Cooperation between framework and pore templates in the synthesis of hierarchical MCM-22 zeolites to the glycerol valorization

Author(s)

Mariana Veiga Rodrigues

• Document type: Doctoral Thesis
• Press: Araraquara. 2018-10-05.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2018-09-28
• Advisor: Leandro Martins

Abstract

The application of zeolites with a hierarchical pore distribution in reactions with bulky molecules has been highlighted, mostly caused by the improved accessibility to the inner active sites, overcoming the main drawback in zeolites in the current scenario, the constraints imposed by the micropores. Following this view, this work proposed the synthesis of hierarchical MWW zeolites by the combination of templates, firstly with the use of organosilanes as a mesopore directing agent by a bottom-up method and a top-down method, the delamination process to the exfoliated ITQ-2. Organosilanes with chains sizes up to 18 carbons were applied in synthesis of hierarchical MWW zeolites. Increasing the organosilane chain sizes, the framework changes become more severe, however chain sizes larger than 12 carbons, the organosilane incorporation in the zeolite framework was very low, than these materials did not show the desired mesoporosity. The synthesized zeolites with organossilanes up to 12 carbons were applied in the glycerol condensation to solketal. The hierarchical zeolites showed better performances toward the glycerol conversion and solketal selectivity, due to the improved accessibility obtained with the mesopores and the hydrophobic character of these materials, caused by the decreased aluminum content in the zeolitic structure. The synthesized zeolites in the bottom-up and the delaminated MWW derivative ITQ-2 synthesized by top-down method were applied in the glycerol dehydration to investigate the accessibility to the active sites in the reaction. In-situ studies were realized with the infrared spectroscopy to determine the reaction intermediates, aiming the improvement of the catalysts performance, seeking for the best design to these. The delaminated zeolite showed high acrolein yield and glycerol conversion compared to the other materials, though as its Brønsted acid sites were weaker than the MCM-22 ones, the microporous zeolite showed an improved yield even better than the ITQ-2 and then it is neccessary to glycerol dehydration a catalyst with improved accessibility and strong Brønsted acid sites. This work approached the seeding method to synthesize MWW zeolites either, seeking for a future application of this method as a facilitator in a direct synthesis to delaminated catalysts. (AU)

• FAPESP's process: 14/12942-3 - Cooperation between supramolecular chemistry and emulsion in the synthesis of delaminated lamelar catalysts
• Grantee: Mariana Veiga Rodrigues
• Support Opportunities: Scholarships in Brazil - Doctorate