Pillared Montmorillonite Clay Research Articles

Positron annihilation spectroscopic investigation of pillared clay-based catalytic hybrid nanocomposites

Positron annihilation lifetime spectra for pillared montmorillonite clay (PILC), as encapsulated with chitosan (CS) chains, supported with Pd nanoparticles, fresh and recovered PILC-CS@Pd heterogeneous catalysts, along with the starting montmorillonite clay (MC) were measured. After pillaring modification, as the interlayer nano-space expanded, the sub nanometer level free-volume nanohole size increases obviously from 0.182 nm (MC) to 0.246 nm (PILC). Then, as the CS chains and active Pd species encapsulated within the interlayer nano-space, the o-Ps lifetime (τ3) and intensity (I) undergo a continuous decrease, indicating the decrease of the free-volume nanohole size and concentration. Meanwhile, in practical catalytic application scenarios, it is found that the variations of the free-volume parameters show close correlation with the recycling aging behavior and catalytic performance decline of the catalytic nanocomposites. The decrease in density of sub nanometer level molecular stacking due to the leaching of Pd species and degradation of CS chains in the interlayer galleries nano-space of the recovered PILC-CS@Pd hybrid nanocomposite has been sensitively detected by the o-Ps probe.

Modification of Pillared Intercalated Montmorillonite Clay as Heterogeneous Pd Catalyst Supports.

Montmorillonite clay was modified by pillaring with AlMn oxides in different Al/Mn ratios and intercalation of two kinds of N-containing polymers (i.e., chitosan (CS) and polyvinyl pyrrolidinone (PVP)) chains. The modified pillared montmorillonite clay (PM) showed a rich two-dimensional layered porous structure with tunable parameters, such as large interlayer spacing, high specific area, and large porous volume. They were then used as supports for Pd nanoparticles. As applied in coupling reactions of aryl halides with terminal alkynes, Pd@CS/AlMn-PM showed better comprehensive catalytic performance than Pd@PVP/AlMn-PM. This was mainly attributed to its higher specific area, stronger chelation to Pd species, and better solvent resistance.

Positron annihilation study of chitosan and its derived carbon/pillared montmorillonite clay stabilized Pd species nanocomposites

To establish the structure-properties relations of an organic polymer-inorganic hybrid nanocomposite, insightful investigation of the molecules packing and interfacial interactions is essential. Positron annihilation lifetime spectroscopy (PALS) has been proven as one of the most suitable technique to characterize the free volume structure (molecular packing) of polymer matrices. However, most of the attentions were paid limitedly in organic polymer-based hybrid systems rather than inorganic-based hybrid systems. Classic spherical model was the most frequently used model in free volume holes size calculation of polymer matrix. In the present study, molecular level micro-defects within inorganic-based hybrid systems encaging polymers and carbon species, i.e. novel biological macromolecules of chitosan and its derived carbon/Al pillared montmorillonite clay (CS/PILC and CS-derived C/PILC) stabilized palladium species hybrid nanocomposites, have been investigated by PALS. Besides the classic spherical model, cuboidal and cylindrical models were used to evaluate the molecules packing behavior within the interlayer space of PILC matrices encaging of polymers of CS or CS-derived carbons. The layered porous structure of the nanocomposites was also characterized with other methods, such as X-ray diffraction, N2 adsorption/desorption, and high-resolution transmission electron microscopy, etc. The correlations of the microstructure and catalytic properties applied in Sonogashira coupling reactions of the nanocomposites were discussed.

Vanadium Supported on Titanium Pillared Montmorillonite Clay for the Selective Catalytic Oxidation of Benzyl Alcohol

Vanadium Supported on Titanium Pillared Montmorillonite Clay for the Selective Catalytic Oxidation of Benzyl Alcohol

Chemical upcycling of waste polyolefinic plastics to low-carbon synthetic naphtha for closing the plastic use loop

Designing an effective pathway to remove waste plastics from landfill and incineration plants and create a circular economy requires a more appropriate technology beyond the conventional mechanical recycling by melting and re-molding. This study aims to convert waste plastic into low-carbon synthetic naphtha which can be used as a feedstock for new plastic production, via a new and simple technical approach. To be specific, waste plastics are decomposed and reformed into naphtha fractions via a one-step catalytic pyrolysis over Al2O3 pillared montmorillonite clay catalyst. Experimental results show that Al2O3 pillared montmorillonite clay produces up to 60.3% C5-C12 alkanes, while ZSM-5 gives high contents of aromatics (46%) and olefins (35%). The promising results of Al2O3 pillared M-clay may be due to the special features of this material, including the large pore size and Al2O3-induced active sites (more Brønsted acid sites). The further batch experiments confirm the feasibility of scaling up and processing the polyolefinic plastic mixture.

Enhanced gelled hydrocarbon well treatment fluids

Abstract Compared with water-based well treatment fluid systems, hydrocarbon-based fluids possess advantages such as better fluid compatibility and lower formation damage, especially in water-sensitive formations. Hydrocarbon-based fluids are therefore often used in oilfield operations including hydraulic fracturing, sand control, and coiled tubing cleanout. The metal-crosslinked, phosphate ester-based gelled hydrocarbon (or gelled oil) fluids have been the preferred choice among hydrocarbon-based fluids since they are cost effective, robust at elevated temperatures, and operationally simple as only a couple of fluid additives are involved. Functioning as the gelling agent in gelled oil fluids, phosphate ester could cause fouling in refinery equipment. It is therefore desirable to lower the dosage of the phosphate ester-based gelling agent as much as possible, but without adversely affecting the fluid performance. A number of materials have been identified that could enhance the gelled oil viscosity and stability, which in turn translates into the reduction of the phosphate ester needed in the gelled oil. Among these enhancing materials, a type of aluminum pillared montmorillonite clay (the additive) was found to enhance the gelled oil viscosity to the largest extent. In laboratory tests, 30 ppt (30 pounds per thousand gallons) of the additive increased the gelled oil viscosity by 84% (± 5%) at 250 °F when compared with the baseline gelled oil without the additive. With the additive dosage at 30 ppt, the amount of the phosphate ester in the gelled oil could be reduced by 25% without decreasing the fluid viscosity. The additive was successfully applied to the crude oil-based gelled fluid, resulting in multiple times of viscosity increase in the study. In addition to the gelled oil viscosity enhancement, the additive also increased the regained permeability in the coreflow tests to near 3 times.

Aluminum pillared montmorillonite clay-based self-healing coatings for corrosion protection of magnesium alloy AZ91D

In the present study, aluminum pillared montmorillonite clay was modified with cationic corrosion inhibitors Ce3+/Zr4+. The modification of the montmorillonite clay was carried out by two methods; (a) by simple mixing of inhibitor solutions along with clay by stirring for 30 min and (b) by homogenization of inhibitor solutions and clay for a very short time of 15 min followed by evacuation. The modified and as-received clays were dispersed in hybrid organic-inorganic sol-gel matrix silica sol, which were coated on magnesium alloy AZ91D and cured in air at 130 °C for 1 h. Corrosion protection ability of coatings was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss measurements after exposure to 3.5 wt% NaCl solution for different exposure durations between 24 h to 120 h. Coatings were evaluated for their self-healing ability using scanning vibrating electrode technique for varying time duration from 1 h to 24 h. Coatings generated with the sol using the pillared montmorillonite clay after modification as described in (b) were found to exhibit better anticorrosive properties even after prolonged exposure to the corrosive medium.

Design, synthesis and characterization of vanadia-doped iron-oxide pillared montmorillonite clay for the selective catalyticoxidation of H2S

A series of vanadia-doped iron-oxide-pillared clays (V/Fe-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H(2)S was investigated. V/Fe-PILCs were characterized using X-ray diffraction (XRD), surface area- and pore volume measurements, chemical analysis, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H(2) (H(2)-TPR). V/Fe-PILCs showed better catalytic performance than Fe-PILC without any significant SO(2) emissions. The H(2)S conversion over V/Fe-PILCs increased with increasing vanadia content up to 7 wt.%. However, it decreased at higher vanadia loading due to the decrease in surface area and the formation of the crystalline V(2)O(5) phase. The presence of water vapor in the reactant mixture resulted in a decrease of H(2)S conversion.

Cooperative coadsorption of 4-nitrophenol and basic yellow 28 dye onto an iron organo–inorgano pillared montmorillonite clay

Sorption properties of an iron surfactant-modified pillared montmorillonite (Fe-SMPM) toward two organic pollutants, basic yellow 28 dye (BY28) and 4-nitrophenol (4-NP), were studied at different pH values in both single component and binary pollutant systems. The pseudo-first-order model fits well with the kinetic data obtained in single component studies and sorption capacities of both BY28 and 4-NP increased with the pH value. A sorption synergetic mechanism was observed in binary systems; 4-nitrophenol adsorption was enhanced by the presence of BY28 in the mixture and increased with dye concentrations. Isotherms were described using the Freundlich model in single component systems and the Sheindorf–Rebhun–Sheintuch (SRS) model, an extended Freundlich model, in binary mixtures systems. Hydrophobic interactions between the surfactant-modified pillared clay and the pollutants were suggested to explain the sorption mechanisms.

Synthesis of metal-oxide pillared montmorillonite clay for the selective catalytic oxidation of H 2S

In the present work, titania-pillared clay (Ti-PILC) and zirconia-pillared clay (Zr-PILC) were synthesized, and their catalytic performance was studied for the selective oxidation of H 2S to elemental sulfur. The obtained pillared clays (PILCs) were characterized by X-ray fluorescence spectroscopy (XRF), infrared (FTIR) spectroscopy, BET surface area measurements, X-ray photoelectron spectroscopy (XPS), UV–vis-diffuse reflectance spectroscopy (UV–vis-DRS), temperature-programmed desorption of ammonia (NH 3-TPD), and thermogravimetric (TG) analysis. The reaction tests were carried out in a continuous flow fixed-bed reactor at temperature ranging from 220 to 300 °C. The conversion of H 2S increased with increasing temperature for all PILCs while the selectivity to SO 2 remained almost constant. The good catalytic performance of the metal-oxide pillared clays may be due to the high surface area and the presence of Brönsted and Lewis acid sites.

Visible light induced TiO2 pillared MMT photocatalyst coupling-doped with S and N

Visible light induced titanium dioxide (TiO2) pillared montmorillonite clay (MMT) photocatalyst coupling-doped with S and N elements was prepared by the two-step adsorption method. The photocatalyst was characterized by X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) absorption spectroscopy. The photocatalysic efficacy of the prepared photocatalyst for degrading gaseous formaldehyde was evaluated under visible light irradiation. The degrading rate of gaseous formaldehyde is nearly 85% in 300 min visible light irradiation. The results demonstrate that the much higher visible light photocatalytic activity of the photocatalyst is due to the synergistic effects of coupling-doping of S and N elements to TiO2, extensive specific surface area of MMT and quantum sized efficacy between layers of MMT.

Cu–Ce mixed oxides supported on Al-pillared clay: Effect of method of preparation on catalytic activity in the preferential oxidation of carbon monoxide

The possibility of using Al-pillared montmorillonite (Al-PILC) clay as a high-surface-area support for CuO–CeO2-based catalysts has been investigated. The preparation of the samples was done by three different methods, viz., amorphous citrate route (ACR), deposition precipitation (DP) and wet impregnation method (WIM). Samples with different CuO–CeO2 loadings (10–50wt.%) were prepared by each of the three methods. The catalytic activity of these samples was investigated for the preferential oxidation (PROX) of carbon monoxide (CO) in excess of H2. The samples prepared by DP and WIM methods show better activity than the samples prepared by ACR method. At low Cu content, the samples prepared by DP method have a slight edge over samples prepared by WIM method. The DP-30 sample shows a very high CO conversion of 96.1% at 423K. A higher dispersion of CuO–CeO2 on pillared montmorillonite clay and better reducibility of copper oxide species may be responsible for the good activity of these samples even at lower reaction temperatures. A higher O2/CO ratio increased the CO conversion but led to a reduction in oxidation selectivity. No methanation of CO or CO2 was observed at the reaction temperature. These CuO–CeO2/Al-PILC samples could be considered as comparable in performance with supported noble metal catalysts for the preferential oxidation of CO in excess hydrogen.

Oxidation of cyclohexane with molecular oxygen in presence of characterized macrocyclic heteronuclear FeCu complex catalyst ionically bonded to zirconium pillared montmorillonite clay

Heteronuclear macrocyclic complex of iron and copper, FeCuL(NO 3) 24H 2O [L = (CH 3C 6H 2CH 2O(CH 2) 3N) 2] was synthesized and characterized using CHN and X-ray crystallography. A general scheme for bonding the complexes ionically on acidified montmorillonite clay was evolved and the thermogravimetric analysis of the final catalyst showed that it was stable up to 400 °C. The increased thermal and chemical stability of the complex bonded to the clay has been explained through enhanced interactive energy between them and its higher catalytic efficiency has been demonstrated through the following reaction. The oxidation of cyclohexane in presence of this catalyst using molecular oxygen in the absence of intiators, promoters and coreactants was studied in the temperature range of 150–210 °C. All commercial catalyst reported are known to form cyclohexanol and cyclohexanone in about equimolar ratio, but with our catalyst, cyclohexanone along with small amount of uncharacterized waste products (D) were formed and the selectivity of the former decreases (due to the formation of large amount of D) with increase in temperature. The experimental data were analyzed against different kinetic scheme available in literature and the rate constants of the best scheme were determined using Genetic Algorithm. From the experiments carried out at different temperatures and pressures, we found that for every rate constant, an Arrhenius type relation (independent of reactor pressure) could be established.

Noble metal containing Al/Ce/Mg pillared montmorillonite clay as catalysts in the hydrotreating of LCO fractions

An Al/Ce/Mg=50.0/1.0/1.0 atomic ratio (a.r.) pillared montmorillonite was used to support 1.0 wt.% of the bimetallic species Pd/Pt=5.0 and Pd/Au=5.0 a.r. The resulting catalysts were characterized by XRPD, N 2 physisorption, ammonia TPD and FT-IR spectroscopy. The catalytic activity in the hydrogenation and hydrogenolysis/ring-opening of naphthalene and thio-tolerance to dibenzothiophene were investigated at 6.0 MPa in a flow reactor. Both catalysts showed interesting performances. Of the two catalysts, the former showed higher productivities in hydrogenation and hydrogenolysis/ring-opening compounds together with lower losses in carbon balance and higher thio-tolerance. These results not only confirmed that Pd/Pt is one of the most suitable bimetallic pair for noble metal containing hydrotreating catalysts, but also that the Al/Ce/Mg PILC can be used as low cost support for noble-metal-containing active phases.

Enhanced Adsorption Capacity and Photo-Catalytic Oxidative Activity of Dyes in Aqueous Medium by Hydrothermally Treated Titania Pillared Clay

Titania pillared montmorillonite clay was prepared by two different routes viz. 1) conventional ion exchange method and 2) modified method wherein the post hydrothermal treatment after ion-exchange was employed. The influence of the post hydrothermal treatment on the textural properties of titania-pillared clays was studied. The calcined clay was characterized by different physico-chemical techniques such as XRD, EDX, low temperature (77 K) nitrogen adsorption and UV-Vis diffuse reflectance spectroscopy. The content of pillared titania remained unchanged irrespective of the method of preparation. The method of preparation and severity of the conditions employed for the hydrothermal treatment resulted in alteration of the crystallinity and crystallite size of the anatase. The changes in the average pore diameter was found to comensurate with the changes in crystallite size of anatase phase. The increase in total pore volume as a function of the severity of the post hydrothermal treatment resulted in the decrease in micropore volume. The severity of the post hydrothermal treatment governed the extent of the blue shift in UV-Vis DRS spectra.

Carbonyl complexes in pillared clays

Mo(CO) 6 is adsorbed between the layers of aluminium pillared montmorillonite clay. The chemistry of interaction with the clay resembles that with zeolite HY; the carbonyl complex interacts with the structural hydroxyl groups of the clay, and can be decarbonylated partially and reversibly at 373 K and completely and irreversibly at 473 K. Complete decarbonylation is accompanied by oxidation of the molybdenum to the 5 + state. The method allows preparation of pillared clays containing about 1 wt.% transition metal. Similar chemistry occurs with Fe(CO) 5.

An x-ray diffraction and thermodynamic study of krypton and xenon adsorption in pillared clay

X-ray diffraction and thermodynamic studies have been made upon adsorption of xenon and krypton in a pillared montmorillonite clay over a wide range of temperatures. Krypton forms within the interlamellar region an ordered «internal bilayer» at all temperatures and coverages but xenon forms sequentially a monolayer and then a bilayer. Evidence is found for a phase transition in the adsorbed xenon bilayer. The separation between pillars in the clays is estimated to be ca. 30 A