| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 74036 | Microporous and Mesoporous Materials | 2012 | 6 Pages |
The stability of natural STI zeolite in saturated steam at high temperatures (defined as hydrothermal stability as well) is first studied. The stability of parent STI (denoted as R-STI) in steam is better than that in air. The NH4+ type STI zeolite possesses the best hydrothermal stability. The structure, composition and adsorption properties of NH4-STI treated in steam from 350 to 750 °C are characterized with X-ray diffraction (XRD), 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence scattering spectroscopy (XRF), and N2 adsorption and desorption, respectively. High-temperature steam can make aluminum atoms escape from the zeolite framework to become non-framework aluminum. The NH4+ cations in NH4-STI, which can block the pores as well as the non-framework aluminum, can be fully decomposed to get H-STI at 550 °C. The framework SiO2/Al2O3 ratio can enhance from 6.5 to 21.3 though the chemical SiO2/Al2O3 ratio is almost unchanged.
Graphical abstractMesopore-rich STI zeolite with FSAR of 21.3, prepared by de-alumination of NH4-STI, still keeps the framework in steam at 750 °C for 3 h, which contain tetrahedral ([AlO4], 55 ppm), distorted tetrahedral or pentahedral ([AlO5], 28 ppm) and octahedral ([AlO6], 0 ppm) on 27Al MAS NMR spectrum.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The thermal and hydrothermal stability of natural STI zeolite is very weak. ► The order of hydrothermal stability is followed as NH4-STI > H-STI > Ca-form STI. ► The framework SiO2/Al2O3 ratio increases linearly as temperature from 6.5 to 21.3. ► The surface area and pore volume increase from 350 to 550 °C, and decrease from 550 to 750 °C.
