title: Highly selective Lewis acid sites in desilicated MFI zeolites for dihydroxyacetone isomerization to lactic acid.
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.
authors.affiliation: ETH Zurich, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland.
authors.forename: Pierre Y
authors.initials: PY
authors.lastname: Dapsens
authors.forename: Cecilia
authors.initials: C
authors.lastname: Mondelli
authors.forename: Javier
authors.initials: J
authors.lastname: Pérez-Ramírez
mesh_terms: D002384:Catalysis; D004098:Dihydroxyacetone / Q000737:chemistry*; D007536:Isomerism; D019344:Lactic Acid / Q000737:chemistry*; D058116:Lewis Acids / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D017641:Zeolites / Q000737:chemistry*
chemical_list: D058116:Lewis Acids; D017641:Zeolites; D019344:Lactic Acid; D012822:Silicon Dioxide; D004098:Dihydroxyacetone