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.

Upgrading of the heavy reformate fraction (HR), containing mainly C aromatics, is usually performed by dealkylation or by transalkylation with added benzene and/or toluene to obtain the more valuable xylenes. However, when the costs related to the use of benzene and toluene are considered, the one-step dealkylation/transalkylation of the C alkylaromatics to xylenes becomes economically attractive. Thus, in a first step, ethylmethylbenzenes (EMB) will have to be dealkylated to toluene, which will then react with the trimethylbenzenes (TMB) present in the HR feed to produce xylenes by transalkylation. Medium pore zeolites will favor dealkylation, whereas large pore zeolites will be more adequate for carrying out the transalkylation reaction. In this work, we present the one-pot synthesis of beta-pentasil aggregates with tunable ratios of the large pore beta to the medium pore component. We show that the close proximity of the beta and pentasil nanocrystals obtained by one-pot co-crystallization synthesis, results in a highly efficient catalyst for the consecutive dealkylation/transalkylation process. The bifunctional catalyst based on the co-crystallized aggregate is more active and selective to xylenes than a catalyst based on a physical mixture of equivalent beta and pentasil nanozeolites synthesized following an analogous procedure. The small crystallite sizes of the co-crystallized zeolites provide the additional advantage of a lower deactivation rate as compared to a reference benchmark catalyst. Results are shown on both, model molecules and industrial HR feed. ; This work has been supported by Saudi Aramco, by the Spanish Government-MICINN through "Severo Ochoa" (SEV 2012-0267) and RTI2018-101033-B-I00, 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. We thank Belén Esparcia for technical assistance, and the Electron Microscopy Service of the UPV for their help in sample characterization.