One-Pot Synthesis of Ultra-Small Pt Dispersed on Hierarchical Zeolite Nanosheet Surfaces for Mild Hydrodeoxygenation of 4-Propylphenol

The rational design of ultra-small metal clusters dispersed on a solid is of crucial importance in modern nanotechnology and catalysis. In this contribution, the concept of catalyst fabrication with a very ultra-small size of platinum nanoparticles supported on a hierarchical zeolite surface via a one-pot hydrothermal system was demonstrated. Combining the zeolite gel with ethylenediaminetetraacetic acid (EDTA) as a ligand precursor during the crystallization process, it allows significant improvement of the metal dispersion on a zeolite support. To illustrate the beneficial effect of ultra-small metal nanoparticles on a hierarchical zeolite surface as a bifunctional catalyst, a very high catalytic performance of almost 100% of cycloalkane product yield can be achieved in the consecutive mild hydrodeoxygenation of 4-propylphenol, which is a lignin-derived model molecule. This instance opens up perspectives to improve the efficiency of a catalyst for the sustainable conversion of biomass-derived compounds to fuels

Post-synthesis metal (Sn, Zr, Hf) modification of BEA zeolite:Combined Lewis and Br⊘nsted acidity for cascade catalysis

Zeolites modified by Lewis acidic metal centers such as Sn, Zr, and Hf are promising catalysts for numerous reactions relevant to biorefining, such as isomerization of carbohydrates and Meerwein-Ponndorf-Verley (MPV) reduction of furans. Preferred catalysts contain these metal ions in the framework of large-pore BEA zeolite, requiring often complex multistep preparation procedures based on expensive organometallic precursors. Herein, we developed a facile approach for obtaining highly dispersed isolated Sn, Zr, and Hf incorporated in dealuminated BEA zeolite with high metal content (Si/M ratio of 50–75) via a solid-state grinding approach using simple inorganic metal precursors. The efficient incorporation of isolated metal sites in the BEA framework with high content was achieved by methanol treatment before calcination, which removes excess metal. The Lewis acid sites derive from isolated metal ions in open sites for Sn, Zr, and Hf, while Sn-modified BEA also contains closed Sn sites. The open Sn sites display the highest Lewis acidity. The Br⊘nsted acidity stems from silanols perturbed by Lewis acidic metal ions of open metal sites and the OH group connected to the open metal sites. The metal-modified zeolites are active in the cascade reductive etherification of cinnamaldehyde, involving the MPV reduction to cinnamyl alcohol and the subsequent etherification to cinnamyl propyl ether with the isopropanol solvent over Lewis and Br⊘nsted acid sites, respectively. Sn-modified BEA was the most active sample, which stems from its strongest Lewis acidity, which is crucial for the first MPV step. Sn modification of the optimized solid-state ion-exchange method was applied to various BEA zeolites with different morphologies (nanocrystalline, hierarchical, and conventional BEA), showing that pore hierarchization can further benefit cascade reductive etherification reaction.</p