Al Hydrotalcite Research Articles

Impact of the memory effect on the catalytic activity of Li–Al hydrotalcite-like compounds for the cyanoethylation reaction

Abstract The target of this work is to investigate structural and textural modifications of Li–Al hydrotalcite-like compounds by memory effect and their impact on the catalytic activity of these solids for the cyanoethylation reaction. The samples have been characterized by XRD, FT-IR, TG–DTG, surface area and porous structure. The catalytic test results showed that the reconstruction of the hydrotalcite leads to a decrease of the catalytic activity compared to the parent hydrotalcite. This fact may be related either to the smaller specific surface area of the reconstructed form or to the leaching of Li+ during reconstruction. It has been also noticed that the calcination of Li–Al hydrotalcite leads to the formation of a α-LiAlO2 stable phase.

Surface coatings for improving the corrosion resistance and cell adhesion of AZ91D magnesium alloy through environmentally clean methods

Two different coatings, Mg–Al hydrotalcite and aragonite (CaCO 3), were produced on die-cast AZ91D Mg alloy (Mg–9wt.%Al–1wt.%Zn) through environmentally clean methods. The corrosion resistance and human mesenchymal stem cell adhesion properties of the coatings on AZ91D were investigated. Results showed that through environmentally clean methods, both Mg–Al hydrotalcite and aragonite CaCO 3 surface coatings could be produced on AZ91D surfaces. These coatings increased the corrosion potential and polarization resistance and decreased the corrosion rate of AZ91D in simulated body fluid. Both surface coatings also improved stem cell spreading and interaction in culture. Further long-term animal testing is suggested before these surface coatings can be recommended for use in clinical applications.

An eco-friendly N-sulfonylation of amines using stable and reusable Zn–Al–hydrotalcite solid base catalyst under ultrasound irradiation

Synthetic nanosized Zn–Al–hydrotalcite (Zn–Al–HT) with 20 nm crystallite size and 61 m 2/g BET-surface area is found to be a mild and efficient catalyst for N-sulfonylation of amines in quantitative yields under ultrasound irradiation. Exclusive synthesis of sulfonamides, using Zn–Al–HT, under ultrasound irradiation, was realized by compatible basic sites of catalyst used. The products were isolated after simple work-up in high yields and purity.

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O2

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O2

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O2

Abstract Potassium-promoted Mg–Al hydrotalcite mixed oxides were studied for soot combustion with O2. The significant activity was elucidated by an oxygen spillover mechanism. First, the surface-activated oxygen on K sites might spill over to the free carbon sites on soot to form a carbon–oxygen complex, ketene group, which was identified as the reaction intermediate. Then the ketene group combined with another active oxygen species to give out CO2. Two kinds of K species, Mg(Al)–O–K (tightly bound to Mg or Al) and free (isolated) K, were determined to be catalytically active sites by kinetic investigations. They could increase the reactivity and amount of surface active oxygen responsible for formation of the ketene group. The stability of K was greatly improved through the interaction with Al, which is a contribution to soot combustion of Al addition into MgO to form a K-promoted composite oxide via the hydrotalcite route.

Biodiesel from palm oil via loading KF/Ca–Al hydrotalcite catalyst

Abstract The solid base catalyst KF/Ca–Al hydrotalcite was obtained from Ca–Al layered double hydroxides and successfully used in the transesterification of methanol with palm oil to produce biodiesel. With the load of KF, the activity of Ca–Al mixed-oxides had been improved much. For the mass ratio 80 wt.%(KF·6H 2 O to Ca–Al mixed-oxides) catalyst, under the optimal condition: 338 K, catalyst amount 5%(wt./wt. oil) and methanol/oil molar ratio 12:1, after 5 h reaction, the fatty acid methyl esters yield could reach 97.98%; for the mass ratio 100 wt.%(KF·6H 2 O to Ca–Al mixed-oxides) ones, under the same reaction condition, only needed 3 h to get the FAME yield of 99.74%, and even only reacted 1 h, the FAME yield could obtain 97.14%.

Use and observation of the hydrotalcite “memory effect” for VOC oxidation

Cobalt supported on calcined hydrotalcite catalysts were prepared using the memory effect of Mg–Al hydrotalcite. Mg–Al was calcined at different temperatures from 500 to 900 °C and dipped in a Co nitrate aqueous solution for surface hydrotalcite regeneration. The calcination at 500 °C of the sample Co/Mg–Al(700) leads to an interesting Co mixed oxide supported on calcined hydrotalcite with high specific area and highly active and selective for toluene oxidation. The surface Co hydrotalcite regeneration was observed especially by Infrared Spectroscopy and Scanning Electron Microscopy combined with Energy Dispersive detection of emitted X-ray photons. The reconstruction of the layered structure influences positively the iteraction between cobalt species and the support.

Synthesis of Propylene Glycol Monomethyl Ether Over Mg/Al Hydrotalcite Catalyst

Mg–Al hydrotalcites with different Mg/Al molar ratios were prepared and characterized by XRD, FT-IR, SEM and BET analyses. The calcined hydrotalcite with Mg/Al molar ratio of 4.0 (LDO Mg/Al 4.0) exhibited the highest catalytic activity in the synthesis of propylene glycol methyl ether (PM). The catalytic activity relating to the amount of the basic sites and crystallinity depended on the Mg/Al molar ratio. The optimal equilibrium of acid–base property and high crystallinity made the LDO Mg/Al 4.0 an excellent catalyst in the reaction. Etherification of propylene oxide (PO) with methanol over the LDO Mg/Al 4.0 was researched. The optimized reaction conditions were as follows: 140 °C, catalyst amount 0.9 wt%, methanol/PO molar ratio 4.0 and 6 h. The PO conversion and PM selectivity were 93.2 and 97.4%, respectively. Above all, almost all the PM was 1-methoxy-2-propanol, for no 2-methoxy-1-propanol was detected by GC analysis in the reaction products, and the catalyst could be reused for five times. The particles of the LDH Mg/Al 4.0 showed well-developed hexagonal plates with narrow size distribution (2–4 μm) and were in line with the typical morphology for hydrotalcite-like materials. The optimal equilibrium of acid-base property and high crystallinity made the LDO Mg/Al 4.0 an excellent catalyst in the synthesis of propylene glycol methyl ether (PM) from methanol and propylene oxide (PO).

ChemInform Abstract: Photocatalytic Aerobic Epoxidation of Alkenes under Visible Light Irradiation by an Iron(III) Porphyrin with Mg—Al Hydrotalcite Anionic Clay.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O 2

Potassium-promoted Mg–Al hydrotalcite mixed oxides were studied for soot combustion with O 2. The significant activity was elucidated by an oxygen spillover mechanism. First, the surface-activated oxygen on K sites might spill over to the free carbon sites on soot to form a carbon–oxygen complex, ketene group, which was identified as the reaction intermediate. Then the ketene group combined with another active oxygen species to give out CO 2. Two kinds of K species, Mg(Al)–O–K (tightly bound to Mg or Al) and free (isolated) K, were determined to be catalytically active sites by kinetic investigations. They could increase the reactivity and amount of surface active oxygen responsible for formation of the ketene group. The stability of K was greatly improved through the interaction with Al, which is a contribution to soot combustion of Al addition into MgO to form a K-promoted composite oxide via the hydrotalcite route.

Support and Size Effects of Activated Hydrotalcites for Precombustion CO2Capture

A series of Mg−Al hydrotalcites (HTs) with lateral platelet sizes ranging from 40 nm to 2 μm were prepared hydrothermally. Small HT platelets (∼20 nm) were obtained by deposition onto a carbon nanofiber (CNF) support. The CO2 sorption capacity at 523 K for the activated unsupported HT was low (∼0.1 mmol·g−1), regardless of the platelet size of the HT precursor. In addition, no relation was found between the CO2 sorption properties of activated HTs and their specific surface area. The sorption capacity of the activated CNF-supported HTs was increased, depending on the HT loading, by an order of magnitude (1.3−2.5 mmol·gHT−1) compared to that of the activated unsupported HT. We propose that the CO2 sorption capacities of HTs are determined by the amounts of low-coordination oxygen sites in the Mg(Al)Ox nanoparticles, which is highest on supported HTs.

Syngas production from CO 2 reforming of methane using Ce-doped Ni-catalysts obtained from hydrotalcites by reconstruction method

Ce-doped Ni, Mg and Al hydrotalcites were synthesized through the reconstruction method in the presence of the [Ce(EDTA)] − complex. The hydrotalcites and the mixed oxides derived after their thermal decomposition at 500 °C (16 h) were characterized by XRD, TGA-DTA, ICPS, IR, Raman, SEM-EDX, TEM, TPR-H 2, TPD-CO 2, XPS and N 2 sorptometry. The reconstruction of the mixed oxide is not total in [Ce(EDTA)] − solutions with Ce between 1 and 10%wt. The hydrotalcite is reconstructed as hydroxyl-type phase; the reconstruction takes place in the external edges of the oxide granules. The complex is deposited, with high distribution, on the external surface of the reconstructed layered structure as species of Ce 4+ and after the calcination generates surface CeO 2-doped periclase oxides. Solids were used in the production of syngas through CO 2 reforming of methane (CH 4:CO 2:Ar 5/5/40) using a total fixed flow of 50 mL min −1 and WHSV = 30 L g −1 h −1 between 500 and 800 °C with prior reduction. The increase in the Ce load had a promoter effect in catalytic conversions. H 2/CO ratios between 0.8 and 1.2 were obtained. Ce had a positive effect in the elimination of coke, since a nominal optimal value of 3%wt. was obtained.

Biodiesel Synthesis Catalyzed by the KF/Ca−Mg−Al Hydrotalcite Base Catalyst

A series of solid base catalysts, KF/Ca−Mg−Al hydrotalcite (KF mass ratio of 100%) with different cation ratios, were prepared and studied in this research. Effects of the cation ratio of the Ca−Mg−Al hydrotalcite and the methanol/oil molar ratios on the fatty acid methanol ester (FAME) yield of the transesterification of palm oil with methanol were investigated. The results of the transesterification reactions showed that all of these kinds of catalysts had a very high activity for the biodiesel yields, obtaining 90% or more with 10 min of reaction under the conditions of 338 K, 12:1 methanol/oil molar ratio, and 5% (wt/wt oil) catalyst amount. In addition, the FAME yield could reach 99.6% in 10 min catalyzed by the optimal catalyst KF/Ca−Mg−Al hydrotalcite (2.2:0.8:1 Ca/Mg/Al; KF mass ratio of 100%), under the same reaction conditions as above.

Fluorine-modified Mg–Al mixed oxides: A solid base with variable basic sites and tunable basicity

The fluorine-modified Mg–Al mixed oxides were synthesized by thermal decomposition of the fluorine-containing Mg–Al hydrotalcites, and their physicochemical properties were characterized by ICP, TGA, XRD, FTIR, CO 2-TPD and N 2 adsorption/desorption techniques. It was found that weak basic sites were gradually transformed into moderate and strong basic sites during thermal decomposition, and thus weak basic sites (OH − groups), moderate basic sites (Mg–O, Mg–F and Al–O pairs) and strong basic sites (coordinatively unsaturated F − and O 2− ions) were all produced in the as-prepared samples. Furthermore, the basicity of moderate basic sites could be controlled by the change of fluorine content, which caused the change in the amounts of Mg–F pairs. In the synthesis of propylene glycol methyl ether from methanol and propylene oxide, the base-catalytic performance of the obtained samples was shown to be closely associated with their moderate basic sites.

Perturbing the properties of layered double hydroxides by continuous coprecipitation with short residence time

A previous work (S. Abello and J. Perez-Ramirez, Adv. Mater., 2006, 18, 2436) revealed an unanticipated variation in the textural properties of Mg–Al hydrotalcite, prepared by continuous coprecipitation with short residence time, τ = 1 s which, at that time, was not fully understood. Herein, we report the generalisation of such variation in physical properties to layered double hydroxides (LDHs) of different composition (Ni–Al, Mg–Al, and Mg–Fe hydrotalcite-like compounds). In particular stable colloidal suspensions and, on drying, impervious LDH particles have been prepared using the in-line dispersion precipitation (ILDP) method with τ = 1 s. This is thought to be a consequence of variation in the mechanism of inter-crystallite interactions with decreasing crystallite size. The resulting materials are characterised using multiple techniques and are compared to analogous materials attained at longer residence times (τ = 12 s). We show that despite the apparent compositional similarity and structural isomorphicity of the precipitates, their textural and morphological properties and their thermal stability differ strongly. Thermal activation of the LDHs, however, resulted in the development of comparable textural properties in the corresponding oxides, independent of the residence time.

Synthesis of glycerol carbonate from glycerol and dialkyl carbonates using hydrotalcite as a reusable heterogeneous base catalyst

An uncalcined Mg–Al hydrotalcite catalyst involving hydromagnesite with a high surface area acted as a highly active base catalyst for glycerol carbonate synthesis from glycerol and dialkyl carbonates under moderate reaction conditions.

Epoxidation of Cyclohexene With H2O2 and Acetonitrile Catalyzed by Mg–Al Hydrotalcite and Cobalt Modified Hydrotalcites

The paper presents a comparison between the results obtained for cyclohexene epoxidation in the presence of base catalysts: Mg0/75Al0.25-hydrotalcite (HT), the corresponding mixed oxide (CHT), the reconstructed hydrotalcite (RHT), a hydrotalcite containing cobalt in the brucite-type layer ((Co-Mg0.75)Al0.25)) and one containing cobalt complex-species supported on HT carrier (Co-complex/HT). The selective conversion of cyclohexene to the corresponding epoxide is closely related to the base strength of the catalysts.

Partial hydrogenation of propyne over copper-based catalysts and comparison with nickel-based analogues

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al 2O 3 and Cu/SiO 2). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N 2 adsorption, H 2-TPR, XPS, and N 2O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H 2:C 3H 4 ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C 3H 6 selectivity up to 80% at full C 3H 4 conversion and stable performance in long-run tests at T ⩾ 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.

ChemInform Abstract: Cu—Al Hydrotalcite: An Efficient and Reusable Ligand‐Free Catalyst for the Coupling of Aryl Chlorides with Aliphatic, Aromatic, and N(H)‐Heterocyclic Amines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Biodiesel production from soybean oil and methanol using hydrotalcites as catalyst

Esters of fatty acids, derived from vegetable oils or animal fats, and known as biodiesel, are a promising alternative diesel fuel regarding the limited resources of fossil fuels and the environmental concerns. In this work, methanolysis of soybean oil was investigated using Mg–Al hydrotalcites as heterogeneous catalyst, evaluating the effect of Mg/Al ratio on the basicity and catalytic activity for biodiesel production. The catalysts were prepared with Al/(Mg + Al) molar ratios of 0.20, 0.25 and 0.33, and characterized by X-ray diffraction (XRD), textural analysis (BET method) and temperature-programmed desorption of CO 2 (CO 2-TPD). When the reaction was carried out at 230 °C with a methanol:soybean oil molar ratio of 13:1, a reaction time of 1 h and a catalyst loading of 5 wt.%, the oil conversion was 90% for the sample with Al/(Mg + Al) ratio of 0.33. This sample was the only one to show basic sites of medium strength. We also investigated the reuse of this catalyst, the effect of calcination temperature and made a comparison between refined and acidic oil.