Controllable synthesis of EU-1 molecular sieve with high SiO2/Al2O3 ratios in thermodynamic stable sol system

Abstract

A new green chemical route was designed in this paper for the synthesis of high-silica EU-1 molecular sieve in TEAOH–SiO2–Al2O3–HMBr2–H2O system in which tetraethylammonium hydroxide (TEAOH) substituted for sodium hydroxide (NaOH) as an alkali source. The physicochemical properties of the synthesized samples characterized by such means as X-ray powder diffraction (XRD), electrophoresis apparatus, precise pH meter, scanning electron microscope, Fourier infrared spectrometer (FT-IR), thermo gravimetric analyzer (TG) and temperature programmed desorption (NH3-TPD). The research results showed that the SiO2/Al2O3 ratio of EU-1 molecular sieve could reach 706 with TEAOH as an alkali source. The SiO2/Al2O3 ratio of the product was improved greatly to 1046 with the template agent increasing. The new synthetic route has also significantly expanded the synthetic phase region. The absolute value of zeta potential of the TEAOH sol system was obviously higher than that of the NaOH sol system, indicating the thermodynamic stability of the former sol system was higher and better for the synthesis of pure high-silica EU-1 molecular sieve. The FT-IR spectra and TG/DTG diagrams of products indicated that TEA+ occluded in the final products could balance electronegative framework. The amount of strong, weak and the total acidity reduced with the increase of SiO2/Al2O3 ratio. The catalytic results of methanol-to-hydrocarbon demonstrated that the molecular sieve prepared by the new method has better catalytic performance.