Lewis acid zeolite catalysts via chemical modification of extra-large pore germanosilicates

Abstract

Lewis acid zeolites containing tetravalent metals, such as Sn or Zr, are of great interest as catalysts for various reactions owing to their tunability, activity, and reusability. In the context of emerging trends in biomass-related substrates processing, the synthesis of Lewis acid zeolites with extra-large pores presents a key step by addressing diffusion restriction associated with these molecules. In this paper, we report on the incorporation of Sn and Zr into extra-large pore zeolites UTL and *CTH through a four-step approach, including synthesis of parent germanosilicate zeolites, followed by their post-synthesis stabilization, degermanation, and metal incorporation. The resulting zeolites were examined in Meerwein-Ponndorf-Verley (MPV) reduction of furfural in batch and flow reactors. In a batch, the designed Lewis acid extra-large pore zeolites exhibited similar yields to the MPV reduction product as the respective Sn- and Zr-substituted zeolite *BEA known as the optimum catalysts for this reaction. On the other hand, a better mass balance was observed for the MPV reduction of furfural over UTL/Sn (91%) vs. *BEA/Sn zeolite catalysts (73 – 91%) in a batch mode, suggesting the hindered formation of insoluble furfural transformation products in the extra-large pore system of UTL zeolite. Showing stable performance in MPV reduction in a flow reactor (50% selectivity to MPV reduction product at 20 – 25% furfural conversion), the extra-large pore Sn-UTL zeolite designed in this study was verified as a promising solid Lewis acid catalyst under industrially relevant conditions.