Ultrasound-promoted synthesis of a copper-iron-based catalyst for the microwave-assisted acyloxylation of 1,4-dioxane and cyclohexene.

A copper-iron-based catalyst has been prepared by a low-temperature co-precipitation and sonication method. The use of high-energy ultrasound reduces the time required for the preparation process from one workweek to one day with respect to the catalysts obtained by conventional coprecipitation and thermal treatment methods. The resulting material has been characterized at compositional, textural, structural, and chemical levels by ICP-AES, BET, SEM-EDS, XRD, TEM, and FTIR among other techniques. The material shows catalytic activity in the acyloxylation reaction of 1,4-dioxane and cyclohexene under microwave irradiation. In parallel with the optimized catalyst synthesis, the use of microwaves allowed for a substantial improvement in the outcome of the reaction in terms of cleanliness, yield, and time.

Ultrathin Washcoat and Very Low Loading Monolithic Catalyst with Outstanding Activity and Stability in Dry Reforming of Methane.

A Ni/CeO2/ZrO2 catalyst with improved redox properties has been washcoated onto a honeycomb cordierite monolith in the form of a nonconventional alumina-catalyst layer, just a few nanometers thick. In spite of the very low active phase loading, the monolith depicts outstanding performance in dry reforming of methane, both in terms of activity, with values reaching the thermodynamic limit already at 750 °C, even under extreme Weight Hourly Space Velocities (WHSV 115-346 L·g-1·h-1), as well as in terms of stability during prolonged Time on Stream (TOS 24-48 h).

Lead removal from aqueous solution by means of integral natural clays honeycomb monoliths.

Different natural Moroccan clays were used as adsorbents for the removal of lead from aqueous solution. The study was performed not only employing the starting clays in the form of powder but also after their extrusion as honeycomb monoliths, this representing the major novelty of this work respect to the current state-of-art. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to an exhaustive characterization of the clays by means of X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, laser granulometry, N2 physisorption, infrared spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the lead adsorption of variables such as adsorbent dosage, pH, contact time with the adsorbate and initial concentration of lead. Considering the cheap and abundant character of the raw materials, their easy processing (no additives were required for their extrusion) and the time and energy save due to no need for further modification through chemical/thermal activation, the obtained results (with retention over 90% for 30 ppm of lead) demonstrated the potential of the proposed design as low cost solution that may be competitive versus other technologies for water depollution, especially in developing regions.

Acyloxylation of 1,4-Dioxanes and 1,4-Dithianes Catalyzed by a Copper-Iron Mixed Oxide.

The use of a copper-iron mixed oxide as a heterogeneous catalyst for the efficient synthesis of α-acyloxy-1,4-dioxanes and 1,4-dithianes employing t-butyl peroxyesters is reported. The preparation and characterization of the catalyst are described. The effect of the heteroatoms and a plausible mechanism are discussed. The method is operationally simple and involves low-cost starting materials affording products in good to excellent yields.

TAP study of toluene total oxidation over a Co3O4/La-CeO2 catalyst with an application as a washcoat of cordierite honeycomb monoliths.

The total oxidation of toluene was studied over a Co3O4/La-CeO2 catalyst in a Temporal Analysis of Products (TAP) set-up in the temperature range 713 K to 873 K in the presence and absence of dioxygen. It has been demonstrated that the reaction proceeds via a Mars-van Krevelen mechanism. The reaction rate increased 8.4 times if both toluene and dioxygen were present in the feed. The partial reaction order with respect to O2 diminished from 0.9 to 0.6 with an increase in temperature from 763 to 873 K. Adsorbed oxygen species with a lifetime of ∼8 s have been found on a catalyst fully oxidized by dioxygen. Catalysis of isotopically labeled (18)O2/(12)C6H5(13)CH3 results in the formation of products containing (18)O, which indicates that both lattice and adsorbed oxygen are involved in the total oxidation of toluene. The role of adsorbed oxygen is activation of the C-H bond in toluene. The reaction network of the catalytic total oxidation of toluene consists of the following sequence: adsorption of toluene on the catalyst surface; activation of toluene by dehydrogenation with adsorbed oxygen; oxidation of activated toluene mainly by the lattice oxygen and re-oxidation of the reduced catalyst by dioxygen.

Non-cordierite clay-based structured materials for environmental applications.

The applications of clay-based structured materials, excluding cordierites, for environmental protection are examined. In particular, their use in the abatement of some of the main hazardous species in polluted emissions such as nitrogen oxides, carbon monoxide, volatile organic compounds and heavy metals is discussed. A distinction is made between adsorption and catalytic processes. In addition, a general overview of the methods and general principles followed to prepare structured materials from clays is also given. Special attention is paid to those employed to obtain honeycomb monoliths and foams.