Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production
| Autor: | Johnny Abboud, Eric Marceau, Nicolas Cadran, Céline Chizallet, Anne-Félicie Lamic-Humblot, Kim Larmier, Sylvie Maury, Hélène Lauron-Pernot |
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| Přispěvatelé: | IFP Energies nouvelles (IFPEN), Laboratoire de Réactivité de Surface (LRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Biologie des Ligneux et des Grandes Cultures (LBLGC), Institut National de la Recherche Agronomique (INRA)-Université d'Orléans (UO), Sorbonne Université (SU), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Universités |
| Jazyk: | angličtina |
| Rok vydání: | 2015 |
| Předmět: |
Reaction mechanism
diisopropylether γ-Al2O3 Alcohol Ether Photochemistry Catalysis Propene chemistry.chemical_compound sodium poisoning propene medicine Organic chemistry alcohol dehydration [CHIM]Chemical Sciences Dehydration Density Functional Theory chemistry.chemical_classification Alkene technology industry and agriculture General Chemistry equipment and supplies medicine.disease isopropanol chemistry activation energy kinetics Selectivity δ-Al2O3 entropy |
| Zdroj: | ACS Catalysis ACS Catalysis, 2015, 5 (7), pp.4423-4437. ⟨10.1021/acscatal.5b00723⟩ ACS Catalysis, American Chemical Society, 2015, 5 (7), pp.4423-4437. ⟨10.1021/acscatal.5b00723⟩ |
| ISSN: | 2155-5435 |
| DOI: | 10.1021/acscatal.5b00723⟩ |
| Popis: | International audience; Alcohol dehydration is of prominent relevancein the context of biomass conversion. This reaction can beefficiently catalyzed by alumina surfaces, but the nature ofactive sites, the mechanisms involved, and the key parametersto tune both the activity and the alkene/ether selectivityremain a matter of debate. In the present paper, isopropanoldehydration to propene and diisopropylether over γ-alumina,δ-alumina, and sodium-poisoned γ-alumina was investigatedthrough a combined experimental and theoretical study. Theexperimental kinetic study shows that dehydration occursfollowing the same reaction mechanism on all materials, although γ-alumina activated above 450 °C exhibits the highest densityof active sites and the highest global activity. Results suggest that all the reaction pathways involved in dehydration require thesame set of adjacent active sites located on the (100) facets of γ-alumina. DFT transition-state calculations of the formation ofpropene and diisopropylether on the main terminations of alumina, (110) and (100), were also performed. The less activatedpathways for both the formation of the olefin (E2 mechanism) and the formation of the ether (SN2 mechanism) were found on aAlV Lewis acidic site of the (100) termination, with calculated activation enthalpies (125 and 112 kJ·mol−1 for propene anddiisopropylether formation, respectively) in good agreement with the experimental values (128 and 118 kJ·mol−1, respectively).The higher or lesser selectivity toward propene or ether appears to originate from significantly different activation entropies. Theeffect of coadsorbed sodium on the reaction is linked to the poisoning of Al sites by neighboring, Na-stabilized OH groups, butno influence of sodium on distant sites is evidenced. Reaction temperature is identified as the main key parameter to tune alkene/ether selectivity rather than morphology effects, which in turn affect drastically the number of available active sites, and thuscatalytic activity. |
| Databáze: | OpenAIRE |
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