Studies on natural STI zeolite: modification, structure, adsorption and catalysis

A natural STI zeolite discovered in China was identified as a calcium-rich and stellerite-isotype zeolite of stilbite with high crystallinity and an o pen pore system. Both ion exchange and dealumination can stabilize the fram ework of the zeolite. The structural properties of the parent and the modif ied STI zeolites were investigated by X-ray diffraction (XRD), thermogravim etric/differential thermogravimetric/differental thermal analysis (TG/DTG/D TA), Fourier transform infrared spectroscopy (FTIR), and Si-29 and Al-27 ma gic-angle spinning (MAS) nuclear magnetic resonance spectroscopy (NMR). The Langmuir surface area and pore volume of H-STI and Na-STI were similar to 550 m(2) g(-1) and similar to 0.20 ml g(-1), respectively, as measured by N -2 adsorption. The adsorption heats of NH3 and CO2 on H-STI were determined from the adsorption isotherms at different temperatures. Investigation of the adsorption isotherms of ethylene, propylene, water, methanol, ethanol a nd 1-propanol on Na-STI reveal an unusual selectivity to the length of the carbon chain in the organic molecules. The zeolite shows good catalytic sel ectivity in the isomerization of n-butene to iso-butene. (C) 2000 Elsevier Science B.V. All rights reserved.