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Title: Lewis Acid Pairs for the Activation of Biomass-derived Oxygenates in Aqueous Media

The objective of this project is to understand the mechanistic aspects behind the cooperative activation of oxygenates by catalytic pairs in aqueous media. Specifically, we will investigate how the reactivity of a solid Lewis acid can be modulated by pairing the active site with other catalytic sites at the molecular level, with the ultimate goal of enhancing activation of targeted functional groups. Although unusual catalytic properties have been attributed to the cooperative effects promoted by such catalytic pairs, virtually no studies exist detailing the use heterogeneous water-tolerant Lewis pairs. A main goal of this work is to devise rational pathways for the synthesis of porous heterogeneous catalysts featuring isolated Lewis pairs that are active in the transformation of biomass-derived oxygenates in the presence of bulk water. Achieving this technical goal will require closely linking advanced synthesis techniques; detailed kinetic and mechanistic investigations; strict thermodynamic arguments; and comprehensive characterization studies of both materials and reaction intermediates. For the last performance period (2014-2015), two technical aims were pursued: 1) C-C coupling using Lewis acid and base pairs in Lewis acidic zeolites. Tin-, zirconium-, and hafnium containing zeolites (e.g., Sn-, Zr-, and Hf-Beta) are versatile solid Lewis acids that selectively activate carbonyl functionalmore » groups. In this aim, we demonstrate that these zeolites catalyze the cross-aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid-base pairs in the Si-O-M framework ensemble promote soft enolization through α-proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions. 2) One-pot synthesis of MWW zeolite nanosheets for activation of bulky substrates. Through post-synthetic modifications, layered zeolite precursors can be transformed into 2-dimensional (2D), zeolites with open architectures. These novel hierarchical microporous/mesoporous materials with exposed active sites can facilitate the conversion of bulky substrates while maintaining higher stability than amorphous mesoporous materials. However, post-synthetic exfoliation techniques are energy intensive, multi-step and require highly alkaline conditions that result in low silica yields and a partially amorphous product. In this aim, we demonstrate an effective one-pot synthesis method to generate exfoliated single-unit-cell thick MWW nanosheets. The new material, named MIT-1, is synthesized using a rationally-designed OSDA and results in a material with high crystallinity, surface area, and acidity that does not require post-synthetic treatments other than calcination. A parametric study of Al, Na, and water content reveals that MIT-1 crystallizes over a wide synthetic window. Characterization data show that MIT-1 has high mesoporosity with an external surface area exceeding 500 m2g-1 and a high external acid site density of 21 x 10-5 mol g-1. Catalytic tests demonstrate that MIT-1 has three-fold higher catalytic activity for the Friedel-Crafts alkylation of benzene with benzyl alcohol as compared to that of other 3D MWW topology zeolites.« less
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
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Technical Report
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Related Information: For the final period: 1. Luo, H., et al. Lewis Acid Zeolites for BiomassConversion: Perspectives and Challenges on Reactivity, Synthesis,and Stability. Annu. Rev. Chem. Biomol. Eng. 7 (2016). 2. Wang, Yetal. Synthesis of Itaconic Acid Ester Analogues via Self-AldolCondensation of Ethyl Pyruvate Catalyzed by Hafnium BEA Zeolites.ACS Catal. ASAP doi:10.1021/acscatal.6b00561 (2016). 3. Van deVyver, S. & Román-Leshkov, Y.* Metalloenzyme-Like Zeolites asLewis Acid Catalysts for C-C Bond Formation. Angew. Chem. Int. Ed.54:12554-12561 (2015). 4. Luo, H. Y., et al. One-pot synthesis ofMWW zeolite nanosheets using a rationally designed organicstructure-directing agent. Chem. Sci. 6:6320-6324 (2015). 5. Lewis, J.D., et al. Acid-Base Pairs in Lewis-Acidic Zeolites Promote DirectAldol Reactions by Soft Enolization. Angew. Chem. Int. Ed. 54:9835-9838 (2015). 6. Luo, H. Y. & Román-Leshkov, Y.* Al-MFI Nanosheetsas highly active and stable catalysts for the conversion of propanal tohydrocarbons. Top. Catal., 58:529-536 (2015). 7. Hunt, S., et al.Bimetallic Tantalum Tungsten Carbide Nanoparticles Exhibit HighHydrogen Evolution Activity and Increased ElectrochemicalOxidation Resistance. J. Phys. Chem. C., 119:3691-13699 (2015). 8.Van de Vyver, et al. Solid Lewis Acids Catalyze the Carbon−CarbonCoupling of Biomass-Derived Molecules with Formaldehyde. ACS.Catal. 5:972–977 (2015). 9. Luo, H., et al. Investigation of the reactionkinetics of isolated Lewis acid sites in Beta zeolites for the Meerwein-Ponndorf-Verley reduction of methyl levulinate to γ-valerolactone. J.Catal. 320:198–207(2014). 10. Lewis, J. D., et al. A Continuous FlowStrategy for the Coupled Transfer Hydrogenation and Etherificationof 5-(Hydroxymethyl)furfural using Lewis Acid Zeolites.ChemSusChem 7:2255–2265 (2014).
Research Org:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
09 BIOMASS FUELS; zeolites; Lewis acids; C-C coupling; nanosheets