Search

Microspherical MFI mesoporous zeolites (MMZ-5) with different mesopore volumes and similar silica-alumina ratios were prepared by the bond-blocking principle and confirmed by physical methods. The zeolite materials with high external surface areas contained inter- and intra-crystalline mesostructures. NH-TPD and in situ FT-IR spectra techniques were used to characterize the acidic properties of the mesoporous zeolites. The results showed that the Py-Brönsted acid sites of the MMZ-5 samples are very similar to that of the conventional ZSM-5 zeolite, but the latter Py-Lewis acid sites are greatly larger than the former. Further, the concentration of DMPy-Brönsted acid sites in the mesoporous zeolites arrived at 70 μmol/g, namely, the 2,6-dimethylpyridine (DMPy) molecule can probe 97 % of the Py-Brönsted acid sites in the MMZ-5 zeolites. The introduction of the mesoporous structure into the MMZ-5 zeolites increased strongly the accessibility of the more bulky molecules, such as the DTBPy molecules. As expected, HMMZ-5-2 sample as an acid catalyst displayed a high reaction activity and an uniform product selectivity in the benzylation of p-xylene with benzyl chloride. Graphical Abstract: [Figure not available: see fulltext.]. [ABSTRACT FROM AUTHOR]

Abstract: The Mg2+ and Ca2+ exchange properties in the meso-zeolite LTA were investigated. These meso-zeolite materials with intracrystalline mesopores ca. 3nm were prepared using organic functioned fumed silica as silica source. The Dual-site Langmuir (D-L) expression appropriately describes the equilibrium data for the Ca2+ and Mg2+ exchange. The fitting results with D-L model suggest that two kinds of ion-exchange sites in the meso-zeolites exist, one in the part of intrinsic micropore structure (internal surface area) and the other one in the part of established mesopore structure (external surface area). The latter site has lower enthalpy values of Ca2+ or Mg2+ exchanges than the former one. Ca2+ or Mg2+ exchange kinetics is conducted at 273K, 288K and 308K. The results show the emergence of mesopores lowering the activation energy of ion exchange and accelerating Mg2+ exchange extremely in the materials. The diffusion rate of hydrated Mg2+ in the meso-zeolite LTA increases by 17.5 times, higher than that of conventional LTA at 273K. And the meso-zeolite LTA possesses large Mg2+ competitive ability in a solution containing Ca2+ and Mg2+. These properties make the meso-zeolite LTA a suitable material which could be used effectively in hard water softening and detergent building for Mg2+ removing. [Copyright &y& Elsevier]

Abstract: A series of nanosized ZSM-5 zeolite samples with intracrystalline mesopores has been synthesized using organosilane functioned fumed silica as silica source and tetrapropylammonium hydroxide as microporous structure directing agent. The organic moiety linked on the surface of fumed silica blocks the growth of zeolite crystal, forming the nanosized zeolite crystal and intracrystalline defects inside the nano-crystal. The formation of the mesopores is by bond-blocking function in crystallization. The XRD results indicate that the samples are high crystalline ZSM-5 and the TEM images show that the samples are nanosized with the size ca. 20nm and the intracrystalline mesopores about 3nm exist inside the nanosized crystal. [Copyright &y& Elsevier]