Platelike MFI Crystals with Controlled Crystal Faces Aspect Ratio

International audienceZeolite crystals offering a short diffusion pathway through the pore network are highly desired for a number of catalytic and molecule separation applications. Herein, we develop a simple synthetic strategy toward reducing the thickness along b-axis of MFI-type crystals, thus providing a short diffusion path along the straight channel. Our approach combines preliminary aging and a fluoride-assisted low-temperature crystallization. The synthesized MFI crystals are in the micron-size range along a-and c-axis, while the thickness along the b-axis is a few tens of nanometers. The synthesis parameters controlling the formation of plate-like zeolite are studied, and the factors controlling the zeolite growth identified. The synthesis strategy works equally well with all-silica MFI (silicalite-1) and its Al-and Ga-containing derivatives. The catalytic activity of plate-like ZSM-5 in the methanol-to-hydrocarbons (MTH) reaction is compared with a commercial nano-sized ZSM-5 sample, as the plate-like ZSM-5 exhibits a substantially extended lifetime. The synthesis of plate-like MFI crystals is successfully scaled up to a kilogram scale

Synthesis and catalytic application of nanorod-like FER-type zeolite

International audienceNanosize dimensions have an important impact on zeolite properties and catalytic performance in particular. Herein, we develop a direct synthesis route to obtain nanosized nanorod-like ferrierite (FER) zeolite with the assistance of ammonium fluoride (NH 4 F) and employing a conventional structure-directing agent (Pyrrolidine). The resultant nanorod-like FER zeolite crystals exhibit a greatly reduced diffusion path along the c-axis. The physicochemical properties of nanorod-like FER and its conventional micronsized plate-like counterpart were analyzed by N 2 adsorption-desorption, 27 Al, 1 H, 29 Si MAS NMR, NH 3-TPD, and in situ D 3-acetonitrile and pyridine adsorption followed by FTIR. The nanorod-like FER zeolite possesses superior characteristics in terms of larger external area, better accessibility to the acid sites, and a larger number of pore mouths per unit crystal surface than the micron-sized counterpart synthesized without NH 4 F. The improved properties provide the nanorod-like FER zeolite with high selectivity and low deactivation rates in 1-butene skeletal isomerization. The thermogravimetry analysis (TGA) of the coke amounts revealed a better capability of coke tolerance of the nanorod-like FER zeolite. The in situ Ultraviolet-visible (UV/Vis) and Fourier transform infrared spectroscopy (FTIR) spectroscopy investigations of the organic intermediates formed on FER zeolite catalysts during the catalytic reaction further verified the enhanced catalytic activity and stability of the nanorod-like FER zeolite