John Leonello Casci

Strategies in developing routes to commercialization of novel high silica zeolites

In this paper we will contrast the exciting initial work of finding new molecular sieves and the follow-up items needed to address moving forward with application development of a material. Principally, to arrive in the marketplace, the economics must be attractive for introducing new technology. A key hurdle in the production of high silica zeolites, metallophosphates, metalloorganic frameworks, and many novel silicogermantes, is the management of the costs concerning the guest organo-cations and amines used as structure directing agents (SDAs). In this discussion we will describe several novel routes attempting to create a positive impact on this issue.

Macro-cellular silica foams: synthesis during the natural creaming process of an oil-in-water emulsion

The room-temperature synthesis of a macro-mesoporous silica material during the natural creaming process of an oil-in-water emulsion is reported. The material has 3-dimensional interconnected macropores with a strut-like structure similar to meso-cellular silica foams with mesoporous walls of worm-hole structure. The material has very high surface area (approximately 800 m2 g(-1)) with narrow mesopore size distribution.

Molecular modelling of templated zeolite synthesis

A Monte Carlo–simulated annealing (MC–SA) method has been used to predict the location and conformation adopted by template molecules within the bulk and on the growing surface of the zeolite products they form. This approach has been used to give a unique insight into several important aspects of zeolite synthesis, including structure-blocking effects. New approaches for novel synthesis work and computational strategies are identified.

Template design for high-silica zeotypes: A case study of zeolite nes synthesis using a designed template

Abstract This paper describes a combined Preparation, Structure Determination and Modelling study aimed at the design of a novel template for the NES zeotype. The starting point for this work was the knowledge of the structural relationship between the NES and EUO frameworks and the modelling and crystallography that provided the location and conformation of the template (hexane- 1,6-bis(trimethylammonium)) originally used to prepare the EUO zeolite structure. The structural and template conformation information was combined with knowledge of the unit cell composition (number of aluminium atoms and hence charge) to provide a “model” of an alternative template “family”: a di-quaternary ammonium species. Various members of this “template family” were modelled (in NES structure). Based on binding-energy calculations, a particular member was selected. This hypothetical template was then synthesised and used in NES type preparations. Under particular conditions, specifically for gallo-silicate compositions, high purity NES was formed.

Hierarchically ordered porous silica composites: Ordering on three different lengths with three dimensional pore inter-connectivity

A room temperature synthesis of hierarchically ordered porous silica is reported using colloidal spheres and a tri-block co-polymer surfactant as templates. Macropore size and ordering were controlled using a close-packed monolith of polystyrene latex spheres whereas mesoscale ordering was controlled using a surfactant containing different EO-PO-EO groups (F127:EO108PO70EO108 or P123:EO20PO70EO20) in the presence of a co-surfactant (n-butanol or n-pentanol). The thickness and pore interconnectivity of macropores was controlled either using a silica gel containing such surfactants or using a colloidal suspension of silica or zeolite nano particles as building units. Macrospheres with interconnected windows (70–130nm) are formed when surfactant containing silica gel was used as building units whereas hollow silica macrospheres without interconnecting windows are formed when nano particles were used as building units. XRD, TEM and N2 adsorption results suggest the presence of mesopores. Nitrogen adsorption results indicate the presence of micropores (<2nm) in the mesoporous walls. The mesopores are interconnected with macropores and micropores. The surface area of such materials was improved when the polystyrene latex template was removed by solvent extraction before calcination at a specific temperature. The probable mechanism of formation of such hierarchically ordered porous silica is presented.

Modelling mesoporous materials

Publisher Summary Mesoporous materials of the MCM or SBA variety are by nature organized amorphous materials. To describe their structure, it is necessary to utilize a model that can accommodate both the organization and the disorder. A structural model allows further properties of a phase to be anticipated and also allows the visualization of a structure, which helps understand these novel complex materials. The wall structure of mesoporous materials can be described via an analytical expression. In situations where a mesoporous material is synthesized from a surfactant mesophase based upon a three-dimensional packing of globular micelles, the mathematics based on the exponential scale of a Gaussian distribution works very well. This chapter describes the structure of SBA-1 in this manner; the details of the micellar structure, including oblate distortions of globular micelles, are retained in the final inorganic structure. A preliminary mechanism for a window size in mesoporous materials is also discussed in the chapter.

Synthesis and activation for catalysis of Fe-SAPO-34 prepared using iron polyamine complexes as structure directing agents

The use of transition metal cations complexed by polyamines as structure directing agents (SDAs) for silicoaluminophosphate (SAPO) zeotypes provides a route, via removal of the organic by calcination, to microporous solids with well-distributed, catalytically-active extra-framework cations and avoids the need for post-synthesis aqueous cation exchange. Iron(II) complexed with tetraethylenepentamine (TEPA) is found to be an effective SDA for SAPO-34, giving as-prepared solids where Fe2+–TEPA complexes reside within the cha cages, as indicated by Mossbauer, optical and X-ray absorption near edge spectroscopies. By contrast, when non-coordinating tetraethylammonium ions are used as the SDAs in Fe-SAPO-34 preparations, iron is included as octahedral Fe3+ within the framework. The complex-containing Fe-SAPO-34(TEPA) materials give a characteristic visible absorption band at 550 nm (and purple colouration) when dried in air that is attributed to oxygen chemisorption. Some other Fe2+ polyamine complexes (diethylenetriamine, triethylenetetramine and pentaethylenehexamine) show similar behaviour. After calcination in flowing oxygen at 550 °C, ‘one-pot’ Fe(TEPA) materials possess Fe3+ cations and a characteristic UV-visible spectrum: they also show appreciable activity in the selective catalytic reduction of NO with NH3.

Understanding the growth mechanism in SBA-1 synthesis

Abstract We have used a combination of time resolved energy dispersive x-ray diffraction, 17 O, 29 Si and 14 N NMR, to examine the kinetics of hydrolysis, organisation and polymerisation in the synthesis of SBA-1. We have also examined the phase diagram for the surfactant used in the preparation, cetyltriethylammonium bromide, by optical polarised light microscopy and 14 N NMR. We establish the order and timing of a number of events in SBA-1 formation.

Post-Mortem investigation of Fischer Tropsch catalysts using cryo- transmission electron microscopy

Co/Al2O3 catalysts are widely used in the Fischer-Tropsch, gas to liquids (GTL), catalytic reaction where syngas (CO2 and H2) is converted into higher hydrocarbon wax products. One important use of the wax product is through cracking to produce clean diesel fuel. In most production routes the catalyst is initially in the form of highly dispersed Co-oxide particles on a high surface area gamma alumina with up to 1 wt% addition of a precious metal promoter. The catalyst can then be reduced to its active state in-situ in the FT reactor or supplied in pre-reduced form. In the case of the prereduced catalyst the material is encapsulated in a wax product to prevent re-oxidation of the cobalt. Post reaction the catalyst is suspended in the wax product of the FT reaction. It is of paramount importance to analyse the initial state and the final state of a catalyst in order to understand how the reaction has progressed. Any pre or post-reactor analysis therefore needs to deal with the wax but leave the catalyst unchanged. However, the dewaxing procedures traditionally applied to the catalyst, (Soxhlet extraction and calcination at 350°C) before examination, not only partially oxidize the Co but also cause some changes in the microstructure. Consequently, the combination of Cryoelectron microscopy and cryo-microtomy offer a straightforward, but unique, route to analyse the catalyst within its original wax environment.

Targeting formation in microporous and mesoporous materials

Inorganic, ordered microporous and mesoporous materials have utility in a continuum of applications. However, the formation of these materials relies on different, yet overlapping chemistry. As a consequence the tools at our disposal to study the formation mechanisms have to be carefully selected. The goal of this paper is to illustrate some of these techniques using the mesoporous silica SBA-1 as an example with a view to understanding how both structural and kinetic measurements can be married in such a way to produce a consistent picture of the mechanism of formation.