one (FA), is a critical reaction due to the application of the final product as a flavoring agent in various food items. Traditionally, this reaction is catalyzed by liquid-based catalysts. However, homogeneous liquid-base catalysis often leads to environmental damage. Solid-base catalysis is highly desirable to address the environmental issue due to liquid-base catalysis as it reduces the need for excessive solvents and reagents, thus preserving the environment. In this study, a series of Mg-Al hydrotalcites (HT) intercalated with nitrate ion (HT-NO3), carbonate ion (HT-CO3), or acetate ion (HT-CH3COO) were prepared using three different coprecipitation procedures. Upon calcination at 450 °C, the solids were transformed into mixed metal oxides. Among the calcined hydrotalcites, the catalysts with acetate anion (cHT-CH3COO) or carbonate anion (cHT-CO3) exhibited the highest basicity and thus showed superior catalytic activity for the aldol condensation reaction. Optimal conversion and selectivity were achieved at 90 °C for 2 h using the most basic catalysts (cHT-CO3 and cHT-CH3COO). These catalysts yielded over 98 % conversion with FA selectivity of 76 % for cHT-CO3 and 65 % for cHT-CH3COO, respectively. Notably, the catalyst cHT-CH3COO exhibited higher selectivity towards F2A (32 %) than the cHT-CO3 catalyst (18 %). The effect of interlayer anions on the structural properties of the Mg-Al hydrotalcites was analyzed using X-ray diffraction. Fourier-transform infrared spectroscopy (FT-IR) was employed to investigate the interactions corresponding to different types of anions. The specific surface area and pore volume of the calcined Mg-Al hydrotalcites were determined using nitrogen adsorption (BET), while their total basicity was evaluated through acid-base titration. The reaction kinetics were monitored using gas chromatography.

The Q-Tube-Assisted Green Sustainable Synthesis of Fused Azines: New Synthetic Opportunities via Innovative Green Technology

An efficient, economical, and green, sustainable synthesis of fused azines using Mg-Al hydrotalcite under a high-pressure Q-Tube reactor has been developed. This reaction proceeds through the aza-Michael addition of α,β-unsaturated ketone with different aminoazoles. This method offered excellent yields in a short reaction time that economically saved energy in addition to the protocol showing the reuse of the catalyst seven times without losing its catalytic activity.

Synthesis of High-Crystallinity Mg-Al Hydrotalcite with a Nanoflake Morphology and Its Adsorption Properties for Cu2+ from an Aqueous Solution

A magnesium–aluminum-layered double hydroxide (Mg-Al LDH) with a nano-lamellar morphology was prepared by using a homogeneous precipitation and hydrothermal method, and a calcination product (Mg-Al LDO) of the Mg-Al LDH was also obtained in this work. The XRD, TEM, SEM, FTIR, N2 ad/desorption, and TG-DTG techniques were employed to characterize the microstructures, morphologies, and thermostability levels of these two materials in detail. The results showed that both the Mg-Al LDH and Mg-Al LDO had mesoporous structures and nanoplate morphologies, with diameters of 50~200 nm. The Mg-Al LDH was transformed into Mg-Al LDO at 773 K in an air atmosphere. The adsorption properties of the Mg-Al LDH were investigated systematically with a copper chloride solution as a simulated waste. The experimental results demonstrated that the pH value of the solution had an obvious influence on its Cu2+ adsorption capacity, and the optimal pH value was approximately 5.0. The adsorption kinetics results showed that the Mg-Al LDH had a rapid adsorption rate, and the equilibrium adsorption capacity was 62.11 mg/g. Additionally, the Cu2+ adsorption could be commendably described using a pseudo-second-order model, demonstrating that the adsorption behavior is regulated by chemical sorption. The adsorption thermodynamic results indicated that the adsorption process was spontaneous at temperatures above 318 K. Moreover, the ΔG0 values decreased as the temperature was raised, which indicated that a higher temperature can cause a greater impetus for Cu2+adsorption. In addition, the positive values of the ΔH0 indicated that the Cu2+ adsorption was endothermic, and the positive ΔS0 values revealed an increase in the confusion at the solid–liquid interface of the adsorbent.

The in-situ formation of Mg-Al hydrotalcite and its effect on the properties of MgO-bonded alumina castables

MgO-bonded castables are one of the promising non-cement bonded refractories used for ladle lining. To make crack-free MgO bonded castables, the formation of layered double hydroxides (Mg-Al hydrotalcite) is proposed. In the present work, the influences of Al(OH)3 and hydratable alumina (ρ-Al2O3) and different curing temperatures (40 °C, 60 °C, 80 °C) on the formation of hydrotalcite are investigated. The hydration behavior and corresponding hydrates are examined using electrical conductivity, XRD, SEM, FTIR, and TG-DSC analyses. The results show that the increase in curing temperature is more conducive to the formation of hydrotalcite, where ρ-Al2O3 significantly promotes the formation due to the enhanced reactions between intermediates of Mg(OH)2 and Al(OH)3. After high-temperature treatment, the decomposition of a larger amount of hydrotalcite and Al(OH)3 and thereafter growth of microcrystalline spinel contribute to refined pore size distribution. Consequently, a higher hydration degree of ρ-Al2O3 and the formation of more hydrotalcite provide a higher bonding strength at room temperature, and the optimized microstructure enhances high-temperature strengths.

Ni-based hydrotalcite-derived catalysts for enhanced CO2 methanation: Thermal tuning of the metal-support interaction

Metal-support interaction (MSI) is recognized as an important factor affecting catalyst activity in CO2 methanation, but a feasible strategy to adjust MSI during catalyst preparation is not yet very clear. Herein, we designed a series of Mg-Al hydrotalcites calcined at different temperatures as supports for Ni-based catalysts preparation and investigated the relationship between MSI and catalytic activity. Through various characterizations, it is confirmed that the MSI can be tailored by thermal treatment resulting from phase transformation, and Ni/MAO1000 (which has strong MSI) showed the highest activity for CO2 conversion (1821 mmolCO2 mol−1 Ni min−1). Furthermore, in-situ DRIFTS experiments and DFT calculations proved that methoxy/carbonyls are key intermediates and Ni(111) is the determined crystal plane to produce CH4. This work provides an effective way to tailor the MSI of Ni-based catalysts for enhanced performance in CO2 methanation.

Removal of HCl from gases using modified calcined Mg-Al-CO3 hydrotalcite: Performance, mechanism, and adsorption kinetics

To achieve carbon neutrality, it is essential to remove HCl resulting from the extensive use of alternative fuel feedstock in thermochemical plants. In this work, the HCl removal performance of modified calcined Mg-Al hydrotalcite (Mg-Al-CO3) on gaseous stream was investigated. The layered structure of Mg-Al-CO3 intercalated with CO32– was successfully prepared using the coprecipitation method with a molar ratio of Mg/Al equal to 3.1. The optimal performance of Mg-Al-CO3 for HCl removal was observed at 300 °C, and the breakthrough chlorine capacity was 102.7 mg g−1. Among calcined Mg-Al samples, only Mg-Al-400 exhibited better HCl removal performance than Mg-Al-CO3. The specific surface area of Mg-Al-400 was 183.73 m2 g−1, which was 2.8 times greater than that of Mg-Al-CO3. The average HCl removal rate was 90.11 % within the first 120 min, which was 1.12 times higher than that of Mg-Al-CO3. Moreover, the breakthrough chlorine capacity of Mg-Al-400 was increased by 16.9 %, reaching 120.1 mg g−1. Two reaction paths were identified for Mg-Al-400, first Mg2+ reacts with Cl− to generate MgCl2, and then Cl− acted as a new interlayer anion of hydrotalcite. According to the results of adsorption kinetics, the pseudo-second-order and the Bangham model were found to fit well with the HCl removal process of Mg-Al-400.

Tailoring basic and acidic properties of MgAl hydrotalcite by fluoride anions: Effect on glycerol oligomerisation

In this work, two families of catalysts based on mixed metal oxides derived from MgAl hydrotalcites were synthesized with a Mg/Al molar ratio of 3. On the one hand, in the first family, the fluoride anion was incorporated in the interlayer space by using ammonium fluoride, exploiting the “memory effect” characteristic of hydrotalcites. In the second family, fluoride anions substituted oxides anions in the layer, incorporating directly them during the precipitation of hydroxides, by using cryolite as a precursor for both fluorine and aluminium. The hydrotalcites were transformed into mixed metal oxides by thermal treatment and tested in the glycerol etherification reaction at 230 ºC, in a batch reactor at atmospheric pressure. The hydrotalcites and the corresponding mixed metal oxides were characterized by different experimental techniques, such as X-ray diffraction (XRD), elemental analysis (CHF), N2 sorption at − 196 ºC, thermogravimetric analysis (ATD-TG), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of CO2 and NH3 (CO2-TPD and NH3-DTP) and solid state nuclear magnetic resonace (ssNMR) of 19F. It was found that the mixed metal oxides prepared from hydrotalcites, where fluorine was incorporated in the synthesis step using cryolite, achieved the maximum conversion values and complete selectivity towards diglycerol. Diglycerols were the unique detected products and, in some cases, the formation of triglycerols was also detected.

Efficient reduction of Cr(VI) and recovery of Fe from chromite ore processing residue by waste biomass

The traditional chromite ore processing residue (COPR) detoxification process is carried out in strong acid or anoxic high-temperature condition, which not only has a high input cost but leading difficulties for resource utilization of treated COPR. This study first reported the efficient reduction of Cr(VI) and recovery of Fe from COPR by waste molasses-assisted hydrothermal treatment. Under optimal conditions (i.e., the Na2CO3 dosing of 0.5 mol/L, the molasses/COPR mass ratio of 10%, hydrothermal treatment at 140 °C for 150 min), the Cr(VI) reduction efficiency reached 99.96 ± 0.01%, and the leaching toxicity of total Cr met the USEPA regulatory limit of 5 mg/L. Moreover, Fe was recycled in the form of magnetic magnesioferrite with Fe2O3 grade of 52.58 ± 0.90%, which can be used as raw material in steel industry. The Cr(VI) reduction reaction conforms to a pseudo-first-order kinetic model, and the reaction rate constants increase with increasing temperature (120 ∼160 °C). As a potential mechanism of the reaction, the Mg-Al hydrotalcite (LDHs) structure collapses in the presence of Na2CO3 during the hydrothermal treatment, and the embedded Cr(VI) is released, which is then reduced to Cr(OH)3 by reducing substances such as fructose, sucrose, and glucose in waste molasses. From the standpoint of a circular economy, this study may provide a potential strategy for minimizing resource input and waste/emission production by harmless disposal and resource utilization of COPR and waste molasses.

Controlling hydration of hydratable alumina via co‐grinding with Mg–Al hydrotalcite

AbstractThe on‐site industrial application of hydratable alumina (HA)‐bonded castables is inhibited by the high hydration rate of HA. In this study, the hydration behavior of HA co‐ground with sheetlike Mg–Al hydrotalcite (MAT) is investigated. The properties of castables bonded with MAT‐bearing HA are systematically assessed. The hydration rate of HA co‐ground MAT decreases as this allows MAT sheets to be effectively inserted into the microcracks of HA particles during grinding, thus decreasing the direct contact area between HA and water. The strength of MAT‐bearing castables (0.5 and 1 wt%) fired at 800°C improved slightly owning to the generation of magnesia–alumina spinel. The mechanical strength of castables fired at 1100 and 1550°C decreased as the MAT content increased owing to an increase in porosity. Based on an analysis of the hydration behavior of HA and the properties of HA‐bonded castables, the optimal MAT/HA weight ratio is approximately 1/10.

Study on preparation and slow release properties of Magnesium-Al hydrotalcite with alanine intercalation

The precursors of Mg-Al hydrotalcite (Mg/Al-LDHs-NO3) were prepared by low saturation coprecipitation method (constant pH method). In addition, alsine-intercalated magnesium-aluminum hydrotalcite (LDHs-Ala) was synthesized by low saturation coprecipitation (constant pH) and nucleation/crystallization isolation methods when the pH value was higher than the isoelectric point of alanine. The release properties of alanine intercalated hydrotalc in simulated gastric fluid (hydrochloric acid solution with pH=1.5) and intestinal fluid (phosphate solution with pH=7.4) were measured by spectrophotometer in vitro. The results showed that LDHs-Ala had good slow-release properties in simulated intestinal fluid and gastric fluid in vitro. Then sodium alginate was used to coated alanine intercalated hydrotalc for slow release in simulated intestinal fluid and simulated gastric fluid. It can be concluded that the coated intercalated hydrotalc has a low slow release rate in gastric fluid, but has a good slow release performance in simulated intestinal fluid. It can be concluded that the coated intercalated hydrotalc is expected to be a intestinal targeted release agent, which can be applied in biomedicine.

Tailoring Basic and Acidic Properties of Mgal Hydrotalcite by Fluoride Anions: Effect on Glycerol Oligomerisation

Tailoring Basic and Acidic Properties of Mgal Hydrotalcite by Fluoride Anions: Effect on Glycerol Oligomerisation

Adsorption of CO2 and N2 on bimetallic Mg-Al hydrotalcites and Z-13X zeolites under high pressure and moderate temperatures

The adsorption of carbon dioxide on a commercial hydrotalcite (HT) was investigated using gravimetric analysis at 473 K, 573 K and 673 K and pressures up to 10 bar. The CO2 adsorption performance of HT was correlated with a wide range of physicochemical characterisation techniques. For further understanding and comparative purposes, the same adsorption and characterisation measurements are reported for a commercial zeolite 13X (Z-13X). The HT exhibited higher adsorption capacities per unit mass of sorbent at relatively low pressures and per unit surface area over the whole range of pressures analysed, compared to zeolite 13X. However, HT showed adsorption-desorption isotherms with a hysteresis loop indicating a stronger binding energy. The HT also presented deactivation upon cycling (up to ∼ 10%, depending on conditions) suggesting the need for future studies focused on improvement of its regenerability. The same performance regarding hysteresis and deactivation was observed in the presence of N2. The CO2 adsorption isotherms of HT were successfully fitted to the Freundlich model. The values of heat of adsorption calculated -56 and -84 kJ mol−1 for the 1st and 5th cycle, are indicative of a chemisorption process. The data of this work provide information regarding fundamentals of CO2 adsorption of the materials that is useful in the design of realistic adsorption units in conventional and novel H2Carbon Dioxide Capture processes, especially in the sorption-enhanced H2 reaction process.

Preparation and performance of Cd-MgAl-LDHs@RGO in high efficiency electrocatalytic reduction of CO2 to CO

As global carbon dioxide (CO2) emissions continuous increase, the greenhouse effect is becoming an inevitable problem and the conversion of CO2 into carbon-containing clean energy is a hot topic of research. In this paper, a kind of Cd-doped MgAl hydrotalcite composite electrocatalyst (Cd-MgAl-LDHs@RGO) grown in situ on reduced graphene oxide (RGO) was prepared by hydrothermal synthesis. The results show that Cd-MgAl-LDHs@RGO has excellent performance in CO2RR with multiple active sites, high selectivity and good stability. The structure of Cd-MgAl-LDHs@RGO can facilitate the adsorption and mass transfer of CO2 on the catalyst and has the relatively best electrochemical performance than the MgAl-LDHs and Cd-MgAl-LDHs. Its Faraday efficiency (CO FE) is up to 91.5% for the reduction of CO2 to carbon monoxide (CO) (-1.1 V vs. RHE), when the partial current density of CO is 3.39 mA·cm−2 and can be maintained for at least 7.5 h (-1.2 V vs. RHE). Therefore, the catalyst may be prospectively used for efficient electrocatalytic reduction of CO2 to CO, and also provides a promising strategy for the design of efficient electrocatalysts in the field of molecular catalysis.

Kinetic Salt Effect on Base-Catalyzed Isomerization of d-Glucose into d-Fructose.

Isomerization of d-glucose (Glc) into d-fructose (Fru) is of great importance for food sector as well as for valorization of lignocellulosic biomass. Soluble and solid bases exhibit high catalytic activity for the isomerization. Here, we report a salt effect on the base-catalyzed aqueous-phase Glc-Fru isomerization. Addition of soluble salts (Na2 SO4 , NaNO3 , K2 SO4 , and NaCl) results in an increased apparent reaction rate (factors of 1.5 to 6). The salt effect was observed both in the presence of soluble base NaOH at constant pH value and solid bases MgO, Li3 PO4 , and Mg-Al hydrotalcite. Apparent activation energy and UV absorption spectra were not significantly influenced by addition of salts. Potentiometric titration showed that the acidity constants of the saccharides increase in the presence of electrolytes. Since the rate of the isomerization depends on the thermodynamic acidity constant of Glc, the isomerization is accelerated by the presence of electrolytes.