Stephen A. Bagshaw

Mesoporous [M]-MSU-x metallo-silicate catalysts by non-ionic polyethylene oxide surfactant templating acid [N0(N+)X-I+] and base (N0M+I-) catalysed pathways

Solutions of low and high pH have been used to form non-ionically templated mesoporous metallo-silicates [M]-MSU-x materials; where [M]=Al, Ti, V and Zr. Two new assembly routes are proposed which exploit the acid and base catalysed hydrolysis and simultaneous condensation of metal oxo-salts and silicon tetraethoxide. Acid catalysed hydrolysis, labeled N0X−I+ or N+X−I+ (N0=nonyl-phenyl polyethylene oxide, X−=Cl− or SO2−4, I+=protonated tetraethyl orthosilicate), produces well-defined materials with uniform pores in the small mesoporous region and moderate pore volumes, but reduced metal incorporation owing to the high solubilities of metal cations in acidic solutions. Base catalysed hydrolysis, labeled N0M+I− (N0=nonyl-phenyl polyethylene oxide, M+=Na+ or NH+4, I−=hydroxylated tetraethyl orthosilicate), also leads to materials with uniform channels in the small mesoporous region. Pore volumes and metal substitution are higher and framework shrinkage during calcination is reduced as a result of thicker pore walls. These new pathways show distinct similarities to those described by Attard et al. [Nature 378 (1995) 366] and Zhao et al. [Science 279 (1998) 548] for the formation of hexagonally symmetric silica from non-ionic surfactants under acidic conditions and also to mesoporous MCM-41 assembly routes via (S+X−I+) anion mediated acid catalysed assembly. The results demonstrate the feasibility of preparing templated mesoporous metallo-silicates from non-ionic polyethylene oxide surfactants and metal oxy-hydroxy cationic precursors, but indicate that further optimisation of the reaction conditions is required to maximise the potential of this synthesis approach.

Super-Microporous Silicate Molecular Sieves

A new synthesis of supermicroporous silica (1.6–2.0 nm diameter), using micelles of a quaternary ω-hydroxyalkylammonium salt, is presented by the authors. The material exhibits highly ordered pore arrays (see Figure). Details on pore size determination by adsorption techniques are given. In an outlook, the effects of template chain length and of Al or Ti doping (catalytic centers) on pore size and array stability are discussed.

The effect of dilute electrolytes on the formationof non-ionically templated [Si]-MSU-X mesoporous silica molecularsieves

The effect of adding dilute electrolytes to the synthesis of non-ionically templated [Si]-MSU-X mesostructures has been investigated. An assembly process, (N0M+)(X−I0), is described that takes into account both the non-ionic template/electrolyte and the silicate/electrolyte interactions. Monovalent cations (H+, Li+, Na+, K+, Cs+, NH+4) intervene in the template/silicate assembly process directing either the shape or the order of the macro-molecular templating structures to form worm-like and hexagonally ordered pore structures or bimodal mixtures of the two. Anions (F−, Cl−, Br−, I−, SO2−4, NO−3, OAc−) interact with the tetraethylorthosilicate (TEOS) silica precursor to effect modifications in the rate of TEOS hydrolysis, the rate of particle nucleation and hence final particle size and the extent of silica cross-linking in the final templated material.

Highly ordered mesoporous MSU-SBEA/zeolite Beta composite material

The synthesis, in one-pot, of an intimate composite material that simultaneously possesses ordered mesostructured MSU-SBEA and well-defined zeolite Beta (*BEA) material over micron-scale domains is described. The synthesis is a simple solution-based two-step reaction that is a modification of the Al-MSU-SBEA system and permits control of most physico-chemical aspects of both components of the composite material. The method appears to significantly improve the materials and catalytic properties of either of the individual components of the composite. Through manipulation of reaction alkalinity, Si/Al reagent ratio and crystallization time, control over the micropore/mesopore ratio, the SiO2/Al2O3 ratio and the extent of crystallization can be achieved. While the composite material simultaneously exhibits highly ordered arrays of hexagonal mesopores and microporous zeolite Beta (*BEA), the particles tend to exhibit only the morphology of *BEA. The synthesis system also allows highly ordered pure end members of zeolite *BEA or hexagonal Al-MSU-SBEA to be prepared. The structural properties of the material combine aspects of both micro- and mesostructure, while the catalytic properties reflect those of zeolite *BEA with improved diffusional characteristics of the mesostructure. The catalytic properties of the new material do not exactly match those of physical admixtures of Al-MSU-SBEA and *BEA, thereby suggesting that the new material is more structurally and catalytically homogeneous than a simple mixture.

Wairakei geothermal silica, a low cost reagent for the synthesis of mesostructured M41S alumino-silicate molecular sieves

A precipitated silica, produced as a waste product from the Wairakei geothermal field and power station in the central North Island of New Zealand, has been found to be highly active in the hydrothermal synthesis of high quality mesostructured M41S alumino-silicate molecular sieve materials.

Synthesis of novel super-microporous silicates by ω-hydroxy alkyl ammonium halide bolaform surfactant templating

Abstract Using a new family of ω-hydroxy alkyl ammonium bromide bolaform surfactants as supramolecular templates we have prepared a range of novel templated super-microporous (1.0–2.0 nm) SiO 2 , Al– and Ti–SiO 2 molecular sieve materials. The unique bi-functional molecular structure of the template induces smaller micelle diameters of the template assemblies along with interesting aggregation symmetries. These properties allow templating of porous materials that exhibit technologically important small pore sizes and interesting pore symmetries that bear similarity to Lα, P6 3 /mmc and Mα (cmm) phases.

MORPHOSYNTHESIS OF MACROCELLULAR MESOPOROUS SILICATE FOAMS

Silicate macroskeletons which have both templated mesoporosity and open-cell macrovoid structures have been prepared in monolithic form at near ambient temperatures from continuous metastable foams of non-ionic alkylpolyethylene oxide surfactants under aqueous, neutral pH reaction conditions.

Bimodal pore systems in non-ionically templated [Si]-MSU-X mesoporous silica through biomimetic synthesis in weakly ionic solutions

Non-ionically templated [Si]-MSU-1 mesoporous silicas have been prepared in weakly ionic sodium salt solutions from a non-ionic silica precursor and exhibit highly symmetric bimodal mesopore systems and demonstrate the immense flexibility of the non-ionic templating system.

Wairakei geothermal silica; a low cost reagent for the synthesis of low, intermediate- and high-silica zeolites

Abstract A precipitated silica, produced as a waste product from the Wairakei geothermal field and power station in the central North Island of New Zealand, has been found to be active in the hydrothermal synthesis of a range of zeolite molecular sieves of various structure types: Sodalite (SOD), Linde type A (LTA), Linde type Y (FAU), Mordenite (MOR), ZSM-5 (MFI) and Beta (*BEA). The natural silica reagent contains reactive aluminium (Al) and iron (Fe) impurities that can be either included or excluded from the zeolite frameworks depending on the synthesis conditions. High alkalinity syntheses (SOD, LTA, FAU, MOR) tend to include Al, while Fe is excluded from the zeolite lattices. The crystalline zeolite products that result are white to off-white in colour. Lower alkalinity syntheses that require organic structure-directing agents (SDA), zeolites MFI and *BEA, include less Al but higher amounts of Fe, producing off-white to pale brown products. Both the crystallinities and compositions of zeolites MOR, MFI and *BEA are modified by rotation of the autoclave during synthesis.

Novel super-microporous silicate templating by ω-hydroxyalkylammonium halide bolaform surfactants

Templated silicate molecular sieves exhibiting templated super-micropores in the range 1.0–2.0 nm and interesting pore symmetries bearing similarity to the Lα, SBA-2 (P63/mmc) and Mα (cmm) phases have been prepared by exploiting the novel aggregation properties of a new family of ω-hydroxyalkylammonium bolaform surfactants.