Calcined Hydrotalcite Research Articles

Palm oil biodiesel synthesized with potassium loaded calcined hydrotalcite and effect of biodiesel blend on elastomer properties

Biodiesel was prepared from palm oil by transesterification with methanol in the presence of 1.5%K loaded–calcined Mg-Al hydrotalcite. Fatty acid methyl esters content of 96.9% and methyl ester yield of 86.6% were achieved using a 30:1 methanol to oil molar ratio at 100 °C for 6 h and 7 wt% catalyst. The biodiesel was characterized and its impact on elastomer properties was evaluated. The compatibility of B10 diesel blend (10% biodiesel) with six types of elastomers commonly found in fuel systems (NBR, HNBR, NBR/PVC, acrylic rubber, co-polymer FKM, and terpolymer FKM) were investigated. The physical properties of elastomers after immersion in tested fuels (for 22, 670, and 1008 h at 100 °C) were measured according to American Society of Testing and Materials (ASTM). These include swelling (mass change and volume change), hardness, tensile and elongation, as well as the dynamic mechanical property. The results showed that properties of NBR, NBR/PVC and acrylic rubber were affected more than other elastomers. This is due to the absorption and dissolving of biodiesel by rubber in these samples. Co-polymer FKM and terpolymer FKM which are fluoroelastomers show little property change.

Rehydration of Calcined Mg-Al Hydrotalcite in Acidified Chloride-Containing Aqueous Solution

The rehydration of periclase-like Mg-Al mixed oxide obtained by calcination of hydrotalcite- like precursor with a Mg/Al molar ratio of 2 was carried out in KCl-HCl solutions at various pH and constant concentration of Cl-. A buffer equilibrium accompanied by leaching out of Mg2+ cations from the solid was observed during rehydration, when reconstruction of the layered hydrotalcite structure takes place. With increasing HCl concentration in the rehydration solution, the Mg/Al molar ratio in the obtained solid gradually decreased from about 1.5 to 0.3. An anomaly was found, when the increasing concentration of acid resulted in increasing pH of final solution. The XRD measurements showed that the initially formed hydroxide form of hydrotalcite is transformed into randomly interstratified forms of the Mg-Al hydroxide hydrate/Mg-Al chloride hydroxide hydrate, which are accompanied by the release of OH- anions into solution. The crystalline structure of rehydrated product decreased as Mg2+ cations were released into solution, which was accompanied by incorporation of Cl- into the solid.

Ion Exchange Properties of Natural Zeolite in the Preparation of an Agricultural Cultivation Solution from Seawater

The objective of this study was to investigate the ion exchange properties of natural zeolite for preparation of agricultural cultivation solutions from seawater. An anion-depleted solution from seawater was prepared using calcined hydrotalcite, and this was then treated with natural zeolite at 5, 25 and 60 °C. The highly alkaline, anion-depleted solution was neutralized, Na+ concentration reduced and Mg2+ and Ca2+ concentrations were increased by treatment with zeolite. Before the neutralization of pH, the effect of temperature on Na+ behavior was similar to those of pH and K+ due to surface adsorption. After neutralization, the effect of temperature on Na+ became similar to those of Mg2+ and Ca2+ due to ion-exchange.

Thermal Evolution of a MgAl Hydrotalcite‐Like Material Intercalated with Hexaniobate

AbstractA MgAl hydrotalcite‐like material intercalated with hexaniobate has been prepared by the anion exchange method from the corresponding nitrate precursor; the sample and the oxides obtained upon its calcination were characterized by element chemical analysis, powder X‐ray diffraction, thermal analyses (thermogravimetric and differential), nitrogen adsorption‐desorption isotherms at –196 °C, transmission electron microscopy, and FT‐IR and UV/Vis spectroscopy. The results show the formation of a microporous hydrotalcite‐type solid with a gallery height of 7.2 Å where the H3Nb6O195– anions are oriented with their C3 axes perpendicular to the layers. This material preserves its layered structure upon calcination up to 400 °C; calcination above this temperature causes decomposition of the hexaniobate and the layered structure collapses, giving rise to amorphous mesoporous solids (Nb‐Mg‐Al‐O) with a large specific surface area (157 m2 g–1). At 800 °C crystallization of Mg4Nb2O9 takes place. FT‐IR studies on the acid‐basic properties carried out by pyridine and 2‐propanol adsorption, showed that all solids obtained through hydrotalcite calcination present Lewis‐type acid and Brönsted‐type basic sites. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Kinetic and thermodynamic parameters of 99Mo sorption on thermally treated hydrotalcite

Thermally treated hydrotalcite was synthesized and its ability to sorb 99Mo from aqueous solutions was studied under static conditions as a function of initial concentration, amount of sorbent and pH. X-ray diffraction was used to characterize synthesized calcined hydrotalcite. The values of sorption data were fitted to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms. The mean energy of sorption was calculated as 5.24 kJ. mol-1from D-R sorption isotherm. The Lagergren equation has been used for the study of the kinetic process. The rate constants of 99Mo sorption on calcined hydrotalcite were calculated at various temperatures (293-323 K). The thermodynamic constans have been calculated and the standard enthalpy of the system was found to be DH°=11.5±0.3 kJ. mol-1. The values of calculated DG° and DS° were -13.9±2.0 kJ. mol-1and (8.7±0.2). 10-2kJ. K-1. mol-1, respectively. These results show that the sorption process is endothermic, spontaneous in nature and the degree of freedom of ions is increased by sorption.

Application of calcined Mg–Al hydrotalcites for Michael additions: an investigation of catalytic activity and acid–base properties

Mg–Al hydrotalcite catalysts with different Mg/Al molar ratios (0.6, 1.4, 2.2, 3.0) were calcined and tested in liquid-phase Michael additions at room temperature. The catalysts and pure oxides (MgO and Al 2O 3) were characterized by XRD, XPS, N 2 adsorption experiments, 27Al MAS NMR, and TG-DTA. The acid–base properties of the samples were investigated by (a) FTIR spectroscopy after pyridine and CO 2 adsorption and (b) microcalorimetry with CO 2 and benzoic acid. Both acid sites (Lewis) and base sites (Lewis and Brønsted) are present on the surface of calcined hydrotalcites. The calcined hydrotalcites (CHT) catalyzed the Michael additions of CH-acid compounds to methyl vinyl ketone to give high product yields with 100% selectivity; the Al-rich sample exhibited the highest activity.

Purification of chromium(VI) finishing wastewaters using calcined and uncalcined Mg-Al-CO 3-hydrotalcite

The applicability of calcined and uncalcined hydrotalcite for the purification of industrial effluents has been studied using chromium finishing wastewaters. Using a batch method, the influence of the initial concentration of chromium (10–450 mg/l), hydrotalcite (HT) dose (0.5–5 g/l) and time (0.5–72 h) has been evaluated. The process could be described by the Langmuir model and gave a maximum removal of chromium of 16.3 mg Cr(VI)/g on uncalcined HT and 128 mg Cr(VI)/g on calcined hydrotalcite (C-HT). Removal using the calcined product provided an effective system to treat chromium finishing wastewaters with the most stringent discharge limit for such industrial streams being achieved with between two and four consecutive removal cycles on C-HT at a dose of 2 g/l.

Intercalation of Tartrazine Into ZnAl and MgAl Layered Double Hydroxides

The intercalates of Tartrazine Acid Yellow were prepared by heating [Zn0.67Al0.33(OH)2]- (CO3)0.165·0.5H2O or [Mg0.70Al0.30(OH)2](CO3)0.15·0.5H2O with a solution of an acid form of Tartrazine in an open reaction vessel or by stirring the powdered calcined hydrotalcites with a Tartrazine solution at room temperature. The intercalates were characterized by chemical and thermal analysis, X-ray powder diffraction and UV-VIS spectroscopy. The intercalates prepared by stirring the calcined host powders have worse crystallinity than those prepared by ion exchange. A possible arrangement of the Tartrazine anions in the intercalates was suggested on the basis of their chemical compositions and interlayer distances, taking into account van der Waals dimensions of the guest anions and assuming that the structure of the host layers is not changed during the intercalation process.

Calcined Mg–Al, Mg–Cr and Zn–Al hydrotalcite catalysts for tert-butylation of phenol with iso-butanol—a comparative study

Calcined hydrotalcites (CHTs) are studied for the tert-butylation of phenol using iso-butanol in the temperatures ranging from 350 to 500 °C. The major products of this reaction on calcined magnesium–aluminium hydrotalcites (CMA-HTs) are O- tert-butyl phenol ( tert-butyl phenyl ether, OTBP) and 2- tert-butyl phenol ( o- tert-butyl phenol, 2TBP) with O-butenyl phenol (butenyl phenyl ether, OBP) and 2-butenyl phenol ( o-butenyl phenol, 2BP) as useful by-products. With a view to understand the reaction mechanism and the reaction path, tert-butylation of phenol is studied by changing both Mg[M(II)] and Al[M(III)] ions with Zn 2+ and Cr 3+, respectively. Thus, Mg–Al (MA), Mg–Cr (MC) and Zn–Al (ZA) hydrotalcites (with M 2+:M 3+ ratio=2) are prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), differential thermal analysis/thermo gravimetric analysis (DTA/TG), BET-surface area (BET-SA) and acidity–basicity measurements (temperature-programmed desorption (TPD) of NH 3 and CO 2). Mixed oxides obtained from CHTs are found to be more active over their individual oxides for the tert-butylation of phenol. The butylation activities of the three different CHTs are in the order CMA-HT>CZA-HT>CMC-HT. A different product distribution is obtained over calcined Mg–Cr and Zn–Al hydrotalcites for the tert-butylation of phenol showing the influence of acid–base properties on the activity of the catalysts. A probable mechanism based on the experimental observations has been proposed in order to explain the formation of butenyl phenols.

Hydrogen Transfer Reduction of 4-tert-Butylcyclohexanone and Aldol Condensation of Benzaldehyde with Acetophenone on Basic Solids

The liquid-phase reduction of 4-tert-butylcyclohexanone into 4-tert-butylcyclohexanol by reaction with isopropanol at 355 K has been studied on solid bases: mixed oxides obtained by calcination of hydrotalcites, NaBEA zeolites, KF/alumina, and La2O3 characterized by calorimetric FTIR adsorption of CO2 and FTIR pyridine adsorption. The aldol condensation of benzaldehyde and acetophenone at 423 K was investigated in parallel to clarify the mechanism of deactivation. For hydrogen transfer, the addition of amine to the reaction medium had only a small effect, but benzoic acid strongly decreased the rate, suggesting catalysis by basic sites. Hydrotalcite was also active and selective for the hydrogenation of cinnamaldehyde into cinnamylalcohol. The stronger bases such as KF/alumina and La2O3 showed a low activity for hydrogen transfer, due to deactivation by the products of the parallel aldolization of the ketone. The exchange of BEA by Na+ increased the selectivity to cis-alcohol with little effect on activity. NaBEA zeolites retained extraframework Al species of strong Lewis acidity and catalyzed the reduction of cinnamaldehyde into isopropyl-cinnamyl ether, thus suggesting an acidic mechanism in that case.

Synthesis of Pseudoionones by Acid and Base Solid Catalysts

The preparation of pseudoionones by aldol condensation reaction between citral and acetone have been carried out in the presence of acid (HY and beta zeolites), an acid–base (amorphous aluminophosphate) and basic catalysts such as an aluminophosphate oxynitride, MgO and different activated hydrotalcites. The results showed that acid or acid–base catalysts were not successful for performing in one pot the preparation of ionones. MgO and calcined hydrotalcites showed excellent activity and selectivity to pseudoionones, with calcined hydrotalcite more selective than MgO. Moreover, the rate of reaction can be improved by activating the hydrotalcite through rehydration. This activation can be successfully done by simply adding the optimum amount of water to the calcined hydrotalcite before reaction. The inhibiting effect of the concentration citral on the catalytic activity of rehydrated hydrotalcites that has been reported to occur at 273 K can be avoided by working at a reaction temperature of 333 K.

Isomerization of Styrene Epoxide on Basic Solids

The isomerization of styrene oxide has been investigated on mixed oxides obtained by calcination of hydrotalcites, rare earth phosphates and KF supported on alumina. All solids form β-phenylacetaldehyde. Basic catalysts deactivate rapidly or show a lower selectivity, most probably due to the formation of heavy products by aldolisation. ZnAl catalyst shows a selectivity towards β-phenylacetaldehyde >98% with no deactivation after 7 h on stream, in a flow gas phase process at 423 K.

On the stability of mixed M2+/M3+ oxides

The stability of Mg(Al)O formed by calcination of Mg–Al-containing hydrotalcites has been studied under steam-rich conditions (H2O:N2=1:1) at 600–650°C and 1atm. It was found that the MgO structure as well as a high specific surface area are maintained after calcination at temperatures up to 800°C. It has further been observed that the steam stability of Mg(Al)O towards sintering is improved after calcination of hydrotalcite at higher temperatures: calcination at 800°C gave an improved stability of Mg(Al)O compared to calcination at 700°C. Further, the stability towards sintering was influenced by the Mg/Al ratio of the hydrotalcite. Mg(Al)O materials formed from hydrotalcites with a Mg/Al ratio of 5 exhibit better long-term stabilisation characteristics compared to a Mg/Al ratio of 3 after calcination at 800°C. A partial or full substitution of aluminum with gallium in the oxide did not improve the steam stability. Changing the hydrotalcite synthesis procedure from co-precipitation to the alkoxide route did not significantly alter the steam stability after calcination.

Influence of acid–base properties of mixed oxides derived from hydrotalcite-like precursors in the transfer hydrogenation of propiophenone

Reductive dehydration of propiophenone to β-methylstyrene has been carried out over different calcined hydrotalcites viz MgAl, CoAl, NiAl, and CuAl under transfer hydrogenation conditions in the temperature range 498–548 K. The performance of calcined MgAl hydrotalcites is found to be much better than MgO and the physical mixture of MgO and Al 2O 3. It is found that selectivity of β-methylstyrene is improved upon the substitution of Mg 2+ by Ni 2+ or Cu 2+ as a result of the formation of stronger acid sites. The overall conversion of propiophenone is influenced by the number and strength of basic sites whereas the selectivity of alkene is affected by the strength of acidic sites present on the catalyst surface.

Structure activity relationship in Pd/hydrotalcite: effect of calcination of hydrotalcite on palladium dispersion and phenol hydrogenation

Hydrotalcites (HTs) are prepared by low supersaturation and high supersaturation methods containing Mg 2+ and Al 3+ cations in the brucite-like sheets and having interlayer CO 2− 3 anions. Pd/HT with Pd 2+ in the brucite layer was also prepared for comparison. Catalysts containing 1 wt% of Pd are prepared by impregnation method using different Pd precursors. HT and Pd on HT samples are well characterised by XRD and surface area analysis. CO chemisorption is used to estimate the dispersion and metal area of Pd. The supported metal catalysts are evaluated for phenol hydrogenation. Metal dispersion and catalytic activity depend on the calcination temperature of the HT support.

Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds

Catalytic decomposition of nitrous oxide into nitrogen and oxygen has been carried out on `in situ' thermally calcined hydrotalcites of general formula M(II)–M(III)-CHT where M(II)=Mg, Co, Ni, Cu or Zn and M(III)=Al, Fe or Cr having different M(II)/M(III) atomic ratios. The reaction was performed in a recirculatory static reactor at 50 Torr (133.3 Pa) initial pressure of N 2O in the temperature range 423–773 K. Among the catalysts screened, Ni and Co containing catalysts with Al as the trivalent cation showed good activity (even at 423 K) wherein 50% and 100% conversion was achieved at 463 K and 523 K, respectively. Results on effect of composition for Co–Al system indicated that the activity increased with increase in the active metal ion concentration (Co 2+), with closer dependence on the surface concentration (as determined by XPS). The observed activity pattern is explained on the basis of redox property and electronic effects. These materials were further evaluated under flow conditions (at Air Products and Chemicals, USA) simulating the industrial process streams (10% N 2O, 2% H 2O, 2% O 2 and balance N 2 and GHSV=18,500). Among the non-precious metal ions investigated, cobalt-based catalysts offered comparable activity similar to metal-exchanged zeolites for removing N 2O from combustion and Nylon-6,6 processes.

131I− Sorption by Thermally Treated Hydrotalcites

AbstractThe sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131I− sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by γ-spectrometry. Solids were characterized by thermal analysis, X-ray diffraction (XRD), electron microscopy and Brunauer-Emmett-Teller (BET) analysis. For 0.1 M Na I solution, labeled with 131I−, sorption capacity was found to be 0.24 meq g−1 (7.2% of the anion exchange capacity, AEC). But, if the sample was previously calcined at 773 K and the HT structure destroyed, the sorption of I− increased considerably, up to 2.08 meq g−1 (63% of the AEC) and the HT structure was reconstructed. The 131I− sorption at very low concentrations (10−14M) was 0.04 × 10−14 meq of 131I− g−1 in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 × 10−14 meq g−1. Calcination temperature determines the surface area of the resulting mixed oxides, and that property seems to be the most important factor controlling the I− sorption. If the calcination temperature was increased to 873 K, the specific surface area of the oxide mixture increased and I− sorption increased as well, whereas calcination of HT at 973–1073 K resulted in a low surface area and a low I− retention.

Effect of substitution of [formula omitted] on the alkylation of phenol with methanol over magnesium-aluminium calcined hydrotalcite

Hydrotalcite (HT)-like compounds with the general formula, Mg 0.8M(III) 0.2(OH) 2(CO 3) 0.1·yH 2O with M(III)=Al, Fe and Cr ( Mg Al atomic ratio 4) were synthesized by coprecipitation method using a mixture of NaOH Na 2CO 3 as precipitant. The Powder X-ray diffraction (PXRD) of aluminium and iron containing samples (M(III)=Al, Fe) showed single phase corresponding to HT when a mixture of HT and MgCrO 4·7H 2O phase was detected for chromium containing sample (M(III)=Cr). These samples after calcination at 450°C/8 h/air, were used as catalyst for vapour phase alkylation of phenol with methanol. MgAl 4.0-CHT showed nearly 100% phenol conversion around 400°C and the reaction was found to proceed predominantly through the formation of anisole (O-alkylation). Isomorphous substitution of Al 3+ by Fe 3+ or Cr 3+ in the HT framework resulted in a decrease in phenol conversion in the order MgAl 4.0-CHT MgCr.0-CHT MgFe 4.0-CHT and the alkylation reaction was found to proceed exclusively at C-centres (C-alkylation) to give o-cresol as a major product. The catalytic performance for the methylation of phenol has been correlated with acid-base properties of the catalysts as determined by test reactions such as decomposition of 2-methyl-3-butyne-2-ol (MBOH) and cyclohexanol.

Highly active hydrotalcite supported palladium catalyst for selective synthesis of cyclohexanone from phenol

Hydrogenation of phenol was studied over uncalcined and calcined hydrotalcite supported palladium catalysts and compared with the conventional Γ-Al 2O 3 and MgO supported catalysts. Pd on uncalcined hydrotalcite support (Pd/UHT) showed very high conversions (≥ 95%) and high selectivities (≥ 85%) towards cyclohexanone. These catalysts maintained their activity for nearly 4 h and the results are presented.

Selective C-alkylation of phenol with methanol over catalysts derived from copper-aluminium hydrotalcite-like compounds

Copper aluminium hydrotalcites (CuAl-HT) with a Cu/Al atomic ratio of 2, 3 and 4 (CuAl 2.0-HT, CuAl 3.0-HT, CuAl 4.0-HT) were synthesised by the coprecipitation method using a mixture of NaOH/Na 2CO 3 as precipitant. The pure crystalline hydrotalcite (HT) phase was detected by X-ray diffraction when the copper-aluminium hydrotalcite was prepared without ageing (CuAl 3.0-WAHT). Vapour phase alkylation of phenol with methanol was carried out over CuAl-HT calcined at 450°C/8 h in air (CuAl-CHT). The activity and selectivity of these catalysts were compared with those of magnesium-aluminium calcined hydrotalcites (MgAl 4.0-CHT) from our earlier report. MgAl 4.0-CHT showed higher selectivity for 2,6-xylenol whereas CuAl-CHT was selective for o-cresol. Among the CuAl-CHT studied, CuAl 3.0-CHT showed higher phenol conversion at low temperatures (250–350°C). The catalyst derived from pure copper-aluminium hydrotalcite (CuAl 3.0-WACHT) showed lowest phenol conversion compared to other copper based catalysts obtained from a mixture of HT and malachite phases. The selectivity for o-cresol decreased in the order CuAl 3.0-CHT > CuAl 2.0-CHT > CuAl 3.0-WACHT ≈ CuAl 4.0-CHT > MgAl 4.0-CHT at low phenol conversion levels (15–20%). A suitable reaction pathway for the alkylation of phenol with methanol over these catalysts has been proposed after a careful examination of the reaction sequence. The selective C-alkylation to give o-cresol and 2,6-xylenol over CuAl-CHT could be attributed to the higher acidity of these catalysts as evidenced by the higher cyclohexanol dehydration activity.