Novel methods for synthesis of zeolites and zeolite-encapsulated metal particles

Zeolites and zeolite supported metals are used extensively in the chemical industry. They have a wide range of applications including cracking of oil and removal of harmful exhaust gasses. Unfortunately, encapsulation of metal and metal nanoparticles in zeolites still remains a challenge. Improving the zeolite synthesis for encapsulation of metal nanoparticles is therefore of utmost importance.
This dissertation describes the synthesis of zeolites and metal nanoparticle encapsulation in important zeolite structures using novel methodologies. One of the focuses for the synthesis of the zeolites was on limiting the environmental impact by producing less waste and reducing the use of organic structure directing agents (OSDAs).
Nano-sized chabazite (CHA) was synthesized by modification of different synthesis parameters for the OSDA-free interzeolite transformation of faujasite (FAU). The nano-sized CHA showed a high CO2 capacity of 4.26 mmol/g and a high porosity. Additionally, it was shown that CO2 preferentially adsorbs as chemisorbed species and then as physisorbed species. With a similar approach, successful encapsulation of 1-2 nm size platinum nanoparticles in CHA was accomplished via encapsulation of platinum in the FAU zeolite and subsequent recrystallization to form CHA. The platinum containing CHA zeolite demonstrated significantly higher catalytic activity compared to the platinum containing FAU zeolite
Solvent-free synthesis of zeolites both reduce the requirement for synthetic equipment and enhance reaction yields. Thus, an in situ encapsulation of metals via a solvent-free mechanochemical synthetic approach was attempted by the addition of metal precursors to the synthesis. However, base metals formed phyllosilicates even when protected by a carbon shell during synthesis. For both base and precious metals, inhomogeneous distribution of the metals in the zeolite crystals was observed.
Interzeolite transformation provides an alternative route to the classical synthesis of zeolites. Synthesis of GME, MFI and MOR zeolites from FAU by an OSDA-free mechanochemical interzeolite transformation was attempted. The product purity was found to be highly dependent on the temperature, NaOH concentration, and zeolite seeds. Highly porous GME zeolites were synthesized from low silica FAU (Si/Al = 2.6) while MFI and MOR were synthesized from high silica FAU (Si/Al = 30). Preliminary investigation into the encapsulation of platinum in MFI was performed by interzeolite transformation of Pt containing FAU and showed promising results.
Selectivity is a key parameter in catalysis and zeolites offer useful properties to help achieve this selectivity. In an effort to develop a size-selective hydrogenation catalyst, a hierarchical core silicalite-1 zeolite with a microporous silicalite-1 shell was synthesized via a steam-assisted approach. Encapsulation of platinum in the mesopores of the core hierarchical zeolite was accomplished by introduction of platinum in a hierarchical zeolite prior to growth of the microporous shell. The synthesized platinum containing zeolite exhibited complete size-selective hydrogenation of targeted alkenes.