Noreen Hanif

Growth models in microporous materials

Crystallisation pathways in framework materials, such as zeolites, have been monitored using a combination of atomic force microscopy, high-resolution electron microscopy and modelling. The principle conclusions of this study is that many open-framework crystals grow via a layer growth mechanism. The layers have a thickness which is related to the unit cell parameter in the direction of growth. The development of each layer can be sub-divided into a number of individual growth processes including nucleation of a new layer (or terrace), growth at edge sites and kink sites. Modelling of atomic force micrographs yields relative probabilities for these individual growth processes and reveals that growth at kink sites is favoured with nucleation of new terraces the slowest process. The layer mechanisms proposed explain the incorporation of defects in framework structures and further elucidate the role of structure directing agents.

Crystal growth in framework materials

Crystal-growth phenomena in open-framework microporous materials are explored using a combination of atomic force microscopy, high-resolution electron microscopy and modelling. Analogies are drawn between these open-framework systems and dense phase structures. In particular we discuss the role of organic structure-directing agents, commonly known as templates and suggest a new philosophy for predicting suitable molecules. We also discuss the role of defects in the crystallisation of open-framework materials and the effect of crystallisation processes on the incorporation of defects and intergrowths.

Fundamental Zeolite Crystal Growth Rates from Simulation of Atomic Force Micrographs

An accurate model of the surface growth of one of the most important industrial zeolites, zeolite A, has been created. Comparison of the simulation with experimental data in the form of atomic force micrographs highlights the non-diffusion-limited nature of zeolite growth and provides the first ever quantification of fundamental crystal growth processes in zeolites.

The effect of stirring on the synthesis of intergrowths of zeolite Y polymorphs

This paper is concerned with the role of organic structure-directing agents during competitive synthesis of zeolite intergrowths. The system chosen for study is that of the intergrowth between the cubic (FAU) and hexagonal (EMT) polymorphs of zeolite Y. These two polymorphs can be synthesised using crown ether templates and it has been previously shown that mixtures of crown ethers produce intimate intergrowths of FAU and EMT. It was also previously suggested that concentration gradients of crown ethers at crystal growing surfaces are responsible for an oscillation of the structure between the two phases rather than a completely random intergrowth. In this current work we have made a detailed study of comparative syntheses, both stirred and static, in order to assess the role of diffusion of structure-directing agents to a growing crystal surface. Using a combination of high-resolution electron microscopy, X-ray diffraction and modeling we have established that diffusion-limited transport of structure-directing agents to growing crystal surfaces is an important factor controlling the final product. We also establish the “true” threshold concentration of crown ethers to synthesise each individual phase. This work has consequences for our general understanding of structure-directed growth of microporous crystals.

02-O-05 - Atomic force microscopy (AFM) used to relate surface topography growth mechanisms in SSZ-42

Publisher Summary This chapter describes the atomic force microscopy (AFM) of the three faces of the microporous material SSZ-42. Interesting surface features have been observed on each face that is distinct and related to the structure of SSZ-42. These features have been used to determine the crystal growth mechanism of SSZ-42. This chapter describes a layer growth mechanism whereby the growth of crystals occurs at terrace sites and edges from nutrient in the solution and elucidates the templating mechanism.

Ordered intergrowths of ETS-10

Abstract When solving the structure of ETS-10, Anderson et al. [1,2] discovered the crystals to be highly disordered. This disorder was shown to arise as a consequence of stacking faults, and defects. The density of defects is expected to be of considerable significance to the physical and chemical properties of ETS-10. It is therefore important that methods for the quantification of defects are developed. The number and type of defects within a sample is likely to be related to the synthetic conditions used during sample preparation. Hence, it may be possible to control the disorder through variation in synthetic parameters. In particular, variation in the synthesis temperature, mode of heating (conventional/microwave), starting reagents and the use of structure-directing agents may influence the degree of disorder within the product. To date, little detailed work had been carried out on the characterisation of disorder within ETS-10. A recent study by Howe et al. has attempted to correlate catalytic activity, crystal morphology and spectroscopic techniques to disorder within the structure[3]. Here we develop a method for quantification of structural defects in ETS-10 and show that a significant degree of skew towards one particular polymorph can be induced and controlled. The results also indicate that a new structure, related to ETS-10, with a 3-dimensional wide-pore channel system is observed to intergrow with ETS-10. This new titanosilicate structure is likened to the polymorph C of zeolite beta.

04-O-05-Synthesis and characterisation of novel large-pore vanadosilicates AM-13 and AM-14

Publisher Summary This chapter discusses the synthesis and characterization of novel large-pore vanadosilicates Aveiro–Manchester, structure number13 (AM-13) and 14 (AM-14). Characterization techniques, such as bulk chemical analysis (ICP), powder X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy, and N 2 , n -hexane, benzene, tripropylamine and perfluorbutylamine adsorption measurements are used for the structural studies. The acid–base and redox properties of these materials are assessed by the conversion of isopropanol and ethanol oxidation, respectively. Both materials exhibit high selectivity to acetaldehyde indicating that these two novel vanadosilicates are promising redox catalysts.