Wasteless Synthesis and Properties of Highly Dispersed MgAl₂O₄ Based on Product of Thermal Activation of Gibbsite

The study showed that the interaction of the product of centrifugal thermal activation of gibbsite with an aqueous solution of magnesium nitrate at a cationic ratio Mg:Al = 1:2 leads to the formation of mixed double hydroxides both under hydrothermal treatment at 150 °C and at room temperature. The subsequent thermal treatment at 550 °C of the product of mild interaction leads to ~90% alumina-magnesia spinel and ~10% MgO, while the treatment of the hydrothermal interaction product leads to ~100% spinel with the stoichiometric composition MgAl2O4. The obtained spinel samples possess a high specific surface area (above 100 m2/g) and a hierarchical pore structure formed by the micron-level particles of different sizes (1–2 and 10–20 μm) consisting of ~70 nm crystallites with ~3 nm pores; the samples differ mostly in the total volume and quantitative ratio of the pores. The samples have Lewis acid sites of moderate strength on the surface, the amount of which is much lower to how it is when compared with a sample prepared by precipitation in that they also differ by quantity from each other as well (503 μmol/g for stoichiometric spinel and 304 μmol/g for sample with admixture of MgO). As the calcination temperature is raised to 850 °C, the acidity decreases—only weak Lewis acid sites are observed, the amount of which is also higher for stoichiometric spinel (161 and 39 μmol/g, respectively). The method proposed for the synthesis of alumina-magnesia systems provides a high dispersion and a much lower surface acidity for the oxides; in addition, it minimizes or completely excludes wash water, in distinction to the precipitation method

Ethanol dehydration pathways in H-ZSM-5 : insights from temporal analysis of products

Ethanol dehydration to ethene via direct and ether mediated paths is mechanistically investigated via transient experiments in a Temporal analysis of products, TAP-3E reactor over a temperature range of 473-573 K in Knudsen regime conditions. Pulse experiments of ethanol over H-ZSM-5 do not yield diethyl ether as a gas phase product. Cofeed experiments with diethyl ether and C-13 labeled ethanol show that ethene formation from diethyl ether is the preferential route. Kinetic parameters from ab initio based microkinetic modelling of ethanol dehydration are compared to the experimental data of the TAP reactor by an in-house developed reactor model code TAPFIT. Rate coefficients in ethene adsorption are in agreement with the ab initio based microkinetic modelling parameters. The experimental data from a diethyl ether feed are compared to the simulated responses from the ab initio based kinetic parameters and further optimized by regression analysis. Reaction path analysis with the optimized kinetic parameters identifies the preference of an ether mediated path under the applied transient experimental conditions

CoMoNi Catalyst Texture and Surface Properties in Heavy Oil Processing. Part II: Macroporous Sepiolite-Like Mineral

A set of novel CoMoNi hydrotreating catalysts supported on sepiolite-like mineral and modified by H₃PO₄ have been prepared and studied in hydrodesulfurization (HDS) and hydrodemetallization (HDM) of heavy Tatar oil with extremely high viscosity and sulfur content. Catalysts had a multiphase composition, represented by calcium/magnesium oxides, silicates, or phosphates, and were found to be of great interest for studying the role of support surface properties in heavy oil hydrotreating. For monitoring the catalyst properties, all the samples have been investigated by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), CO- and CDCl₃-Fourier transform infrared (FTIR), mercury porosimetry, and N₂ adsorption methods. The catalyst with a small phosphate content showed higher initial HDS conversion due to the more developed specific surface area, increased Lewis acidity, and better active component distribution; however, the sulfur removal substantially reduced during 240 h on stream. The sample with a high amount of phosphates demonstrated better stability, higher HDM, and hydrocracking/hydroisomerization activity despite lower acidity and poor active phase dispersion that may be accounted for by the higher fraction of macropores

Ni-loaded nanocrystalline ceria-zirconia solid solutions prepared via modified Pechini route as stable to coking catalysts of CH4 dry reforming

Mixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1