Giovanni Perego

Layered structure of ERB-1 microporous borosilicate precursor and its intercalation properties towards polar molecules

Abstract As-synthesized ERB-1 borosilicate has a bi-dimensional layered structure, and the three-dimensional (3D) microporous structure is formed after calcination at 270°C. X-Ray powder diffraction (XRD), temperature-programmed desorption (TPD) and 29 Si magic-angle spinning nuclear magnetic resonance (MAS NMR) analyses demonstrated that the formation of the 3D ordered structure occurs through the condensation of silanol groups present on the surfaces of the layers. As-synthesized ERB-1 displays intercalation properties towards polar molecules such as ethylene glycol, isopropanol and [2,2,2]-azabicyclooctane.

Ti Substitution in MFI Type Zeolites: a Quantum Mechanical Study

Ab initio quantum mechanical calculations were performed to study isomorphous substitution of Ti for Si in orthorhombic MFI type zeolite. A minimum energy was found for pentameric Ti(OSiO 3 H 3 ) 4 clusters, having the same geometry determined in MFI framework by crystal structure analysis, corresponding to a Ti-O bond length of 1.80 A. The latter value is in good agreement with the experimental value derived by both XRD and EXAFS analysis. No clear evidence in favour of preferential crystal sites for Ti substitution was achieved.

Structural characterization of as-synthesized B- and Ti-containing MFI-type molecular sieves☆

The influence of tetrapropylammonium ( TPA) ions on the structural properties of as-synthesized Ti- (TS-1) and B-containing (BOR-C ) MFI zeolites crystallized from alkali-free gels is investigated. Thermogravimetric analysis shows that the negative charge of the BOR-C framework is compensated by the TPA ions, while only ‘soft’ interactions between TPA and Ti sites are observed. Rietveld analysis of the synchrotron X-ray powder diVraction patterns reveals that incorporation of Ti and B causes an expansion and a contraction of the MFI framework, respectively. Regression curves describing the unit cell parameters variation can be used to determine the real framework composition. The presence of TPA ions inside the pores strongly influences the apparent d TiMO and d BMO tetrahedral bond distances, which are shorter than those in the calcined forms. The mobility of the TPA cations in silicalite-1, TS-1 and BOR-C samples with the highest Ti and B content is studied by 13C NMR and molecular dynamics simulations. As expected, the TPA cation mobility increases as the pore size increases (BOR-C

B-containing molecular sieves crystallized in the presence of ethylenediamine. Part II: crystal structure of as-synthesized B-MFI

Abstract Hydrothermal treatment of an aqueous solution containing tetramethoxysilane, boric acid and ethylenediamine (EN) led to the crystallization of B-MFI (BOR-C) accompanied by small amounts of B-ferrierite (B-FER). Single crystal X-ray diffraction studies were performed on a platy B-FER crystal, with the unit cell dimensions a=18.512(2), b=13.865(1), c=7.317(1) A, V=1877.9 A3, space group Immm. Framework incorporation of 6.5±0.5 B atoms/unit cell was evidenced with no extra-framework B species, in line with wavelength dispersive spectroscopy analysis of the B-FER crystals (6.5 B atoms/unit cell). Two crystallographically independent EN molecules were located with a total occupancy corresponding to 3.6 molecules/unit cell. Since the synthesis was performed in the absence of alkali metal ions, the EN molecules have to be in the dicationic form to compensate the negative framework charge or, at least, they interact with Bronsted protons forming N⋯H–O hydrogen bonds.

The synthesis of the new zeolite, ERS-7, and the determination of its structure by simulated annealing and synchrotron X-ray powder diffraction

The new zeolite ERS-7 (EniRicerche-molecular-Sieve-7), which was synthesized within a narrow temperature and compositional range using N,N-dimethylpiperidinium as a structure directing agent, has a structure consisting of 17-sided (46546582) picnic-basket-shaped cages connected by 8-membered ring windows.

Synthesis and Characterization of Molecular Sieves Containing Transition Metals in the Framework

Apart from applications as molecular sieves, zeolites were considered for many years only as acid catalysts and used for reactions performed at relatively high temperature, in the gas phase. Only after isomorphous replacement of transition elements for silicon and aluminum had been demonstrated, were red-ox properties of zeolites seriously considered. This achievement not only allows the opening of new perspectives for selective oxidations, but it also draws the attention toward the capabilities of zeolites to generate free radicals in the presence of even trace amounts of oxygen, affecting the catalyst performances also in acid catalyzed reactions [1].

ERS-8: a new class of microporous aluminosilicates

The synthesis of micro-mesoporous aluminosilicates via gelation of a reaction mixture containing Si(OC 2 H 5 ) 4 , Al(OC 3 H 7 ) 3 , C 2 H 5 OH, H 2 O and alkali-free NR 4 -OH (R=C 3 H 7 , C 4 H 9 , C 5 H 11 , C 6 H 13 ) is described. X-ray amorphous mesoporous aluminosilicates (MSA) or microporous aluminosilicates, characterized by a broad peak in the low angle region of XRD pattern (ERS-8), are obtained, depending on the NR 4 -OH/SiO 2 molar ratio and on the number of C atoms in the R groups. A structural model is proposed concerning the arrangement of the NR 4 + cations within the gel, which accounts for the experimental data.

Structure of layered α-zirconium phosphite and zirconium phosphate—phosphites from X-ray powder diffraction data

Abstract The α-type layer-based structure of Zr(HPO 3 ) 2 and zirconium phosphate—phosphites (ZPP) of the general formula Zr(HPO 4 ) x (HPO 3 ) 2- x · n H 2 O ( x =0.36, n =0 for ZPP-1; x =0.85, n =0.5, for ZPP-2; x =0.85, n =0 for ZPP-2A; and x = 1.72, n =1 for ZPP-3) were investigated by thermogravimetric analysis and X-ray diffraction. Structures were refined by the Rietveld method, taking into account the anisotropic line broadening effects due to the different crystallite sizes along the direction parallel and perpendicular to the layers, respectively. In order to reduce the number of structural parameters, refinements were performed in the rigid body approximation. The structure previously proposed, based on non-homogeneous distribution of phosphate and phosphite groups within each sheet, was confirmed for ZPP-1 and ZPP-2. The layer stacking typical of Zr(HPO 3 ) 2 characterizes the crystal structure of ZPP-1. A regular alternation of phosphate and phosphite type of stacking characterizes the crystal structure of ZPP-2. ZPP-3 has the same structure of α-Zr(HPO 4 ) 2 ·H 2 O with phosphite groups randomly distributed on both sides of each sheet.

Structural characterization of borosilicates synthesized in the presence of ethylenediamine

Hydrothermal treatment of an aqueous solution containing tetramethoxysilane, boric acid and ethylenediamine (EN) led to the crystallization of B-MFI (BOR-C) accompanied by small amounts of B-ferrierite. Single crystals X-ray diffraction studies were performed on a small prismatic crystal of BOR-C, unit cell dimensions a =19.869(2), b =19.661(3), c =13.207(2) , space group Pnma , and on a platy FER-type crystal with unit cell dimensions a =18.512(2), b =13.865(1), c =7.317(1) , space group Immm . Different routes (unit cell volume, T-O distances, refinement of B and Si scattering curves) reveal the incorporation of boron in the framework corresponding to 14±1 and 6.5±0.5 B atoms/unit cell in MFI and FER structures, respectively. Three different EN sites in BOR-C and two different EN sites in B-FER (all with partial occupancy) were found; the total number of EN, almost one half than boron incorporated in the framework, confirms that EN should be in dicationic form to compensate the negative charge of the framework. Molecular modeling simulations confirmed that those found in the refinements of the X-ray diffraction data are really the most preferred location sites for EN molecules in the two porous systems.

Isomorphous Substitution in Zeolite Catalysts

Publisher Summary The high silica zeolites, discovered first by Mobil, brought an enormous amount of studies in several directions. Among them, many attempts were done to incorporate in the framework elements different from silicon and aluminum, with the aim of synthesizing zeolites possessing novel catalytic properties. Assessing the occurrence of a real incorporation is generally a difficult task, so that only in few cases it was possible to get conclusive evidence in this regard. X-ray diffraction, MAS-NMR, IR, Electron microscopy and other techniques were used for the structure characterization of these materials. Experimental evidence was achieved. This convincingly demonstrates boron and titanium to be really in the framework. More recently, efforts were devoted to the achievement of a better insight into the detailed structure of the active sites within the pores as well as into the mechanisms of catalytic activity.