Hierarchical zeolites are a class of microporous catalysts and adsorbents that also contain mesopores, which allow for fast transport of bulky molecules and thereby enable improved performance in petrochemical and biomass processing. We used repetitive branching during one-step hydrothermal crystal growth to synthesize a new hierarchical zeolite made of orthogonally connected microporous nanosheets. The nanosheets are 2 nanometers thick and contain a network of 0.5-nanometer micropores. The house-of-cards arrangement of the nanosheets creates a permanent network of 2- to 7-nanometer mesopores, which, along with the high external surface area and reduced micropore diffusion length, account for higher reaction rates for bulky molecules relative to those of other mesoporous and conventional MFI zeolites.

http://science.sciencemag.org/content/sci/336/6089/1684.full.pdf

Synthesis of self-pillared zeolite nanosheets by repetitive branching.

Dinuclear ruthenium complex, with a bridging carbide and a hydride ligand, and methyltricyclohexylphosphonium chloride result from thermal decomposition of olefin metathesis catalyst, (ImesH_2)(PCy)_3)(Cl)_2Ru CH_2. Involvement of dissociated phosphine in the decomposition is proposed. The dinuclear complex has catalytic olefin isomerization activity, which can be responsible for competing isomerization processes in certain olefin metathesis reactions.

Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions

Molecular simulation studies of methane in silicalite at room temperature are reported. Adsorption isotherms and diffusion coefficients have been calculated for a range of pressures. At low pressures (<20 bar) adsorption is predominantly at specific potential-energy minima in the silicalite channels while at higher pressures adsorption is determined by the total accessible channel volume. Diffusion is found to be strongly anisotropic with the fastest diffusion along the straight channels. Good agreement is obtained with experimental results for orientationally averaged diffusion coefficients. At low pressure, diffusion is well described by a pseudo-Bosanquet formula which identifies two independent contributions to diffusional resistance (from collisions with walls and from intermolecular collisions). At short times significant molecular force correlations arise due to the diffuculty of methane molecules passing each other in the channel intersections of the silicalite lattice. Some preliminary results for butane diffusion coefficients in silicaliate are also reported.

Molecular simulation of methane and butane in silicalite

The structure-controlling role of organic templates for the synthesis of porosils in the systems SiO2/template/H2O

Synthesis and catalytic properties of crystalline, microporous vanadium silicates with MEL structure

The lattice structure of a pure and completely siliceous sample of zeolite ZSM-11 has been investigated by a combination of high-resolution solid-state {sup 29}Si MAS NMR and synchrotron-based X-ray powder diffraction techniques. The structure is temperature dependent in the range 263-363 K and a good fit to the diffraction data at 363 K is obtained with space group I{anti 4}m2 and a{sub 0} = 20.067 (1) and c{sub 0} = 13.411 (1). At room temperature the XRD data cannot be refined as the structure is intermediate and the lattice structure of the limiting low-temperature, low-symmetry form will only be deduced from data collected at 263 K.

Detailed investigation of the lattice structure of zeolite ZSM-11 by a combination of solid-state NMR and synchrotron x-ray diffraction techniques

Considerable progress has been made in recent years in the investigation of the structures of zeolite catalysts by solid-state high-resolution /sup 29/Si MAS NMR techniques. For low Si/Al ratio materials, the spectra give a description of the distribution of Si and Al throughout the lattice, while for completely siliceous analogues the spectra may be related directly to the lattice structures. The effect of removing all of the aluminum from the lattice is to give very narrow resonances in the /sup 29/Si MAS NMR spectrum which are all due to Si(4Si) environments and which reflect the number and populations of the crystallographically inequivalent lattice sites in the unit cell. These latter spectra have been used to probe various subtle effects on the lattice structures via the short-range ordering and are a very useful complement in structural investigations to the more conventional powder XRD technique. In the present communication, they describe how these spectra combined with variable-temperature operation can be used to detect the existence of high-symmetry phases for various zeolites at elevated temperatures. It is only with materials of sufficiently high quality such as those investigated that the spectra resolution is good enough to detect and characterize these phases.

High-symmetry, high-temperature zeolite lattice structures

Detailed Investigation of the Lattice Structure of Zeolite ZSM-11 by a Combination of Solid-State NMR and Synchrotron X-Ray Diffraction Techniques.

The catalytic properties of zeolite catalysts are dependent on their unique structural features, such as pore geometry, distribution and concentration of T-atoms and adsorbed species, presence of defects, and temperature. Solid state NMR is highly sensitive to changes in the local environments of T-atoms, and when used in conjunction with X-ray diffraction provides a more complete description of zeolite framework structures. This combined use of XRD and MAS NMR to determine the changes in the framework of zeolite catalysts due to temperature and organic molecule adsorption will be discussed in detail.

C. T. Pasztor

Papers

Detailed investigation of the lattice structure of zeolite ZSM-11 by a combination of solid-state NMR and synchrotron x-ray diffraction techniques

High-symmetry, high-temperature zeolite lattice structures

Detailed Investigation of the Lattice Structure of Zeolite ZSM-11 by a Combination of Solid-State NMR and Synchrotron X-Ray Diffraction Techniques.

The Effect of Sorbates and Elevated Temperatures on the Structures of Some Zeolite Catalysts

High-Symmetry, High-Temperature Zeolite Lattice Structures.