P. De Luca

Rietveld refinement of the zorite structure of ETS-4 molecular sieves

Abstract The crystal structure of ETS-4 titanosilicate [Na9Si12Ti5O38(OH)·12H2O] was refined using synchrotron X-ray powder diffraction and the Rietveld method (Rp=0.050; Rwp=0.063; RB=0.169). Our diffraction data provide direct evidence that ETS-4 has the same structure as the zorite mineral. The framework of zorite can be described as nenadkevichite-like chains, laterally connected by 4[SiO4]/[TiO6] units, corresponding to two different chemical environments for Si. Similar to previous observations, a discrepancy was found between the population ratio of Si positions as calculated by the occupancy refinement of atomic sites related to these two environments, and that inferred from 29 Si MAS NMR. This is tentatively explained here on the basis of the large amounts of protons in the proximity of the Si2 site as indicated by 29 Si CP/MAS NMR. The low thermal stability of the zorite/ETS-4 structure is explained in terms of relevance of the hydrogen bonding between extra framework water molecules and framework oxygens.

Synthesis and characterization of the microporous titanosilicates ETS-4 and ETS-10

In the last years the interest in new zeolitic structures has increased. Some of these materials possess improved catalytic and adsorptive properties in comparison with the classical aluminosilicates. Among these materials are the AlPOs which opened new roads in the study of zeotypes. Subsequently, the study of titanium- and silicon-based molecular sieves was deepened. Among the numerous synthesized structures ETS-10 is a totally synthetic one while ETS-4 is the synthetic counterpart of the mineral zorite. In this paper a complete study is devoted to the ETS-10 and ETS-4 crystallization fields as a function of the quantities of Na2O and TiO2 in the initial gel. The influence of the initial pH on the two phases was also studied. The crystallization curves as a function of time for ETS-10 and ETS-4 with different initial Na and Ti contents were determined and analyzed. The SEM pictures allowed one to determine the morphology of the two ETS phases. Their compositions were determined by chemical analysis, and local structural characteristics were derived from NMR analysis.

Direct formation of self-bonded pellets during the synthesis of mordenite and ZSM-11 zeolites from low water content systems

Abstract Zeolite synthesis was performed from low water containing initial gels. The batch composition was: a M 2 O– b Na 2 O– b Al 2 O 3 –150SiO 2 –2 b TAABr–490H 2 O with M=Li, Na, K; TAA is tetramethyl, tetraethyl and tetrabutyl-ammonium; 2.25⩽ a ⩽8.82 and 1.87⩽ b ⩽30. Self-bonded pellets of high mechanical resistance of mordenite and ZSM-11 were obtained from two systems: the first one did not contain any organic cations, while the second one was made in presence of tetrabutylammonium bromide. The other systems led either to nonpelleted mordenite, ZSM-5 or sodalite.

Study of the thermal dehydration of metal-exchange ETS-10 titanosilicate

The ion exchange of nickel, cobalt and copper on ETS-10 and the dehydration kinetics of metal-exchanged ETS-10 titanosilicate were studied by means of X-ray diffraction, scanning electron microscopy and thermal analyses. The number of water molecules in the metal-exchaned ETS-10 is higher than in parent ETS-10 and the activation energies for dehydration vary in the sequence: ETS-10> Ni-ETS-10 >Co-ETS-10 >Cu-ETS-10. A part of copper cations precipitate on the strong basic surface of ETS-10 as claringbullite (Cu4Cl(OH)7·0.5H2O). The differential thermogravimetry (DTG) curves show that the maxima of dehydration temperature are shifted towards lower temperature as the metal concentration increases.

Synthesis of Mordenite and ZSM-11 zeolites from very dense systems: formation of self-bonded pellets

Zeolite synthesis was performed from very dense systems of initial gel composition: aM 2 O-bNa 2 O-bAl 2 O 3 -150SiO 2 -2bTAABr-490H 2 O with M=Li, Na, K; TAA=tetramethyl, tetraethyl and tetrabutyl-ammonium; 0.9≤a≤8.82 and 1.66≤b≤15. Self-bonded pellets of high mechanical resistance of mordenite and ZSM-11 were obtained from two systems: the first one did not contain any organic cation, while the second one was made in presence of tetrabutylammonium bromide.

Influence of zirconium on the crystallisation kinetics of ETS-4 molecular sieves

The scope of the paper is to synthesize and characteirze ETS-4 molecular sieve starting from gels containing titanium and zirconium: xNa2O-0.2TiO2-0.6KF-yZrO2-1.28xHCl-1.49SiO2-39.5H2O with 0.5≤x≤1.5 and 0.0≤y≤0.2. The study is based on the physicochemical characterization of the various products and on the determination of the kinetic parameters.

Microporous titanosilicate synthesized with vanadium

Abstract The present paper relates to the synthesis and characterization of microporous titano silicate synthesized with vanadium, isomorph of ETS-4 and ETS-10 and named respectively: ET(V)S-4 and ET(V)S-10. The effect of composition of the reaction mixture on the selectivity towards ET(V)S-10 and ET(V)S-4, on the kinetic parameters, on the morphology, size and composition of the crystals was thoroughly studied.

Ionic exchange and thermal characterisation of different cation exchanged forms of ETS-4

Abstract The main object of this paper is the study of thermal stability and ionic exchange capacity of ETS-4 exchanged with different cations. The ETS-4 molecular sieve sample was exchanged with Li + , Na + , K + and NH 4 + . Different cation exchanged forms of ETS-4 were heated at different temperatures for 2 hours and the degree of cristallinity was determined by X-ray diffraction. Moreover, an exchange was effectuated with solutions at different concentrations in order to determine the ionic exchange capacity of different ionic forms of ETS-4.

Synthesis of ETS-10 molecular sieve from systems containing TAABr salts

The synthesis conditions of the ETS-10 molecular sieve from the system aNa 2 O−bKF−cTiO 2 −dTAABr−1.28aHCl−1.49SiO 2 −39.5H 2 O where TAABr corresponds to TMABr, TEABr, TPABr and TBABr and .0.9≤a≤3.5, 0≤b≤1.3, 0.25≤c≤1.2, 0≤d≤1.1 are studied. The effect of the reaction mixture composition on the selectivity of the system, on the kinetic parameters on the morphology and on the composition of the ETS-10 crystals, is discussed. The role of the organic added to the gel on the reaction mechanism is proposed.

The role of carbon nanotubes and cobalt in the synthesis of pellets of titanium silicates

In the present work self-bonded pellets of Engelhard Titaniun Silicates, ETS-4 and ETS-10, containing cobalt and carbon nanotubes, were synthesized by hydrothermal synthesis at 190 °C, from gels of the initial composition x–Na2O–0.2TiO2–0.6KF–(1.28x − 2y)HCl–2yHNO3–1.49SiO2–yCoO–39.5H2O, with x equal to 0.8; 1; 1.5; 2.5 mol and y equal to 0.015; 0.03; 0.06; 0.1. To the initial gels were then added different weight percentages of carbon nanotubes compared to the dry gel. The obtained pellets were characterized by X-ray diffraction analysis, thermal analysis (TG, DTG, DSC), tests of mechanical resistance to compression and nuclear magnetic resonance.