Pavla Eliášová

Post‐Synthesis Stabilization of Germanosilicate Zeolites ITH, IWW, and UTL by Substitution of Ge for Al

Germanosilicate zeolites often suffer from low hydrothermal stability due to the high content of Ge. Herein, we investigated the post-synthesis introduction of Al accompanied by stabilization of selected germanosilicates by degermanation/alumination treatments. The influence of chemical composition and topology of parent germanosilicate zeolites (ITH, IWW, and UTL) on the post-synthesis incorporation of Al was studied. Alumination of ITH (Si/Ge=2-13) and IWW (Si/Ge=3-7) zeolites resulted in the partial substitution of Ge for Al (up to 80 %), which was enhanced with a decrease of Ge content in the parent zeolite. In contrast, in extra-large pore zeolite UTL (Si/Ge=4-6) the hydrolysis of the interlayer Ge-O bonds dominated over substitution. The stabilization of zeolite UTL was achieved using a novel two-step degermanation/alumination procedure by the partial post-synthesis substitution of Ge for Si followed by alumination. This new method of stabilization and incorporation of strong acid sites may extend the utilization of germanosilicate zeolites, which has been until now been limited.

Atomic force microscopy of novel zeolitic materials prepared by top-down synthesis and ADOR mechanism.

Top-down synthesis of 2D materials from a parent 3D zeolite with subsequent post-synthetic modification is an interesting method for synthesis of new materials. Assembly, disassembly, organisation, reassembly (ADOR) processes towards novel materials based on the zeolite UTL are now established. Herein, we present the first study of these materials by atomic force microscopy (AFM). AFM was used to monitor the ADOR process through observation of the changes in crystal surface and step height of the products. UTL surfaces were generally complex and contained grain boundaries and low-angle intergrowths, in addition to regular terraces. Hydrolysis of UTL to IPC-1P did not have adverse effects on the surfaces as compared to UTL. The layers remained intact after intercalation and calcination forming novel materials IPC-2 and IPC-4. Measured step heights gave good correlation with the X-ray diffraction determined d200 -spacing in these materials. However, swelling gave rise to significant changes to the surface topography, with significantly less regular terrace shapes. The pillared material yielded the roughest surface with ill-defined surface features. The results support a mechanism for the majority of these materials in which the UTL layers remain intact during the ADOR process as opposed to dissolving and recrystallising during each step.

Highly selective synthesis of campholenic aldehyde over Ti-MWW catalysts by α-pinene oxide isomerization

Campholenic aldehyde is a highly valuable fine chemical that can be obtained by multistep synthesis from monoterpene α-pinene isolated from turpentine oil. Therefore, economical and environmentally benign synthesis of this aldehyde is of great interest. In this study, different titanosilicates were prepared and tested in selective campholenic aldehyde synthesis via isomerization of α-pinene oxide. Titanosilicates with MWW zeolitic structure were synthesized directly and compared with Ti impregnated SBA-15 and commercial titanium silicalite-1. The catalysts were thoroughly characterized and compared in terms of their catalytic activity and selectivity toward the desired aldehyde in isomerization reactions performed either in toluene as a solvent at 70 °C or in N,N-dimethylacetamide at 140 °C. Ti-MWW catalysts showed very high catalytic activity with total conversion of α-pinene oxide. The highest selectivity to campholenic aldehyde, being 96% at the total conversion, was reached over the Ti-MCM-22 catalyst in toluene at 70 °C. This result substantially exceeds any other results published so far in the literature. The great catalytic performance of Ti-MCM-22 was attributed to the combination of the presence of isolated tetrahedrally coordinated Ti species, which act as crucial Lewis acid centres, the absence of undesired Bronsted acidity, and the MWW architecture that facilitates the formation of the target aldehyde.

Chapter 5:Two-dimensional Zeolites

Two-dimensional zeolites are a relatively new branch of material science attracting still growing attention. They are formed as crystalline nanosheets in various spatial arrangements. We can perceive the zeolite layers as new building blocks for the fabrication of hierarchically porous materials. Unlike their bulk three-dimensional counterparts 2D zeolites excel in facile molecular transport while keeping the strong intrinsic acidity of the zeolite framework. Moreover, due to their large external surface areas they can be employed for bulky molecule reactions. In the presented chapter we discuss 2D zeolites from their early days up to the most recent state-of-the-art methods. Special attention is paid to the progress in structure-directing-agent design, which led to the discovery of directly synthesized hierarchical 2D zeolites.