Zirconia-pillared Montmorillonite Research Articles

Novel sulphated zirconia pillared clay nanoparticles as catalyst in microwave assisted conversion of citronellal

Preparation of novel sulphated zirconia pillared montmorillonite and saponite clays nanoparticles (SZ/MMT and SZ/SAP) were studied to find a highly active, economist and environment friendly catalysts in the conversion of citronellal into menthol. Sulphated zirconia pillared MMT was prepared by direct sulphation into zirconia pillared MMT, which is a new and fast technique. Comparative study also conducted by evaluating the activity of SZ/MMT with sulphated zirconia nanoparticle (SZ). Material characterisation was performed by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscope and also surface acidity by mean pyridine adsorption Fourier transform infrared analysis and total acidity by butylammine titration. Catalytic activity of both SZ/MMT and SZ/SAP was observed in a reaction of citronellal conversion. The operation parameters consist of technique of reaction; tandem cyclisation–hydrogenation and catalytic hydrogen transfer mechanism were investigated. The results show that the pore size of catalyst and the presence of surface acidity affect significantly to increase the isomerisation as well as hydrogenation mechanism. The catalytic hydrogen transfer over microwave irradiation was observed as the more efficient process compared to the tandem cyclisation–hydrogenation from the selectivity of the product and also the other factor influencing the surface mechanism. In another aspect, the results clearly indicated the reusable properties of the sulphated zirconia pillared clay catalysts under varied conditions. Correlation between physicochemical characters and the reaction mechanism is discussed in this study.

Ni Dispersed on Sulfated Zirconia Pillared Montmorillonite as Bifunctional Catalyst in Eco-Friendly Citronellal Conversion

Nickel dispersed on sulfated zirconia pillared montmorillonite was prepared by three main steps; zirconia pillarization, sulfation and nickel dispersion. The synthesized material was characterized with FTIR spectroscopy, elemental analysis, x-ray diffraction and gas sorption analyzer before was tested for microwave assisted citronellal conversion via catalytic hydrogen transfer mechanism. The results showed that the obtained material gave high total conversion and demonstrated cyclization, isomerization and hydrogenation mechanism in one pot reaction. The presence of sulfate and nickel in the catalyst play important role within the mechanism.

Effect of Sulfation on Zirconia-Pillared Montmorillonite to the Catalytic Activity in Microwave-Assisted Citronellal Conversion

Preparation of sulfated zirconia-pillared montmorillonite was carried out in two steps; zirconia pillarization and sulfation to zirconia-pillared montmorillonite. The prepared materials were characterized by using X-ray diffraction (XRD), measurement of the specific surface area, total pore volume and pore size distribution by the N2adsorption method, scanning electron microscopy-energy dispersive X-ray (SEM-EDX), and surface acidity determination by using pyridine adsorption-FTIR analysis. The activity of the materials as catalysts was evaluated for a microwave-assisted conversion of citronellal. The results showed that the prepared materials had a physicochemical character that promoted high catalytic activity to convert citronellal. From varied Zr content and study of the effect of sulfation on the activity, it was found that Zr content and sulfation increase the surface acidity of the material as shown by the higher total conversion and tendency to produce menthol as a product of the tandem cyclization-hydrogenation mechanism.

Synthesis, characterization and catalytic performance of vanadia-doped delaminated zirconia-pillared montmorillonite clay for the selective catalytic oxidation of hydrogen sulfide

A series of vanadia-doped zirconia-pillared clays (V/Zr-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H 2S was investigated in this study. V/Zr-PILCs were characterized using X-ray diffraction (XRD), surface area-pore volume measurements, chemical analysis, X-ray photoelectron spectroscopy (XPS), 51V spin-echo NMR, temperature-programmed reduction by H 2 (H 2-TPR) and temperature-programmed desorption of ammonia (NH 3-TPD). V/Zr-PILCs showed better catalytic performance than as such Zr-PILC at temperatures ranging from 220 to 300 °C without any considerable SO 2 emission. The H 2S conversion over V/Zr-PILCs increased with increasing vanadia content up to 6 wt.%. This superior catalytic performance might be related to the uniform dispersion of vanadia in the form of monomeric and polymeric species. However, it decreased at higher vanadia loadings due to the decrease of surface area and to the formation of crystalline V 2O 5 phase. The presence of water vapor in the reactant mixture resulted in the decrease of the H 2S conversion.

Zirconia Pillared Montmorillonite for Removal of Arsenate from Water

Zirconia pillared montmorillonite, a clean adsorbent with increased specific areas of 40.118 m2/g and high basal spacing of 2.20 nm, was prepared for the removal of arsenate from water. Zirconia pillared montmorillonite is effective for the removal of arsenate. Adsorption is favored under acid conditions. Ca2 + and Mg2 + in the solution slightly enhance the adsorption. Over 95% removal was observed under natural pH conditions from 20 mg/L arsenate solutions containing 5.0 mg/L Ca2 + or Mg2 +. High adsorption capacity of over 120 mg/g was observed from arsenate solutions with different Ca2 + concentrations. The Freundlich model can describe the adsorption equilibrium data well. The column test shows that the column allows the passage of the feeding solution for approximately 225 times the bed volume if the removal percentage of arsenate was monitored not to be lower than 98%. The adsorbed arsenate can be desorbed with NaOH and the desorption efficiency reaches 85% and 88% when the concentration of NaOH reaches 0.2 and 0.5 mol/L. Zirconia pillared montmorillonite can be regenerated and the regenerated adsorbents still have good adsorption capacities.

Synthesis, characterization and catalytic evaluation of zirconia-pillared montmorillonite for linear alkylation of benzene

Zirconia-pillared montmorillonite was synthesized by an ultrasonication method and characterized by XRD, FT-IR of adsorbed pyridine, XPS, XRF and low temperature nitrogen adsorption techniques. The basal spacing of d(0 0 1) reflection of the pillared clay estimated by XRD was found to be 20 Å. XRD study showed well distribution of pillars without any non-pillared portion of the clay. FT-IR studies showed the formation of both Lewis and Brönsted acid sites due to pillaring. Pyridine desorption studies revealed that the Brönsted sites were stronger than Lewis acid sites. The activity of the Zr-PILC for the alkylation of benzene with long chain α-olefins [C 10–C 13] was investigated. The Brönsted acid sites played major role in this reaction.

Effect of microwave irradiation time on the synthesis of zirconia-pillared clays

In this work, we present the synthesis, at different zirconia/clay ratios, of zirconia-pillared montmorillonite in presence of microwave irradiation. The effect of irradiation time (5, 10, 20 and 30 min) on the structure and properties of the solids was also studied. The samples were characterized by X-ray diffraction, nitrogen adsorption (BET surface area) and thermo-programmed desorption of ammonia. It is shown that the irradiation time is critical between 5 and 10 min. For times longer than 10 min, no effect on the pillared clay features is observed.

Influence of preparation parameters on characteristics of zirconia-pillared clay using ultrasonic technique and its catalytic performance in phenol hydroxylation reaction

Ultrasonication method was employed for preparation of zirconia-pillared montmorillonite (Zr-PILC) by using polyhydroxy zirconium cation. The influences of various preparation parameters such as pH, concentration of pillaring agent, aging period on physico-chemical properties of Zr-PILCs are reported. The characterization was done by using different characterizing tools such as powder X-ray diffraction (XRD), thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), X-ray photo-electron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF) and surface area measurements. Effective pillaring was obtained in the pH range 2.0–2.8 at reduced preparation time by using ultrasonication. Ultrasonication, especially at higher pH and concentration of pillaring agent with no aging after ultrasonic agitation of the clay slurry was found to increase zirconium content and specific BET surface area leaving no scope for remarkable increase in d001 spacing. The presence of -OH groups attached to Zr has been revealed by pyridine-adsorbed FITR, TG/DTA and XPS techniques. The acidic character, ease of accessibility and good dispersion of active sites in Zr-PILC were found to be controlling factors for the challenging activity in hydroxylation reaction of phenol. Probably, this first report on the use of Zr-PILC in hydroxylation of phenol and its preparation by employing ultrasonication technique may attract great attention in the catalysis area of academic and industrial importance.

Energy-Filtered Imaging of Zirconia Pillars in Montmorillonite

The ability to vary the plane spacing in different clays is becoming increasingly important in catalysis and other technological applications [Baker and Murrell, 1990]. Considerable effort is now being devoted to understanding the mechanisms involved in pillaring such materials with a view to being able to fine-tune parameters such as the plane spacing and active sites for the application of interest. We have been able to use analytical electron microscopy to directly image the pillars in zirconia pillared montmorillonite. By using a combination of TEM techniques, we are able to correlate morphological information with elemental composition and conclusively identify the location of the zirconia pillars.A sample of natural montmorillonite clay, trade name HPM-20, was obtained from American Colloid and used as received. Zirconia pillared clays were prepared following published procedures [Bartley, 1988]. The Z1O2 pillars were prepared by using hydroxyzirconium cations produced by the solvation of zironyl chloride.

Controlling the chemistry of the micropore volume in pillared clays and micas

Pillared clays are microporous materials formed by propping apart clay layers with robust inorganic polyoxocations. The chemistry of the micropore space can be tailored by choosing suitable pillaring species, by adding various functionality to the pillar surfaces, and by incorporating small metal particles within the micropores. We have found that by using a commercially available zirconyl acetate solution as the zirconia polyoxocation precursor, zirconia-pillared micas with superior properties of crystallinity and microporosity can be produced. Catalytic tests have shown that treatment of a zirconia-pillared montmorillonite with sulfate increases the acid site strength and density of the zirconia pillars. In addition to materials with enhanced acidity, it is desirable to produce materials with little or no acidity for use as metal supports for catalysts in applications such as light alkane dehydrogenation, where support acidity leads to undesirable side reactions. Tetrasilicic fluoromica can be pillared by silsesquioxane oligimers derived from the in situ hydrolysis of an aminosiloxane reagent. After a two step calcination, the silica-pillared fluoromica produced has a high surface area and crystallinity, and the combination of the inert fluoromica layers with the non-acidic silica pillars makes this new material an interesting nonacidic support for noble metal catalysts.

ESR characterization of catalytically active V centres supported on alumina-, titania-, and zirconia-pillared montmorillonite clays

Vanadium-doped alumina-, titania-, and zirconia-pillared montmorillonites obtained by various preparative procedures have been investigated with the aid of ESR. Analysis of the spectra shows that localization of vanadium dopant in the pillared clay structure depends on the type of pillared matrix and on the mode of preparation. In V-doped alumina- and titania-pillared clays the vanadyl ions are bound to the pillars. In zirconia-pillared samples, beside the vanadyl centres bound to the pillars, also species associated with the interlayer surface of clay play an important role. In all cases copillaring produces species of relatively stronger in-plane π covalency than that observed for other members of the respective series, the effect being most pronounced for (V-Ti)-PILC and (V-Zr)-PILC samples. Catalytic experiments with oxidative dehydrogenation of propane demonstrate superior catalytic properties of these centres. This effect is interpreted in terms of the in-plane π covalency facilitating electron transfer between the electron donor and electron acceptor sites at the catalyst surface.

Preparation and Property of Zirconia-Pillared Montmorillonite Having Different Pillar Populations

Abstract Zirconia-pillared clay was prepared by ion-exchanging montmorillonites having different cation exchange capacities (CEC’s) in an aqueous solution of ZrOCl2. The amount of zirconia incorporated as pillars varied depending on the CEC of the starting clay. The interlayer distance was almost the same: ca., 0.8 nm. These findings suggest that the distance between pillars or the lateral distance should be different from one zirconiapillared clay to another. As a result of pillaring the surface area was 200–260 m2 g−1. The thermal stability was examined in terms of a decrease in the surface area after heating at elevated temperatures.

Alumina-pillared clays and their adsorptive properties.

This work has explored the synthesis of alumina-pillared montmorillonite and Laponite. The importance of stoichiometry has been examined. A zirconia-pillared montmorillonite is also reported. All these products are fully characterised by X-ray diffraction and by the adsorption of nitrogen, water, n-butane, methanol, and neo-pentane. The implications for the real microstructures of these materials are discussed.