Sonia Moreno

Catalytic wet peroxide oxidation of phenol over Al-Cu or Al-Fe modified clays

Al–Fe or Al–Cu modified clays were prepared from two natural montmorillonites and employed in the phenol oxidation with hydrogen peroxide in water. The samples were efficient in phenol elimination under mild experimental conditions (atmospheric pressure, 293 K and small quantities of hydrogen peroxide) without considerable leaching of the metal ions. The clays modified with Fe achieved high conversions of phenol and TOC thus showing to be very selective towards the formation of CO2 and H2O.

n-heptane hydroconversion over aluminosilicate mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves (designated Al-MMS) have been prepared at room temperature using the primary amine hexadecylamine as organic templating surfactant. The materials have textural properties typical of mesoporous materials with short-range hexagonal order but exhibit higher Brønsted acidity compared to aluminium-containing MCM-41. The Pt-impregnated materials are efficient catalysts for the hydroconversion of n-heptane. At low Si/Al ratio (≤ 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al = 21) and in addition exhibit considerable cyclisation at temperatures above 350°C. Our catalytic results show that the Pt-impregnated Al-MMS samples attain a good balance between the metal and acidic functions and that activity and selectivity are dependent on the Brønsted acid content and consequently on the amount of tetrahedral aluminium in the catalysts. The amount of Pt (in the range 0.25-1 wt%) mainly affects the selectivity to cyclised products which increases with Pt content at the expense of cracking; total conversion and selectivity to isomers remain largely unaffected.

Dealumination of small- and large-port mordenites: A comparative study

Large-port (LP) and small-port (SP) mordenites with different particle size and shape have been submitted under similar conditions to known dealumination procedures in view of comparing their respective behavior, and establishing the similarities and discrepancies among the dealuminated solids. The dealuminated zeolites have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), acidity measurements with ammonia and X-ray photoelectron spectroscopy (XPS). The particle size of the starting mordenite markedly influenced the extraction of Al when dealumination was performed by direct acid attack or dry thermal treatment. Admission of steam during calcination noticeably improved the removal of Al from SP mordenite compared with other methods. Elimination of the extra-framework Al species produced at the calcination step required acid concentration as high as 6 M. (Hydro)thermally dealuminated LP mordenites exhibited similar surface and bulk chemical composition. Conversely, dealuminated SP mordenites showed surface enrichment in Al up to Si/Al ratios of about 40, and depletion in Al at higher ratios. These surface/bulk heterogeneous distributions were suppressed when dealumination combined preliminary acid leaching and steaming. Dealuminated small-and large-port mordenites exhibited differences in their textural characteristics, and for both, a contraction of the unit cell volume and the development of meso- and secondary microporosity

Al-pillared hectorite and montmorillonite prepared from concentrated clay suspensions: structural, textural and catalytic properties

Abstract Concentrated suspensions of hectorite and montmorillonite have been pillared with base-hydrolyzed aluminum solutions with different OH/Al molar ratios. The pillared clays have been characterized, and their catalytic performances have been evaluated over Pt-impregnated samples using the hydroisomerization of heptane.

Hydroisomerization of decane on Pt/Al, Ce-pillared vermiculites

Vermiculite mineral has been pillared with aluminum-cerium hydroxyl solutions after hydrothermal treatment, prior to the pillaring process. The pillared clays exhibited an increase of the microporosity and acid properties respect to the natural clay. The catalytic and textural properties were investigated in the hydroisomerization of decane. The modified vermiculites were very active with respect to most of the pillared clays and the pore size closed to 10 and 12-ring zeolites. The products distributions from decane isomerization showed that their profile is comparable to that of active zeolites.

Development of Pillared Clays for Wet Hydrogen Peroxide Oxidation of Phenol and Its Application in the Posttreatment of Coffee Wastewater

This paper focuses on the use of pillared clays as catalysts for the Fenton-like advanced oxidation, specifically wet hydrogen peroxide catalytic oxidation (WHPCO). This paper discusses the limitations on the application of a homogeneous Fenton system, development of solid catalysts for the oxidation of phenol, advances in the synthesis of pillared clays, and their potential application as catalysts for phenol oxidation. Finally, it analyzes the use of pillared clays as heterogeneous Fenton-like catalysts for a real wastewater treatment, emphasizing the oxidation of phenolic compounds present in coffee wastewater. Typically, the wet hydrogen peroxide catalytic oxidation in a real effluent system is used as pretreatment, prior to biological treatment. In the specific case of coffee wet processing wastewater, catalytic oxidation with pillared bentonite with Al-Fe is performed to supplement the biological treatment, that is, as a posttreatment system. According to the results of catalytic activity of pillared bentonite with Al-Fe for oxidation of coffee processing wastewater (56% phenolic compounds conversion, 40% selectivity towards CO2, and high stability of active phase), catalytic wet hydrogen peroxide oxidation emerges as a viable alternative for management of this type of effluent.

Synthesis, characterization and catalytic activity of LayMOx (M=Ni, Co) perovskite-type particles intercalated in clay via heterobinuclear complexes

Clays intercalated with LayMOx (M = Ni, Co) nanospecies with perovskite-type structure have been prepared from heterobinuclear complexes MLa(fsaen)NO3, LaM(H2L)(NO3)(3), and [LaML(NO3)](2). The cationic form of these binuclear complexes was introduced between the clay sheets via an exchange process and a d-space of 17.7-24.8 Angstrom was achieved. After heating and removal of the organic part LayMOx nanospecies were formed and the d-space was around 12.3-14.0 Angstrom. The specific surface area of the fired solids was found to be between 92 and 178 m(2) g(-1), depending on the method of preparation used. The products were investigated by XRD; TG/DTA, specific surface area and acidity (Bronsted/Lewis) measurements, as well as by EDX analysis for their composition. Their catalytic activity was evaluated in the reaction of isopropanol and cracking/isomerisation of heptane. These solids showed essentially dehydrating activity in isopropanol decomposition, and hydrogenolytic activity in heptane reaction. The extent of catalytic conversion for the isopropanol decomposition for the intercalated materials was lower as compared to non-intercalated samples. The conversion for the heptane hydrogenolysis reached similar to 100% at similar to 350 degrees C and proceeds mainly towards cracking rather than isomerization which reached only similar to 8%

Mn, Mn-Cu and Mn-Co mixed oxides as catalysts synthesized from hydrotalcite type precursors for the total oxidation of ethanol

Abstract In this work, nanoparticulates of compounds precursors of LDHs for preparing Mn, Mn-Cu and Mn-Co mixed oxides were successfully synthesized by the reverse microemulsion method. It was observed that the precursor obtained from the above method had similar characteristics for preparing mixed oxide catalysts used in the oxidation of ethanol. This method was compared with the conventional co-precipitation method.

Heterogeneous Catalysts in Pictet-Spengler-Type Reactions

Several solid catalysts were evaluated as an alternative for 1,2,3,4-tetrahydroisoquinoline synthesis by means of the Pictet-Spengler reaction. The reaction catalysed by a mixed oxide (Mg and Al) led to the best yield and good regioselectivity; using an Al-pillared bentonite led to good yields and total regioselectivity. The results revealed no direct relationship between catalyst acidity and yield.

Raschig Rings Based on Pillared Clays: Efficient Reusable Catalysts for Oxidation of Phenol

Abstract Extrudates of AlFe and AlCeFe pillared bentonites shaped as Raschig rings were used in the oxidation of phenol by a Fenton process, and the catalytic activity in terms of reuse was evaluated. All the tests of oxidation were carried out in a semibatch basket reactor, which operates under extremely mild reaction conditions (25 °C and atmospheric pressure). Extrudates of AlFe and AlCeFe pillared bentonites are reusable catalysts for the oxidation of phenol, reach 100% phenol conversion and between 36-42% selectivity towards CO2 after 8 h of reaction. In addition, Raschig rings showed efficient catalytic activity up to 10 consecutive uses and preserved structural and textural properties of the powdered active phases, even after reuse. The use of cerium as a promoter in the extruded material not only improved the catalytic activity but also increased the mechanical stability of extruded catalyst in the reaction medium.