Synthesis of metal-oxide pillared montmorillonite clay for the selective catalytic oxidation of H2S

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 H₂S 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 (NH₃-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 H₂S increased with increasing temperature for all PILCs while the selectivity to SO₂ 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.     

Effect of pillared clays on the hydroisomerization of n-heptane

Different montmorillonites and saponites were pillared with Al polyoxocations to obtain catalytic supports for the hydroisomerization of n-heptane. The catalysts were characterized by different techniques such as X-ray diffraction, elemental analysis and N₂ adsoprtion. The temperature-programmed desorption of ammonia indicated that pillared clays exhibited moderate and strong acid sites. The concentration of the acid sites depended on the starting clays as well as the type of the clays. The pillared saponites are more effective for the hydroisomerization of n-heptane at 300 °C, however, it decreased over the Al-pillared montmorillonites, and mainly cracking products were obtained.     

Effect of Ultrasound on the Structural and Textural Properties of Al–Fe Pillared Clays in a Concentrated Medium

A modification of bentonite with the Al–Fe mixed system in a concentrated medium was performed, assisting the intercalation with ultrasound. The solid pillaring agent and clay powder were placed in a dialysis membrane in contact with a minimum amount of water, and ultrasound was used to promote species exchange. Al–Fe pillared clays (2, 5 and 10 mol% Fe) were characterized by XRF, CEC, XRD, H₂-TPR and N₂ adsorption at 77 K, revealing changes in the structural and textural properties of the modified clays in the presence of ultrasound during the intercalation. The catalytic properties of pillared clays were evaluated by using the catalytic wet peroxide oxidation of phenol in a diluted aqueous medium, showing an activity comparable to that of a solid modified through the conventional method.     

Synthesis of pillared clays with Al13-Fe and Al13-Fe-Ce polymers in solid state assisted by microwave and ultrasound: Characterization and catalytic activity

A new methodology for the synthesis of pillared clays with the Al₁₃-Fe and Al₁₃-Fe-Ce polymers in solid state was developed by using microwaves and ultrasound in the aging of the olygomeric solution, in the precipitation of the corresponding sulphates, and in the intercalation of the polymer with the powdered clay. This methodology reduces significantly the water consumption in the intercalation process, and the time for the synthesis of both the polymer in the solid state, and the pillared clay. The resulting polymers were characterized by XRF, XPS, XRD and SEM. The XRF analysis showed that a high percentage of Fe and Ce associated to Al₁₃-Fe and Al₁₃-Fe-Ce sulphates, was dissociated during the exchange process with nitrate. Using XPS analyses we established the presence of Ce (III) in the polymers. By means of XRD and SEM we determined that Al₁₃ and Al₁₃-Fe sulphates present a monoclinical structure, whereas the Al₁₃-Fe-Ce sulphates present two crystalline phases, monoclinical and cubical, whose cell parameters are slightly different from those of the sulphates reported in literature. The XRD, XRF and sortometry analyses showed that the pillared clays (synthesized with the proposed methodology), show more intense and remarkably homogenous pillaring signals, and also better textural properties than the clays pillared by the conventional method of synthesis. The catalytic activity was assessed in the phenol oxidation in dilute aqueous medium at 25 °C and at atmospheric pressure. The solids synthesized showed similar catalytic properties than those reported for the solids synthesized by the conventional method.     

Synthesis of Keggin-type lacunary 11-tungstophosphates encapsulated into mesoporous silica pillared in clay interlayer galleries and their catalytic performance in oxidative desulfurization

Keggin-type lacunary polyoxotungstates [PW₁₁O₃₉(H₂O)]^7 − (PW₁₁) and metal-modified [PW₁₁O₃₉(H₂O)M]^5 − (M = Ni^2 + or Co^2 +) were incorporated into the mesoporous silica pillared clays (MSPC) by a hydrothermal sol–gel method. The resulting materials retain the layered structure of the clay precursor and possess a mesoporous structure. The catalytic performance of the materials was tested using oxidative desulfurization of dibenzothiophene-containing model oil as a probe reaction. The results indicated that PW₁₁-MSPC possess an excellent catalytic performance.     

Porous materials obtained by acid treatment processing followed by pillaring of montmorillonite clays

Montmorillonite clay was treated with hydrochloric acid and subsequently pillared with aluminum polyoxocations. The acid-treated samples were evaluated for the removal of structural elements (Al, Fe and Mg) and for conservation of the lamellar organization. The more severe the treatment, the greater the specific area obtained. Despite the loss of structural organization, all samples were pillared, with a displacement of peak (001) to 2θ lower angles. The pillaring of all acid-treated samples promoted an increase in the specific area of these materials. Pillared samples previously treated at 50 °C with HCl concentrations of 2 and 4 mol L^− 1 underwent an increase in their specific areas of approximately 45%. Pillared samples treated with 4 mol L^− 1 of HCl at 80 °C underwent the lowest percent increase in surface area, approximately 10%, compared to the untreated samples. All samples possessed greater uniformity in pore size. Acid treatment prior to pillaring promoted an increase in the number of acid sites of moderate strength compared to pillared natural clay.     

Selective catalytic reduction of nitric oxide by ethylene in the presence of oxygen over Cu ion-exchanged pillared clays

Cu²⁺ ion-exchanged pillared clays are substantially more active than Cu²⁺-ZSM-5 for selective catalytic reduction (SCR) of NO by hydrocarbons. More importantly, H₂O (or SO₂) has only mild effects on their activities. First results on Cu²⁺-exchanged TiO₂-pillared montmorillonite were reported by this laboratory (Yang and Li, Ref. [1]), that showed overall activities two to four times higher than Cu²⁺-ZSM-5.

A delaminated pillared clay was subjected to Cu²⁺ ion-exchange and studied for SCR by C₂H₄ in this work. The Cu²⁺ ion-exchanged delaminated Al₂O₃-pillared clay yielded substantially higher SCR rates than both Cu²⁺-exchanged TiO₂-pillared clay and Cu²⁺-ZSM-5 at temperatures above 400°C. The peak NO conversion was 90% at 550°C and at a space velocity of 15,000 h⁻¹ (with O₂ = 2%). The peak temperature decreased as the concentration of O₂ was increased. The macroporosity in the delaminated pillared clay was partially responsible for its higher peak temperatures (than that for laminated pillared clays). At 1000 ppm each for NO and C₂H₄, the NO conversion peaked at 2% O₂ for all temperatures. H₂O and SO₂ caused only mild deactivation, likely due to competitive adsorption (of SO₂ on Cu²⁺ sites and H₂O on acid sites). The high activity of Cu²⁺-exchanged Al₂O₃-pillared clay was due to a unique combination of the redox property of the Cu²⁺ sites and the strong Lewis acidity of the pillared clay. The suggested mechanism involved NO chemisorption (in the presence of O₂) on Cu²⁺OAl³⁺-on the pillars, and C₂H₄ activation on the Lewis acid sites to form an oxygenated species.     

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 [C₁₀–C₁₃] was investigated. The Brönsted acid sites played major role in this reaction.     

Synthesis of Smectites and Porous Pillared Clay Catalysts: A Review

This paper reviews the synthesis of smectites and porous pillared clay catalysts. Synthetic as well as natural smectites serve as precursors for the synthesis of Al, Zr, Ti, Fe, Cr, Ga, V, Si, and other pillared clays as well as mixed Fe/Al, Ga/Al, Si/Al, Zr/Al and other mixed metal/Al pillared clays. The use of these pillared clays in some catalytic reactions is also briefly reviewed.     

The microstructure of alumina pillared acid-activated clays

Factors which affect the microstructure of pillared materials derived from acid activated clays have been investigated by varying the conditions used in their preparation and the level of acid treatment of the host clay prior to pillaring. The pillared acid-activated clays prepared are found to exhibit both micro and mesoporosity with a higher proportion of mesoporosity compared to conventional pillared clays. For materials calcined at 500°C, typical values obtained are in the range 0.02–0.1 cc/g and 50–200 m²/g for micropore volume and surface area respectively with corresponding mesopore values ranging between 0.2–0.4 cc/g and 150–250 m²/g. In all cases, the development of microporosity is at the expense of mesoporosity and therefore, high micropore values are accompanied with low mesopore values and vice versa. The microstructure developed by these materials is critically dependent on the amount (and nature) of pillaring species incorporated by the host clay. Consequently, the preparation conditions (i.e., Al/clay ratio and pillaring (exchange) temperature) affect the microstructure in as much as they influence the amount of alumina incorporated as pillar. The development of microporosity is highest for air-dried materials prepared at 80°C at an Al/clay ratio of 6 mmole/g.     

聚羟基铁铝复合柱撑蒙脱石的微结构特征

利用Keggin结构可以发生类质同象置换的性质，制备了含过渡金属离子Fe的聚羟基铁铝复合柱撑蒙脱石。运用紫外一可见吸收光谱、^17Al核磁共振谱等技术对复合柱撑溶液中的Fe和Al的状态进行了研究。运用X射线定向衍射技术、红外光谱、顺磁共振等技术对复合柱撑粘土中Keggin结构的作用及热稳定性进行了研究。结果表明：Fe／Al摩尔比对聚羟基铁铝柱撑液的结构、d(001)值、复合柱撑粘土的热稳定性均有较大的影响，随着Fe／Al摩尔比的增加，d(001)逐渐增大，热稳定性下降，过量的Fe对Keggin结构有破坏作用，Keggin结构的存在增加了复合柱撑粘土的热稳定性。     

Intercalation of various organic molecules into pillared carbon

Intercalation of various organic molecules into pillared carbon prepared from the pyrolysis of graphite oxide silylated with methyltrichlorosilane for three times was investigated. Liquid n-alkylamine molecules with various alkyl chain lengths were intercalated into the resulting pillared carbon and the interlayer spacing increased with increasing in the alkyl chain length, until it became a constant value of 2.24 nm for chains having more than six carbon atoms. This suggests that the length of the pillar is 1.9 nm. Various organic molecules including non-polar xylene isomers and alcohol molecules can also penetrate into pillared carbon. The n-hexadecylamine molecules with a higher melting point than room temperature were intercalated into pillared carbon simply by mixing them with pillared carbons in hexane, though the interlayer spacing was smaller. The space between the layers of pillared carbon was saturated with n-hexadecylamine molecules when 1.8 molecules per 40 carbon atoms were added. The n-hexadecylamine molecules occupied 51% of the micropore volume of pillared carbon. For the intercalation of organic molecules into pillared carbon, the shorter axis of them should be smaller than 0.87 nm.     

Hydroxylation of phenol over rare earth exchanged iron pillared montmorillonites

Iron pillared montmorillonite prepared by partial hydrolysis method was exchanged with La, Ce and Th metal salts. The pillared montmorillonite showed considerable increase in basal spacing and surface area. EDAX showed presence of about 2% rare earth metals. ²⁷Al and ²⁹Si NMR spectra showed relaxation effects due to iron paramagnetic centres. The prepared systems are excellent catalysts for hydroxylation of phenol underlining the use of environmentally friendly clay catalysts for effective removal of pollutants. A detailed study of reaction variables suggests that oxidation of phenol increases with temperature and maximum conversion is obtained at 80?°C. Hydroquinone selectivity increases with phenol and solvent concentrations but decreases with time.     

Hydrodechlorination of 4-chlorophenol in aqueous phase with Pt–Al pillared clays using formic acid as hydrogen source

Catalysts based on pillared clays with Al and Pt were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as the target compound and formic acid as the hydrogen source. Stable Pt–Al pillared clays were obtained, showing a high activity and a strong fixation of the active phase to the support. The influence of the method of introduction of Pt in the pillared clay (ion-exchange or impregnation) and the Pt content in the catalytic activity was checked. Likewise, operating variables such as reaction temperature, catalyst concentration and formic acid to 4-CPhOH molar ratio were studied; higher values of these variables gave rise to a higher 4-CPhOH conversion to phenol. An important deactivation of the catalyst was observed, probably due to the formation of carboneous deposits since no appreciable Pt leaching was detected.     

Catalytic performance of vanadia-doped titania-pillared clay for the selective catalytic oxidation of H2S

A series of vanadia-doped titania pillared clay (V/Ti-PILC) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H₂S was investigated in this study. V/Ti-PILCs were characterized using X-ray diffraction (XRD), BET apparatus, and X-ray photoelectron spectroscopy (XPS). V/Ti-PILCs showed better catalytic performance than as such Ti-PILC at temperatures ranging from 220 to 300 °C without any considerable SO₂ emission. The H₂S conversion over V/Ti-PILC increased with increasing vanadia content up to 5 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 10 wt.% vanadia loading due to the decrease of surface area and to the formation of crystalline V₂O₅ phase. The presence of water vapor in the reactant mixture resulted in the decrease of the H₂S conversion.     

Catalytic performance of vanadia-doped alumina-pillared clay for selective oxidation of H2S

The catalytic oxidation of hydrogen sulfide over V₂O₅ supported on Al-pillared clay (V/Al-PILCs) was studied. The synthesized catalysts were examined using a variety of characterization techniques such as XRD, BET, XPS, ⁵¹V NMR, H₂-TPR and NH₃-TPD. A catalytic activity study performed by using V/Al-PILC catalysts showed that H₂S was successfully converted to elemental sulfur without considerable emission of sulfur dioxide. The H₂S conversion over V/Al-PILCs increased with the vanadia content up to 6 wt.%. This superior catalytic performance might be related to the uniform dispersion of vanadia species on the Al-PILC support.     

Al-pillared clay supported CuPd catalysts for nitrate reduction

PdCu catalysts on clay and Al-pillared clay supports were prepared by wet impregnation procedure and characterized by powder x-ray diffraction (PXRD), Scanning Electron Microscope Dispersive x-ray analysis (SEM-EDAX) and Transmission Electron Microscopy (TEM). The incorporation of [Al₁₃O₄(OH)₂₄(H₂O) ₁₂]⁷⁺ clusters in the clay interlayers and subsequent formation of Al-pillared clays was confirmed from PXRD patterns. The EDAX analysis indicated good homogeneous mix of metallic components, in the form of monometallic or inhomogeneous bimetallic particles, on the clay and pillared clay surfaces. TEM pictures showed striking particle size differences upon Al₂O₃-pillaring. The metallic particles were much smaller in size on Al-pillared clay than those formed on parent clay. The clay supported PdCu catalysts were tested for nitrate ion reduction in aqueous phase under hydrogen atmosphere. Preliminary results show that the catalysts with Pd and Cu components together exhibit superior performance in activity and selectivity to nitrogen compared to their monometallic particles supported on both clay samples. This study indicates the possibility of using PdCu catalysts supported on pillared clays as environmental friendly and efficient catalysts for nitrate reduction reactions.     

层柱黏土合成和催化应用的研究进展

概述了层柱黏土的组成和性能,总结了层柱黏土合成中的影响因素及层柱黏土的催化应用,提出了层柱黏土研究中亟待解决的问题,并对其发展前景进行展望.     

HDS of thiophene over CoMo/AlMCM-41 with different Si/Al ratios

A series of AlMCM-41 molecular sieves with different Si/Al ratios were synthesized followed by the deposition of cobalt and molybdenum oxides on these mesoporous supports by co-impregnation. Such materials were further calcined and catalysts with 15 wt.% of cobalt and molybdenum and a Co/(Co + Mo) atomic ratio of 0.30 were obtained. These materials were characterized by X-ray diffraction (XRD), transmission electron microscopy and selected area electron diffraction (TEM/SAED), X-ray fluorescence (XRF), and nitrogen adsorption. Hydrodesulphurisation (HDS) of thiophene was carried out at 350 °C in a fixed bed continuous flow micro reactor coupled on line to a gas chromatograph. The main XRD peaks of MCM-41 phase were observed in all samples and peaks due to MoO₃ and CoMoO₄ phases were also identified from XRD results. It was found that the as-synthesized catalysts presented reasonable conversion results for HDS of thiophene, when compared to other supported catalysts. The main products of HDS of thiophene were H₂S, isobutene, 1-butene, n-butane, 2-butene-trans, and 2-butene-cis. It was observed that the reactivity of the as-synthesized catalysts is a direct function of the Si/Al ratio, nature and concentration of the active species on the mesoporous supports.     

Hydroxy-interlayered vermiculite genesis in Jiujiang late-Pleistocene red earth sediments and significance to climate

To understand the paleoclimatic significance of the red earth sediments in Jiujiang, southern China, hydroxy-interlayered vermiculite (HIV) in the deposits was investigated using X-ray diffraction (XRD), chemical extraction, and high resolution transmission electron microscopy (HRTEM). The XRD results indicated that the clay mineral assemblages of the sediments are mainly illite, kaolinite, HIV, vermiculite, with minor illite-HIV mixed-layer clays. The 1.41-nm reflection did not expand after Mg saturation and glycerol solvation, but it shifted to 1.38 nm and 1.20 nm when the samples were heated to 350 °C and 550 °C, respectively. The 1.41-nm spacing showed partial collapse after K⁺ saturation at 80 °C in association with the reinforcement of the 1.0 nm reflection. Collapse of the HIV (001) spacing was related to the release of Al, Mg, and Ca from the interlayer after KCl extraction. The Al was probably present as hydroxy-Al in HIV interlayers before being released. The HRTEM image revealed 1.4-nm lattice fringes interstratified with illite 1.0 nm fringes and two illite lattice fringes merged into one HIV fringe. This suggests that the HIV clays in Jiujiang soils resulted from illite weathering. The shift of a small X-ray diffraction reflection between 1.0 and 1.4 nm for an air-dried and glycerol-solvated sample to 0.997 nm after heating at 550 °C indicated the presence of an irregularly interstratified illite–HIV mineral. The common occurrence of HIV minerals in the Jiujiang red earth sediments suggests a climate with frequent wet and dry cycles prevailed during late-Pleistocene time.