Calcined Hydrotalcite Research Articles

Optimization of CO2 adsorption capacity and cyclical adsorption/desorption on tetraethylenepentamine-supported surface-modified hydrotalcite

The objective of this research was to investigate CO2 adsorption capacity of tetraethylenepentamine-functionalized basic-modified calcined hydrotalcite (TEPA/b-cHT) sorbents at atmospheric pressure formed under varying TEPA loading levels, temperatures, sorbent weight to total gaseous flow rate (W/F) ratios and CO2 concentrations in the influent gas. The TEPA/b-cHT sorbents were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT–IR), thermal gravimetric analysis (TGA), Brunauer–Emmet–Teller (BET) analysis of nitrogen (N2) adsorption/desorption and carbon–hydrogen–nitrogen (CHN) elemental analysis. Moreover, a full 24 factorial design with three central points at a 95% confidence interval was used to screen important factor(s) on the CO2 adsorption capacity. It revealed that 85.0% variation in the capacity came from the influence of four main factors and the 15.0% one was from their interactions. A face-centered central composite design response surface method (FCCCD–RSM) was then employed to optimize the condition, the maximal capacity of 5.5–6.1mmol/g was achieved when operating with a TEPA loading level of 39%–49% (W/W), temperature of 76–90°C, W/F ratio of 1.7–2.60(g·sec)/cm3 and CO2 concentration of 27%–41% (V/V). The model fitted sufficiently the experimental data with an error range of ±1.5%. From cyclical adsorption/desorption and selectivity at the optimal condition, the 40%TEPA/b-cHT still expressed its effective performance after eight cycles.

Selectivity engineering in hydroxyalkoxylation of phenol by ethylene carbonate using calcined hydrotalcite

The high consumption of mono-ethylene glycol phenyl ether in various sectors requires clean and green synthesis. Herein, we report an efficient, selective and green route of hydroxylation using calcined hydrotalcite (CHT) for the preparation of mono-ethylene glycol phenyl ether. Various types of solid base catalysts were prepared and well characterized by TGA–DSC, FTIR, XRD, CO2-TPD, NH3-TPD, SEM and BET surface area. The catalyst CHT (3:1) possesses very high activity for hydroxyalkoxylation of phenol and ethylene glycol with 96% conversion at 180 °C in 2 h with catalyst loading of 0.03 g cm−3. The insight of reaction reveals that it is kinetically controlled with second-order reaction and follows power law model. The apparent activation energy for the reaction is 21.3 kcal mol−1. The catalyst is highly reusable and shows green chemistry prospective and gives excellent results up to four runs.

Effects of the cobalt content of catalysts prepared from hydrotalcites synthesized by ultrasound-assisted coprecipitation on hydrogen production by oxidative steam reforming of ethanol (OSRE)

This paper reports a study of the catalytic performance of CoMgAl mixed oxides (with 5, 10, 15 and 20% Co content) in the oxidative steam reforming of ethanol (OSRE). The catalysts were produced by calcination of hydrotalcites prepared using the ultrasound-assisted coprecipitation method and were H2-activated before the catalytic reaction. The mixed oxides were extensively analyzed by X-ray diffraction (XRD), Raman spectroscopy, H2 temperature-programmed reduction (H2-TPR), N2 adsorption-desorption, transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (SEM-EDX), finding significant differences in their structural, reduction–oxidation (redox), textural and morphological properties, which directly affect the H2 production from OSRE. Catalysts with 10 and 15% Co concentrations generate the highest H2 yields, which results from the formation of solids with an adequate active phase dispersion, an absence of agglomerates, a decreased content of Co3+ species and a high surface area.

Activity and selectivity of different base catalysts in synthesis of guaifenesin from guaiacol and glycidol of biomass origin

Guaiacol and glycidol can be obtained from biomass valorization. Guaiacol (2-methoxyphenol) and glycidol (2,3-epoxy-1-propanol) have been used for the efficient synthesis of guaifenesin ((RS)-3-(2-methoxyphenoxy) propane-1,2-diol). Different catalysts such as hydrotalcite (HT), calcined hydrotalcite (CHT), calcinated hydrotalcite supported on hexagonal mesoporous silica, magnesium oxide, alumina and, potassium promoted zirconium oxide were synthesized, out of which CHT was found to be the most active, selective and reusable catalyst. The catalyst characterization was done by different techniques. Both Oxide and hydroxide phases were observed on calcination of HT in air at 450°C for 6h. CHT possess both acidic and basic sites and basicity of CHT was the highest. Crystallite size, surface area and pore size of CHT play important role in catalytic activity and selectivity. Reaction was carried out in a batch reactor and influence of different parameters was systematically studied. The reaction mechanism involving two sites, acidic and basic, was proposed. A suitable kinetic model was developed and fitted against experimental data. A second order rate equation was derived on the basis of Langmuir–Hinshelwood–Hougen–Watson mechanism with weak adsorption of reactants, intermediates and products. Kinetics was used to predict reaction conditions to obtain guaifenesin selectively. Guaifenesin was efficiently obtained with 94.8% selectivity at guaiacol conversion of 38.2% over CHT at 80°C after 4h.

Modification of anionic and cationic clays by zwitterionic imidazolium ionic liquid and their effect on the epoxy-based nanocomposites

Zwitterionic imidazolium-based ionic liquid (ZIL) constituted by imidazolium cation and sulfonate anion was used to modify both cationic and anionic clay minerals, represented by montmorillonite (Na+-Mt) and calcined hydrotalcite (CHT). The organophilized clays were characterized using X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The ZIL was successfully intercalated into the interlayer space of Na+-Mt, and incorporated at the surface of the CHT, as indicated by XRD and FTIR analysis. Then, the unmodified and modified clays were mixed with epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA). The modified clays resulted in epoxy networked materials with higher intercalation degree, and good transparency, as indicated by XRD, transmission electron microscopy (TEM) and Ultraviolet- visible (Uv-Vis) spectroscopy. The best intercalation was observed for the systems containing modified montmorillonite (ZIL-Mt). In addition, the clay-epoxy nanocomposites were also characterized by dynamic-mechanical analysis (DMA).

Effects of Composition and Structure of Mg/Al Oxides on Their Activity and Selectivity for the Condensation of Methyl Ketones

The effects of chemical composition and pretreatment on Mg–Al hydrotalcites and alumina-supported MgO were evaluated for the gas-phase, self-condensation reaction of C3–C5 biomass-derived methyl ketones. We show that the selectivity toward the acyclic dimer enone and the cyclic enone trimer can be tuned by controlling the temperature of hydrotalcite calcination. Methyl ketone cyclization is promoted by Lewis acidic sites present on the hydrotalcite catalysts. XRD and thermal decomposition analysis reveal that the formation of periclase MgO starts above 623 K accompanied by complete disappearance of the hydrotalcite structure and is accompanied by an increase in hydroxyl condensation as the formation of well-crystallized periclase. 27Al MQMAS and 25Mg MAS NMR show that at progressively higher temperatures, Al3+ cations diffuses out of the octahedral brucite layers and incorporate into the tetrahedral and octahedral sites of the MgO matrix thereby creating defects to compensate the excess positive charge ge...

Direct synthesis of dimethyl carbonate from methanol and carbon dioxide: A thermodynamic and experimental study

The direct synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol is an atom economic, green and promising process. The present work focuses on this process using calcined hydrotalcite (CHT) supported on hexagonal mesoporous silica (HMS) as a catalyst and phosphonium based ionic liquid (IL) as a promoter. Phosphonium based ionic liquids are good solvents for carbon dioxide and are better alkali promoters. Different modified Keggin type cesium modified heteropoly acids (HPA) supported on HMS were also used as catalysts, which give good comparison between dual site catalysts with altered acidity or/and basicity. The conversion and selectivity were measured as a function of concentration of reactants, catalyst and temperature. The experimental results were compared with the thermodynamic calculations and simulated results. Kinetic model was developed by proposing a reaction mechanism. Sustainability of the process was justified by using a heterogeneous catalyst and by avoiding the use of harmful organic solvents in the presence of an ionic liquid with supercritical CO2.

Defluoridation Performance Comparison of Nano-hydrotalcite/Hydroxyapatite Composite with Calcined Hydrotalcite and Hydroxyapatite

Fluoride retention from water is nowadays a serious health problem. This study reports the potential of a newly developed nano-hydrotalcite/hydroxyapatite (n-HT/HAp) composite, and its constituent materials, hydrotalcite (HT) and hydroxyapatite (HAp), in fluoride removal. Calcined hydrotalcites (cHT) showed a remarkable fluoride removal ability from water through memory effect mechanism. HAp, the mineral compound of bones, adsorbs fluoride as well but through ion exchange mechanism. Fluoride substitutes hydroxyls to produce fluorapatite. Among the tested calcined hydrotalcites, cHT Mg-Al (4:1) sample, composed of magnesium divalent cation to aluminum ratio of 4, was identified as the best-performing hydrotalcite. The differences among cHT samples in fluoride removal capacities are attributed to hydrotalcite composition as well as to particle size. The performance of these materials is compared with that of n-HT/HAp composite whose main features are basic acidic material and not yet tested in fluoride retention. Interestingly, n-HT/HAp also performs best, 98 %, slightly higher than the best cHT Mg-Al (4:1) sample with 97 % fluoride removal efficiency from such a high initial fluoride solution of 20 mg/L at 10 g/L dose, yielding the final residual fluoride concentrations of 0.36 and 0.6 mg/L, respectively; both meet the WHO standard for drinking water. Besides, the uncalcined hydrotalcite constituent added virtue to the advantage of using n-HT/HAp in fluoride removal as the efficiency was compensated by the nanometric size of the hydrotalcite particle.

Applications of CoMo/calcined quaternary hydrotalcites for hydrotreatment reactions

Co2+, Ni2+, Zn2+ and Al3+ quaternary hydrotalcite-type materials were synthesized at: 0.33; 0.25 and 0.20 (M3+)/(M3++M2+) ratios. Then, these as-synthesized hydrotalcites were calcined and impregnated with Mo (15wt.% MoO3) and Co (3Mo:Co) to obtain the catalytic precursors. As-synthesized and impregnated calcined hydrotalcites were characterized by different physico-chemical techniques such as: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), BET surface area measurements and NH3-temperature programmed desorption (NH3-TPD). Finally, CoMo/calcined hydrotalcites were tested in hydrodesulfurization (HDS) and hydrogenation (HYS) reactions of thiophene and cyclohexene. Results showed that the 0.25 (M3+)/(M3++M2+) ratio was the most active for the HDS reaction of thiophene, while the 0.33 (M3+)/(M3++M2+) ratio showed the best performance for the HYD reaction of cyclohexene.

Synthesis of glycerol carbonate by direct carbonylation of glycerol with CO2 over solid catalysts derived from Zn/Al/La and Zn/Al/La/M (M = Li, Mg and Zr) hydrotalcites

Zn/Al/La and Zn/Al/La/M (M = Li, Mg, Zr) mixed oxides were obtained by calcination of hydrotalcites and tested for glycerol carbonate synthesis from CO2 carbonylation.

Unprecedented selectivities in aldol condensation over Mg–Al hydrotalcite in a fixed bed reactor setup

Aldol condensation of furfural with acetone (molar ratio 1:10) was carried out in a flow fixed bed setup at 50°C using calcined hydrotalcite with Mg/Al of 3 as a catalyst. Complete conversion of furfural and stable catalyst performance was obtained during the initial 50h on stream. This period was followed by a rapid catalyst deactivation. In contrast to previous reports, higher molecular weight products that were identified as products of successive aldol condensation of acetone with furfural were observed. Their concentration was time-dependent with a maximum formation after 10 to 30h on stream.

A study on the intercalation of heavy metal ions in a wastewater by synthetic layered inorganic adsorbents

This study examined the intercalation mechanism of Co2+, Ni2+, Zn2+, Mn2+ and Fe3+ ions into synthetic layered inorganic adsorbents—hydrotalcite and gyrolite under different conditions. It was observed that the process parameters above depend on the chemical nature of both solutions and adsorbents. An extremely high and selective uptake of Fe3+ ions was observed in both cases (~98–99%). The selectivity sequence of studied metal ions by gyrolite can be written as follows: Co2+ > Zn2+/Mn2+/Ni2+ > Fe3+, while with calcined hydrotalcite: Co2+/Ni2+/Mn2+ > Zn2+ > Fe3+. It was determined that, during simultaneous adsorption, the intercalation of heavy metal ions into the structure of gyrolite or calcined hydrotalcite proceeds differently, because the amount of adsorbed Mex+ ions is higher than the amount of leached Ca2+ and Mg2+ ions, resulting in the occurrence of two types of chemical reactions – substitution and addition. It should be noted that almost all heavy metal ions (~99.84%) are chemisorbed by both adsorbents. Moreover, after chemisorption, no other compounds were observed in X-ray powder diffraction patterns of both adsorbents. It was observed that hydrothermally treated and calcined hydrotalcite reconstructs its structure during the chemisorption process, while the structure of gyrolite remains stable.

Characterization and functionalities of Pd/hydrotalcite catalysts

Abstract A series of palladium supported on calcined hydrotalcite (CHT) catalysts with varying palladium (Pd) loadings (1.0–8.0 wt%) were prepared by impregnation method. Their catalytic performance was evaluated for the reductive amination of phenol to aniline that showed a tremendous interest in the chemical industry. The catalysts were characterized by BET surface area, XRD, TEM, XPS, TPR of H2, TPD of CO2 and CO chemisorption. BET surface area decreased continuously with increase in Pd content. XRD results confirmed the changes in the crystalline phases with altering Pd content. TEM results showed the formation of fine particles at lower loadings and agglomerates at higher loadings. TPR profiles revealed that the reducibility increases with increase of Pd loading. CO2 TPD results illustrate the catalysts basicity increases with increase of Pd loading up to 4.0 wt% and decreases at higher loadings. Pd dispersion, metal area and crystallite sizes were determined by CO chemisorption method. Pd dispersion and metal area decreases with increase of Pd content and crystallite sizes. The results demonstrated that the Pd dispersion and basic properties are depending on the Pd loading. The catalytic performance clearly showed that the increase Pd loading the conversion of phenol increased up to 2.0 wt% and level off beyond the loading. The catalytic properties are well correlated with the active Pd sites determined by CO chemisorption, dispersion and basicity.

Desalination Behavior of Calcined Hydrotalcite From Seawater for Preparation of Agricultural Cultivation Solution Using Natural Zeolite

The desalination behavior of calcined hydrotalcite (CHT) from seawater used to treat seawater that was subsequently subjected to zeolite treatment prior to application of irrigation water was investigated. The results revealed that CHT removed Cl–, SO42–, Mg2+ and Ca2+ from seawater, but that Na+ and K+ were almost unchanged, and that CHT treatment made the pH of the solution alkaline. As the solution temperature increased, the solution pH increased, the rate of Mg2+, Ca2+, Cl– and SO42– removal improved, and greater Cl– removal was observed. Following CHT treatment, the obtained solution (CHT-solution) had a high Na+ content and high pH (approximately 12), while treatment of CHT-solution with natural zeolite neutralized the pH of the CHT-solution and reduced the Na+ content. Although germination of radish sprouts did not observed using seawater and CHT-solution, the growth of radish sprouts could be observed using the final solution after natural zeolite treatment of CHT-solution.

Adsorption of 99TcO4 − onto hydrotalcite and calcined hydrotalcite under basic conditions: influence of humic acids and anions

The remediation of technetium-99 (99Tc) at contaminated sites remains a major challenge, as Tc high solubility and anionic nature under oxic conditions lead to high contaminant mobility. Hydrotalcite, a form of anionic clay, can strongly retain anions, especially upon mineral calcination. However, naturally occurring humic acids can also sorb onto hydrotalcite, therefore competing with TcO4− for sorption sites. This work explores the ability of hydrotalcite to retain TcO4− in presence of humic substances to evaluate the efficacy of hydrotalcite for Tc remediation in natural environment. Results show that calcined hydrotalcite can immobilize TcO4−, while the presence of 23 ppm humic acids has little influence on TcO4− uptake. However, additional monatomic and polyatomic anions in solution can compete with TcO4− for sorption sites on hydrotalcite.

Effect of HNO<sub>3</sub> and H<sub>3</sub>PO<sub>4</sub> on Ion Exchange of Natural Zeolite for Making Agricultural Cultivation Solution from Seawater

Effects of HNO3 and H3PO4 on ion exchange of natural zeolite in a new-simple process, which is a twostep process using calcined hydrotalcite and natural zeolite, for making agricultural cultivation solution were examined. The anion-reduced solution obtained by the treatment of seawater with calcined hydrotalcite (CHT-solution) was neutralized with phosphoric (CHT-solution-H3PO4) or nitric acids (CHT-solutionHNO3), and each four solutions (seawater, CHT-solution, CHT-solution-H3PO4 and CHT-solution-HNO3) was treated with natural zeolite to compare the ion exchange behaviors among these solutions. The pH of the all solutions can be neutralized to 5.5 by zeolite treatment, and the Na+ content can be removed from the all solution. The tendencies of Na+ removal in all solutions are almost same, and percentages of Na+ removal from all solutions are above 95% over 8 times zeolite treatment. The amounts of supplies for K+, Mg2+ and Ca2+ to the CHT-solution-HNO3 is higher than those of other solutions up to 6 times treatment. While almost PO43- was removed, NO3- was remained in the solution, over 6 times treatment with natural zeolite. Therefore, NO3- is possible to be supplied to the solution as nutrient in the two-step process, but PO43- isn't possible.

Aqueous-phase catalytic hydrogenation of furfural to cyclopentanol over Cu-Mg-Al hydrotalcites derived catalysts: Model reaction for upgrading of bio-oil

A series of Cu-Mg-Al hydrotalcites derived oxides with a (Cu+Mg)/Al mole ratio of 3 and varied Cu/Mg mole ratio (from 0.07 to 0.30) were prepared by co-precipitation and calcination methods, then they were introduced to the hydrogenation of furfural in aqueous-phase. Effects of Cu/Mg mole ratio, reaction temperature, initial hydrogen pressure, reaction time and catalyst amount on the conversion rate of furfural as well as the selectivity toward desired product cyclopentanol were systematically investigated. The conversion of furfural over calcined hydrotalcite catalyst with a Cu/Mg mole ratio of 0.2 was up to 98.5% when the reaction was carried out under 140 °C and the initial hydrogen pressure of 4 MPa for 10 h, while the selectivity toward cyclopentanol was up to 94.8%. The catalysts were characterized by XRD and SEM. XRD diffraction of all the samples showed characteristic pattern of hydrotalcite with varied peak intensity as a result of different Cu content. The catalytic activity was improved gradually with the increase of Cu component in the hydrotalcite.

Photocatalytic hydrogen evolution over the hetero-junction CoAl2O4/ZnO

The photoevolution of hydrogen is demonstrated on the new hetero-junction CoAl2O4/ZnO. The nano sized spinel obtained from hydrotalcite calcination exhibits a high specific surface area (130 m2 g−1) and good photocatalytic activity. The optical transition of the spinel CoAl2O4 (1.56 eV), directly allowed, is due to Co2+: d–d transition. The capacitance measurements indicate a negative slope, characteristic of p type conduction with a flat band potential of −0.11 V SCE. The photoactivity is thermodynamically predicted from the energy band diagram. The potential of the conduction band (−1.51 V SCE) is more negative than the hydrogen level, leading to spontaneous hydrogen liberation. The spinel is activated by visible light and the electrons are transferred to water via ZnO. A reducing agent is required to prevent the photocorrosion, SO3 2− being particularly favorable and CoAl2O4 approaches 100 % stability. The hetero-junction consists of a mixture of powders (x%CoAl2O4/125 mg ZnO) exhibits self-sensitization for the hydrogen production in basic medium (pH~12.5) with an evolution rate of 2.04 × 10−2 cm3 h−1 (g catalyst)−1 under optimal conditions.

Adsorption of Chloride Anion by Calcined Mg-Al-Fe Layered Double Hydroxides in Wastewater

Mg-Al-Fe layered double hydroxides (LDHs) were prepared by coprecipitation method and calcined hydrotalcite (CLDH) was applied to remove chloride anion from wastewater. The influences of calcination temperature, adsorption temperature, adsorption dosage, pH on the removal of chloride have been investigated. The optimum temperature and range of pH were obtained in the experiments and the adsorption capacity reached the highest when the temperature was 30 °C and the pH was 5~11. The residual chloride anion was found to be 2 mg/L with an initial concentration of 100 mg/L. The maximum adsorption capacity was obtained at the LDH calcination temperature of 500 °C. Characterizations of the LDHs were performed using XRD and SEM.

Boron sorption from aqueous solution by hydrotalcite and its preliminary application in geothermal water deboronation

Hydrotalcite and its calcination product were used to treat pure water spiked with various concentrations of boron and geothermal water containing boron as a major undesirable element. The kinetics process of boron sorption by uncalcined hydrotalcite is controlled by the diffusion of boron from bulk solution to sorbent-solution boundary film and its exchange with interlayer chloride of hydrotalcite, whereas the removal rate of boron by calcined hydrotalcite rests with the restoration process of its layered structure. The results of isotherm sorption experiments reveal that calcined hydrotalcite generally has much stronger ability to lower solution boron concentration than uncalcined hydrotalcite. The combination of adsorption of boron on the residue of MgO-Al2O3 solid solution and intercalation of boron into the reconstructed hydrotalcite structure due to "structural memory effect" is the basic mechanism based on which the greater boron removal by calcined hydrotalcite was achieved. As 15 geothermal water samples were used to test the deboronation ability of calcined hydrotalcite at 65 °C, much lower boron removal efficiencies were observed. The competitive sorption of the other anions in geothermal water, such as HCO3-, SO4(2-), and F-, is the reason why calcined hydrotalcite could not remove boron from geothermal water as effectively as from pure boron solution. However, boron removal percents ranging from 89.3 to 99.0% could be obtained if 50 times of sorbent were added to the geothermal water samples. Calcined hydrotalcite is a good candidate for deboronation of geothermal water.