108 research outputs found
El sistema SiO₂-AlPo₄ como catalizador de craqueo de fracciones petrolíferas
Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, leída en 1977.Fac. de Ciencias QuímicasTRUEProQuestpu
Efficient Removal of Nonylphenol Isomers from Water by Use of Organo-Hydrotalcites
The presence of potent organic endocrine-disrupting chemicals (EDCs) in natural aquifers can have adverse impacts on public health and the environment. 4-nonylphenol, one such EDC, can be efficiently removed from water by adsorption onto a clayey material. In this work, we created an effective sorbent for this purpose by using co-precipitation and subsequent ion-exchange to intercalate the organic anion deoxycholate into a Mg/Al hydrotalcite. Intercalating deoxycholate ions increased the organophilicity of the hydrotalcite surface. The solid was used to adsorb 4-nonylphenol at different pollutant concentrations and temperatures. The adsorption process was subjected to a kinetic study. Based on the results, the EDC was adsorbed by chemisorption. In addition, based on the equilibrium isotherms used for the process, the Freundlich model was the most accurate in reproducing the adsorption of 4-nonylphenol onto deoxycholate-intercalated hydrotalcite
Three-Dimensional Hierarchical Hydrotalcite–Silica Sphere Composites as Catalysts for Baeyer–Villiger Oxidation Reactions Using Hydrogen Peroxide
The development of effective, environmentally friendly catalysts for the Baeyer–Villiger reaction is becoming increasingly important in applied catalysis. In this work, we synthesized a 3D composite consisting of silica spheres coated with Mg/Al hydrotalcite with much better textural properties than its 2D counterparts. In fact, the 3D solid outperformed a 2D-layered hydrotalcite as catalyst in the Baeyer–Villiger reaction of cyclic ketones with H2O2/benzonitrile as oxidant. The 3D catalyst provided excellent conversion and selectivity; it was also readily filtered off the reaction mixture. The proposed reaction mechanism, which involves adsorption of the reactants on the hydrotalcite surface, is consistent with the catalytic activity results
Thiol-functionalized ethylene periodic mesoporous organosilica as an efficient scavenger for palladium : confirming the homogeneous character of the Suzuki reaction
This work describes the synthesis of thiol-functionalized periodic mesoporous organosilicas (PMOs) prepared using the precursor 1-thiol-1,2-bis(triethoxysilyl)ethane, alone or mixed with 1,2-bis(triethoxysilyl)ethane. The thiol groups incorporated into the structure were found to be efficient for palladium binding. This has allowed these materials to be used as catalysts in the Suzuki cross-coupling reaction of bromobenzene and phenylboronic acid. Their performance has been compared to palladium-supported periodic mesoporous (organo)silicas and important differences have been observed between them. The use of different heterogeneity tests, such as hot filtration test and poisoning experiments, has provided a deep insight into the reaction mechanism and has confirmed that the reaction occurs in the homogeneous phase following a "release and catch" mechanism. Furthermore, the thiol-functionalized periodic mesoporous organosilica, synthesized using only 1-thiol-1,2-bis(triethoxysilyl)ethane as a precursor, has proven to be an efficient palladium scavenger
Fast ultrasound-assisted synthesis of highly crystalline MIL-88A particles and their application as ethylene adsorbents
Highly crystalline MIL-88A particles have been successfully synthesized via fast ultrasound-assisted processes. The influence of the sonication generator and synthesis time on the structure, crystallinity, morphology and surface area of the materials were studied in detail. Under this modified ultrasonic method, X-ray diffraction patterns of MIL-88A particles showed highly crystalline structures in contrast to those reported in literature. Significant differences on surface areas and microporosity were appreciated under ultrasound conditions employed. Specific surface areas in the range between 179 and 359 m2 g−1 were obtained. That material synthesized under ultrasound batch conditions during 1 h had the highest surface area and microporous character. Different particle sizes and morphologies were obtained depending on the synthesis procedure. In general, probe sonicators led to smaller particle sizes. Moreover, a comparative study of the ethylene adsorption of the MIL-88A particles and several common MOFs in the ethylene adsorption was investigated. The results suggest that the modified ultrasound-assisted procedure for the synthesis of MIL-88A is effective to obtain highly crystalline particles, which are very efficient to adsorb ethylene molecules
Preparation of Palladium-Supported Periodic Mesoporous Organosilicas and their Use as Catalysts in the Suzuki Cross-Coupling Reaction
Three periodic mesoporous materials, i.e., two organosilicas with either ethylene
or phenylene bridges and one silica, have been used as supports for Pd nanoparticles. All
Pd-supported samples (1.0 wt%) were prepared by the incipient wetness method and
subsequently reduced in an H2 stream at 200 °C. Both hydrogen chemisorption and
temperature programmed reduction experiments revealed significant differences depending
on the support. Pd2+ species were more reducible on the mesoporous organosilicas than on
their silica counterpart. Also, remarkable differences on the particle morphology were
observed by transmission electron microscopy. All Pd-supported samples were active in
the Suzuki cross-coupling reaction between bromobenzene and phenylboronic aci
- …