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| Author(s): |
Francisca Solânea de Oliveira Ramos
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Química |
| Defense date: | 2016-10-10 |
| Examining board members: |
Heloise de Oliveira Pastore;
Leandro Martínez;
Michèle Oberson de Souza;
Fernando Aparecido Sígoli;
Celso Aparecido Bertran
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| Advisor: | Heloise de Oliveira Pastore |
| Abstract | |
The Na-RUB-18 layered silicate presents a two-dimensional framework in which the basic unit is a cage made of four five-membered rings, [54] cages, composed of SiO4 tetrahedra. The surface of the layers is covered by Si-OH and Si-O- groups, displaying negative charge balanced by [Na(H2O)6]+ ions. Both acidity of the Si-OH groups and low surface area of the Na-RUB-18 limit its catalytic application. This study describes the structural incorporation of the heteroatoms Al3+, B3+, Fe3+, Ti4+ e V5+ with nominal molar ratios Si/M = 15, 30 and 60 (M= heteroatom) via post-synthesis hydrothermal method. The presence of tetracoordinated Al3+ and V5+ in the network into Na-[Al]-RUB-18 and Na-[V]-RUB-18, respectively, and also Al3+ octahedral in the sample with nominal molar ratio Si/Al = 15 were observed. Contrerily, Fe3+ and Ti4+ are mostly extra-framework sites, while Na-[B]-RUB-18 was obtained only when gel composition was Si/B = 15. Elemental analysis of the these solids showed that Al3+ was incorporated in a higher amount (Si/AlICP = 22 - 42), followed by B3+ (Si/BICP = 99) and V5+ (Si/VICP = 589 - 11959). Based on these results, Na-[M]-RUB-18 (M= Al, B) were used as precursors of pillared solids, using hexadecyltrimethylammonium bromide (CTABr) in the swelling step, octylamine as catalyst of the hydrolysis step of the silica galleries which precursor was tetraethyl orthosilicate (TEOS). These materials presented surface areas of 63 - 323 m2 g-1 and pore sizes of 2 ¿ 4 nm. The acidity of the pillared solids was evaluated by in situ reaction probe ethanol dehydration monitorated via FTIR spectroscopy. The selectivity was higher to diethyl-ether and ethene, and the production of these compounds was proportional to the amount of Al3+ in the catalysts. The sample with the smaller amount of Al3+ produced acetaldehyde besides diethyl-ether and ethane. Pure silica pillared sample showed selectivity mostly to acetaldehyde due to siloxane groups. The interlayer condensation of the adjacent layers without elimination of N-methylformamide (SDA) generated H-[Al]-RWR zeolites with higher crystallinity when compared with the solid obtained with CTABr as SDA. To the best of our knowledge, the structure of H-[Al]-RWR was not reported before (AU) | |
| FAPESP's process: | 12/09001-7 - [M]-RUB-18: a precursor of micro e mesoporous solids and nanolayers |
| Grantee: | Francisca Solânea de Oliveira Ramos |
| Support Opportunities: | Scholarships in Brazil - Doctorate |