Kazuo Torii

Effect of layer charge on fixation of cesium ions in smectites

In order to rationalize the influence of layer charge on cesium fixation in smectite, remaining Cs+ or Na+ in cesium- or sodium-saturated smectite specimen (Cs- or Na-specimen), respectively, were examined after Ba2+ exchange using a tracer method. The location of sorbed Cs+ in smectite was also studied by X-ray photoelectron spectroscopy (XPS). A linear multiple regressive model has been used to formulate a relation between the amount of cesium left after Ba-exchange of Cs- specimen and the layer charge characteristics. A good correlation between the amount of remaining Cs and octahedral charge was observed for the Cs-specimen whereas for Na-specimen there was no viable change. From the analysis of the chemical states of sorbed-Cs by XPS, two sorption sites were proposed for the Cs-specimen.

Acidity and 1-butene isomerization of synthesized smectite-type catalysts containing different divalent cations

Abstract Smectite-type materials which contain different divalent cations (Ni 2+ , Co 2+ , Mg 2+ , and Zn 2+ ) in octahedral sheets have been synthesized and characterized by pyridine adsorption and catalytic effectiveness for the isomerization of 1-butene. All smectite-type materials examined have Lewis acid sites; however, the activity values for the isomerization of 1-butene significantly depend on the divalent cation species included. Nickel-containing smectite-type catalysts are stable and the most active among the smectite catalysts.

RHEOLOGICAL PROPERTIES OF ORGANOPHILIC SYNTHETIC HECTORITES AND SAPONITES

To determine the dependency of rheological properties on mineralogical characteristics, eleven organophilic hectorite and nine organophilic saponite samples were prepared from hydrothermally synthesized smectites and a quaternary ammonium salt containing mainly octadecyl groups as alkyl chains and were examined by X-ray powder diffraction (XRD), particle size, chemical, and rheological procedures. The rheological properties of the organophilic products dispersed in toluene were found to depend chiefly on (1) particle size, (2) the expansion behavior of the stacked clay platelets, in which the amount and location of negative charge of the silicate layer affected the expandability, and (3) the amount of methanol added as a polar activator. By the addition of 2–4% methanol, apparent viscosities of the hectorite clays were drastically increased at low shear rate, although even a 10% addition did not significantly affect the saponite clays. Under the most suitable gellation conditions, the saponite clays showed lower apparent viscosity than the hectorite clays. Inasmuch as the former had its negative charge near the surface of the silicate layer and formed strong bonds to the organic ion, the expansion of the platelets was apparently difficult. An optimum layer charge for increasing the viscosity was found; specifically 0.45–0.50 and 0.50–0.55 equivalents per half unit cell for saponite and hectorite clays, respectively. Because the saponite clays contained a denser population of organic ions than the hectorite clays, the ion density in the interlayer of both clays was considered to be the same, i.e., about 0.4 organic ions per unit ab area.

Hydrothermal Synthesis of Novel Smectite-Like Mesoporous Materials

Hydrothermal reaction of slurries made from Si-Mg hydrous oxide and water yielded trioctahedral smectite-like mesoporous materials (SMMs). The OH anion had a marked effect on the properties of SMMs under hydrothermal condition whereas Na cation did not influence SMMs properties. With the increase in synthesis pH at 200°C, pore volume, specific surface area and average pore diameter decreased whereas methylene blue adsorption increased in the pH range of 8.5 to 11.4. Therefore, the SMMs having different layer charges could be synthesized. Both micropore and macropore formation rates decreased with increasing synthesis temperature in the range of 125–200°C and the formation of latter increased over 200°C. As a result, the SMMs synthesized at 200°C from slurries of pH 9.0–9.3 revealed the maximum mesopore formation rate: 0.98 and gave a narrow pore size distribution curve of 3–5 nm. The SMMs were characterized by specific surface areas of 243–679 m2 g-1, pore volumes of 0.20–0.48 cm3 g-1, average pore diameters of 2.2–5.4 nm and methylene blue adsorption values of 0.16–0.96 meq · g-1.

Use of silicate crystallite mesoporous material as catalyst support for Fischer-Tropsch reaction

Abstract Novel uniform mesoporous materials (silicate crystallite mesoporous material, SCMM) were synthesized by hydrothermal treatment of Si, Mg and/or Al containing hydroxide precipitates, along with quaternary ammonium salt, and were applied as catalyst support for Fischer–Tropsch reaction. SCMM is composed of aggregates of homogeneous layer silicate crystallites, as identified by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) photographs which are structurally analogous to smectite clay. The mesopore of SCMM corresponds to interparticle space of disk-shaped crystallites (6–25 nm in diameter) aggregated by edge-to-face bonding. Two kinds of SCMM with variable negative charge locations were used as support materials of Co-catalysts for hydrogenation of CO. Conversion of CO was high on SCMM compared with that of silica gel. Furthermore, the main products obtained were hydrocarbons. In case of SCMM type with negative charge near the surface, olefins and branched hydrocarbons were efficiently produced in CO conversion reaction; where as another SCMM type having negative charge at the middle of crystallite platelets produced mainly normal hydrocarbons for the same reaction. This may be due to the role of the negative charge of SCMM which affects the chemical state of Co-catalyst supported on SCMM. The function of SCMM as compared to other mesoporous materials is better in terms of homogeneous and site-specific distribution of negative charge, which is further helpful in controlling the surface phenomenon as confirmed by the existence of linear CO species adsorbed on Co.

Electronic and structural properties of montmorillonite—a quantum chemical study

The importance of geometry and its relation with property in montmorillonite have been studied in terms of octahedral aluminum and tetrahedral silicon present in the framework. Quantum chemical (QC) calculations were performed using MNDO (modified neglect of differential overlap) and DFT (density functional theory) is reported. Cluster calculations were performed on two octahedral aluminum sites present in the unit cell of montmorillonite to show the distinguishability between the two octahedral aluminums. The energy difference between two aluminum octahedral cluster was 1.12 eV. This was further justified by the calculation of magnesium substitution energy for two different positions of aluminum. This difference in two octahedral aluminum sites was mainly due to the typical orientation of the bridging hydroxyl groups attached with the octahedral aluminums. Calculations were also performed on tetrahedral silica hexagons with and without aluminum substitution to predict the Bronsted acid strength of the surface both by MNDO and DMOL QC methods; which shows that aluminum substitution is an unfavorable process in this type of clay. The above structure property relationship in case of montmorillonite will further help in explaining the catalytic activity of the material.

Cobalt-containing smectite-like mesoporous material as a new type of catalyst for hydrodesulfurization of thiophene

Cobalt‐containing mesoporous smectite‐like material (SM(Co)) was prepared by a hydrothermal method and used as a catalyst for hydrodesulfurization (HDS) of thiophene. It is active by itself and produces mainly butenes and a small amount of n-butane. When platinum is added to this material, the HDS activity is enhanced by 50%, while the product distribution does not change so much. The platinum‐loaded sample should have two types of active sites, one originally present in the smectite‐like material and the other with platinum, the latter being different in nature from a sample of platinum supported on silica gel. Thus, the SM(Co) and Pt/SM(Co) samples are new types of HDS catalysts.

Catalytic properties of hectorite-like smectites containing nickel

Abstract The catalytic behavior of a series of newly synthesized smectites which contain nickel in the lattice was investigated for the decomposition of 2-propanol. The smectites were found to have both weak acid and base sites, the latter prevailing. The main product of the decomposition was acetone which was accompanied by a series of dimers and trimers of propene and condensates between acetone and propene. These oligomers are believed to be formed in the interlayer of the smectites where 2-propanol is easily accessed but propene is not. The activity depends on the composition of the smectites; those containing nickel are active, while those containing fluorine atoms lose activity. An empirical correlation was obtained between the activity and the elemental composition of the smectites.

Hydrothermal treatment and strontium ion sorption properties of fibrous cerium( IV ) hydrogenphosphate

Fibrous cerium hydrogenphosphate, CeP, has been treated hydrothermally in 1 mol dm -3 phosphoric acid solution. CEP and its hydrothermally treated product, CeP(HT), have been characterized by X-ray powder diffractometry, scanning electron microscopy, solid-state 31 P MAS NMR spectroscopy, FTIR spectroscopy, chemical and thermal analyses. A poorly crystalline fibrous CeP with a d-spacing of 1.1 nm converted into a highly crystalline CeP(HT) with platelet morphology by hydrothermal treatment. Solid-state 31 P MAS NMR and FTIR measurements confirmed that one kind of phosphate (H 2 PO 4 ) is present in CeP and two kinds of phosphate (HPO 4 , PO 4 ) are present in CeP(HT), in which the integrated intensity ratio of HPO 4 to PO 4 is 2:1. From chemical and thermal analyses, structural formulae for CeP and CeP(HT) are assumed to be CeO(H 2 PO 4 ) 2 2H 2 O and Ce(HPO 4 ) (PO 4 ) 0.5 (OH) 0.5 , respectively. The Na + exchange capacity of CeP amounted to 4.5 mmol g -1 at pH 11 while that of CeP(HT) was less than 1.0 mmol g -1 in the pH range 2–12. The pH dependence of the metal ion distribution coefficients exhibited ideal ion-exchange behaviour on CeP while metal ion distribution coefficients on CeP(HT) scarcely depended on pH. The metal ion selectivities of CeP and CeP(HT) increased in the order: Na + <Ca 2+ <Sr 2+ <K + , and Na + <K + <Ca 2+ <Sr 2+ , respectively. The distribution coefficient for the Sr 2+ ion of CeP(HT) was higher than that of CeP under hydrothermal conditions.

Hydrodesulfurization of thiophene over synthetic cobalt-containing smectite-like mesoporous materials

Abstract Mesoporous smectite-like materials containing cobalt, SM(Co), were synthesized by a hydrothermal method under different conditions. The materials were used as catalysts for hydrodesulfurization (HDS) of thiophene. The SM(Co) sample is a new type of active HDS catalyst. The activity depends on the synthetic conditions used, but the product distribution does not change so much, giving trans -2-butene, cis -2-butene, and 1-butene with a minor product of n -butane. The high HDS activity of SM(Co) samples may be explained by higher degrees of cobalt dispersion due to the method of preparation used. In addition, the treatment of SM(Co) samples with ammonia solution is effective in enhancing their HDS activities, in particular for originally less active ones. The treatment removes Na + species involved and this may suppress structural changes of SM(Co) samples by HDS reactions. The ammonia-treated samples maintain high surface area and include much lower concentrations of Na + species, which would have a negative effect on the activity, and so they indicate enhanced HDS activity.