A. Yu. Derevyankin

Mesopore size and surface area calculations for hexagonal mesophases (types MCM-41, FSM-16, etc.) using low-angle XRD and adsorption data

This paper is devoted to the geometry of mesoporous mesophase systems (MMSs) of the MCM-41 or FSM-16 texture types. The interrelations among surface areas inside and outside the mesoporous blocks of the MMS, of the size and the volume of mesopores are discussed. The equations for calculating these textural characteristics are derived. These equations are based on adsorption data and X-ray diffraction studies, and are applied for considerations of the silica and zirconia hexagonal MMS texture. The approach was used for a critical review of the results published by other authors for similar systems.

Alkene and thioether oxidations with H2O2 over Ti- and V-containing mesoporous mesophase catalysts

Abstract Well-organized Ti- and V-containing silicate mesoporous mesophase materials (MMM) were synthesized using C 16 H 33 N(CH 3 ) 3 Br and characterized by elemental analysis, IR, DRS-UV, XRD, and N 2 adsorption. Catalytic properties of these materials in alkene and thioether oxidations with aqueous H 2 O 2 were examined. The structure–activity study was performed for the C16-(Ti,Si)-MMM catalysts with the Si/Ti atomic ratio ranged from 19 to 166. The samples with the Si/Ti atomic ratio in the range of 49–124 showed the highest catalytic activities. Both structure perfection of the silicate matrix and degree of isolation of titanium ions in it appeared to be crucial factors determining catalytic activity of C16-(Ti,Si)-MMM in alkene oxidation. For efficient oxidation of more nucleophilic substrates (thioethers) the structural perfection of the C16-(Ti,Si)-MMM catalysts was less important. No titanium leaching occurred even in 1.1 M H 2 O 2 solution at 353 K, whereas vanadium leaching was already pronounced at [H 2 O 2 ]=0.05 M and room temperature. The oxidation processes proved to be true heterogeneous for C16-(Ti,Si)-MMM and mostly homogeneous for C16-(V,Si)-MMM.

Comparative textural study of highly ordered silicate and aluminosilicate mesoporous mesophase materials having different pore sizes

Abstract Honeycomb structure model was applied for describing surface properties in the MCM-41 and SBA-15 types of highly ordered silicas and aluminosilicates with different nominal mesopore diameters: about 4 nm and about 10 nm. As shown, calculations of internal specific surface area A me require a heterogeneity of this surface to be taken into account, the latter being quantified by the roughness coefficient β . These calculations at the condition β =1.0 will allow to estimate the lower limit of specific surface area of the materials only, which will correspond to the perfectly smooth walls of mesopores. This description seems to be valid for the MCM-41 type systems, for which β is about 1.1–1.2. On the contrary, β is found to exceed 1.5 for the SBA-15 type materials. This fact is probably due to an essential non-smoothness of the mesopore surface in these systems and may be associated with their synthesis conditions.

Mesoporous basic zirconium sulfate: structure, acidic properties and catalytic behaviour

Abstract Some properties of a thermostable mesophase of basic zirconium sulfate with texture characteristics close to those of MCM-41 are described. After calcination at 550 °C the mesophase exhibits a specific surface area of mesopores of 450–500 m2g−1. The peculiarities of the catalytic behavior of the mesophase are related to its acidic properties.

The characterization of the structure and texture of pillared interlayer materials

Abstract A method for the correct characterization of the structure and texture of pillared interlayered materials (PIM) is developed. This method is based upon the combined analysis of XRD and adsorption data within the frames of a geometrical PIM model. The application of this method is illustrated by analysis of the structure of pillared montmorillonite clays. Among the structural and textural parameters successfully estimated by this method are specific values of the accessible micropore surface Am and volume Vm, a degree of the interlayer space filling by a guest (pillars), a degree of PIM ordering, the interpillar distance etc.

Mechanism of the formation of porous silicate mesophases

The formation of mesoporous mesophase systems prepared by precipitation of soluble forms of SiO2 at the surface of micelles of cetyltrimethylammonium cations was examined. A molecular mechanism of the formation of a silicate coating and a macroscopic mechanism of the formation of a mesophase were found and discussed. A combination of these mechanisms describes the processes proceeding during the synthesis. It can also explain the observed changes in the structure and texture characteristics of the mesophase.

Physicochemical features of the formation of siliceous porous mesophases: 1. General views on the mechanism

The formation of mesoporous mesophase materialsvia precipitation of soluble SiO2 forms on the surface of cationic cetyltrimethylammonium micelles was studied. The main physicochemical factors determining the formation of siliceous mesoporous materials and providing an explanation of the observed changes in the structural and textural characteristics of the materials were identified and discussed.

Physicochemical Properties of Mesoporous Mesophase Silicate Materials Formed via the Electrostatic S+I– Mechanism

The formation of the structure of a highly organized silicate mesoporous mesophase material (MMM) with hexagonal packing via the S+I–reaction pathway and MMM-based aluminosilicates (Al,Si)-MMM and titanosilicates (Ti,Si)-MMM with different concentrations of the elements are considered. The structural, textural, and catalytic properties of the materials are studied.

Physicochemical features of the formation of siliceous porous mesophases: 2. Effect of the size of the surfactant cation

The formation of siliceous mesoporous mesophase materials (SiO2-MMM) prepared by precipitation of soluble forms of SiO2 with alkyltrimethylalkylammonium bromide CnTMABr (n=12, 14, 16, 18 is the number of carbon atoms in the alkyl chain) was investigated. An increase in then value has no influence on the mechanism of formation of SiO2-MMM but causes an increase in the size and volume of mesopores with the mesopore specific surface area and wall thickness remaining virtually constant.

Physicochemical features of the formation of siliceous porous mesophases 4.* Effect of duration and temperature of the hydrothermal treatment on the structural and textural properties

The results of investigation of mesoporous mesophase materials C12--SiO2--MMM and C16--SiO2--MMM prepared at the optimized composition of the reaction mixture and different durations of hydrothermal treatment (HTT) at 120 °C and 140 °C are presented. Hydrothermal treatment at 120 °C influences slightly the specific surface area and the volume of the mesopores but gives a more ordered structure. Prolonged HTT at 140 °C results in irreversible structure degradation. The samples obtained with the optimal HTT duration are characterized by the minimum width of X-ray reflections, the maximum surface and volume of mesopores, and the minimum external surface.