Full text
| |
| Author(s): |
Paulla Beatriz França de Sousa
Total Authors: 1
|
| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Química |
| Defense date: | 2024-11-07 |
| Examining board members: |
Heloise de Oliveira Pastore;
Marco André Fraga;
Paulo Cesar de Sousa Filho;
Jean Marcel Ribeiro Gallo
|
| Advisor: | Heloise de Oliveira Pastore |
| Abstract | |
In addition to lamellar silicates being known by their ion exchange properties, the isomorphous substitution (IS) of Si4+ by T3+-atoms in the structure confers acidic properties. Thus, these materials can be applied in catalytic processes that demand the accessibility of bulky molecules to the acid sites. While framework-Al (AlTd - (SiO4)4Al) sites on [Al]-RUB-18 materials with Brönsted acidity were active in ethanol dehydration, the acidity of partial framework-Al sites (AlOh or aluminol sites - (SiO4)3Al-(OH)(H2O)2) remains unknown. 31P-NMR of adsorbed trimethylphosphine oxide (TMPO) was used together with catalytic reactions in the presence and absence of water to elucidate the acidity features of aluminol sites on lamellar RUB-18. Acidic non-seeded and seeded lamellar catalysts (nominal Si/Al molar ratios = 8, 15, 30, 60) were synthesized and characterized by XRD, XRF, 29Si- and 27Al-MAS-NMR. The synthesis of lamellar Na-[Al]-RUB-18 yielded materials with Si4+ species ratios (Q3/Q4) = 2, indicating structural defects due to the large presence of silanol groups. This influenced the process of IS with the incorporation of AlTd/AlOh species in different proportions into its structure. Herein, spectroscopic analysis indicates the 31P signals arise from TMPO adsorbed on the lamellar surface, silanol/aluminol sites, and Brönsted acid sites. The crystallinity degree of the structure, amount of aluminum in the structure, completely and partially framework-Al species, and TMPO loadings, under wet and dry conditions, all lead to changes in 31P resonances. Two resonance signals at the BAS range were attributed to AlTd and AlOh species. A clear correlation between the adsorption capacity of the active sites and peak intensities in the BAS region proves the influence of water in the adsorption process. This study brings additional evidence that the (SiO4)4Al and (SiO4)3Al-(OH)(H2O)2 species played a crucial role in biomass-derivative conversion reactions. The identification of ethyl levulinate as the final product in the furfuryl alcohol reaction is indicative of the presence of medium-strength BAS. For the dihydroxyacetone and pyruvaldehyde conversions, it was revealed the simultaneous activity of Brönsted/Lewis acid sites, with the possibility of the aluminol sites acting as Lewis acid sites. The present study clarifies the acidity features of aluminol sites on lamellar [Al]-RUB-18 and brings attention to the evaluation of these features in the solid catalysts under aqueous-phase conditions (AU) | |
| FAPESP's process: | 22/05743-0 - Lamellar Aluminosilicate acidity in the presence and absence of water |
| Grantee: | Paulla Beatriz França de Sousa |
| Support Opportunities: | Scholarships in Brazil - Master |