Jean-Michel Goupil

Template-free nanosized faujasite-type zeolites

Nanosized faujasite (FAU) crystals have great potential as catalysts or adsorbents to more efficiently process present and forthcoming synthetic and renewable feedstocks in oil refining, petrochemistry and fine chemistry. Here, we report the rational design of template-free nanosized FAU zeolites with exceptional properties, including extremely small crystallites (10-15 nm) with a narrow particle size distribution, high crystalline yields (above 80%), micropore volumes (0.30 cm(3) g(-1)) comparable to their conventional counterparts (micrometre-sized crystals), Si/Al ratios adjustable between 1.1 and 2.1 (zeolites X or Y) and excellent thermal stability leading to superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene, probing sites mostly located on the external surface of the nanosized crystals. Another important feature is their excellent colloidal stability, which facilitates a uniform dispersion on supports for applications in catalysis, sorption and thin-to-thick coatings.

High Energy Ion Irradiation-Induced Ordered Macropores in Zeolite Crystals

The present study demonstrated the possibility to form a secondary system of parallel macropores in zeolite crystals. The secondary pore formation was predetermined by the creation of defect zones in ZSM-5 crystals. A high energy (238)U ion beam was employed to form latent tracks in zeolite crystals, which were further subjected to attack with diluted HF solution and thus developed to uniformally sized macropores. The selective extraction of material from latent tracks was due to the higher etching velocity of highly agitated zones created by heavy ion bombardment. The combination of complementary methods unambiguously demonstrated the formation of hierarchical zeolite material comprising parallel macropores that extended through the entire crystal. The catalytic tests revealed improved activity at retained selectivity in the reaction of m-xylene conversion. The possibility to control the number of macropores per unit of crystal surface and thus the catalytic performance of the material was demonstrated. This model material is expected to bring better understanding to the effect of a secondary pore system in the catalytic performance of hierarchical zeolites obtained by the top-down or bottom-up approach.

Coupling sol-gel synthesis and microwave-assisted techniques: a new route from amorphous to crystalline high-surface-area aluminium fluoride.

A non-aqueous sol-gel Al-based fluoride has been subjected to the microwave solvothermal process. The final material depends on the temperature heat treatment used. Three types of material have been prepared: 1) for low temperature heat treatment (90 degrees C) X-ray amorphous alkoxy fluoride was obtained; 2) for the highest temperature used (200 degrees C) the metastable form beta-AlF3 was obtained with a very large surface area of 125 m2 g(-1). The mechanism of the amorphous=crystalline transformation has been rationalised by the occurrence of a decomposition reaction of the gel fluoride induced by the microwave irradiation. 3) Finally, at intermediate temperature (180 degrees C) a multi-component material mixture exhibiting a huge surface area of 525 m2 g(-1) has been obtained and further investigated after mild post-treatment fluorination using F2 gas. The resulting aluminium-based fluoride still possesses a high-surface-area of 330 m2 g(-1). HRTEM revealed that the solid is built from large particles (50 nm) identified as alpha-AlF3, and small ones (10 nm), relative to an unidentified phase. This new high-surface-area material exhibits strong Lewis acidity as revealed by pyridine adsorption and catalytic tests. By comparison with other materials, it has been shown that whatever the composition/structure of the Al-based fluoride materials, the number of strong Lewis acid sites is related to the surface area, highlighting the role of surface reconstruction occurring on a nanoscopic scale on the formation of the strongest Lewis acid sites.

Chlorinated alumina as an alkylation catalyst: influence of acidity moderators

Chlorinated alumina catalysts obtained by reacting a gamma-alumina with hydrogen chloride show high initial activity in isobutane-butene alkylation. After a few hours on stream however, the conversion decays due to self poisoning. This work attempts at improving the catalyst lifetime by modifying the Al2O3-Cl catalyst. Best results were obtained by adding small amounts of alkaline cations to the alumina before chlorination. For a particular cation, lithium or sodium, the improvement in catalyst lifetime depends on the chlorination procedure (pre-treatment with CCl4, final temperature). Addition of cations also enhances the selectivity for octanes, mainly by decreasing the amount of cracked products. Degradation of 2,2,4-trimethylpentane was found to occur over the Al2O3-Cl catalysts at 273 K. The influence of cation addition on this process was examined. Thus, the occurrence of dimethylhexanes and cracked or heavier alkanes among alkylation products may be explained by the degradation of 2,2,4-TMP.

Alkylation of isobutane by ethylene using a solid Friedel-Crafts catalyst

Alkylation of isobutane with ethylene was investigated over a γ-Al2O3-Cl catalyst at temperatures below 380 K. Ethylene was fully converted over a period of 5–20 h, then conversion steadily decreased. The only products were alkanes, mainly C6 and C8. The composition of the alkylate varied with the isobutane/ethylene ratio and with time-on-stream. Among the C6, 2,3-dimethylbutane became predominant (>95%) after a few hours. The composition of octanes appeared less selective. The kinetic distributions of isomers are interpreted by a new mechanism based on cyclopropane-carbonium ions. Upon catalyst ageing, alkane isomerization decays faster than alkylation, oligomerization being least affected.

Competitive reactions catalyzed by NiMo-containing zeolites

The rates of benzene hydrogenation and of n-heptane hydroconversion were measured simultaneously over a series of bifunctional catalysts. The catalysts were Y zeolites containing a Ni or Mo sulfide. At 280 °C, and for the more acidic catalysts, both rates appeared linearly correlated, suggesting that the hydrogenation function was limiting.

Chlorinated alumina as an alkylation catalyst : influence of superficial HCl

Abstract Chlorinated alumina catalysts were obtained by reacting gamma-alumina with gaseous CCl4 or hydrogen chloride under various conditions. They had chlorine contents between 4 and 6% by weight, and differed in surface acidity. They were tested as catalysts for the alkylation of isobutane with 2-butene using a fixed bed plug flow reactor. Alumina reacted with CCl4 was found inefficient for this reaction. However, the solid chlorinated with HCl above 800 K was able to catalyze alkylation at a temperature as low as 273 K. Moreover, the CCl4-reacted solid could be activated upon further treatment with HCl at moderate temperatures (370 to 550 K). However, the catalytic activity decays after a few hours on stream. The composition of the alkylate varied somewhat with time on stream: large amounts of cracked products appeared during the initial period, after which the selectivity to trimethylpentanes (TMP) was comparable to that of other solid catalysts. The presence of hydrogen chloride bound to the catalyst surface was established by measuring the temperature-programmed desorption (TPD) of HCl from the various Al2O3–Cl. For the active catalysts, desorption started at temperatures (350–400 K) well under those for the CCl4-treated sample, but all solids continuously released HCl above 650 K. Thus, HCl interacts with particular Lewis acid sites of Al2O3–Cl, and creates the strong Bronsted sites required for catalytic alkylation.

Adsorption of NO2 on modified Y zeolites

Comparative NO 2 adsorption was studied over microcrystalline zeolite Y and two chromium-exchanged samples, at temperatures between 251 and 403 K. Maximum adsorptive capacities, and heats of adsorption, were found very similar for the three zeolites. An analysis of the adsorption kinetics established the diffusion coefficient D at 1.1 × 10 −16 m 2 s −1 , whatever the chromium content in the zeolite.

Green removal of aromatic organic pollutants from aqueous solutions with a zeolite–hemp composite

A composite based on zeolite L nanocrystals (LTL-type structure) and hemp fibers was prepared. The intimate growth of zeolite nanocrystals in the hemp fibers is achieved by direct hydrothermal crystallization. The crystalline phase, particle size distribution, porosity and zeolite loading in the composite are measured by X-ray diffraction, dynamic light scattering, thermo-gravimetric analysis, and nitrogen sorption. Further, the composite is used for the removal of aqueous aromatic organic pollutants (benzene, toluene and chlorobenzene), and the sorption ability is studied by IR and UV spectroscopy. The zeolite–hemp composite exhibited a high removal degree (above 80%), and a high flux of 19.3 kg m−2 h−1, 20.9 kg m−2 h−1 and 19.9 kg m−2 h−1 for benzene, toluene and chlorobenzene, respectively. Also, the zeolite–hemp composite shows substantially higher water flux than that of pure zeolite. The better performance of the composite is explained by an improved absorption ability of the zeolite–hemp material coupled with higher dynamic separation efficiency. A kinetic model based on the sorption ability of the composite and solubility of the contaminants in water is proposed. Both the zeolite L nanocrystals and the natural hemp fibers are environmentally friendly compounds, which make the composite particularly appropriate for water purification.

Alkylation of isobutane by ethylene catalyzed by chlorided alumina: influence of experimental conditions

Chlorided alumina obtained by reaction of alumina with tetrachloromethane was tested as a catalyst for alkylation of isobutane with ethylene at 273–373K. The alkylate composition and the catalyst deactivation were examined under various experimental conditions. At high isobutane/ethylene ratios the catalyst was deactivated rather slowly. A high dilution of ethylene also favoured the production of hexanes versus octanes, isopentane and heavier products, however the primary products of alkylation were largely isomerized. Whatever the dilution of ethylene, the catalyst stability was improved when the reaction temperature was lowered to 273 K. Then the isomerization of the primary products was less pronounced. Increasing the catalyst mass led to better stability, hexane production was enhanced at the expense of heavier products. Alumina catalysts treated with various chlorinating agents (hexachloroethane, thionyl chloride, hexachloropropanone, hydrogen chloride) were also examined: no marked improvement in either stability or selectivity was noted. Added metal cations did not appear beneficial either.