The Research In Synthesis And Zirconium Modification Of ZSM-5 Molecular Sieve

ZSM-5 molecular sieves are widely used in adsorption, catalysis, coal chemical industry because of its specific shape selectivity, excellent hydrothermal stability and good hydrophobic property. In order to improve the ZSM-5 molecular sieves in existing fields of application, and expand the application of shape selecting catalysis and acid catalyst, a great many of researchers pay much attention to modification of molecular sieves. After modification treatment, product selectivity, service life of the catalyst, acidic acid amount of modulation, the activity of catalyst were got improved obviously.This paper is based on the preliminary study of the laboratory, optimizing the synthesis process, and ultimately determine the best process for: Material mole ratio of n（Na₂O）:n（SiO₂）:n（Al2O₃）:n（H2O） =12:X:Y:（956¹312）,（X:Y=100:2, 76:2）, aluminum sulfate as aluminum source, sodium silicate and ludox as double silicon source, dropping ludox toward sodium silicate, and aluminum source dropping silicon source, regulating pH=10¹2.5. The in-situ synthesis of silicon aluminum ratio of 38 and 50 molecular sieves was carried out on the basis of the optimum synthesis process.This paper choose the ZrOCl₂ · 8H2 O as modifier to synthesize Zr-ZSM-5 molecular sieves because of abundant resources, low cost, and high catalytic activity, moisture resistance, low toxicity and high stability.Microstructure and surface properties of different Si/Al ratio of Zr-ZSM-5 were characterized by XRD, Raman, UV-Vis, BET, SEM, NH3-TPD, Py-IR. The results show that:With the increase of the content of zirconium, the characteristic peak intensity of the modified molecular sieve with different ratio of silicon and aluminum decreased, and the relative crystallinity decreased. The characteristic peak of ZrO₂ was not detected on the XRD diagram, which showed a high degree of dispersion. SEM images of the molecular sieve showed, crystal structure from the hexagonal prismatic structure transition to lamellar structure, and XRD results showed that the molecular sieve framework remained completely.It appeared new absorption peak at 214 nm by UV-Vis and showed that the peak enhanced at 464 cm-1 and appeared new absorption peaks at 1009 cm-1by Raman. These changes illustrate that zirconium atoms are introduced into framework of molecular sieve.At the same time, the change of apparent density showed that Zr has entered the molecular sieve macroscopically.BET of different Si/Al ratio results showed that molecular sieve surface area decreased, total pore volume and pore size increased with increase of the molar content of zirconium. These changes will affect shape selective catalysis of the molecular sieve.Py-IR and NH₃-TPD of different Si/Al ratio showed that zeolite acidity and acidstrength decreased with increasing molar content of zirconium, the distribution of acid type changed, the proportion of Lewis acid increased, Bronsted acid ratio decreased. The change of these acid properties is bound to affect the acid catalytic performance of molecular sieves.Through the comparison of two kinds of different silica alumina ratio, it is found that the ratio of silicon to aluminum can affect the amount of zirconium atoms into the framework of the molecular sieve.