Z. Gabelica

Bio: Z. Gabelica is an academic researcher from University of Liège. The author has contributed to research in topics: Thermal decomposition & Oxalate. The author has an hindex of 7, co-authored 19 publications receiving 233 citations.

High resolution solid state mas 11b-nmr evidence of boron incorporation in tetrahedral sites of zeolites

Abstract: High resolution solid state MAS 11B-NMR was used to detect quantitatively variously coordinated BOx structural units in zeolites. Boron stemming from Pyrex autoclaves is progressively incorporated ...

Magic-angle-spinning 29Si-NMR study of the structure of ZSM-5 and ZSM-11 zeolites.

Abstract: Eight magnetically different 29Si-NMR lines are clearly distinguished in the solid state high resolution spectra of HZSM-5 zeolite with a high Si/Al ratio (1000) and some of them are assigned. The resonance line at −105 ppm in both HZSM-5 and HZSM-11 zeolites is attributed to Si atoms in the second coordination sphere of an Al atom, i.e. Si (1 Al). The −115 ppm lines stem from Si atoms in 4-membered rings. The splitting of these lines originates from a probable strain in these small rings. The incorporation of Al atom occurs exclusively in the 5-membered rings.

DETERMINATION OF SILICON-ALUMINIUM ORDERINGS IN MORDENITE AND ITS ALUMINIUM DEFICIENT FORMS USING HIGH-RESOLUTION MAGIC-ANGLE-SPINNING 29Si-NMR

Abstract: A series of chemically dealuminated mordenites were investigated by 29Si and 27Al NMR spectroscopy High-resolution magic-angle-spinning (HRMAS) solid state 29Si NMR lines with varying intensity were observed at δ=−95, −105 and −110 ppm When it is assumed that the Al atoms are located exclusively in the 4-membered rings of the structure, these variations can be explained by assigning the resonance lines to silicon atoms surrounded by 2, 1 and 0 Al atoms respectively The 27Al NMR spectrum yields quantitative information on the amount of octahedrally coordinated aluminium formed during various chemical treatments of Na-mordenite

Acid-catalyzed synthesis of mono- and dialkyl benzenes over zeolites: active sites, zeolite topology, and reaction mechanisms

Abstract: This review describes mechanisms of catalytic reactions leading to mono- and dialkyl benzenes over zeolites, which represent an important part of petrochemical products. The emphasis is given to the effect of the type of acid sites, zeolite structure, and reaction conditions on the activity and selectivity of these complex reactions, and particularly to the individual products with respect to their iso- vs. n- and ortho-, meta-, and para-isomers. The first part of the paper deals with the description and analysis of the structure and properties of the acid sites, and zeolite pore inner structure applied in synthesis of alkyl benzenes. Individual reactions leading to the synthesis of propyl benzene, xylenes, ethyl toluenes, diethyl benzenes, and transformation of trimethyl benzenes to xylenes from the view point of the reaction mechanism, function of the acid sites, and inner pore geometry of zeolites are described in the second part.

New Route to Pentasil-Type Zeolites Using a Non Alkaline Medium in the Presence of Fluoride Ions

Abstract: Silica-rich, Al-, B- and (Al + B) MFI zeolites called Zeosilites, Aluzeosilites, Borozeosilites and Aluborozeosilites respectively were obtained by hydrothermal crystallization at 60–200°C from mixtures containing F anions and tetra-, tri- and di-propylamraonium cations as templates; pH values were 3–10. Crystal size is a function of the Si substitution degree, it may reach 800 um in some cases. DSC, DTA and TG curves corresponding to the decomposition of the templates occluded as fluoride salts are different from those observed for samples obtained in alkaline medium. Mass spectrometer analysis shows that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination. High resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework.

Spectroscopic Definition of the Copper Active Sites in Mordenite: Selective Methane Oxidation

Abstract: Two distinct [Cu–O–Cu]2+ sites with methane monooxygenase activity are identified in the zeolite Cu-MOR, emphasizing that this Cu–O–Cu active site geometry, having a ∠Cu–O–Cu ∼140°, is particularly formed and stabilized in zeolite topologies. Whereas in ZSM-5 a similar [Cu–O–Cu]2+ active site is located in the intersection of the two 10 membered rings, Cu-MOR provides two distinct local structures, situated in the 8 membered ring windows of the side pockets. Despite their structural similarity, as ascertained by electronic absorption and resonance Raman spectroscopy, the two Cu–O–Cu active sites in Cu-MOR clearly show different kinetic behaviors in selective methane oxidation. This difference in reactivity is too large to be ascribed to subtle differences in the ground states of the Cu–O–Cu sites, indicating the zeolite lattice tunes their reactivity through second-sphere effects. The MOR lattice is therefore functionally analogous to the active site pocket of a metalloenzyme, demonstrating that both the ...

Industrial application of shape-selective catalysis

Abstract: In the 26 years since the term “shape-selective catalysis” was coined by P. B. Weisz and V. J. Frilette [1] to describe the unique catalytic properties of small pore molecular sieve zeolites, great strides in the use of shape-selective zeolites have been made, both scientifically and technologically. Since then, in addition to small pore zeolites, synthetic medium pore zeolites, such as ZSM-5 [2], ZSM-11 [3], ZSM-22 [4], ZSM-23 [5], ZSM-35 [6], ZSM-38 [7], ZSM-48 [8], etc., have been discovered. The availability of these synthetic medium pore zeolites has expanded the realm of “shape selectivity” beyond the original discovery of selective conversion of straight chain molecules to include certain branched molecules, single-ring aromatics, naphthenes, and nonhydrocarbons with a critical molecular dimension smaller than about 6 A.