X-ray diffraction (XRD) patterns with broad background are commonly found in powders where crystallization is incomplete or mixed with amorphous material. This is the case of alumina used for, for example, heterogeneous catalysis purposes where a certain degree of amorphicity is desired for obtaining prescribed material texture (e.g., porosity and area). This work uses detrended fluctuation analysis (DFA), a method intended for fractal analysis of noisy signals, to characterize an XRD pattern with broad background. The idea is that an XRD with broad background is not fully random, but contains information on regularity patterns expressed as correlations of the intensity signal. Sol–gel alumina fired at 500 °C and mixed aluminum/zirconium oxides fired at three different temperatures were used as examples for illustrating the applicability of the method. It is shown that the fractal DFA is able to locate angular regions associated ideal Powder Diffraction File-ICDD lines of diverse alumina phases. The results are discussed in terms of the corresponding Raman spectrometry analysis for contrasting the possible phases contained in the material. A crystallinity index is introduced in terms of a distance to randomness, so the regularity of a given phase can be quantified when the material is not fully crystalline.

Solvothermal synthesis of mesoporous materials based on amphiphilic molecules as structure-directing agents can be enhanced using non-conventional technologies for stirring and thermal activation. Here, we disclose a green synthesis approach for the preparation of cerium-modified hexagonally ordered silica sieves. Ultrasound micromixing enabled us to obtain well-dispersed Ce in the self-assembled silica network and yielded ordered materials with high cerium content (Ce/Si molar ratio = 0.08). Microwave dielectric heating, applied by an innovative open-end coaxial antenna, was used to reduce the overall hydrothermal synthesis time and to improve the surface area and textural properties. These mesoporous materials were used as a Ni catalyst support (10 wt.% metal loading) for the ethanol steam reforming reaction. The new catalysts featured complete ethanol conversion, high H2 selectivity (65%) and better stability, compared to the same catalyst prepared with magnetic stirring and conventional heating. The Ce-promoted silica sieves offered a suitable support for the controlled growth of nanocarbon that does not result in catalyst deactivation or poisoning after 6 h on stream.

Modelado de la biodegradación en biorreactores de lodos de hidrocarburos totales del petróleo intemperizados en suelos y sedimentos (Biodegradation modeling of sludge bioreactors of total petroleum hydrocarbons weathering in soil and sediments)

In this work, the influence of pressure and temperature experimentally applied on reactive distillation (RD) under lower conditions than conventional hydrotreating (HDT) processes, the hydrodesulfurization (HDS) reaction of 4,6–dimethyldibenzothiophene (4,6–DMDBT) molecule and the experimental performance of a down-flow micro trickle bed reactor (micro-TBR) with n–dodecane and decalin were studied. Thermodynamic analyses to evaluate hydrogen solubility in liquid hydrocarbons and evaporation for n–dodecane and decalin as lineal and cyclic representative solvents, respectively, were considered. It was possible to define experimental conditions, producing a small deviation of the plug flow model (PFM) and diminished the gas–liquid (G–L) mass transfer limitation as determined from a reactor model at 2.5 MPa. The axial dispersion model (ADM) and PFM models adjust the experimental data at 2.5 MPa operational pressure and the 4,6–DMDBT conversion obtained was ca. 20–50% using n–dodecane; 1.5 times higher when decalin was using. This behavior was due to the liquid hydrogen fraction of n–dodecane was two times higher than for decalin for all operational pressures. In this sense, the use of n–dodecane as a solvent decreased the mass transfer resistance at the G–L and liquid–solid (L–S) interphases. The internal mass transfer resistance in the G–L interphase not only depends on the diffusivity of the solvent, but it also depends on both, the temperature and hydrogen pressure, finding that the RD conditions with n–dodecane are viable in the treatment of sterically impaired molecules in HDS processes.

A series of CoMo/γ-Al 2 O 3 catalysts was synthesized by a reverse microemulsion method using 1-butanol as organic agent and cetyltrimethylammonium bromide as surfactant. The aqueous phase was used to form the solution of three corresponding Co, Mo and Al precursor salts. The materials were prepared at different solution concentrations in order to obtain different metal contents. All samples were characterized by X-ray diffraction, Raman spectroscopy, nuclear magnetic resonance and nitrogen physisorption. A chemical species distribution study was performed to establish conditions of preparation and the preponderant species present in solution as a function of pH. The materials obtained present high surface areas which decrease as the metal content (Co + Mo) increases. All samples with the exception of that with the highest metal content were amorphous as shown by X-ray diffraction. By Raman spectroscopy, MoO -Mo and MoO 2t species were observed in all calcined samples. MoO Co , Al-O-Mo, monomers and heteropolymolybdates were observed for the lower metal content samples, and the formation of CoMoO 4 and aluminum molybdate species for the higher metal contents. These results suggest that the materials with lower metal loading have species that are easily sulfidable and provide high activity in hydrodesulfurization reactions. A model for the interaction of the species in the aqueous phase of the micelle is presented.