F. Thibault-Starzyk

The use of the consecutive adsorption of pyridine bases and carbon monoxide in the ir spectroscopic study of the accessibility of acid sites in microporous/mesoporous materials

A new approach to the evaluation of the accessibility of acid sites in microporous/mesoporous materials is developed and tested using a series of dealuminated mordenites. This approach is based on an IR-spectroscopic study of the consecutive adsorption of substituted alkylpyridines (pyridine, 2,4,6-trimethylpyridine, and 2,4,6-triethylpyridine) and carbon monoxide. This method allowed us to determine the strength and number of acid sites with various degrees of accessibility. The adsorption of 2,4,6-triethylpyridine on various types of materials is studied. The extinction coefficients of alkylpyridines are determined using a McBain balance placed in a cell for IR-spectroscopic measurements.

Correlation between activity and acidity on zeolites: a high temperature infrared study of adsorbed acetonitrile

The influence of the temperature on the protonation of acetonitrile by acidic zeolites was studied by infrared spectroscopy. Acidity at room or low temperature was not correlated with the protonation temperature, but the zeolitic structure played an important role. A new technique is presented for the study of the acidity of solids under reaction conditions. A good correlation was obtained in a series of various zeolites between the catalytic activity in the cracking of n-hexane and the protonation temperature of acetonitrile.

NO+ ions as IR probes for the location of OH groups and Na+ ions in main channels and side pockets of mordenite

Abstract NO + , generated from NO and O 2 , is an infrared probe for the differentiation of Bronsted sites in the main channels and side pockets of mordenites, and for the location and accessibility of sodium ions in the structure. Na + ions in cationic positions in the main channels are replaced by NO + , and sodium nitrate is formed. The band assignment was checked by isotopic experiments.

Thiol-oxidation with zeolite encapsulated phthalocyanines: influence of the solid support

Abstract The catalytic activity of zeolite encapsulated cobalt-pathalocyanine for thiol autoxidation varies with the composition of the zeolite support. Different zeolites were compared with carbon supports. The Si Al ratio in the zeolite appears to be the key factor: it determines the hydrophobicity of the support, and it influences the loading of active complex in the zeolite. Two different types of reaction were tested: in an aqueous alkaline medium, the activity increases with hydrophobicity of the support (thus giving carbon a substantial advantage), while in an organic medium, were the commonly used systems are less efficient, sodium Y zeolite is more active than the usual carbon support.

Mesoporous aluminophosphate thin films with cubic pore arrangement.

Mesoporous aluminophosphate thin films with 3D cubic (Im3m) pore arrangement were synthesized for the first time. Thin films were templated with block copolymer nonionic templates Pluronic F127 and F108 and deposited on a glass substrate by dip-coating. In situ SAXS investigations show the formation of a highly ordered mesostructure upon the dip-coating process, which remains stable up to at least 670 K. A cubic mesostructure was observed also by TEM. Template removal process was monitored by TG and FT-IR. A transition from an amorphous aluminophosphate gel to a well-defined aluminophosphate framework was observed by MAS NMR.

NO+: Infrared probe for basic zeolites

A new infrared spectroscopic method is proposed for the characterisation of zeolites basicity. NO2 disproportionation on alkaline zeolites is used to generate nitrosonium (NO+) and nitrate ions on the surface, and the infrared vibrations observed are very sensitive to the cation chemical hardness and to the basicity of zeolitic oxygen atoms. The influence of residual water is described. The method has been applied to X and Y zeolites with Li, Na, K, and Rb cations. The method is very easy to use and gives a linear response with chemical hardness of the cation.

Synthesis and characterization of triclinic MeAPO-34 (Me ¼ Zn, Fe) molecular sieves

Triclinic ZnAPO-34 and triclinic FAPO-34 were synthesized by hydrothermal crystallization from zinc(II)- and iron(II)-containing gels. The products are thermally stable up to 900 °C. XANES and EXAFS analyses were applied to study the local environment of zinc in the ZnAPO-34 samples, while XANES analysis and Mossbauer spectroscopy were performed on the iron-substituted samples. Zn(II) remains in the same oxidation state during synthesis and after thermal treatment, while iron exhibits Fe(II) and Fe(III) oxidation states. Analysis of the local structure showed that Zn(II) is located on tetrahedral sites of the framework, while Fe(II) and Fe(III) are present on octahedral sites. Infrared study of carbon monoxide adsorption at 100 K showed the presence of strong Bronsted acid sites on the Zn and Fe(II) samples, indicating the substitution of the metals in the framework. Rhombohedral FAPO-34 can be reversibly oxidized in the infrared cell, evidencing the disappearance of the Bronsted acid sites in the Fe(III) oxidation state.

MOF materials as catalysts for organic transformations and as selective hosts in recognition of organics

[Cu 3 (BTC) 2 ] is a highly selective Lewis acid catalyst for isomerizations of terpene derivatives, such as the rearrangement of α-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, the active sites in [Cu 3 (BTC) 2 ] were proven to be hard Lewis acid sites. Further evidence for the Lewis acid nature of [Cu 3 (BTC) 2 ] was found in an IR spectroscopic study on adsorbed carbon monoxide and acetonitrile. CO adsorbs on a small number of Cu(I) impurities and particularly on the Cu(II) coordination sites in the framework. With acetonitrile as a probe, a strong interaction with the [Cu 3 (BTC) 2 ] framework is revealed. As reaction rates vary depending on the solvent, a first exploration of liquid phase adsorption on [Cu 3 (BTC) 2 ] has been undertaken. Finally, molecular recognition of dichlorinated benzene isomers is demonstrated with [Cu 3 (BTC) 2 ] as adsorbent.

In situ infrared study of hydroxyl groups poisoned by coke formation from hydrocarbons conversion on H -zeolites

Abstract In situ infrared study of zeolites deactivation with on line analysis of the reaction products was studied for demanding or facile reactions of hydrocarbons on various zeolites. Localisation of coke species on the various hydroxy groups was determined. Two different types of coke species were observed, for which the infrared spectra were described. A mechanism is given for deactivation and coke formation in xylene isomerisation on H-beta zeolite. Influence of coke formation on the extraframework phase in steamed Y zeolite is reported.

Incorporation of heteroatoms (Me = Zn, Co, Mn) into framework sites of the gallophosphate molecular sieve ULM-5

Abstract Zinc-, cobalt- and manganese-containing microporous gallophosphates (GaPOs) with the ULM-5 structure have been hydrothermally synthesized in the presence of fluoride ions and 1,6-diaminohexane as the structure-directing agent. X-ray diffraction, elemental and thermogravimetric analyses of ULM-5 and MeULM-5 (Me=Zn, Co, Mn) indicated the incorporation of 2 wt.% for Zn, 1 wt.% for Co and 0.5 wt.% for Mn into the GaPO framework. The UV–VIS spectrum collected on the as-synthesized CoULM-5 sample revealed five-coordinated cobalt(II) in the structure. X-ray absorption spectroscopy (EXAFS) showed that zinc(II), cobalt(II) and manganese(II) substituted gallium on non-tetrahedral sites in the MeULM-5 framework and revealed structural changes of ULM-5 and MeULM-5 in the calcination process. The template-free samples are not thermally stable in the ambient atmosphere.