Hydrotalcite Type Research Articles

Preparation of Ni/Zn/Al Type Hydrotalcite Non-Noble Metal Catalysts and Application in the Synthesis of N-Substituted Indole Derivatives Via Alcoholamine Method

Preparation of Ni/Zn/Al Type Hydrotalcite Non-Noble Metal Catalysts and Application in the Synthesis of <i>N</i>-Substituted Indole Derivatives Via Alcoholamine Method

Operando DRIFT-MS study of oxidative steam reforming of ethanol (OSRE) on Ni-Co mixed oxides under non-equilibrium conditions

The oxidative steam reforming of ethanol (OSRE) reaction to produce hydrogen under non-equilibrium conditions was successfully achieved using mixed oxides (MO) of Ni and Co. The catalysts were synthesized with hydrotalcite (HT) type as a precursor by simultaneous coprecipitation assisted by microwaves. The solids were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The OSRE reaction was also implemented under operando conditions by diffuse reflectance infrared spectroscopy with Fourier transform coupled to mass spectrometry (DRIFT-MS) to study the path of molecules on the surface of these solids. The results confirmed the presence of the reduced phases of Ni and Co for all the systems and revealed that the OII/OI ratio increased for the samples containing Co, indicating that the greatest number of oxygen vacancies is present in these solids, which explains their high capacity to oxidize CO to CO2 in the catalytic test. It was possible to show that the NiCo bimetallic phase presents better catalytic performance for the production of hydrogen by effectively breaking the C-C bond and oxidizing the CHx species on the surface, which is reflected in the complete conversion of ethanol and a high selectivity to CO2 and H2 over other products such as CO, CH4, and acetaldehyde.

Efficacy of hydrotalcite Mg-Al membrane based on ghassoul and olive stone in the removal of polyphenols from olive mill wastewater

The current study aims to fabricate a Hydrotalcite Mg-Al membrane (HT-Gh-OS3) based on Ghassoul and olive stone composite as a microfilter to remove of polyphenols from olive mill wastewater. Also, the results and efficiency of HT-Gh-OS3 membrane was compared with HT-Gh-AC3 membrane used in our previous study where Gh=Ghassoul, OS=olive stone, AC=activated carbon, number 3 relating to the percentage of AC or OS, and HT=Hydrotalcite type MgAlCO3. The hydrotalcite was deposited on the ceramic supports ‘Ghassoul’ and characterized by Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning electron microscopy coupled with Energy-dispersive X-ray spectroscopy (SEM/EDX). The diluted OMW with water 40 %, 60 %, and 80 % contains 60 mg/L, 40 mg/L, and 30 mg/L concentrations of polyphenols respectively, which used in the filtration process by the new membrane. The results showed that the olive stone membrane has good porosity and reduced polyphenols by 74 % compared to 61 % by commercial activated carbon membrane. The macroporous structure of olive stones enhances the porosity of the support during sintering, resulting in a higher membrane porosity and better polyphenol reduction. The Hydrotalcite membrane based on the natural material (Ghassoul clay and olive stone) give a good retention of polyphenols of OMWW than the membrane with activated carbon.

Synthesis and Characterization of the Carbonate Hydrotalcites (NiAl-HT, CoAl-HT, and NiCoAl-HT), and Its Application for Removal of the Anionic Azo Dye Titan Yellow from Aqueous Solution

This work focuses on studying the removal of Titan Yellow (TY) dye, which is a water pollutant using three matrices of layered double hydroxide (LDHs; M+2Al-HT), with M+2 = Ni, Co, or NiCo were synthesized using the co-precipitation technique in a solution with a constant pH. The X-ray diffraction (XRD) pattern of the formed solids shows that the synthesized phase is the LDH type with the average interlamellar distance (dspacing ≈ 7.595 Å). The Fourier-transform infrared spectroscopy (FT-IR) spectra were compared, before and after adsorption, confirming the displacement of the carbonated interlayers and confirmed the presence of the S=O bond in the dye under study. Thermogravimetric-differential thermal analysis (TG/DTG) shows temperatures of decarbonation of the LDHs. The BET specific surface areas of NiAl-HT, NiCoAl-HT, and CoAl-HT were found equal to 156.819 m2∙g−1, 142.72 m2∙g−1, and 56.98 m2∙g−1, respectively, and the SEM-EDX micrographs results confirmed the creation of the hydrotalcite type material. The UV–visible study of the adsorption of TY is performed by varying different parameters such as pH of the solution, mass, contact time, and temperature. The obtained isotherms from this kinetic study show that the adsorption of TY dye is more efficient in NiAl-HT. It can, therefore, be stated that the adsorption process of TY is endothermic and spontaneous. The results of this study could be extended to other anionic azo dyes having similar chemical structures.

Cerium-based conversion films developed on LiAl-layered double hydroxide coatings for corrosion protection of AA7075 aluminum alloys

The paper presents several experimental results regarding the influence of various procedures applied to incorporate Ce species in hydrotalcite–type chemical conver­sion coatings on the overall corrosion performance for AA 7075 aluminum alloy as a metallic substrate. Two routes were envisaged: (i) chemical incorporation of Ce by immersion in cerium nitrate solutions and (ii) electrochemical deposition of hydro­phobic Ce - based layer involving ethanolic solutions of stearic acid and cerium nitrate. The chemical route involving immersion in cerium nitrate solutions led to the incorpo­ration of 2.46 – 6.84 wt.% Ce in the composition of the porous conversion layer. The electrochemical process facilitated the formation of a hydrophobic cerium stearate layer on porous hydrotalcite conversion coating showing water contact angles of about 132o and a higher Ce content incorporated of 6.55 – 9.73 wt.%. The corrosion performance of the Ce-based conversion coatings is also discussed.

Effect of Fe and La on the Performance of NiMgAl HT-Derived Catalysts in the Methanation of CO2 and Biogas

Bulk Ni-based catalysts derived from hydrotalcite-type (HT) compounds show enhanced stability in the hydrogenation of CO2 into CH4, in comparison to their supported counterparts. The composition of the parent hydrotalcite determines the Ni loading and particle size, as well as the basicity of the catalysts. In this work, a comparison between the effect of Fe and La on the performance of NiMgAl HT compounds (Ni/Mg/Al = 25/50/25 atomic ratio) calcined at 600 °C is investigated. After a reduction pretreatment at 750 °C, both promoters enhance the activity in the low-temperature range; however, the La-containing catalyst reaches a better CH4 productivity rate at high oven temperature (i.e., 200 L gNi–1 h–1 at 325 °C). Although the formation of the NiFe alloy improves the activity, lanthanum keeps smaller Ni0 particles and provides a higher basicity to the mixed oxide than Fe. The activity of the NiMgLaAl catalyst can be further tailored by increasing the Ni loading from 25.6 wt % (Ni25Mg50La5Al20) to 44.6 wt % (Ni50Mg25La5Al20). Lastly, the feasibility of HT-derived catalysts in the direct methanation of clean biogas is proved.

Study of the Catalytic Activity of the Compounds Hydrotalcite Type Treated by Microwave in the Self-Condensation of Acetone.

The self-condensation reaction of acetone, producing diacetone alcohol (DAA), is of great industrial importance. It was used to study the catalytic activity of Mg-Al catalysts synthesized by the coprecipitation method. For this purpose, we synthesized Mg-Al based hydrotalcite with a molar ratio of 3, obtained either after conventional heating or after microwave irradiation with of 100 W for three minutes. Structural and chemical properties of the obtained catalysts were characterized, using different techniques: X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscope (SEM), equipped with energy dispersive X-ray (EDX), and specific surface area of the catalysts were determined by the methylene blue (MB) adsorption method. Also, these catalysts were tested in the self-condensation reaction of acetone at 273 K in the liquid phase without solvent, a reaction which requires very high catalytic activity. The microwave treatment improves the catalyst activity, and the conversion of acetone to diacetone alcohol increases from 13.2 to 18.3% after 8 h of reaction. Moreover, the microwave-treated hydrotalcite catalyst, calcined at 723 K and rehydrated under a flow of N2, is the most active and gives conversion of acetone of 52% under the same reaction conditions.

Water reuse after removing a textile dye methyl orange using a recyclable hydrotalcite material

Hydrotalcite type material based on zinc, aluminum and carbonates was synthesized by coprecipitation method and its derived calcined at 500°C (CHT) was used to remove the textile dye methyl orange (MO). This adsorbent has a great potential for removing pollutants from aqueous solutions without generating sludge. Adsorption was performed in batch experiments. A rapid process of retention confirmed by kinetics reflects a high affinity between CHT material and MO dye. The adsorption isotherms follow the Langmuir model (L type). The results of several techniques suggest the intercalation of the pollutant between the hydrotacite sheets reconstructed from mixed oxides with a gallery of 2.35 nm. The retention capacity reaches 2500 mg/g with a removal rate of 100% for an optimum mass ratio MO/CHT of 0.3. After the recycling studies the material CHT justify its recyclability and confirms its efficiency for eliminating such pollutant.

Surfactant Intercalated Mono‐metallic Cobalt Hydrotalcite: Preparation, Characterization, and its Bi‐functional Electrocatalytic Application

AbstractA series of surfactants are intercalated into mono‐metallic hydrotalcite type α‐Co(OH)2 through ion exchange method to produce organic‐cobalt hydrotalcite (HT‐SDS, HT‐TMA and HT‐SL). The resultant material maintains its inner laminate structure with increased interlayer spacing. FT‐IR spectroscopic studies and powder XRD analysis revealed the successful intercalation of SDS into the interlayers of α‐cobalt hydroxides. TEM and N2 sorption studies further demonstrate the intercalation of organic surfactant in the interlayer spacing of CoHT. XPS studies indicated the presence of surface exposed cobalt in both Co2+ and Co3+ oxidation states. Furthermore, the applicability of these intercalated materials in electrocatalytic applications specifically for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline medium is explored. Among the various investigated materials, sodium dodecyl sulphate (SDS) intercalated material exhibited better performance in terms of higher catalytic current at a lower overpotential value. Moreover, the kinetic parameters associated with electrocatalysis are determined, and the mechanism behind OER and ORR is elucidated. These results clearly demonstrate the potential bi‐functional utility of such layered materials for electrocatalytic applications.

REMOVAL OF REACTIVE RED 120 IN AQUEOUS SOLUTION USING Mg-HYDROTALCITES AS ADSORBENTS SOLIDS: KINETICS AND ISOTHERMS

Reactive red 120 (RR120) is a widely used dye in the textile industry but its release in aqueous wastewater is a serious problem due to its toxicity and low biodegradability. The aim of this work was to evaluate the effect of the trivalent cation of magnesium-based materials type hydrotalcite as adsorbents applied to RR120 dye removal in aqueous solution. The samples were synthesized by continuous coprecipitation and were characterized by surface area measurements, X-ray diffraction and temperature-programmed desorption of CO2. Dye adsorption tests were carried out using different adsorbent dosages and contact time. The kinetic adsorption was studied for the pseudo-first and pseudo-second order models. The equilibrium adsorption data were fitted to the Langmuir, Freundlich and Redlich-Peterson isotherm models. The most suitable adsorption conditions were found at a residence time of 60 min and solid dosage of 2.5 g/Lfor HDL-MgFe, 2 g/L for HDL-MgAl and HC-Mg. The results showed that pseudo-second order model, as well as the Langmuir and Redlich-Peterson models best described the removal process. The Al containing compound presented the best results due to a better interaction between strength and number of basic sites.

Electrodeposition of Rh/Mg/Al hydroxides with different Mg-contents on metallic foams as catalyst precursors

This work investigated the electrodeposition of Rh/Mg/Al mixed hydroxides with different Mg-contents on open-cell foams through the electro-base generation method using nitrate electrolytes. The influence of Mg2+ on both the electrodeposition process and properties of the coating (after electrodeposition, calcination, and catalytic partial oxidation (CPO) of CH4 tests) was studied. The nature of cations being precipitated (Mg2+ or Al3+) influenced significantly the production of OH– through reduction of nitrate and water, which in turn determined the quality of the coating in terms of composition and adhesion. In reference samples, an absence of either Mg2+ (Rh5Al95) or Al3+ (Rh5Mg95) declined the coating quality, namely, more cracks developed due to the prominent reduction of H2O (in case of Rh5Al95) or reduction of Rh3+ to Rh0 occurred (Rh5Mg95 ). On the other hand, the presence of both Mg2+ and Al3+ in Rh/Mg/Al hydrotalcite-type (HT) samples improved significantly the coating loading and its adhesion, even after thermal treatment at 900 °C, as well as the dispersion of Rh in the reduced catalyst. Moreover, increasing the amount of Mg2+ to a given Mg/Al ratio at which a pure Rh/Mg/Al HT precursor was formed (e.g. Rh5Mg70Al25) resulted in significant increment of Rh dispersion compared to those with lower Mg content (i.e. Rh5Mg50Al45). Such modifications on the properties of the coating (loading, adhesion, and Rh dispersion) subsequently influenced the performance in the CPO of CH4. Finally, temperature profiles along the catalytic bed were reported in correlation with CH4 conversion and syngas selectivity.

Monitoring the structural and textural changes of Ni-Zn-Al hydrotalcites under heating

The structural changes of nickel-aluminum and nickel-zinc-aluminum hydrotalcites under heating were studied. The temperature and the activation energy required for hydrotalcites decomposition and NiO formation depend on the kind and on the amount of cations. Upon heating, the cell parameters and the crystal sizes changed, aluminum and zinc delaying crystal sintering and zinc leading to the smallest crystals of nickel oxide. The increase of aluminum and/or zinc content decreases the crystals size of hydrotalcites but zinc decreased the specific surface area. The zinc-containing solids produced oxides at lower temperatures while the zinc-free solids were the most thermally stable, possibly due to the increase of a parameter caused by the larger ionic radius of zinc. All solids were mesoporous with interparticles mesopores, whose shape depends on the composition of the solids and the conditions of collapse of the hydrotalcite type structure.

Tuning the Basic Properties of ZnAl Hydrotalcites Modified with Ce Applied to Transesterification of Soybean Oil

The basicity of ZnAl hydrotalcite type materials was modified through the incorporation of Ce into their structure and used as heterogeneous catalysts in the transesterification of soybean oil. A series of novel ZnAl–Ce(X) catalysts was synthesized by the co-precipitation method varying the loading of Ce (X = Ce/Al molar ratio). The larger ionic radius of Ce3+ (1.01 A) compared with Al3+ (0.53 A) and Zn2+ (0.72 A), hinders the appropriate incorporation of Ce3+ in the brucite-like structure, causing a small segregation of Ce3+ as CeO2. However, the concentration of basic sites (acid–basic Lewis pairs) and specific surface area of the ZnAl–Ce(0.0) sample were enhanced with the incorporation of Ce, improving its catalytic activity. The most appropriate Ce loading was obtained with a Ce/Al molar ratio of 0.03, which was attributed to its large surface area, along with a higher amount of acid–basic Lewis pairs related to the presence of aluminum in pentahedral coordination. Thus, the total amount of basic sites (−OH and M–O−) of ZnAl–Ce(0.03) was triplicated, leading to a FAME yield of 80% with this catalyst, which represents an increase of 11.3% when compared with the ZnAl hydrotalcite without Ce.

Catalytic transfer hydrogenation of furfural to furfuryl alcohol over calcined MgFe hydrotalcites

Catalytic transfer hydrogenation is an alternative catalytic approach for the reduction of carbonyl groups, instead of the use of dihydrogen gas. In this sense, a series of catalysts has been prepared by thermal treatment of layered double hydroxides, hydrotalcite type, of Mg(II) and Fe(III), with different Mg/Fe molar ratios. The resulting mixture of metal oxides was characterized by X-ray diffraction, TEM, N2 adsorption-desorption, CO2-TPD, NH3-TPD and XPS, and then catalysts were tested in the Meenwein-Ponndorf-Verley (MPV) reduction of furfural to obtain furfuryl alcohol. The catalytic results show that the catalyst with a Mg/Fe molar ratio of 3 allows reaching the highest furfural conversion at a lower reaction time, with a FOL yield close to 90% after 6 h of reaction at 443 K. The detailed analysis of these catalysts also revealed that the basicity plays a more predominant role in the MPV reaction than acid sites.

Behavior of a hydrotalcite type material obtained from MgAl alloy for CO2 adsorption

Different research fields have been proposed for the capture and storage of CO2 using various materials, but they do not meet the economic, environmental and availability characteristics. In this work, a hydrotalcite (LDH) porous material was used for CO2 adsorption, which was previously synthesized by an unconventional method. Some physicochemical properties were performed to the LDH and determine its CO2 adsorption capacity under almost environmental conditions. To carry out the adsorption, the material was thermally treated at two temperature values 150 °C and calcined at 350 °C for 4 h; these conditions were more favorable for thermal treatment unlike conventional calcination procedures. High surface area values were obtained with and without thermal treatement. The CO2 adsorption was carried out under conditions of low pressure whose values were 2, 5 and 10 atm. In the same way, temperatures of CO2 adsorption were programmed at 20, 40 and 50 °C, in these conditions the samples were remained in the micro-reactor for 30 min. During the decomposition process, a spinel phase mixed with magnesium oxide was readily produced at a relatively low temperature (350 °C). The thermogravimetric analysis coupled to the masses was used to determine the adsorption capacity in the porous material and to identify CO2. Values between 13 and 30 mg of CO2 per gram of adsorbent were obtained when the material was thermally treated at 150 °C, and 21 to 31 mg/g of LDH when calcined at 350 °C, depending on the pressure and temperature conditions whose adsorption capacity was equivalent to 7.8 and 19.62 wt% on average for both thermal treatments, respectively. The results indicate that this material is a good candidate to be used for the adsorption of such greenhouse gas.

Sulfate removal by Mg–Al layered double hydroxide precipitates: Mechanism, settleability, techno-economic analysis and recycling as demulsifier

Abstract This study investigated sulfate (SO42−) removal by Mg–Al hydrotalcite-type (HT) compound (Mg6Al2SO4(OH)16•mH2O), and analyzed applicable condition of the method from techno-economic perspective. Under optimized condition of pH 8.80, molar ratio of Mg2+ and SO42− (Mg/S ratio) of 6.63 and molar ratio of Al3+ and SO42− (Al/S ratio) of 2.53, HT compound achieved a greatly lower concentration of SO42− (3.76 mmol/L) than conventional gypsum precipitation. The composition and morphological analysis of precipitates showed that HT compound was transformed to Mg(OH)2 at pH > 9.0, and Mg(OH)2, Al(OH)3 and MgAl2(OH)8 at Al/S ratio > 2.5. HT compound had better settleability than Mg(OH)2 and ettringite, and was easier to be flocculated by anionic polyacrylamide to obtain a lower SV30 of 16.4%. Turbiscan showed that HT compound had the highest instability and aggregation property among the three systems. Techno-economic analysis showed that HT compound coupled ettringite route was more economic than Mg(OH)2 coupled ettringite route at Mg/S ratio > 6.08, but was not applicable when concentrations of Mg2+ and SO42− were very low. The precipitated HT compound was recovered as demulsifier and showed more efficient COD removal than conventional demulsifier for chemical cleaning wastewater treatment.

Geopolymer-hydrotalcite composites for CO2 capture

Supporting or shaping a porous powder is important for industrial applications as optimized structure with high mass transfer, low pressure drop and high mechanical and chemical stability can be obtained. A new class of geopolymer-hydrotalcite composites with suitable mechanical and thermal properties were conceived as shaped materials for CO2 adsorption applications at intermediate temperature (200–400 °C). Composite monoliths were produced mixing different commercial hydrotalcite-type (HyT) powders with a metakaolin-based geopolymer matrix with a molar ratio SiO2:Al2O3 = 4.0. The compressive strength at room temperature and 500 °C ranged between 10 and 35 MPa, mainly depending on HyT powder morphology and composite total porosity. The composites were characterized and tested in term of CO2 uptake. After calcination to convert HyT into an amorphous Mg:Al mixed solid oxide able to absorb CO2, the composites were tested in the CO2 adsorption at 200 °C, with cycles of adsorption/desorption performed with intermediate regeneration at 500 °C. CO2 adsorption capacity was in the range 0.375–0.461 mmol g−1 for HyT and between 0.109 and 0.145 mmol g−1 for composites, being 0.052 mmol g−1 the value for the geopolymer matrix. A partial deactivation of the HyT phases was also detected.

Structural Characteristics of Drug Intercalated Hydrotalcites Used in Dental Medicine

Metronidazole active molecules were intercalated in the inner space of MgAl layered double hydroxides by simple coprecipitation method. The new synthesized nanohybrid material and the pristine hydrotalcite were characterized by different techniques such as X-ray diffraction, infrared spectroscopy and UV-vis spectroscopy verifying thus the incorporation of the antibiotic into the lamellar gallery of hydrotalcite type anionic clay. Studies regarding metronidazole controlled release from synthetic nanocomposite showed that the organic-inorganic nanohybrid structure can serve as drug controlled release system for a wide variety of antibiotics and other molecules used in dental medicine in order to maintain good public health dentistry.

Interaction between phosphate ions and Fe-Mg type hydrotalcite for purification of wastewater

In this study, Fe-Mg type hydrotalcite at different molar ratios (Mg/Fe = 3.0 and 5.0, Fe-HT3.0 and Fe-HT5.0) was prepared, and its physicochemical properties were investigated. The adsorption isotherms were measured, and the effects of contact time, temperature, and pH on the adsorption of phosphate ions, and the ad-desorption capability were evaluated. Elemental analysis and binding energy values of the Fe-HT adsorbent surface before and after adsorption of phosphate ions indicated that the adsorption mechanism of phosphate ions was related to the physicochemical properties of adsorbent surface. Adsorption mechanism of phosphate ion relates to ion exchange, electrostatic attraction, and surface inner sphere complex formation in this study. Moreover, the phosphate ions adsorbed onto Fe-HT were easily desorbed using sodium hydroxide solution; thus, five cycles of ad-desorption were carried out. Collectively, these results suggest that Fe-HT is promising for the adsorption and recovery of phosphate ions using sodium hydroxide solution.

Evaluation of sulfate resistance of slag contained concrete under steam curing

This paper mainly investigated the sulfate resistance of the slag incorporated concrete under steam curing. Concrete samples with different replacement ratios (0%, 20%, 50% and 70%) of slag under steam curing were exposed to 5% Na2SO4 solution for up to 540 days. Mass changes, open porosity and sulfate-ion contents of concrete were determined separately. Moreover, XRD, TGA, SEM and MIP were performed on the cement paste samples to investigate the landscape of their microstructures. The results showed that the variation of mass change lagged behind than that of open porosity. Steam curing increased the sulfate penetration and deterioration of the slag concrete. Interestingly, incorporation of 50% slag improved the sulfate resistance of standard-cured concrete and incorporation of 70% slag improved the sulfate resistance of steam-cured concrete. This was because a hydrotalcite type phase in the slag paste hindered the ettringite formation. However, the steam-cured concrete prepared with 20% and 50% slag experienced much worse deterioration, which was mainly due to the combined formation of ettringite and gypsum.