Rates of levoglucosanol hydrogenolysis over Brønsted and Lewis acid sites on platinum silica-alumina catalysts synthesized by atomic layer deposition
| Autor: | James A. Dumesic, George W. Huber, Lifeng Zhang, Siddarth H. Krishna, Ive Hermans, Thomas F. Kuech |
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| Rok vydání: | 2020 |
| Předmět: |
010405 organic chemistry
chemistry.chemical_element 010402 general chemistry 01 natural sciences Catalysis 0104 chemical sciences Amorphous solid Atomic layer deposition chemistry Hydrogenolysis Polymer chemistry Reactivity (chemistry) Lewis acids and bases Physical and Theoretical Chemistry Platinum Brønsted–Lowry acid–base theory |
| Zdroj: | Journal of Catalysis. 389:111-120 |
| ISSN: | 0021-9517 |
| DOI: | 10.1016/j.jcat.2020.05.025 |
| Popis: | Nanoscale coatings of AlOx were deposited onto SiO2 using atomic layer deposition (ALD) to synthesize amorphous silica-alumina (SiAl) catalysts, and these catalysts were investigated for levoglucosanol (Lgol) hydrogenolysis. With decreasing Al2O3 loading, the ratio of Bronsted to Lewis acid sites, measured by NH3-TPD and pyridine-FTIR, systematically increases, while the Al coordination, measured by solid state 27Al NMR, decreases. These structural changes correspond to an increasing mass-normalized rate of Lgol hydrogenolysis. We model the mass-normalized reaction rate as the sum of independent contributions from Bronsted and Lewis sites, showing that Bronsted acid sites on ALD-AlOx/SiO2 catalysts have a 6-times higher turnover frequency (TOF) than Lewis acid sites on these catalysts. Additionally, Lewis acid sites on ALD-AlOx/SiO2 catalysts (potentially related to Al(V) species) have a 4-times higher TOF than Lewis acid sites on bulk γ-Al2O3. The overall mass-normalized reactivity of ALD-AlOx/SiO2 catalysts is due to Lewis acid sites at the highest Al2O3 loading, while it is predominantly due to Bronsted acid sites at the lowest Al2O3 loadings. This work provides a new approach to synthesize amorphous SiAls with tunable Bronsted/Lewis acid site ratio and reveals differences in the reactivity of Bronsted and Lewis acid sites on these materials. |
| Databáze: | OpenAIRE |
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