Influence of the Si/Al ratio and crystal size on the acidity and activity of HBEA zeolites |
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| Affiliation: | 1. Laboratoire de Matériaux à Porosité Contrôlée, 3 Rue Alfred Werner, 68093 Mulhouse, France;2. Centro de Engenharia Biológica e Química, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;3. Laboratoire de Catalyse en Chimie Organique, 40 Avenue du Recteur Pineau, 86022 Poitiers, France;1. J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, CZ-182 23 Prague 8, Czech Republic;2. University of Bucharest, Department of Organic Chemistry and Catalysis, B-dul Regina Elisabeta 4-12, 030016 Bucharest, Romania;1. Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2, Czechia;2. Eni S.p.A., Research & Technological Innovation Dept., R&D Program Energy Transition, Via F. Maritano 26, I-20097, San Donato Milanese, Italy;3. Thermochemical Processes Unit, IMDEA Energy Institute, Móstoles, Spain;4. Chemical and Environmental Engineering Group, ESCET, Rey Juan Carlos University, Móstoles, Spain;5. Faculty of Chemistry, Jagiellonian University in Kraków, Gronostajowa 2, 30-387, Kraków, Poland;1. J. Haber Institute of Catalysis and Surface Chemistry PAS, Niezapominajek 8, 30-239 Cracow, Poland;2. Faculty of Chemistry, Jagiellonian University, Gronostajowa 2, 30-387 Cracow, Poland |
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| Abstract: | Three HBEA samples were prepared through ion exchange followed by calcination under dry air flow at 550 °C from parent samples synthesized with different total Si/Al ratios or crystal sizes and characterized by various techniques. The denomination, Si/Al ratio and crystal size were the following—Cal: 12.5, ∼20 nm; LC: 14.5, 3000–10,000 nm; RAl: 7.0, ∼50 nm. Pyridine adsorption followed by FTIR shows very different values of the Lewis/Brønsted site concentration ratio: 1.2 with Cal, 0.2 with LC and 0.6 with RAl, which indicates a predominant positive effect of the crystal size on the framework stability. Methylcyclohexane transformation at 450 °C was found to occur through both protolysis and the carbenium ion chain mechanism. Protolysis plays a significant role on Cal only. This very difficult reaction which requires very strong protonic sites, most likely sites resulting from interaction of bridging OH groups with neighbouring Lewis sites was 3 and 12 times faster on Cal than on RAl and LC samples, respectively. Furthermore, from the low turnover frequency value of the protonic sites of LC, severe diffusion limitations were demonstrated to occur on this large crystal size sample. |
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