Jean-Louis Paillaud

Synthesis and characterization of gallium-beta zeolite from fluoride-containing media

Abstract A gallosilicate beta zeolite was prepared in the 150–200°C temperature range in the presence of the tetraethylammonium cation as the structuring agent from almost neutral fluoride-containing aqueous gels having Si/Ga ratios between 5 and infinity. Pure and fully crystallized beta samples could only be obtained from the gels with Si/Ga molar ratios higher than or equal to 20. The samples of zeolite beta were characterized by the usual techniques, i.e. powder XRD, SEM, chemical analysis, thermal analysis, N2 adsorption isotherms and 29 Si , 71 Ga , 19 F and 13 C NMR spectroscopy.

IM-17: a new zeolitic material, synthesis and structure elucidation from electron diffraction ADT data and Rietveld analysis

The synthesis and the structure of IM-17, a new germanosilicate with a novel zeolitic topology, prepared hydrothermally with decamethonium as the organic structure directing agent, are reported. The structure of calcined and partially rehydrated IM-17 of chemical formula per unit cell |(H2O)14.4|[Si136.50Ge39.50O352] was solved ab initio using electron diffraction ADT data in the acentric Amm2 (setting Cm2m) space group and refined by the Rietveld method. This new zeolite framework type contains a 3D pore system made of intersecting 12, 10 and 8-ring channels.

Phosphate uptake from water on a Surfactant-Modified Zeolite and Ca-zeolites

The phosphate adsorption kinetics are determined in batch-wise (noted B) and fixed-bed column (noted C) experiments on a Surfactant-Modified Zeolite (SMZ) and various Ca-zeolites. The influence of phosphate concentration (0.08 or 0.8xa0mmol/L), presence of NO3−, HCO3−, SO42− and Cl− competing anions (individual concentrationxa0=xa00.8xa0meq/L) and flow rate Q (1–30xa0mL/min) is studied. Preliminary experiments lead to the selection of the most efficient Ca-LTA and SMZ samples for the subsequent studies. In B experiments, the nature of the used system does not influence the equilibrium removal rate R (≈80%) but affects the adsorption kinetics. The equilibrium times are shorter on SMZ than on Ca-LTA, increasing with the phosphate concentration and the presence of competing anions, respectively in the ~0.5–6 or ~3–24xa0h ranges. In C experiments, the phosphate uptake performances on SMZ are higher than in the corresponding B experiments, with in particular higher final q/qm values. The deterioration of the performances on SMZ in presence of competing anions or with increase of Q is due to the effect of the slow phosphate ion-exchange kinetics and the short used contact time. For similar reasons, sorption on Ca-LTA is lower than on SMZ. For instance, with a 0.8xa0mmol/L phosphate concentration and a 10xa0mL/min flow rate, the time-decreasing R values become close to 50 and 10% after filtration of 10 bed-volumes respectively in presence of SMZ and Ca-LTA. Globally, SMZ is clearly more efficient than Ca-LTA, being furthermore a versatile and easily regenerable material.

Synthesis of AlPO4-16 from fluoride-containing media in the presence of various organic templates

Abstract Various crystallographic forms of AlPO4-16 were prepared from F− containing media in the presence of five different organic templates. Heptamethyleneimine and 3-azabicyclo [3.2.2] nonane lead to the cubic form, whereas hexamethyleneimine and quinuclidine lead to the tetragonal form. Using cobalticinium cations, the symmetry is monoclinic. The products were characterized using several techniques such as SEM, XRD, elemental analysis, thermal analysis and solid-state NMR spectroscopy. The change in symmetry could be related to the value of the site occupancy factor of the D4R [46] units by the fluoride ions.

Using a novel parallel genetic hybrid algorithm to generate and determine new zeolite frameworks

Abstract Zeolite structure determination and zeolite framework generation are not new problems but due to the increasing computer power, these problems came back and they are still a challenge despite the recent progress in terms of structural resolution from X-rays and electron diffraction. The infinite number of potential solutions and the computational cost of this problem make the use of metaheuristics significant for this problem. In this paper, we propose a new approach based on parallel genetic hybrid algorithm for zeolites using a modified modelization of the objective function to find hypothetical zeolite structures, close to the thermodynamic feasibility criterion. A population made of random atoms is initialized. At each generation, a crossover operator and a mutation heuristic are applied. Each individual of the population generates a potential zeolitic structure by applying the symmetry operators of a given crystallographic space group. This structure is evaluated with our objective function. From the unit cell parameters and the number of T atoms in the asymmetric unit, 6 possible zeolitic interesting structures have been found.

Structure orienting role of germanium in zeolite synthesis

Abstract This paper deals with the synthesis results obtained from pure silica and (Si, Ge) systems in presence of hexamethonium cations, Kryptofix2,2,2 and 5-azoniaspiro[ [4] , [5] ]decane derivative cations as organic structure directing agents (OSDA) in hydroxide or fluoride media. The obtained new materials Mu-31, IM-9, IM-10 (UOZ), IM-11(LTA), IM-12 (UTL) all contain D4MR units, confirming the orienting effect of the germanium and/or the fluoride anions towards this small cage. Surprisingly, the extra-large pore IM-12 zeolite could not be obtained in the fluoride medium.

Synthesis and characterization of a new one-dimensional sodium silicate named Mu-29

Abstract The synthesis and the structure of a new one-dimensional sodium silicate, named Mu-29, are reported. This material was prepared in a quasi-non-aqueous medium using ethanol as the main solvent. Its structure was determined by single crystal X-ray diffraction. The symmetry is orthorhombic, space group Pna2 1 , with the following unit-cell parameters: a =27.32(2) A, b =15.40(2) A and c =8.241(8) A. Mu-29 is a new chain-like silicate. Its structure consists of double-crankshaft––[Si 2 O 5 ] 2− ––chains which are in strong interaction with hydrogen atoms and sodium cations. The material was characterized by elemental and thermal analyses, XRD, SEM and 1 H, 23 Na and 29 Si solid state NMR spectroscopy.

Characterization of the acidity of Mu-14 by solid-state NMR and NH3-STD

The distribution and strength of the Bronsted acid sites in three Mu-14 (ITE structure type) samples with different Si/Al ratios (17, 28 and 35) were studied by 1H MAS (magic angle spinning), 1H-{27Al} TRAPDOR (transfer of population in double resonance), 1H-29Si CP-MAS (cross-polarisation magic angle spinning)/ HETCOR (two-dimensional heteronuclear correlation) NMR, and NH3-STD (stepwise thermal desorption). The 1H MAS NMR spectra exhibit two different types of bridging OH groups associated with proton chemical n shifts of ca. 4.2 and 5.3 ppm. From the 1H-29Si HETCOR experiments a single Bronsted [Si-(OSi)3(OAl)1] Q3 site resonating at δ(29Si) = n− 108 ppm, can be distinguished from two different [Si-(OSi)3(OH)1] Q3 sites, at δ(29Si) = n− 101 and − 104 ppm, and one of the Q4 sites resonating at δ(29Si) = n− 108.5 ppm. Aluminum is not randomly distributed in the structure of Mu-14, but rather sits at preferred places isolated from silanols. The acid strength of the Bronsted acid sites, n determined by NH3-STD, is slightly higher in Mu-14 than in a HZSM-5 with a similar Si/Al ratio.

Cation redistribution upon dehydration of Na 58 Y faujasite zeolite: a joint neutron diffraction and molecular simulation study

Using neutron scattering and Monte Carlo simulation, we investigate the distribution of cations in Na58Y faujasite upon (de)hydration. We introduce a new method for the assignment of cations to specific sites in molecular simulations from their local environment. This allows us to bypass the need of the coordinates of crystallographic sites, which vary as water adsorption induces changes in the zeolite framework structure. Although the agreement between experiments and simulation is excellent at high temperature, some differences are observed below 150°C. We show that these differences are due to the presence of water and that temperature itself as well as adsorption-induced deformation of the framework play a less important role. We demonstrate the migration of sodium to sites III upon water adsorption, not observed for other Si:Al ratios.

Recent developments in the use of hexamethonium salts as structure directing agents in zeolite synthesis

Abstract Hexamethonium salts are well known as structure directing agents in zeolite synthesis. Usually, hexamethonium bromide is used in alkaline medium to give zeolite EU-1 (EUO structure-type) or ZSM-48 (no structure-type). A new method of synthesis which consists in using organic precursors of the hexamethonium cation for the preparation of EU-1 zeolite will be described. The present paper also reports the use of hexamethonium dihydroxide in fluoride media which allowed the formation of a ZSM-48 type-material and of 2 new zeolites. The structure of the latter display D4R (double four-membered-ring) cages with F− ions occluded inside. IM-7 zeolite is identical to ITQ-13 zeolite recently published by Corma et al [9], whereas the silicogermanate or germanate IM-10 zeolite corresponds to a new topology.