Mesoporous zeolites obtained by desilication

Mesoporous zeolites obtained by desilication

Groen, J.C.

Moulijn, J.A. (promotor)
Pérez-Ramírez, J. (promotor)

Applied Sciences

2007-06-26

Zeolites are crystalline microporous materials consisting of silicon, aluminium and oxygen atoms. A unique combination of properties such as high surface area, high (hydro)thermal stability, and strong acidity, makes that zeolites are frequently used as catalysts in various (petro)chemical processes. The pores of molecular dimensions are responsible for the desired high surface area and shape selectivity but simultaneously suppress the physical transport of reactants and products, which often induces an inefficient utilization and even deactivation of the catalyst. In this thesis the methodology of controlled silicon extraction from the zeolite framework (desilication) in alkaline medium has been developed in order to design combined micro- and mesoporous zeolites. Aluminium in framework positions plays a crucial role in this treatment and directs the mesopore formation process. The treatment has shown to be reproducible, can be extrapolated to various zeolite families, and has successfully been scaled up to the kg-scale. The interplay of micro- and mesopores has led to an improved physical transport of gas molecules in the micropores up to 2-3 orders of magnitude. Importantly, the original acidic properties, associated with the presence of aluminium in framework positions, are still available in the hierarchical zeolite structure, which is in contrast to the typically applied dealumination procedures. These preserved active acid centers play a vital role in catalysis and coupled to the enhanced physical transport, an improved catalytic performance in the liquid-phase alkylation of benzene with ethylene has been achieved. Application of the desilication approach to iron-containing zeolites results besides mesopore formation in a rearrangement of the iron sites and more active catalysts in e.g. direct N2O decomposition

zeolites
desilication
mesoporosity
diffusion
hierarchical porosity
acidity
catalysis
physical transport
silicon extraction
deactivation

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Institutional Repository

doctoral thesis

(c) 2007 J.C. Groen