Stuart W. Carr

Materials chemistry communications. Synthesis of a zeolite NaA membrane

A self-supporting zeolite NaA membrane has been synthesized from an initially homogeneous hydrothermal solution. Membranes ca. 7 µm thick were formed successfully on polyethylene, glass and poly(tetrafluoroethylene) substrates.

Intergrowths of cubic and hexagonal polytypes of faujasitic zeolites

Intergrowths of hexagonal and cubic phases of faujasitic structure have been synthesised using crown ether templates and the phase integrity monitored by high-resolution electron microscopy.

Synthesis of self-supporting zeolite films

Self-supporting polycrystalline films of zeolites ZSM-5 and gmelinite, one crystal thick, have been synthesized on polymer substrates. The films exhibit high crystallinity and high adsorption capacities and demonstrate the potential for growing molecular-sieve membranes.

The structure of the calcined aluminophosphate ALPO4-5 determined by high-resolution X-ray and neutron powder diffraction

Rietveld refinements of the structure of calcined ALPO4-5 have been performed using synchrotron and neutron powder diffraction data. The high-resolution synchrotron X-ray diffraction pattern shows splitting of some peaks, which indicates that the symmetry is lower than the hexagonal cell observed in earlier studies. The neutron powder pattern is of lower resolution and no splitting is apparent, but the different scattering lengths of Al and P, and the higher scattering power at high angle, provide a sound test for the different models investigated. Good fits of the neutron and synchrotron data were obtained in space group Pcc2 with cell parameters a= 13.794(3)A, b= 23.900(6)A, c= 8.4168(6)A. In this space group there is a strict alternation of Al and P in the framework, as the 31P and 27Al MAS NMR spectra indicate, and two crystallographically distinct 12-ring channels run parallel with the c axis.

Observations on the Role of Crown Ether Templates in the Formation of Hexagonal and Cubic Polymorphs of Zeolite Y

Intergrowths of hexagonal and cubic polymorphs of zeolite Y have been synthesized using crown-ether templates and the manner of the intergrowth between the polymorphs was studied by high-resolution electron microscopy. The images reveal that both polymorphs grow via a layer mechanism and it is suggested that double-six ring units are the key unit for crystal growth. The growing mechanism accounts for surface structures, defect structures and overall particle morphology. Oscillatory growth occurs in syntheses from multiple crown ether preparations whereby the crystal makeup changes from hexagonal to cubic as surface concentrations of crown ethers fluctuate during crystallization. Finally, the structure directing role of the crown ethers is discussed.

14 N NMR study of surfactant mesophases in the synthesis of mesoporous silicates

Surfactant mesophase formation during the synthesis of M41S, the mesoporous material, has been studied using 14N nuclear magnetic resonance spectroscopy. Siliceous gels producing M41S materials displaying hexagonal and lamellar powder X-ray diffraction patterns have been observed to contain hexagonal mesophases which revert to an isotropic solution after heating while X-ray diffraction shows the silicate to be ordered.

Synthesis and characterization of bis(trialkoxysilymethyl)arenes from related bis(trichlorosilylmethyl)arenes. Comparisons between some organosilicate xerogel materials derived from both

A series of bis(trialkoxysilylmethyl)aryl compounds1–17 {[(RO) 3 SiCH 2 ] 2 Ar, R=Me, Et, Pr , Bu, Ar=1,4-C 6 H 4 ; R=Et, Pr, Bu, Ar=1,4-C 6 H 2 Me 2 -2,6; R=Et, Pr, Bu, Ar=1,4-C 6 Me 4 -2,3,5,6 ; R=Et, Pr, Bu, Ar=1,3-C 6 H 4 ; R=Bu, Ar=1,2-C 6 H 4 ; R=Et, Pr, Bu, Ar=9,10-C 14 H 8 } prepared from the related bis(trichlorosilylmethyl)aryl compounds and characterised by 1 H, 13 C and 29 Si NMR and IR spectroscopy, and high resolution mass spectrometry. The X-ray crystal structures of two of the bis(trichlorosilylmethyl)aryl precursor compounds are reported. Organosilicate xerogels prepared from the precursors 2,7 and 12 are discussed. These have been studied by a combination of solid state NMR spectroscopy, scanning electron microscopy (one case) and nitrogen sorption porosimetry and their properties compared with those of xerogels derived from related bis(trichlorosilylmethyl)arenes.

Calculation of the morphology of silica sodalite

The morphology of all-silica sodalite is calculated using surface simulation techniques, and is found to compare favourably with the experimentally observed morphology.

Synthesis and Structural Studies of Porous Organobridged Silicate Amorphous Powder

Novel amorphous organobridged polysilsesquioxane porous powders have been prepared via hydrolytic precipitation from solutions of 1,4-bis(trichlorosilylmethyl)benzene. These new porous materials have been characterized by SEM, nitrogen sorption measurements and solid state 13C and 29Si NMR spectroscopy. The internal structure and porosity of the amorphous materials are correlated to the process conditions.

Fine Structures of Zeolites: Defects, Interfaces and Surface Structures An HREM Study

Abstract HREM study on fine structures of zeolites, especially defects, interfaces and surface structures is reported by taking examples of LTL, FAU and EMT. Four different boundaries in LTL are shown and an easy way to distinguish them is suggested. It is concluded from observations of atomic resolution surface-profile imaging that double-hexagonal rings act in crystal-growth process as growth-units in FAU and probably in EMT. The first observation of the effect of dealumination on FAU and EMT is reported in atomic scale. Application of HREM to determine the complicated structure, which is impossible to be solved without knowledge of the nature of heavy defects, is also shown for the case of ETS-10 in order to show the advantage of the HREM.