Acid-activated Montmorillonites Research Articles

Acid activation of montmorillonite and its application for production of hydrogen via steam reforming of dimethyl ether

A series of acid-activated montmorillonites (Acid-MMTs) were prepared via Na-montmorillonite treated with nitric acid solution at different treatment temperature and time. And the Acid-MMTs used as solid acid were physically mixed with commercial Cu/ZnO/Al2O3 to obtain bifunctional catalysts for steam reforming of dimethyl ether (SRD) reaction. The results showed that the structure, texture and acidity of Acid-MMTs were significantly changed compared with Na-MMT, which was dependent on the acid treatment conditions. The structure and acidity of Acid-MMTs obviously affected the SRD performance over bifunctional catalyst. The bifunctional catalyst composed of the Na-MMT activated in 20% nitric acid solution at 80°C for 12 h (Acid-MMT-80/12) and Cu/ZnO/Al2O3 exhibited the best SRD performance, with the dimethyl ether conversion and H2 yield reaching 97% and 94% under the conditions of p=0.1 MPa, t=350°C, GHSV=3000 h−1, respectively, and DME conversion and H2 yield remained basically constant in 10 h, indicating that the catalyst had better stability.

Композитные мезопористые материалы на основе кислотно-активированных монтмориллонитов

Композитные мезопористые материалы на основе кислотно-активированных монтмориллонитов

Acid-activated montmorillonites as heterogeneous catalysts for the esterification of lauric acid acid with methanol

A standard clay mineral was systematically subjected to activation with phosphoric acid under different concentrations and activation times. The materials were evaluated with regard to their structure, presence of functional groups, textural properties and the presence of Brönsted and Lewis acid sites. After characterization, the best catalyst was evaluated in the esterification of lauric acid with methanol. High conversions were observed in short times (between 91.63 and 96.67%) and relatively mild reaction temperatures, revealing the potential of acid-activated clays as esterification catalysts for industrial applications such as biodiesel production. For comparison purposes, some experiments were also carried out with a standard solid acid catalyst (montmorillonite K10) and conversions of 95.03% were obtained in comparison to the best catalyst obtained in the present study (96.67%).

PREPARATION SOME ACID-ACTIVATED MONTMORILLONITES FROM CU CHI CLAY AND USING AS CATALYST IN ONE-POT CONVERSION OF BENZALDEHYDE INTO BENZONITRILE

Montmorillonite is a "green" solid catalyst and support used in many organic reactions. In this paper, we have prepared some acid-activated montmorillonites from Cu Chi clay. Then, we determinated physical-chemical properties such as specific surface area, cation exchange capacity, X-ray diffraction, chemical composition and acidity of these samples. Finally, we chose the best from these montmorillonites and used as catalyst in the one-pot conversion of benzaldehyde into benzonitrile under solvent-free and microwave irradiation.

Controlled nanopore formation and stabilization of gold nanocrystals in acid-activated montmorillonite

Au o-nanoparticles of 0–10 nm were generated in situ by the reduction of [AuCl 4] − impregnated on acid-activated montmorillonites with maximum pore diameters of about 3, 4, 6, and 8 nm. The size of the Au o-nanoparticles depended on the pore diameter of the micro- and mesopores of the support. The montmorillonite was activated with HCl under control conditions for generating different pore sizes. Powder X-ray diffraction (XRD), FTIR, FESEM-EDX, HRTEM, N 2 adsorption, 29Si and 27Al MAS-NMR and UV–visible spectroscopic analyses were carried out to characterize the solid porous materials before and after Au o-nanoparticle loading. N 2 adsorption data revealed specific surface areas (BET) of 327–579 m 2/g, large specific pore volumes of ∼ 0.7 cm 3/g, and pore diameters of 0–10 nm. TEM, FESEM and X-ray mapping images revealed Au o-nanoparticles of 0–10 nm evenly distributed on the support. The Au o-nanocrystal composites exhibited the cubic face-centered (fcc) lattice with a preferential growth direction along the (111) plane.

PREPARATION OF SOME VIETNAMESE MONTMORILLONITES

Montmorillonite is a "green" solid catalyst and support used in many organic reations. In this paper, we describe the method to prepare two acid-activated montmorillonites from Binh Thuan and Lam Dong clays. We still prepared some cation exchanged montmorillonites as Fe3+ Zn 2+ and Al 3+. The Vietnamese montmorillonites and K-10, KSF (two commercial Fluka montmorillonites) were determinated simultanneously on some physicochemical properties such as crystalline structure, chemical composition, cation exchange capacity, adsorption capacity, porisity, surface area and acidity. The results shows that the quality of Vietnamese montmorillonites are equivalent with K-10 and KSF.

Exfoliation Properties of Acid-Activated Montmorillonites and Their Resulting Organoclays

The intercalation process of acid-treated montmorillonite clays by a cationinc surfactant (decyltrimethylammonuium) from a hydroxide solution was affected by the temperature of acid activation. Although the cation exchange capacity of the treated clay at 90 degrees C (0.74 mequiv g(-1)) was lower compared to that treated at room temperature (0.84 mequiv g(-1)), the uptaken amount of the surfactant (1.24 mmol g(-1)) and thus the basal spacing (3.83 nm) were higher. These values depended on the initial loading concentrations. However, when the clay was treated at room temperature, the uptaken amounts of surfactant (0.81 mmol g(-1)) and the basal spacing (2.20 nm) were lower. These values were independent of the initial loading concentration. The higher basal spacing (3.83 nm) was also affected by the type of the exchange medium and the washing solution by a mixture of ethanolic solutions. The intercalation of the surfactants occurred in two different ways, and was related to exfoliation properties of the acid activated clays. The intercalated surfactant exhibited different conformations in the interlayer space and different thermal stability.

Reaction of acid activated montmorillonites with hexadecyl trimethylammonium bromide solution

Acid-activated montmorillonites (AMt) prepared at different acid\\montmorillonite ratios were reacted with hexadecyl trimethylammonium (C16TMA) bromide solution. The acid treated Mt incorporated smaller amounts of the surfactants than the parent Mt, due to the reduction of the cation exchange capacity after acid-treatment. The powder X-ray diffraction patterns exhibited a similar basal spacing of 3.80 nm but with less ordered structure at higher acid\\montmorillonite ratios. A certain degree of conformational heterogeneity was observed by 13C CP\\NMR spectroscopy due to the different local environment of C16TMA + ions in the interlayer space. The in-situ PXRD patterns showed an increase of the basal spacing of organo acid-activated montmorillonites when heated at intermediate temperatures (100–200 °C), while the basal spacing was almost constant in this range of temperature for the organomontmorillonite. Generally, the stability of the surfactant decreased when intercalated into the montmorillonites compared to the pure C16TMABr. This fact implies that the interlayer space influences the decomposition steps.

Preparation and characterization of 3-aminopropyltriethoxysilane grafted montmorillonite and acid-activated montmorillonite

3-aminopropyltriethoxysilane grafted montmorillonites were synthesized with montmorillonite, acid-activated montmorillonites and 3-aminopropyltriethoxysilane in ethanol-water mixture. The resulting products were investigated using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TG). XRD patterns demonstrated that silane was intercalated into the montmorillonite gallery, indicated by increasing basal spacings. These intercalated silanes probably adopt bilayer arrangement models within the montmorillonite and acid-activated montmorillonites interlayer spaces. TG and DTG curves indicate that acidification results in a decrease of the thermal stability of the resultant montmorillonites. Silane grafting leads to a surface property transformation of montmorillonite from hydrophilicity to lipophilicity and an increase of the thermal stability of the condensed silanes.

Composite nanomaterials on the basis of acid-activated montmorillonites

Properties of Ca-and Na-montmorillonites and their acid-activation products are studied by modern physicochemical methods. New evidence showing that the mechanism of acid activation of montmorillonites involves consecutive deactionation is presented. Features of formation and properties of the composite materials obtained on the basis of acid-activated montmorillonites and alumina are considered. It is shown that such materials hold promise as catalyst carriers and sorbents.

Effect of the Acid Activation Levels of Montmorillonite Clay on the Cetyltrimethylammonium Cations Adsorption

For the first time, the intercalation properties of acid-activated montmorillonites treated at different acid/clay (w/w) ratios with a cationic surfactant cetyltrimethylammonium (C16TMA) hydroxide are reported. The acid activation causes a reduction in the number of cation exchange sides and, hence improves the exfoliation of the silicate sheets at higher pH values. The basal spacing increases significantly from 1.54 to 3.80 nm, and is related to the acid activation extent. The acid activated clays with acid/clay ratios above 0.2 intercalated significant amounts of C16TMA cations with a basal spacing of 3.8 nm compared to the non acid activated montmorillonite with a basal spacing of 2.10 nm. The 13C CP/MAS NMR indicates that the intercalated surfactants exhibit a significant degree of gauche conformation in the acid-activated clays. According to in-situ powder XRD, an increase of the basal spacing to 4.08 nm is observed at intermediate temperatures of 50-150 degrees C for organoclay with basal spacing of 3.80 nm, at higher temperatures above 300 degrees C, the decomposition of the surfactant occurs and the basal spacing decreases to a value of about 1.4 nm, with the persistence of a reflection at 3.8 nm for clay at a higher acid/clay ratio of 0.5.

Isomerization of cis-2-butene and trans-2-butene catalyzed by acid- and ion-exchanged smectite-type clays

Two commercial acid-activated montmorillonites (F24 and F124) were exchanged with different cations (Al 3+, Cr 3+, Fe 3+, and Ni 2+). The catalytic activity of the acid- and the ion-exchanged clays was measured using the isomerization of cis- and trans-2-butene at 300 °C to yield the corresponding isomers. The order of activity for the acid- and the different cation-exchanged forms was: acid clays >Al 3+≈Ni 2+>Cr 3+>Fe 3+, which slightly correlated with the acidity values determined by cyclohexylamine desorption and the d 001 spacing obtained from integral series of reflections. The maximum conversion for the isomerization of cis-2-butene was ≈75% for F24 and F124, while the maximum conversion for the isomerization of trans-2-butene was ≈53% for F24 and F124. Cracking produced propylene and methane and their amounts increased with the acidity.

Bleaching Properties of Alumina-Pillared Acid-Activated Montmorillonite

AbstractThe bleaching of cottonseed oil by alumina-pillared (Al-pillared) acid-activated clays was investigated. Acid activation of a Ca-rich montmorillonite (CMS STx-1) following treatment with 1, 4, and 8 eq/L sulfuric-acid solutions, as well as subsequent pillaring with alumina, produces new materials. These materials have bleaching properties dependent upon the extent of activation of the clay prior to pillaring. The pillared acid-activated montmorillonites possessed higher bleaching efficiency compared to pillared products of the untreated clay. Mild activation of the montmorillonite matrix, pillaring with the Keggin ion [Al13O4(OH)24(H2O)12]7+, and calcination temperatures to 500°C produced materials with the best fractional degree of bleaching. Direct comparison to the performance of a commercial bleaching earth (Tonsil Optimum 214, Sud-Chemie AG. Moosburg, Germany) shows that the efficiency of the Al-pillared acid-activated montmorillonite may be improved. The optimization of the bleaching process is achieved via a judicious utilization of intermediate surface area, relatively high acidity, and enhanced pore volume.

Al-pillared acid-activated montmorillonite modified electrodes

The role of acid activation of the montmorillonite matrix before pillaring and the effect of calcination temperature on the efficiency of Al-pillared acid-activated clay modified electrodes have been investigated. The electrochemical behaviour of untreated and pillared montmorillonites was compared with that of two pillared acid-activated montmorillonites. The pillared acid-activated montmorillonite modified electrodes present better electroactivity than the modified electrodes of the conventional pillared montmorillonite towards cationic and anionic redox active species. Mild acid activation of the montmorillonite matrix and a calcination temperature up to 500°C lead to modifying materials that efficiently concentrate the cationic species. Lower calcination temperatures reverse the electrode activity. For anionic redox active species the best electroactivity was observed for pillared acid-activated montmorillonite films corresponding to a medium acid activation. In that case, a dependence of the electrochemical response on the pH was confirmed. The mechanism responsible for the observed cationic electroactivity was investigated and the behaviour of the Al-pillared acid-activated montmorillonite modified electrodes was attributed to the particular structure as well as the enhanced meso-external surface area and acidity of the clay films.

Synthesis And Characterization Of Pillared Acid-Activated Montmorillonites

ABSTRACTPolymeric hydroxy-Al cations were introduced into the interlayer of acid-activated montmorillonites by cation exchange. The resulting pillared materials possessed layer spacings of 18 – 20 Å, surface areas between 250 – 320 m2/g, pore volumes in the range 0.3 – 0.38 cc/g and pore diameters in the range 32 – 40 Å depending on preparation procedures (i.e pillaring temperature and drying method). Powder XRD analysis indicated that the pillars formed were stable to temperatures above 500 °C. The surface acidity of these type of pillared clays was higher than that of pillared non-activated clays. Preliminary studies on their adsorption capacity for chlorophyll showed that they were superior to pillared non-activated clays.