(513f) The Effect of Brønsted Acidic Zeolites on the Synthesis of Aromatics from Furans
The Effect of Brønsted Acidic Zeolites on the Synthesis of Aromatics from Furans
Ryan E. Patet, Stavros Caratzoulas, Dionisios G. Vlachos
Center for Catalysis and Energy Innovation (CCEI), Department of Chemical and Biomolecular Engineering, University of Delaware, 221 Academy Street, Newark, DE 19716
Aromatic molecules, such as benzene, toluene, and xylenes (BTX) are high volume chemicals used in the industrial manufacturing of polymers, such as plastics and foams.1 BTX products are currently produced by catalytically reforming naphtha from the petroleum industry.1 Production of these BTX aromatics from biomass sources could serve as a high value target for the unused biomass resources and reduce the demand for petroleum.
One viable method for the production of BTX aromatics involves the Brønsted acid-catalyzed dehydrative aromatization of the Diels-Alder product between furans and ethylene, both which can be derived from biomass feedstocks.2-6 One relevant side-reaction has been identified due to the presence of water in the system, in which the furan molecule can ring-open via a Brønsted acid-catalyzed hydrolysis reaction.5-7 The interplay of the Brønsted acid catalysis of the dehydration and hydrolysis influences the selectivity to aromatics, which drops from 90% to p-xylene, in the case of DMF, to 50% to toluene or benzene, in the case of methylfuran or furan, respectively.4
In this study, we investigate the effect of changing the Al substituent in Brønsted acidic zeolites with other potential substituents, such as B or Ga. Using ONIOM models of the zeolite active sites and surrounding pores, we characterize these different zeolite systems using their inherent properties, such as their geometries, deprotonation energies, and vibrational frequencies. Additionally, adsorption studies of relevant probe molecules are used to understand how adsorbates with variable properties would interact with these different Brønsted acidic zeolites.
With this understanding of how the different zeolite systems behave, we investigate their effects on the dehydration reactions of oxanorbornene intermediates to form BTX aromatics and the hydrolysis reactions of furans to form ring-opened aldehydes and ketones. For the dehydration reactions, mapping the electrostatic potential of the reactant and Bader analysis of the bond critical points of the C-O bonds in the oxanorbornene are used to show how different zeolites and alkyl substituents affect the reaction barrier dictated by the C-O cleavage of the oxanorbornene intermediate. For the hydrolysis reaction, similar mapping of the electrostatic potential and Bader analysis of the electron density and of its Laplacian are used to show how once the furan is protonated, a nucleophilic addition of water to the furan is affected by the zeolites and alkyl substituents. Fundamental insight from these investigations could be used when attempting to optimize a catalyst for the production of benzene and toluene aromatics.
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