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Hierarchical ZSM‐5 zeolites were synthesized by in‐situ crystallization of mesoporous carbon‐silica composites with a well‐ordered SBA‐15 structure. The hierarchical ZSM‐5 zeolite possessed a rather high external surface area (205 m2/g) and pore volume (0.35 cm3/g) compared with the reference ZSM‐5 zeolite, as well as higher acid‐site accessibility to large molecules. In the naphthalene benzylation reaction, the hierarchical HZSM‐5 zeolite converted approximate 50 % of benzyl chloride in 100 minutes under mild conditions and showed a high stability, which could be ascribed to the improved diffusion ability and acid‐site accessibility. [ABSTRACT FROM AUTHOR]

Nickel and cobalt salen complexes were simultaneously encapsulated in mesoporous zeolite A by flexible ligand method. The prepared catalyst NiCosalenA was investigated for its electrochemical behavior and electrocatalytic activity towards the oxidation of methanol on glassy carbon electrode in 0.1 M NaOH solution. Upon encapsulation in zeolite A, the NiCosalen complex exhibits the typical cyclic voltammetric response, which can be anticipated for the Ni 2+ Co 2+ (Salen)(OH) 2 /Ni 3+ Co 3+ (Salen)O(OH) redox couple. It also showed much higher electrocatalytic activity towards the oxidation of methanol than pure NisalenA, due to a synergetic effect that may originate from the interaction of Ni(salen) and Co(salen) and/or the formation of dinuclear salen complexes in adjacent or appropriate sites in a nano-cage through the lattice oxygen of the zeolitic host. The mechanism of electrocatalytic oxidation of methanol on NiCosalenA modified electrode was proposed to be EC process. In both the chronoamperometric and chronocoulometric studies, the reaction of methanol electrooxidation followed a Cottrellian behavior and similar diffusion coefficients ( D ) of methanol were found to be 3.82 × 10 −7 cm 2 s −1 and 3.91 × 10 −7 cm 2 s −1 , respectively. The catalytic rate constant ( k cat ) was also calculated to be 5.52 × 10 5 cm 3 mol −1 s −1 in the range of 0.005–2.0 M of methanol. [ABSTRACT FROM AUTHOR]

Nickel and manganese salen complexes were simultaneously encapsulated in the supercages of the mesoporous zeolite A by using the flexible ligand method. The electrochemical behavior and electrocatalytic activity toward the electrooxidation of methanol on glassy carbon electrode coated with NiMnsalenA (NiMnsalenA/GCE) in 0.1 M NaOH solution were studied by cyclic voltammetry (CV), chronoamperometry (CA) and AC electrochemical impedance spectroscopy (EIS). The results showed that the addition of small amounts of Mn species can give rise to much higher electrocatalytic activity than the pure NisalenA toward the oxidation of methanol, mainly due to a synergetic effect that may originate from the interaction of Ni(salen) and Mn(salen) and/or the formation of dinuclear salen complexes via the lattice oxygen of the zeolitic host. Kinetic parameters such as the electron transfer coefficient α , the rate constant k s of the electrode reaction and the charge transfer coefficient of the catalytic reaction, α n were determined to be 0.40, 1.898 s −1 and 0.43, respectively, and the detection limit was found to be 97.66 μM. The mechanism of electrocatalytic oxidation of methanol on NiMnsalenA/GCE was investigated and proposed to be done by reaction with Ni 3+ (salen)O(OH) and also direct electro-oxidation reaction. The impedance behaviors showed different patterns at different applied potentials, indicating the changes of the rate-determining step, from the methanol electrooxidation leading to the formation of intermediates on the surface of electrode gradually to the oxidation and removal of adsorbed intermediates. The influence of methanol concentration on the impedance behaviors was also studied and the results demonstrated that the semidiameters of the Nyquist diagrams decreased with the increase of methanol concentration, signifying the acceleration of the reaction rate of methanol electrooxidation. [ABSTRACT FROM AUTHOR]

A high-acidity HUSY zeolite with mesoporous structure was prepared by alumination with a dilute aqueous NaAlO solution and characterized by XRD, N adsorption, IR framework vibration and Si MAS NMR methods. The results indicated the extra-framework aluminum was reinserted into the tetrahedral framework through isomorphic substitution of framework Si (0Al) sites by Al ions, whereas the crystal and micropore structure were unaltered. FTIR spectra of hydroxyl vibrations and pyridine adsorbed on realuminated zeolites showed that the number of Brønsted acid sites and strong Lewis acid sites increased whereas weak Lewis acid sites decreased twice. The mesoporous structure composed of inter-and intra-crystalline pores in the aluminated HUSY increased the external surface area of the zeolite, improving accessibility of molecules to the active sites and enhancing its catalytic ability. The realuminated HUSY zeolite supported with Ru catalyst exhibited a higher catalytic activity for benzene hydrogenation than the parent HUSY zeolite; the reaction rate in comparison to the mesozeolite increased by 5.5 times. [ABSTRACT FROM AUTHOR]

Mesoporous EU-1 zeolites with adjustable mesoporosity have been prepared by employing silanized silica into the starting synthesis gel, based on the hinder effect of organic moiety to crystal growth. The synthesized mesoporous EU-1 zeolites were characterized by XRD, NMR, SEM/TEM and N 2 adsorption/desorption at 77 K, showing the persistence of inherent microporous framework structure of EU-1 zeolite and the existence of additional mesopores within the range of 3–10 nm. The generation of mesoporosities is from the intercrystalline voids of nanocrystal aggregates. The introduction of mesopores in EU-1 zeolite increased the adsorption of mesitylene with the kinetics diameter larger than the micropore size, and made it possible for the diffusion pattern of n -heptane from one-dimensional in microporous EU-1 to three-dimensional in mesoporous EU-1. This result together with the enhanced accessibility of acidic sites of mesoporous EU-1 improved greatly the catalytic activity and product yields of cumene cracking reaction involving bulky molecules. [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]

Diffusion properties of mesostructured zeolite 5A were investigated by employing n-alkanes as probe molecules using the zero length column (ZLC) method. The mesopores were found to enhance molecule diffusion. Moreover, the effective diffusion time constant ( D/ R) increased with mesoporosity in the zeolites between 308 K and 393 K, whereas the activation energy decreased with increasing mesopore volume. The effective diffusivity values of n-alkanes in mesoporous zeolite 5A were generally higher than that the microporous zeolite 5A sample. This clearly implied the important role of the mesopore in zeolites crystals in facilitating the transport of reaction molecules due to shorter average diffusion path length and less steric hindrance. [ABSTRACT FROM AUTHOR]

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]