Johannes Hendrik Koegler

Zeolitic coatings and their potential use in catalysis

The formation of zeolitic coatings and their properties, such as the thickness, continuity and orientation of the crystals, are related to the presence and macro-organization of a precursor phase. Based on this view, preshaped zeolitic coatings can be prepared which may be either active catalysts themselves or an inert thin membrane on an existing catalyst. They can be applied in low pressure drop reactors, in adsorption units, in catalytic distillation units and in integrated reaction separation systems as zeolitic membranes. Coating preparation and particular aspects of the performance of the zeolitic coatings in a membrane configuration, in selective catalytic conversion of NOx, as an inert membrane on a catalyst phase, and model structured catalyst systems are discussed.

Growth model of oriented crystals of zeolite Si-ZSM-5

A model for the growth of Si-ZSM-5 (silicalite-1) crystals from zeolite synthesis mixtures is proposed. Nucleation and crystal growth occur at the interface of gel particles and liquid, the only place where both the silicon source and template are present in abundance. In the extension of this model to growth on a support surface, a precursor gel layer plays an important role as an anchoring site for the template molecules. Orientation results from the preferential growth of the ac-plane of the crystallites in the plane of the substrate surface. The presence of alkali ions at this surface may adversely affect zeolite nucleation.

Combination of single crystal zeolites and microfabrication: Two applications towards zeolite nanodevices

Abstract We present two novel approaches to using zeolite crystals for ‘nanodevices’. First, single crystal zeolites have been aligned within the grooves of micromachined silicon wafers for a three-dimensional ordering of dye molecules ( p -nitroaniline). The orientation of p -nitroaniline molecules absorbed within the channel system of the aligned zeolites by steric constraints provides an opportunity to study the optical properties of the composite. Second, zeolites with their high surface-to-mass ratio and selectivity are ideal materials to enhance the sensitivity of micron scale sensor devices to loading. As an example, experimental data on humidity sensing using a few single crystal zeolites attached to a cantilever sensor is presented.

Oriented coatings of silicalite-1 for gas sensor applications

Summary Silicalite-1 is grown in an oriented way, on a silicon wafer to study the nucleation and growth mechanisms and also on a quartz substrate to form a well-defined SAW-sensor chemical interface for CO 2 detection. The growth mechanism of the crystals seems to involve a silica-gel layer on the silicon surface which is consumed during crystal growth. Afterwards attachment of the crystals to the surface takes place. The SAW-sensor device employing silicalite-1 as a chemical interface responds well to CO 2 while the sensitivity to water seems not to be severe.