3D Zeolite Research Articles

Preface: phys. stat. sol. (b) 245/3

Preface: phys. stat. sol. (b) 245/3

Structure Elucidation of the Highly Active Titanosilicate Catalyst Ti‐YNU‐1

Three novel zeolites (M-IEZ-MWW, IEZ-FER and IEZ-CDO) have been successfully synthesised from the corresponding precursors. Structure characterisation of those materials was conducted by TEM. Our studies show that the structure of the new zeolites keeps identical layer to the corresponding known 3D zeolite, except for the distinct expansion of the layer spacing. Combining with results from XRD, N2 adsorption, IR and NMR, the expansion can be explained by the pillaring of T sites between the layers. Meanwhile, the intergrowth of 3D MWW and IEZ-MWW was observed in the Al-IEZ-MWW and Si-IEZ-MWW crystals, IEZ-CDO structure was found in the IEZ-FER crystals, and the intergrowth of CDO and new polymorph was observed in the CDS-1 crystal. Moreover, two new zeolites IM-5 and SSZ-57 were also studied by TEM. We found that the space group of IM-5 is non-centrosymmetrical, and in SSZ-57 the new structure with slightly larger c parameter was observed compared to MEL. Chiral mesoporous silica nanotube and chiral mesoporous carbon nanotube were aslo investigated by TEM. We found that the former was synthesised by hollowing out process and it possesses chiral mesopores in the wall, the latter was synthesised by templating and seeding method. Electron tomography was first applied to study the handedness of the chiral mesoporous nanotube. Furthermore, TEM studies verified that bifunctional mesoporous silica has a Fm-3m structure, and mesoporous carbon FDU-16 has a Im-3m structure.

Solid State NMR Method for the Determination of 3D Zeolite Framework/Sorbate Structures: 1H/29Si CP MAS NMR Study of the High-Loaded Form of p-Xylene in ZSM-5 and Determination of the Unknown Structure of the Low-Loaded Form

A general protocol is described for structure determinations of organic sorbate-zeolite complexes based on the selective, through-space, distance-dependent transfer of magnetization from protons in selectively deuterated organics to framework silicon nuclei. The method was developed using the known structure of the high-loaded ZSM-5/p-xylene complex containing p-xylene-d(6) or p-xylene-d(4). It was then applied to determine the unknown structure of the low-loaded ZSM-5/p-xylene complex using NMR alone. For the high-loaded complex improved data were obtained below 273 K, where slow motions and exchange processes of the p-xylene are eliminated. The general approach was validated by the exact agreement of the experimental (1)H-(29)Si CPMAS spectra obtained at a specific contact time and the complete 24-line spectra simulated using 1/T(CP) vs M(2) correlations from only the six clearly resolved resonances. For the low-loaded complex the (29)Si resonances were assigned at 267 K, and variable contact time CP experiments were carried out between 243 and 173 K using the same specifically deuterated p-xylenes. All possible locations and orientations of the p-xylene guests were sampled, and those solutions that gave acceptable linear 1/T(CP) vs M(2) correlations were selected. The optimum p-xylene location in this temperature range was determined to be in the channel intersection with the long molecular axis parallel to [0,1,0] (ring center fractional coordinates {-0.009, 0.250, 0.541}) with the ring plane oriented at an angle of 30 +/- 3 degrees about the crystallographic b axis. A subsequent single-crystal X-ray study confirmed this predicted structure.

Macroporous Zeolitic Membrane Bioreactors

AbstractA simple and effective method is described for the fabrication of robust zeolitic membranes with three‐dimensional (3D) interconnected macroporous structures. The membranes were prepared by electrostatically seeding mesoporous silica sphere (MSS) self‐assembled films with silicalite‐1 nanoparticles, followed by hydrothermal treatment. The membrane thickness, which is determined by the MSS film thickness, can be easily adjusted from tens to hundreds of micrometers by varying the concentration of the MSS dispersion and the solution volume. Biomacromolecule‐functionalized macroporous zeolitic membrane bioreactors were subsequently prepared via the layer‐by‐layer (LbL) electrostatic assembly of polyelectrolytes and enzyme (catalase) on the 3D macroporous membranes. The enzyme‐modified membranes with interconnected macroporous structures display enzyme loading amounts and activities that are one order of magnitude higher than corresponding 3D zeolite films with closed macropores, and approximately three orders of magnitude higher than their non‐porous planar film counterparts assembled on silica substrates. The enzyme loadings and activities were found to be approximately linearly dependent on the thicknesses of the membranes. Furthermore, the immobilized enzyme exhibits enhanced reaction stability in comparison with enzyme in bulk solution. These membranes are potentially useful for separations as they could be used to simultaneously perform reaction and separation steps.

Hydroisomerization of n-butane over Pd/HZSM-5 and Pd/Hβ with and without binder

The influence of the agglomeration with a clay binder on the activity of two 3D zeolites with medium and large pore size (ZSM-5 and beta) for the hydroisomerization of n-butane has been studied. Temperature-programmed desorption of ammonia (TPDA), atomic absorption (AA) spectroscopy, chemisorption and surface area measurements were used to characterize the catalysts. Catalytic performance is strongly influenced by the binder due to the fact that zeolite hydrogen transfer activity, metal/acid site balance, acid site density, and diffusional limitations are altered after agglomeration. A lower conversion is always obtained for the binded catalysts, due to neutralization of some zeolite acid centers. For the catalysts based on ZSM-5, it is compensated by a higher selectivity to iso-butane, but this positive effect is not observed for the catalysts based on beta zeolite.