High-pressure adsorption on methanol in synthetic MFI-zeolites

In the recent years, a raising interest related to the P-induced intrusion of ions/molecules from the so-called “penetrating” P-transmitting fluids into the zeolitic structural cavities have been object of a number of experiments. The P-induced adsorption process is controlled by a number of factors, recently reviewed by Gatta et al. (2018), and is enhanced when the kinetic diameter of the P-transmitting fluid’s molecules is smaller than the free diameter of the framework cavities. This property can be exploited in potentially relevant technological applications. MFI-synthetic zeolites are presently employed as catalyst in the production of olefins (fundamental building blocks in the production of plastics, rubbers, or polymers) starting from methanol. This process is one of the most prominent alternative way for producing olefins avoiding the use of oil derivatives (Stöcker, 1999; Olsbye et al., 2012). The recent literature is focused on investigations of small- and medium pore-type microporous/zeolitic catalysts suitable for the methanol conversion to hydrocarbons. On this basis, in this study we investigated, by means of in situ powder and single-crystal synchrotron X-ray diffraction, the P-induced intrusion of methanol in different samples of synthetic MFI-zeolites, characterized by different framework and extraframework compositions, using a diamond-anvil cell. Thanks to these experiments we were able to : (i) draw conclusions about the use of pressure as preferential way to induce a “cold” adsorption of methanol into the zeolite cavities (and therefore potentially increasing the efficiency of the methanol-to-olefins process); (ii) analyze the role of the framework’s and extraframework’s crystal-chemistry in the adsorption process; (iii) compare the magnitude of the methanol intrusion in single crystal with respect to powders. Gatta G.D., Lotti P., Tabacchi G. (2018) The effect of pressure on open‑framework silicates: elastic behaviour and crystal-fluid interaction. Phys. Chem. Miner., 45,115-138 Olsbye U., Svelle S., Bjørgen M., Beato P., Janssens T.V.W., Joensen F., Bordiga S., Lillerud K.P. (2012). Angew. Chem. Int. Ed., 51, 5810-5831 Stöcker M. (1999) Methanol-to-hydrocarbons: catalytic materials and their behavior. Micropor. Mesopor. Mater., 29, 3-48.