Scientific Papers in SCI

Kinetic analysis remains a powerful tool for studying a large variety of reactions, which lies at the core of material science and industry. It aims at obtaining the kinetic parameters and model that best describe a given process and using that information to make reliable predictions in a wide range of conditions. Nonetheless, kinetic analysis often relies on mathematical models derived assuming ideal conditions that are not necessarily met in real processes. The existence of nonideal conditions causes large modifications to the functional form of kinetic models. Therefore, in many cases, experimental data hardly obey any of these ideal models. In this work, we present a novel method for the analysis of integral data obtained under isothermal conditions without any type of assumption about the kinetic model. The method is valid both for processes that follow and for those that do not follow ideal kinetic models. It consists of using a general kinetic equation to find the functional form of the kinetic model via numerical integration and optimization. The procedure has been tested both with simulated data affected by nonuniform particle size and experimental data corresponding to the pyrolysis of ethylene-propylene-diene.

Renewed interest in CO2 methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO2 methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria-zirconia, and titania. Catalysts' performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150-500 degrees C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO2 methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO2 methanation follows the formate pathway over the catalysts under consideration.

Clay minerals are ceramics materials that are involved in a wide range of economic uses. But, their structure and composition are modified by heating and, consequently, compromise their final applications. The actual tem-peratures at which changes occur vary greatly from one group to another group and even for different specimens within a given group. The aim of this research has been to evaluate the thermal behaviour of a set of design swelling micas, Na-Mica -n (Mn) and compare them with a set of natural smectites. All samples were heated in the range 200 degrees C to 1000 degrees C; afterwards, they were rehydrated thorough water suspension (0.4% wt). The results have shown that swelling micas have better property of hydration/dehydration than natural clay minerals and those with higher layer charge exhibited higher rehydration ability and dehydration temperature.

BACKGROUND: Phenol and its derivatives are considered toxic compounds, even at low concentrations. Their accumulation in water effluents has become a serious problem that could be resolved by using zinc oxide (ZnO)-based photocatalysts.RESULTS: ZnO nanoparticles were synthesized through the precipitation method, using zinc nitrate and sodium carbonate as reagents. The as-synthesized powder was calcined for 4 h at 500 degrees C (2 degrees C min(-1)). X-Ray diffraction analysis confirmed a hexag-onal crystalline phase (wurtzite) with an average crystallite size of 38 nm. The Kubelka-Munk method was used to determine a band gap of 3.27 eV through UV-Vis diffuse reflectance spectrum and a Brunauer-Emmett-Teller (BET) specific area of 12 m(2) g(-1) was obtained from N2 adsorption analysis. The photocatalytic activity of ZnO was evaluated under visible light (300 W) lamp, with 1 mg mL(-1) of photocatalyst and using phenol solutions at different concentrations of 5,10, 25, and 50 ppm; the obtained degradation percentages were 98%, 97%, 94%, and 71%, respectively. Three cycles were performed with the ZnO used in the reactions with phenol at 5 and 50 ppm, decreasing the degraded percentages to 87% and 65%, respectively. The generation of hydroxyl radicals was estimated for the ZnO and ZnO samples after three cycles by means of fluorescence spectroscopy analy-sis. It was observed that the first-used ZnO material generated a significant amount of hydroxyl radicals.CONCLUSION: When compared to ZnO after three cycles of reaction, the amount of generated hydroxyl radicals decreased. It was observed that the higher the amount of phenol, the lower the generation of hydroxyl radicals after reuse; this was probably due to the presence of some adsorbed by-products of the photocatalytic reaction on the surface of ZnO, as the FTIR spectrum of the post-reaction sample showed.