Zeolites are very well-known as catalysts, ion-exchangers and adsorbents in industry. As any crystal, they are never perfectly organized and defects are always present; one of the most annoying is due to missing tetrahedral atoms leading to the presence of silanols (Si-OH groups). These weak points are where zeolites are attacked and loose some of their most sought after properties. Zeolites demonstrated recently a great potential in the conversion of biomass and upgrading of natural gas (CH4), however the reaction conditions are severe (hot liquid water and/or high temperature) and are known to affect drastically zeolite properties, in particular those of nanosized zeolites (< 100nm). There is a need to prepare “defect-free” zeolites to sustain these harsh conditions.
The new zeolite nanocrystals synthesized and comprehensively characterized by teams of LCS and CRISMAT in Caen (ENSICAEN, Normandy University, CNRS) and University of Sofia, Bulgaria meet these new requirements. These point-free defect nanosized zeolites are stable at least up to 900 ºC and become prime candidates for numerous industrially important catalytic applications (olefin metathesis, direct methane aromatization…). Moreover, in the emerging field of biomass upgrading to fuels and chemicals, the newly prepared zeolite with great stability in hot liquid water will contribute to move academically appealing chemistry to an industrial reality.
Researchers at LCS (ENSICAEN / Normandy University / CNRS, Caen) reported a unique one-pot synthesis strategy to prepare defect-free nanosized MFI-type zeolite by introducing tungsten in their framework as a defect-suppressing element. The teams of CRISMAT (ENSICAEN / Normandy University / CNRS, Caen) and University of Sofia, Bulgaria contributed to a thorough characterization of the materials.
These results are published in the journal Nature Mater. (2017) 10.1038/nmat4941
Tungsten incorporation in nanosized MFI crystals modifies many of their properties such as structural features, hydrophobicity, Lewis acidity and stability. These in turn significantly affect their catalytic (e.g. epoxidation of styrene) and separation (e.g. CO2 and NO2) properties as shown in the Nature Materials paper.
The syntheis method was patented (April 2017) before by the LCS- researchers (S. Mintova, S. Talapaneni, J. Grand, J-P. Gilson, Method for the preparation of defect free nanosized synthetic zeolite materials, WO/2017/068387). Significant interest in these patented materials has already been expressed by industry.
Moreover, a fast diffusion of reactants and products inside the (defect-free) zeolite nanocrystals insures an optimal use in catalysis and separation applications. Substantially lower deactivation by coke formation is expected from zeolitic catalysts combining the absence of defect and nanosized crystals. Finally, the superior colloidal stability of the W-MFI zeolite nanocrystals will facilitate their uniform dispersion and applications in medicine, catalysis, sorption, and optical coatings.
These silanol-free and highly stable nanosized zeolites will have a great impact in several fields such as material science, heterogeneous catalysis, sorption and ion exchange processes as well as colloid chemistry. In addition, this new synthesis strategy opens the route to the preparation of highly stable defect-free nanosized zeolites of different types and containing other framework transition metal ions (Mo, Sn, V, Zr…), which have application in a broad range of areas.
Reference: Nature Mater. 10.1038/nmat4941 (2017)
Julien Grand, Siddulu Naidu Talapaneni, Aurélie Vicente, Christian Fernandez, Eddy Dib, Hristiyan A. Aleksandrov, Georgi N. Vayssilov, Richard Retoux, Philippe Boullay, Jean-Pierre Gilson, Valentin Valtchev and Svetlana Mintova “One-pot synthesis of silanol-free nanosized MFI zeolite”
Svetlana Mintova, Catalysis and Spectrochemistry Laboratory – Caen