Suchergebnisse

Taking into account that the transformation of biomass-derived 2,5-dimethylfuran (DMF) to p-xylene involves Diels-Alder (DA) cycloaddition as the limiting step, the use of an ITQ-2 zeolite obtained by direct synthesis (DS-ITQ-2) as a catalyst for this reaction is proposed based on the fact that the organic molecule employed for its synthesis mimics the size and shape of the DA oxanorbornene cycloadduct intermediate. Periodic Density Functional Theory (DFT) calculations reveal a better stabilization of the oxanorbornene intermediate within the external hemicavities or "cups"of the DS-ITQ-2 zeolite (MWW-framework) than in other zeolites employed for this reaction, such as FAU and Beta. Interestingly, experimental results also show improved catalytic conversion values for the DS-ITQ-2 zeolite compared to FAU and Beta, in good agreement with the stabilization energies calculated by DFT. The "ab initio"catalyst design presented here to enhance the catalytic performance for the transformation of biomass-derived products is a valuable example that could be employed for the rationalization of other chemical processes catalyzed by zeolites. ; This work has been supported by the European Union through ERC-AdG-2014-671093 (SynCatMatch) and by Spanish Government through "Severo Ochoa" (SEV-2016-0683, MINECO), MAT2017-82288-C2-1-P (AEI/FEDER, UE) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE). E. M. G. acknowledges "La Caixa – Severo Ochoa" International PhD Fellowships (call 2015). Elisa García is acknowledged for her technical assistance in this work. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. We appreciate the support of ExxonMobil Research and Engineering for their help with our efforts in fundamental catalytic research.

[EN] Taking into account that the transformation of biomass-derived 2,5-dimethylfuran (DMF) top-xylene involves Diels-Alder (DA) cycloaddition as the limiting step, the use of an ITQ-2 zeolite obtained by direct synthesis (DS-ITQ-2) as a catalyst for this reaction is proposed based on the fact that the organic molecule employed for its synthesis mimics the size and shape of the DA oxanorbornene cycloadduct intermediate. Periodic Density Functional Theory (DFT) calculations reveal a better stabilization of the oxanorbornene intermediate within the external hemicavities or "cups" of the DS-ITQ-2 zeolite (MWW-framework) than in other zeolites employed for this reaction, such as FAU and Beta. Interestingly, experimental results also show improved catalytic conversion values for the DS-ITQ-2 zeolite compared to FAU and Beta, in good agreement with the stabilization energies calculated by DFT. The "ab initio" catalyst design presented here to enhance the catalytic performance for the transformation of biomass-derived products is a valuable example that could be employed for the rationalization of other chemical processes catalyzed by zeolites. ; This work has been supported by the European Union through ERC-AdG-2014-671093 (SynCatMatch) and by Spanish Government through "Severo Ochoa" (SEV-2016-0683, MINECO), MAT2017-82288-C2-1-P (AEI/FEDER, UE) and RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE). E. M. G. acknowledges "La Caixa - Severo Ochoa" International PhD Fellowships (call 2015). Elisa Garcia is acknowledged for her technical assistance in this work. The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. We appreciate the support of ExxonMobil Research and Engineering for their help with our efforts in fundamental catalytic research. ; Margarit Benavent, VJ.; Gallego, EM.; Paris, C.; Boronat Zaragoza, M.; Moliner Marin, M.; Corma Canós, A. (2020). Production of aromatics from biomass by computer-aided selection of the zeolite catalyst. Green Chemistry. ...

Unlike homogeneous catalysts that are often designed for particular reactions, zeolites are heterogeneous catalysts that are explored and optimized in a heuristic fashion. We present a methodology for synthesizing active and selective zeolites by using organic structure-directing agents that mimic the transition state (TS) of preestablished reactions to be catalyzed. In these zeolites, the pores and cavities could be generated approaching a molecular-recognition pattern. For disproportionation of toluene and isomerization of ethylbenzene into xylenes, the TSs are larger than the reaction products. Zeolite ITQ-27 showed high disproportionation activity, and ITQ-64 showed high selectivity for the desired para and ortho isomers. For the case of a product and TS of similar size, we synthesized a catalyst, MIT-1, for the isomerization of endo-dicyclopentane into adamantane. ; This work has been supported by the European Union through the European Research Council (grant ERC-AdG-2014-671093, SynCatMatch) and the Spanish government through the " Severo Ochoa Program " (grant SEV 2012-0267). The Electron Microscopy Service of the Universitat Politècnica de València (UPV) is acknowledged for help with sample characterization. The Red Española de Supercomputación (RES) and Centre de Càlcul de la Universitat de València are gratefully acknowledged for computational facilities and technical assistance. E.M.G. acknowledges " La Caixa – Severo Ochoa " International Ph.D. Fellowship (call 2015). We thank I. Millet for technical assistance and V. J. Margarit and Á. Cantín for helpful discussions.

The synthesis of the ZSM-5 and beta zeolites in their nanosized form has been achieved by using simple alkyl-substituted mono-cationic cyclic ammonium cations as OSDA molecules. The particular combination of a cyclic fragment and a short linear alkyl-chain group (preferentially C) within the monocationic OSDA molecules allows directing the crystallization of nanosized zeolites with excellent solid yields (above 90%). Interestingly, the formation of the nanosized ZSM-5 and beta zeolites mostly depends on the size and nature of the cyclic fragment of the OSDA molecule, resulting in all cases in nanocrystalline solids with homogeneous distributions of particle sizes (∼10-25 nm) and controlled Si/Al molar ratios (∼15-30). The achieved nanosized ZSM-5 and beta zeolites have been extensively characterized by different techniques to study their physico-chemical properties, such as chemical composition, pore accessibility or Brønsted acidity, among others. Moreover, the catalytic properties of the nanosized ZSM-5 and beta zeolites have been evaluated for different chemical reactions, including methanol-to-olefins (MTO) in the case of ZSM-5, and alkylation of benzene with propylene to obtain cumene and oligomerization of light olefins to liquid fuels in the case of beta, observing in all cases improved catalytic activity and product selectivity towards target products when compared to related catalysts. ; This work has been supported by the Spanish Government MINECO through "Severo Ochoa" (SEV 2012-0267), MAT2015-71261-R and CTQ2015-70126-R, by the European Union through ERC-AdG-2014-671093 (SynCatMatch) and by the Fundación Ramón Areces through a research contract of the "Life and Materials Science" program. E. M. G. and M. R. D- R. acknowledge "La Caixa – Severo Ochoa" International PhD Fellowships (call 2015). M. E. M- A. thanks MINECO for economical support through pre-doctoral fellowship (BES-2013-066800). ; Peer Reviewed