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Highly Selective Lewis Acid Sites in Desilicated MFI Zeolites for Dihydroxyacetone Isomerization to Lactic Acid

Authors

  • Pierre Y. Dapsens,

    1. ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Straße 10, 8093 Zurich (Switzerland), Fax: (+41) 44-6331405
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  • Dr. Cecilia Mondelli,

    Corresponding author
    1. ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Straße 10, 8093 Zurich (Switzerland), Fax: (+41) 44-6331405
    • ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Straße 10, 8093 Zurich (Switzerland), Fax: (+41) 44-6331405
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  • Prof. Javier Pérez-Ramírez

    Corresponding author
    1. ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Straße 10, 8093 Zurich (Switzerland), Fax: (+41) 44-6331405
    • ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Straße 10, 8093 Zurich (Switzerland), Fax: (+41) 44-6331405
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Abstract

Desilication of commercial MFI-type (ZSM-5) zeolites in solutions of alkali metal hydroxides is demonstrated to generate highly selective heterogeneous catalysts for the aqueous-phase isomerization of biobased dihydroxyacetone (DHA) to lactic acid (LA). The best hierarchical ZSM-5 sample attains a LA selectivity exceeding 90 %, which is comparable to that of the state-of-the-art catalyst (i.e., the Sn-beta zeolite); this optimized hierarchical catalyst is recyclable over three runs. The Lewis acid sites, which are created through desilication along with the introduction of mesoporosity, are shown to play a crucial role in the formation of the desired product; these cannot be achieved by using other post-synthetic methods, such as steaming or impregnation of aluminum species. Desilication of other metallosilicates, such as Ga–MFI, also leads to high LA selectivity. In the presence of a soluble aluminum source, such as aluminum nitrate, alkaline-assisted alumination can introduce these unique Lewis acid centers in all-silica MFI zeolites. These findings highlight the potential of zeolites in the field of biomass-to-chemical conversion, and expand the applicability of desilication for the generation of selective catalytic centers.

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