Mg-Al Hydrotalcite Research Articles

Highly dispersed Cu-ZnO-ZrO2 nanoparticles on hydrotalcite adsorbent as efficient composite catalysts for CO2 hydrogenation to methanol

CO2 hydrogenation to methanol is attracting specific interest because of its potential economic and environmental benefits in transforming waste CO2 to value-added hydrocarbons. Copper-based catalysts are documented as efficient and widely applied, whereas insufficient catalytic properties of conventional catalysts hinder their application. Herein, catalysts using Mg-Al hydrotalcite (HT) as the carrier of Cu/ZnO/ZrO2 (CZZ) nanoparticles were prepared to exploit special advantages of hydrotalcite on copper dispersion and catalytic performance. The results show that CZZ nanoparticles can be uniformly dispersed on external surfaces of HT, elevating BET surface areas of CZZ-HT samples by at least 2.5 times compared to pure CZZ. The HT carrier also enriches strong basic sites and hence elevates CO2 adsorption capabilities in the range of reaction temperature. Both copper surface area and copper dispersion of CZZ-HT samples are improved dramatically. A catalyst containing 45.1 wt% of CZZ shows 1.1 times higher copper surface area per gram CZZ and 1.6 times higher copper dispersion than the reference CZZ. Subsequent reactions demonstrate the CZZ-HT samples show remarkably promoted turnover frequency (TOF) for methanol synthesis and retain considerable catalyst stability. The typical catalyst prepared in this research, at the reaction temperature of 523 K and pressure of 3.0 MPa, presents a 68.2% higher methanol STYCu per gram copper and an 117.0% higher SMeOH/SCO ratio than the commercial catalyst. The support HT plays a crucial role for the enhanced catalytic performance physically and chemically. Thus, the as-prepared CZZ-HT catalyst provides a significant improvement for CO2 utilization.

Evenly distribution of amorphous iron sulfides on reconstructed Mg-Al hydrotalcites for improving Cr(VI) removal efficiency

Hexavalent Chromium (Cr(VI)) in water is a public health concern and has been a challenging research subject in environmental field for many years. Herein, a novel composite material consisting of amorphous iron sulfides supported on hydrotalcites (FeS/HTs) was synthesized by “calcination-reconstruction-calcination” process, which enables homogeneous distribution of iron and sulfur on the surface of hydrotalcites (HT). The composite (mass ratio of FeS/HT was 1/2) could effectively remove over 98% of Cr(VI) within 10 min. A pseudo-second-order kinetic model and a Langmuir isotherm model were well fitted the sorption data with a maximum removal capacity of 206.2 mg/g. The superior adsorption capacity of FeS/HTs could be attributed to the combination of the advantages of abundant adsorption sites on HT and powerful reduction properties of iron sulfides. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggested the adsorbed Cr(VI) on the surface and interlayer of FeS/HTs had been reduced to Cr(III) by reductant iron and sulfur. This study demonstrated that FeS/HTs has potential application prospects in Cr(VI) removal.

Ultrasound-assisted synthesis of single layer MgAl hydrotalcite for the removal of Cr(VI) in solution and soil

The controllability of composition and structure of layered double hydroxide (LDH) is one of the important grounds for their widespread use in removing hexavalent chromium (Cr(VI)) from the environment. In this study, single-layer LDHs were successfully produced through an ultrasound-assisted process in the presence of formamide and characterized by X-Ray diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM) and surface energy. Then LDHs were utilized to remove Cr(VI) in solutions, of which the results demonstrated that delaminated MgAl in formamide with ultrasound (F-U-MgAl) had the highest adsorption efficiency, and the adsorption equilibrium was reached in the first 1 min, with a removal rate of 100%. While the removal rate of Cr(VI) by delaminated MgAl without ultrasound (F-MgAl) and MgAl were only 77% and 12% after 60 min. Based on the XRD patterns and SEM images of samples before and after adsorption, the adsorption mechanisms of F-U-MgAl included anion exchange, surface adsorption and electrostatic attraction.The effects of initial pH, dosage, initial concentration, coexisting anions, and HA were also investigated. In addition, the adsorption in Cr(VI)-containing soil by LDHs was considered, and the results indicated that the single-layer LDHs had a broad application prospect in soil remediation. Besides that, we had also verified the above conclusion through the phytotoxicology tests.

Study on Adsorption Properties of Calcined Mg-Al Hydrotalcite for Sulfate Ion and Chloride Ion in Cement Paste.

In the marine environment, sulfate ions and chloride ions are abundant. Therefore, sulfate attack and chloride ion attack are common failure forms of marine concrete. Mg–Al hydrotalcite is a layered bimetallic hydroxide, which can be used as guest molecular adsorbent. In this experiment, we synthesized Mg–Al hydrotalcite, and the crystal state, surface morphology, and composition of this adsorbent were investigated by modern micro-analysis technology. Mg–Al hydrotalcite was added into the prepared target ion solution, to explore the influence of various factors on the adsorption performance of Mg–Al hydrotalcite, and then calcined Mg–Al hydrotalcite was added into cement paste, to study the mechanical properties and durability of the paste samples. The experimental results show that the optimum conditions for adsorption of chloride ions by calcined Mg–Al hydrotalcite are an adsorption time of 4 h, temperature of 35 °C, LDO (calcined Mg-Al hydrotalcite) dosage of 3.5 g/L, and a pH of 8. The adsorption effect of sulfate ion is best when the adsorption time is 6 h, the temperature is 35 °C, the dosage of LDO is 4 g/L, and the pH = 8. The optimal adsorption conditions of calcined Mg–Al hydrotalcite for chloride ion and sulfate ion are not completely the same, and the adsorption of these two ions in mixed solution shows competitive adsorption. Compared with the common paste specimens without Mg–Al hydrotalcite, the mechanical properties and deformation properties of cement specimens can be significantly improved by adding Mg–Al hydrotalcite.

One-pot multicomponent synthesis of highly substituted pyridines using hydrotalcite as a solid base and reusable catalyst

One-pot synthesis of highly substituted pyridines has been demonstrated via multicomponent reaction of aldehydes, malononitrile and thiophenol using Mg-Al hydrotalcite as a solid base and reusable catalyst. The catalytic activity is intimately connected to the basicity of the catalyst. The best activities were observed with the Mg/Al: 5 catalyst. The catalyst could be reused for further run without a significant loss in activity. The protocol was also applicable for various aromatic aldehydes which affords desired product in good to excellent yield.

Nanostructured catalysts for BIOEthanol transformation to industrially important chemicals

Abstract Utilization of a low-cost biomaterial, such as bioethanol, to produce value–added compounds for current industry has been investigated. This work is focused on the catalytic transformation of bioethanol into industrially significant alkenes. Catalytic transformation of ethanol was studied using catalysts based mainly on nanostructured materials as Mg-Al hydrotalcites, sepiolites and zeolites doped with Cu, K, Sr, Zn and Mn. The catalytic tests were carried out in a plug-flow reactor in the temperature range of 350—550 °C. Undoped zeolites promote acid-catalyzed dehydration of ethanol, while in case of basic catalysts, such as hydrotalcites, the product distribution is shifted toward butadiene. The impact of the hydrotalcites preparation method on their structure and catalytic activity is reported. It was found that hydrotalcite with well-developed layered structure, prepared by slow hydrolysis, promotes the formation of butadiene (with butadiene yield of 28.2 % at 400 °C vs. ethylene yield of 17.2 % at 550 °C).

A solid thermal and fast synthesis of MgAl-hydrotalcite nanosheets and their applications in the catalytic elimination of carbonyl sulfide and hydrogen sulfide

MgAl hydrotalcites with high exposed OH− sites were designed, and showed superior performance for the catalytic elimination of COS and H2S.

A novel Mg-Sn-Zn-Al-Mn magnesium alloy with superior corrosion properties

The corrosion behaviors of the hot-pressed Mg-Sn-Zn-Al-Mn magnesium alloys with the addition of Al in different proportions have been investigated. Paraffin coating technique was applied to Mg powders before production. After debinding at 300 °C, the sintering process was applied at 610 °C under 50 MPa pressure for 70 min. All of the alloys were immersed in Hank’s solution for 10-days. The results indicated that the corrosion properties of the alloys were affected by the production method (hot pressing) and alloying element addition. After immersion, magnesium hydroxide (Mg(OH)2), hydroxyapatite (HA), and Mg-Al hydrotalcite structures were determined by the X-ray diffraction (XRD) analysis on the surfaces of Mg-Sn-Zn-Al-Mn alloys. The Mg-Al hydrotalcite protective layer was effective in preventing corrosion. Superior corrosion properties (weight loss: 1.2%, total volume of evolved H2 gas: 4 ml/cm2, corrosion rate: 0.39 mm/year) were obtained from TZAM5420 alloy (5 wt.%Sn, 4 wt.%Zn, 2 wt.%Al, 0.2 wt.%Mn).

Studies on synthesis, characterisation and effect of calcination on Mg-Al hydrotalcite for the removal of anionic species

The use of Mg-Al Hydrotalcite for removing anionic contaminants such as Bromide, Sulphate, Nitrate, Fluoride and Chloride from aqueous solutions has been studied. The current study analyses the effect of calcination on the anionic removal efficiency of hydrotalcite. The hydrotalcite samples have been calcined batch-wise in a muffle furnace at different temperatures and are added to various anionic solutions in a conical flask and kept for stirring in a shaking incubator for three hours. The filtrate obtained is then analysed using Ion chromatography. The results obtained show a steady increase of anionic removal with an increase in calcination temperature. All anions under study show maximum removal towards calcinated samples than non-calcinated samples.For both calcinated and non- calcinated samples, it is found that the percentage removal of anions decreases with the increase of its ionic radii in the manner F - >Cl - >Br - >NO 3 - >SO 4 2- which clearly states that calcination does not affect this behaviour and ionic radius is an influencing factor even without calcination.

Niobium-modified hydrotalcite catalysts: Sustainable conversion of waste glycerol to valuable chemicals

Nb-modified MgAlmixed oxide catalysts were prepared by ion exchange using an MgAl hydrotalcite and peroxoniobate complex as precursors. After calcination, the Nb-MgAl revealed to be a composite material (MgAl mixed oxide with segregated Nb2O5 nanoparticles), with an increased specific surface area (229 m2 g−1) compared to bare MgAl (88 m2 g−1). XRD confirmed that part of the Nb atoms was inserted in the MgAl lattice thus causing the oxide doping. Furthermore, the Nb precursor favored the incorporation of a high amount of Nb in the catalyst (18 wt.%). Reactions performed in a continuous flow fixed-bed reactor (PBR) on a pilot scale showed that the MgAl and Nb-MgAl are quite active and stable catalysts for the conversion of the waste glycerol (> 90 %), as generated in the biodiesel industry. The valuable chemicals obtained (i.e., diglycerol, formic acid, and dioxane) demonstrates the potential industrial use of the catalysts presented in this work.

Preparation and properties of hierarchical Al–Mg layered double hydroxides as UV resistant hydrotalcite

Anti-ultraviolet Mg–Al hydrotalcite samples (MgAl–P-LDH) with 4-metoxybenzoic acid (PMOBA) ion intercalation were prepared by high temperature reduction method. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Visible absorption spectrophotometry, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry. SEM images indicate that the UV-resistant MgAl–P-LDH had a layered structure. The results of X-ray diffraction analysis showed that the purity of MgAl–P-LDH sample was higher. Compared to MgAl-LDH, the characteristic peak for MgAl–P-LDH shifted towards small angle of 2θ, and it was found that the PMOBA ions have been inserted into the interlayer of MgAl hydrotalcite. The infrared spectra also showed that PMOBA ions were successfully intercalated within Mg–Al hydrotalcite layer. The ultraviolet absorption of MgAl–P-LDH was better than that of PMOBA and MgAl-LDH with the wavelength range of 225–325 nm, and the maximum absorption over 80% was observed.

Interesterification of triglycerides with methyl acetate for the co-production biodiesel and triacetin using hydrotalcite as a heterogenous base catalyst

Biodiesel is a renewable fuel with several advantages over petro-based fuels and is conventionally produced by the transesterification of triglycerides with alcohols. Chemical interesterification of triglycerides is a good alternative as compared to transesterification, as it yields a value-added compound, triacetin, as a co-product instead of the already abundant commodity, glycerol. In this work, interesterification of soybean oil was carried out with methyl acetate to co-produce biodiesel and triacetin, using calcined hydrotalcite as a heterogeneous base catalyst. Several base catalysts were tested for this reaction. Calcined Mg-Al hydrotalcite (Mg:Al mole ratio – 3:1) was found as the best catalyst for achieving 95.9 % conversion of soybean oil triglycerides in 4 h and yielding 5.3 % selectivity of triacetin along with the value-added intermediates - monoacetindiglycerides and diacetinmonoglycerides, produced with a selectivity of 46 % and 48.7 %, respectively. The optimum reaction conditions were found at an oil to methyl acetate mole ratio of 1:50, catalyst loading of 0.04 g/cm3 and a temperature of 200 ºC. The catalysts were fully characterized before and after the reaction, and were found to possess high surface area with both basic and acidic sites. The effect of various reaction conditions on the rate of reaction, conversion of triglycerides and selectivity of triacetin were studied. The concentration profiles of the reactants, intermediates and products obtained at different temperatures were used to obtain the kinetic rate constants and the activation energy of each parallel step was evaluated. Reusability studies showed that the catalyst was stable and reusable up to three cycles.

Effect of Mg/Al molar ratio on the basicity of Mg-Al mixed oxide derived from Mg-Al hydrotalcite

<p>The fundamental character of the Mg-Al mixed oxide (Mg<sub>n</sub>(Al)O), derived from the Mg-Al hydrotalcite (Mg<sub>n</sub>Al-CO<sub>3</sub>-HT), where n corresponds to the Mg/Al molar ratio (n: 2, 2.5, 3, 3.5 and 4), was studied by using the adsorption of phenol as a probe acid molecule. The hydrotalcite precursors were prepared by the coprecipitation method. Their derived mixed oxides were obtained by thermal treatment at 450°C in a flow of air. The resulting solids were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG-DTA), nitrogen physisorption (BET) and phenol chemisorption. The phenol adsorption followed by UV-Visible spectrophotometry shows that the basicity increases with the Mg/Al molar ratio, such that maximum quantity of phenol adsorbed (Q<sub>ads</sub> = 0.54 mmol/g <sub>cat</sub>) was obtained with the mixed oxide derived from the Mg-Al hydrotalcite of Mg/Al molar ratio equal to 3.5.</p>

MgAl Mixed Oxide Derived Alkali-free Hydrotalcite for Transesterification of Waste Cooking Oil to Biodiesel

The heterogeneous catalyst, MgAl hydrotalcite (MgAl HT) was synthesised via alkali-free method spanning from 4:1 to 2:1 ratio of Mg and Al respectively and underwent subsequent calcination process at 450°C for 3 h. The diffraction patterns of MgAl HT indicated the high crystalline structure was obtained. The increasing of the reflection intensity and the sharpness of diffraction lines were seen with the increasing of Mg:Al ratio. Calcination has removed the carbonates and hydroxyl layers, thus left only the mixed oxide of MgO and Al2O3 as proven by XRD, SEM, EDX and FTIR. This catalyst was used in the transesterification reaction with Waste Cooking Oil (WCO) as feedstock for the production of biodiesel. WCO underwent a pretreatment process to remove the impurities and moisture content. Acid-base titration was performed to determine the acid value and percentage of Free Fatty Acid (%FFA). The FFA content was 0.073% (less than 1%), hence transesterification reaction has been proceeded without before esterification process using methanol to oil ratio 30:1 for 24 h. Results show high percentage yield of biodiesel in 5 wt% 3:1 MgAl (87.23%) compared to 84.01% yield in 5 wt% 4:1 catalyst and only 79.23% yield with 5 wt% 2:1 catalyst.

Oxidative dehydrogenation of ethanol over Cu/Mg-Al catalyst derived from hydrotalcite: effect of ethanol concentration and reduction conditions

The copper-modified Mg-Al catalyst (Cu/Mg-Al) was synthesized using the incipient wetness impregnation of copper onto the Mg-Al hydrotalcite derived from co-precipitation method. The effects of copper on the characteristics of catalyst were obtained using several characterization techniques. We found that only copper (I) oxide (CuO) species were obtained on the surface after calcination in air by X-ray Diffraction (XRD). However, the basicity of the base decreases slightly, while the density of the base increases due to the decrease in Brunauer-Emmett-Teller (BET) surface area. We carried out the catalytic activity of the Cu/Mg-Al catalyst in the continuous flow reactor through oxidative dehydrogenation of ethanol. We obtained that the copper enhances the catalytic activity in this reaction, and the ethanol conversion increases with increase in temperature, while the acetaldehyde selectivity decreases because of the decomposition of acetaldehyde to carbon dioxide. The highest acetaldehyde yield of 41.8% was at 350 °C. Moreover, we studied the effects of the ethanol concentration by varying the ethanol feed concentrations (99.9%, 75%, and 50%). The ethanol conversion decreases with a decrease in the ethanol concentration due to the high adsorption of water molecules on the catalyst surface. Thus, the negative effect decreases at higher reaction temperature (350–400 °C). Furthermore, we investigated the effect of the reduction condition of catalyst by varying the reduction temperature (300 and 400 °C). The reduction process affects the catalytic activity. The Cu/Mg-Al was comparatively stable for 10 h upon time-on-stream test. It is used as a promising catalyst in oxidative dehydrogenation of ethanol without any reduction step.

Electronically Coupled PtCo/MgAl Hydrotalcite Catalysts Display Tunable Selectivity Toward Glyceric Acid and Lactic Acid for Glycerol Conversion

Selective oxidation of glycerol is one of the most promising routes to produce value-added fine chemicals from biomass. However, achieving good selectivity towards glyceric and lactic acids still remains a grand challenge in this field. A series of unique electronically coupled PtCo catalysts, supported on layered double hydroxides via co-precipitation method, was reported in this work, as they display tunable selectivity toward glyceric acid and lactic acid during glycerol conversion. It is found that the unusual electronic transfer from MgAl hydrotalcite support to cobalt species, leading to high electron binding energy of PtCo sites on catalyst surface. The presence of cobalt components contributes to synergistic enhancement of oxidation activity at electron deficient Pt sites and more critically, weakened Pt–O strength during glycerol conversion. Such unique electronic reconfiguration, as characterized by XRD and XPS spectroscopy, induces two alternative reaction pathways under different reaction temperatures. While Pt–O bonding strength is significantly weakened by strong Co–O affinity at relatively higher reaction temperature (100 °C), such effect is almost negligible at 50 °C. As a result, lactic acid selectivity of 67% was obtained at 100 °C, while glyceric acid selectivity of 65% was achieved at 50 °C, over the bifunctional PtCo/MgAl hydrotalcite catalysts. The design principles reported in this work offer alternative approaches for manufacturing cost-effective catalytic materials for glycerol conversion to various value-added carboxylic acids and derivatives.

Highly effective adsorption removal of perfluorooctanoic acid (PFOA) from aqueous solution using calcined layer-like Mg-Al hydrotalcites nanosheets.

To study the influence factors of calcined layer-like Mg-Al hydrotalcites nanosheets adsorbing perfluorooctanoic acid (PFOA) in aqueous solution, Mg-Al hydrotalcite (HMA) nanosheets were prepared by one-step hydrothermal synthesis. The effect of calcination temperature on adsorption properties and structure of HMA (CHMA-x, x means different calcination temperature) was investigated. The prepared samples were systematically characterized by the Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), X-ray diffraction (XRD), scanning electronic microscopy (SEM), and nitrogen adsorption-desorption isotherms. The adsorption isotherms and kinetics showed the adsorption equilibrium reached within 2h, and the factors, such as adsorption dosage, pH, and cycles were investigated. It was found that CHMA with 600°C displayed a uniformly morphology, higher surface area about 106.3m2/g, and excellent adsorption properties (1969mg/g). The equilibrium adsorption data perfectly fitted to the pseudo-second-order kinetic model (R2 = 0.999) and the Freundlich model (R2 = 0.994). The main mechanism of CHMA adsorbing PFOA might be the "memory effect." This study provided a new insight to prepare highly effective adsorbents in water treatment.

Synthesis of Nanocrystalline Mg-Al Hydrotalcites in the Presence of Starch-the Effect on Structure and Composition.

The study describes the synthesis of Mg-Al hydrotalcite (Ht) with the use of starch as a structure controlling biotemplate. Syntheses were carried out at room temperature, by co-precipitation at pH = 10. The investigated synthesis parameters included the nature of the precipitating agent (NaOH/Na2CO3 or NH3aq/(NH4)2CO3), the nature of starch (potato, corn and cassava), the method of starch addition to reagents, the method of drying and the effect of washing. The materials were examined with X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and infrared spectroscopy. The data show that synthesis of Ht materials in the presence of starch, with use of the ammonia-based precipitant, enabled preparation of nanocrystalline Ht with very fine (<50 nm) particle size. All investigated starches had a similar effect on the crystallinity and the grain size of Ht precipitates. Ht with the smallest nanocrystals was obtained when starch was present in all solutions used for synthesis, and the final product subjected to freeze drying. Washing with water was found to enhance recrystallization and exchange of nitrates for carbonates. Infrared spectra showed that an interaction exists between the biopolymer template and the Ht particles, resulting in a higher degree of order within the Ht-adhering starch component.

Enriching lithium and separating lithium to magnesium from sulfate type salt lake brine

Extraction of lithium from salt lake brine has become a research highlights due to the rapid development of lithium ion battery. There are abundant lithium resources in sulfate type salt lake in China. In this work, the process of enriching lithium and separating lithium to magnesium from simulated sulfate type brine was carried out based on the reaction of Al/Na2SO4 composite with brine. The results show that Al/Na2SO4 composite can be used to enrich lithium from Li2SO4 solution in the form of Li2Al4(OH)12SO4·xH2O and the lithium precipitation efficiency reaches 89.2% under the optimal conditions. The existence of magnesium in solution is adverse to the precipitation process of lithium. The coating of compact MgAl hydrotalcite on the surface of aluminum based material hinders the reaction of Al/Na2SO4 composite with brine and the lithium precipitation efficiency decreases to 54.7% when the Mg/Li mass ratio in solution is 20:1. However, the Mg/Li mass ratio in precipitate is less than 0.3 under the optimal conditions. The results are beneficial for the enriching lithium and separating lithium to magnesium from sulfate type brine.

A study on the ball-milling effect of calcined Mg-Al hydrotalcite on the CO2 adsorption behavior

A study on the ball-milling effect of calcined Mg-Al hydrotalcite on the CO2 adsorption behavior