Al-pillared Saponites Research Articles

Acetalation of Pentaerithritol Catalyzed by an Al-Pillared Saponite

AbstractAcetalation of pentaerithritol has been carried out in the presence of an Al-pillared saponite. Several carbonyl compounds were used, including aldehydes and ketones. Yields between 72 and 93% were obtained in all cases, except in the case of veratraldehyde where the carbonyl group was blocked. The high conversion could be explained by diffusion effects of intermediates and electronic effects between the reactants in the transition state. The catalyst was found to be active after three cycles.Graphical Abstract[IMAGE]

(Z)-cyclooctene epoxidation and cyclohexane oxidation on Ni/alumina-pillared clay catalysts

This work reports the synthesis of Ni-clay catalysts by impregnation of Al-pillared saponite with various Ni salts, using several Ni loadings. The catalysts were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric and differential thermal analysis, nitrogen adsorption, temperature-programmed reduction studies, and ultraviolet–visible spectroscopy. All the solids displayed good structural properties. FTIR spectroscopy confirmed the total removal of the anionic precursors after calcination of the solids at 500 °C. The presence of NiO and NiAl 2O 4 in the nickel particles formed on the surface of the solids was demonstrated. Deconvolution of TPR curves allowed to identify three Ni-reduction effects, their temperature and relative intensity depended on the preparation of each sample. The catalytic behaviour of the solids for (Z)-cyclooctene epoxidation and cyclohexane oxidation by either iodosylbenzene (a model oxidant) or hydrogen peroxide (a clean oxidant) was studied. In the case of the epoxidation reactions, there was 100% selectivity for the epoxide. As for cyclohexane oxidation, only cyclohexanone was formed, whereas no cyclohexanol was detected. The use of radical scavengers indicated that the high-valent oxo-nickel species is responsible for the oxygen transfer between the oxidant and the substrates.

Hydrogenation of benzene on Ni/Al-pillared saponite catalysts

Benzene hydrogenation has been employed as a test reaction for examining Nickel on Al-pillared saponite systems as hydrogenation catalysts. Catalytic activity was evaluated over a temperature range of 70–160 °C under atmospheric pressure, in a differential bench scale reactor. Surface area measurements and X-ray diffraction were used as tools for characterizing the catalysts. The influence of the support’s acidity on the catalyst activity was studied via diverse modifications of the pillared clay support. The evolution of catalyst activity with nickel loading is also discussed and the results are compared to those previously obtained for nickel on Al-pillared montmorillonite catalyst.

Microporous 18 Å Al-pillared vermiculites: preparation and characterization

A new method for obtaining 18 Å Al-pillared vermiculites is reported. In a first step, the vermiculite is submitted to an acid treatment followed by calcination. These treatments lead to a permanent reduction of the global negative charge of the mineral layers. The extra-framework species are removed by a subsequent leaching with a complexing acid, and the solid is converted to the sodium form by ion exchange. The charge-reduced Na (or Ca)-vermiculite is then brought in contact with the aluminum pillaring solution. The calcined Al-pillared vermiculites exhibit the characteristic features of this class of materials, namely, 18 Å spacing, high surface area, microporosity, and both Brønsted and Lewis acidities. These textural properties are preserved at higher temperatures (up to 800°C) compared with Al-pillared smectites, owing to the higher thermal stability of the vermiculite structure (higher dehydroxylation temperatures). The Brønsted acid content of the Al-pillared vermiculites established by IR spectroscopy of adsorbed pyridine is about twice as high as that of an Al-pillared saponite.

Hydroisomerization of n-hexane and n-heptane over platinum-promoted Cs2.5H0.5PW12O40 (Cs2.5) studied in comparison with several other solid acids

Isomerization of n-hexane and n-heptane was carried out over Cs2.5H0.5PW12O40 (denoted by Cs2.5) promoted by Pt which was introduced by either impregnation of H2PtCl6 or mechanical mixing of Pt/Al2O3 and over non-promoted Cs2.5H0.5PW12O40 in the presence of hydrogen at atmospheric pressure. The reaction temperature studied was relatively low (typically 453 and 423 K for n-hexane and n-heptane, respectively) and the hydrogen pressure was also rather low (standard conditions: feed = n-alkane 0.05 atm, H2 0.20 atm, N2 balance; W/F = 40 g h mol−1). Results were compared with those obtained under the same conditions for other Pt-promoted solid acids, where particular attention was paid to the time courses of the reaction (initial vs. stationary performance). Both the activity and selectivity of Cs2.5 at the initial stage (after 5 min) increased by the addition of the Pt component. Pressure dependencies of the rate at the initial stage were approximately first and −0.5th orders in alkane and hydrogen, respectively. Most remarkable was the suppression of the deactivation during the reaction in the presence of both Pt and hydrogen. For example, the mechanical mixture of Pt/Al2O3 and Cs2.5 (abbreviated as Pt+Cs2.5) showed little deactivation and much improved selectivity; resulting in high stationary conversion and selectivity; e.g., 98.4 and 92.1% selectivities for n-hexane and n-heptane at the conversions of 58.6 and 39.4%, respectively. Most of the results were well explained by a classical bifunctional mechanism, although other mechanisms are not all excluded. As for the other solid acids, the initial activity of Pt-promoted SO4/ZrO2 was high, but decreased rapidly. The deactivation was small with Pt-promoted H-ZSM-5, but the activity was low. The stationary yields of isomerized products were higher for Pt-promoted beta zeolite and Al-pillared saponite (tested only for n-heptane), although higher reaction temperatures were necessary.

Al-pillared saponites Part 4. Pillaring with a new Al13 oligomer containing organic ligands

A saponite from Ballarat (USA) was intercalated with the recently described aluminium polycation [Al13(µ3-OH)6(µ2-OH)12(heidi)6(H2O)6]3+. Different Al:heidi ratios during the preparation of the intercalating solutions and Al:clay ratios during the intercalation process were considered. Solids with a basal spacing of 21.8–25.3 A were obtained in this way, the ordering in their structure depending on the Al:heidi and Al:clay ratios. The surface area of these samples was very low, about 25 g-1, probably because of the large size of the polycations that fill up the internal galleries of the solids. When calcining the intercalated solids at 500°C, pillared solids with basal spacings of about 16–17.5 A were obtained, by elimination of the organic part of the polycations. The surface area of the pillared solids increased to values up to 350 g-1.

Al-pillared clays: from lab syntheses to pilot scale production characterisation and catalytic properties

The textural and structural characteristics, and the acid and catalytic properties of Al-pillared saponites prepared in kg amounts (pilot installation) have been compared with those of lab analogues (few grams, and 100 g batch quantities). The pillared clays have been examined by X-ray diffraction, and characterized by different techniques and methods including nitrogen sorption isotherms, determination of the residual cation exchange capacities and acid contents. The catalytic performances were evaluated by means of the bifunctional hydroconversion of heptane over Pt-impregnated samples. The important differences of the textural characteristics of the lab and pilot samples did not significantly affect the catalytic results. Al-pillared saponites were much more efficient hydroisomerisation catalysts than Al-pillared montmorillonites.

Hydroconversion of Heptane over Pt/Al-Pillared Montmorillonites and Saponites. A Comparative Study

Montmorillonites and saponites have been pillared with oxo-hydroxy-aluminium solutions (OH/Al molar ratio of 1.6). The solids have been examined by X-ray diffraction. The textural properties, residual cation exchange capacities, and acid contents have been established. The pillared clays exhibit thermally stable spacings, specific surface areas, and micropore volumes typical of such materials. Higher acid contents were found for pillared saponites than for pillared montmorillonites. IR spectroscopy of pillared saponites showed a new OH stretching vibration at 3595 cm−1, absent in pillared montmorillonites. The acid character of these OH groups has been assessed by pyridine adsorption. The catalytic properties have been evaluated over Pt-impregnated samples in the heptane hydroisomerisation reaction. Al-pillared saponites, smectites with lattice Si for Al tetrahedral substitutions, showed superior catalytic performances (high conversions, high yields of isomers) compared with Al-pillared montmorillonites, clays with lattice octahedral substitutions. The higher activity of the saponites is attributed to the higher content and strength of the acid sites associated with Si–OH…Al groups produced upon proton attack of the tetrahedral Si–O–Al bonds. Such strong acid sites are absent in Al-pillared montmorillonites.

Al-pillared saponites. Part 3.—Effect of parent clay layer charge on the intercalation–pillaring mechanism and structural properties

A series of synthetic saponites (smectite clays with tetrahedral substitution) have been intercalated by the Al13 polycation followed by pillaring (anchoring of the pillars to the layers on calcination to 500 °C).

Characterization of the porous structure and cracking activity of Al-pillared saponites

A well-characterized saponite was intercalated with [Al13]polyoxo aluminium cations. Its surface area was studied by nitrogen and ethylene glycol adsorption: the relative validity of both techniques in the case of pillared clays was assessed and compared to the theoretically expected value. The structural stability was investigated both in high-temperature treatments and upon aging under air at room temperature. The catalytic properties for cracking of a heavy petroleum feedstock were compared with those of a commercial FCC catalyst and with results from the literature concerning similar systems. Pillared Al-saponites present several interesting properties: thermally stable porous structure and low coking. Their study seems promising in understanding the transformation of the pillars during calcination owing to the location of the aluminium only in the tetrahedral sheets.

Al-Pillared saponites. Part 1.—IR studies

Al-Pillared saponites have been prepared from natural Na-exchanged Ballarat saponite. Acidic properties of these saponites have been studied by IR spectroscopy using pyridine as a probe molecule. Al-Pillared saponites exhibit both Bronsted and Lewis acidity. Lewis sites are evidenced in the parent Na-exchanged clay as well as in the pillared clays. Bronsted acid sites are not evidenced in the parent Na-exchanged saponite but Al-pillared saponites exhibit Bronsted acidity as shown by a pyridinium band at 1549 cm–1. Bronsted acid sites have been related to OH groups at 3740–3720 cm–1 and 3597–3594 cm–1. The same wavenumbers are evidenced for ν(OH) stretchings in acidified saponite and in Al-pillared saponites. It is assumed that an acidic attack of Si—O—Al linkages which may provide Bronsted sites occurs on the clay sheets during the pillaring process.

Catalytic properties of two pre-cracking matrices: a leached vermiculite and a Al-pillared saponite

Two clay materials—a leached vermiculite and a saponite pillared with aluminum clusters—have been prepared and characterized as pre-cracking matrices for the conversion of heavy fuels. These two solids present acidic properties and porosity at high temperature (500–550°C). The microactivity test results (MAT) on a very heavy feedstock (carbon Conradson: 2.9) have been compared to those of γ-Al 2O 3. Acid-treated vermiculite yields more gasoline and less coke and appears to be a promising active matrix. Leached vermiculite is composed of more or less attacked layers retaining their original platy morphology, and of non-crystalline hydrated silica. The high coke production for Al-pillared saponite is probably related to the Lewis acidic sites and not to the Fe content of the original clay.

Stability of Al-pillared saponites: evidence for disorganization during storage in air

Stability of Al-pillared saponites: evidence for disorganization during storage in air