J.J. Fripiat

INFRARED SPECTROSCOPY STUDY OF TETRAHEDRAL AND OCTAHEDRAL SUBSTITUTIONS IN AN INTERSTRATIFIED ILLITE-SMECTITE CLAY

Infrared spectroscopy is used to distinguish between octahedral and tetrahedral substitutions in an interstratified illite-smectite clay. The Hofmann-Klemen (Li) test suggests that the AlMg□ and FeMg□ octahedral vacancies are preferentially occupied by Li after thermal treatment at 250°C. The ammonium (Chourabi-Fripiat) test reveals the beidellitic character by the formation of two OH stretching modes upon deammonation. The illitic layers are not affected since K is not exchangeable.

THE COORDINATION OF ALUMINUM IONS IN THE PALYGORSKITE STRUCTURE

AbstractNMR spectra of PF1-1 Floridan palygorskite strongly suggest that Al3+ occurs only in octahedral coordination. X-ray microanalysis of the palygorskite fibers indicate a chemical composition defined by the atomic ratios: Mg/Si = 0.34, Al/Si = 0.27, and Fe/Si = 0.04. Considering the NMR and CEC data in this report along with the previously published results of IR and Mössbauer spectroscopic studies, the following structural formula is proposed for PF1-1 palygorskite:

Catalytic properties of aluminated sepiolite in ethanol conversion

{\rm{(M{g_{2.12}}A{l_{1.68}}F{e^{3 + }}_{0.24}{\square _{0.96}})S{i_8}{O_{20}}{(OH)_2}{(O{H_2})_4}}}

Poisoning of aldol condensation reaction with H2O on acid catalysts

where □ represents the vacant Ml octahedral sites in the structure, and Al3+ and Fe3+ are all exclusively assigned to the octahedral sites.

Interaction between organic and inorganic pollutants in the clay interlayer

Abstract The modifications of the microporous volume of zeolites resulting from thermal dealumination have been examined by measuring the changes in the unit cell parameters as well as the N2 and n-pentane adsorption isotherms. For the cubic HY and orthorhombic H-ZSM-5 zeolites, the differential decrease of the microporous volume per non-framework aluminum (NFAl) can be predicted by assuming NFAl is concentrated in pores available to N2. For the orthorhombic H-mordenite, NFAl is homogeneously spread in all pores, available or not to N2. The Gurvitch rule (volume of adsorbed N2 = volume of adsorbed pentane) is respected in HY and H-ZSM-5, but not in H-mordenite, irrespective of the degree of dealumination.

1H-27Al heteronuclear dipolar couplings and internuclear distances in alumina: SEDOR and REDOR 27Al study

The aluminated sepiolite, obtained by alkaline treatment with KAlO2, as well as the silver-exchanged aluminated sepiolite were tested in ethanol conversion. The reactions were performed at 280°C and with 50 Torr of ethanol in He. After the alumination through KA1O2, ethanol dehydrogenation and ethanol dehydration resulted from the Lewis acidity. The dispersion of silver led to a bifunctional catalytic system and the overall catalytic activity and the selectivity towards the acetaldehyde production increased. As a result of the Prins reaction, a significant yield in butadiene was observed.

ON THE STRUCTURAL STABILITY OF MONTMORILLONITE SUBMITTED TO HEAVY γ-IRRADIATION

Abstract Fibrous mineral sepiolite is formed of staggered talc sheets. The discontinuous octahedral layers provide for infinite channels along the fiber axis with cross-section ~(10 × 4) A2. During crystal growth, a second set of irregularly shaped pores with a diameter around 100 A is created within the fiber. Zeolitic water fills the narrow and regular channels and is eliminated by outgassing at 100 ° C. At that stage, the specific surface area is ~300 m 2 g . Upon activation at increasing temperature, the structure folds, and ultimately collapses (~500°C), leaving a surface area ~150 m 2 g . The natural mineral lattice is almost neutral, having a cation-exchange capacity (CEC) in the order of 0.07 meq.g−1. It is shown that mild treatment with NaAlO2 results in partial Si-by-Al substitution in the tetrahedral layer. The CEC is almost tripled, and the residual surface area after calcination is about the same as in the original material. The alumination process generated Lewis sites evidenced by pyridine adsorption study. The mechanism of alumination, as well as the structural modifications upon calcination, are discussed on the basis of 27Al and 29Si MAS-NMR spectroscopy. Possible uses of the Al modified sepiolite as catalyst and catalyst support are proposed.

The intercalation process of N-alkyl amines or ammoniums within the structure of KTiNbO5

The effect of chemisorbing water on three catalysts previously evaluated in the acetone condensation reaction has been studied. The active sites in that reaction are Lewis acid sites present either on the surface of alumina or of nonframework alumina in zeolites. These sites are poisoned by water and the reaction rate decreases at the pace of the loss of Lewis sites. The stoichiometry of the poisoning reactions is one water molecule per site on alumina and two water molecules per site on nonframework alumina.