L.M. Gandía

Recent Advances in the Synthesis and Catalytic Applications of Pillared Clays

New methods have been developed in recent years that are now being successfully applied in the preparation of pillared interlayered clays (PILCs). Variations in the procedures concern different parameters involved in the synthesis, such as the starting clay, the intercalating solution, the intercalation process, and the drying and calcination steps of the pillared solids, among others. In the present article, the latest results obtained when introducing modifications in the chemical aspects of PILC synthesis are reviewed. These include (1) pillaring with mixed solutions containing two or more cations, (2) using coordination or organometallic compounds, (3) using polymers and surfactants, (4) pillaring of acid-activated clays, and (5) enhancement of PILC acidity. A separate section is devoted to the specific features of preparing these solids in amounts large enough to make their manufacture on an industrial scale economically feasible. Recent developments in the catalytic applications of PILCs are also reviewed, with emphasis on the progressively more extended use of these materials as catalytic supports.

Hydrogen Production From Water Electrolysis: Current Status and Future Trends

This paper reviews water electrolysis technologies for hydrogen production and also surveys the state of the art of water electrolysis integration with renewable energies. First, attention is paid to the thermodynamic and electrochemical processes to better understand how electrolysis cells work and how they can be combined to build big electrolysis modules. The electrolysis process and the characteristics, advantages, drawbacks, and challenges of the three main existing electrolysis technologies, namely alkaline, polymer electrolyte membrane, and solid oxide electrolyte, are then discussed. Current manufacturers and the main features of commercially available electrolyzers are extensively reviewed. Finally, the possible configurations allowing the integration of water electrolysis units with renewable energy sources in both autonomous and grid-connected systems are presented and some relevant demonstration projects are commented.

Influence of the surface adsorption–desorption processes on the ignition curves of volatile organic compounds (VOCs) complete oxidation over supported catalysts

Abstract The simplicity to obtain ignition curves has resulted in their extended use for the measurement of the catalysts activity in the complete oxidation of VOCs. However, we have found that this method gives incorrect results for some systems, such as conversions greater than 100% or disagreements between the conversion values calculated through the concentration change of the reactants and the products, which can lead to misunderstandings. Toluene oxidation over reduced Pd/Al 2 O 3 and acetone oxidation over supported Mn 2 O 3 have presented those features. The study of these systems has been carried out performing DRIFTS spectra under reaction conditions and TPD experiments. The effect of the start-up procedure of the complete oxidation reactions has been considered as well. After discarding the formation of partial oxidation products and the hydrogen retention on Pd as possible causes, the adsorption–desorption processes of VOCs, surface intermediates and CO 2 were considered. It can be concluded that when the activity of the active phase supported on the Al 2 O 3 is high enough to allow the coupling at relatively low temperature of combustion with the adsorption and desorption processes of toluene or acetone and CO 2 , a sort of chain reaction occurs leading to CO 2 peaks.

Influence of the preparation method and the nature of the support on the stability of nickel catalysts

Abstract The influence of the preparation method and the nature of the support on the stability of the metal dispersion in nickel catalysts was studied. Three different preparation methods, incipient wetness, ion exchange and precipitation-deposition using three different commercial supports, silica, alumina and silica-alumina were used. The metallic dispersion stability was evaluated by hydrogen adsorption measurements after high-temperature calcination of the samples before and after reduction. Results have shown that the behaviour of the samples depends on the balance between positive and negative effects in the metal-support interaction, i.e., the increase of the initial metal dispersion and its resistance against sintering and, the loss of nickel in the form of difficult to reduce interaction compounds. Interaction depends on the preparation method, but can be considerably modified during catalyst life. The reactivity of the support towards nickel plays an important role in these changes. The catalyst prepared by precipitation-deposition over silica showed the best metallic dispersion and stability.

Multiple response optimization of vegetable oils fatty acid composition to improve biodiesel physical properties.

The effect of fatty acids chain length (LC) and its interaction with unsaturation degree (UD) on important biodiesel quality parameters was studied. Low calorific value, kinematic viscosity, flash point, cetane number and cold filter plugging point of biodiesel blends covering a wide range of fatty acids were analyzed. Analytical results were processed with statistical regression to obtain a prediction model for each property, combining LC and UD. Due to the antagonistic effects of the chemical composition over quality properties, the Derringer desirability function was proposed to allow the most suitable fatty acid composition. This target was achieved considering an average of 1.26 double bounds and 17 carbon atoms. A set of combinations of LC and UD values that provides a biodiesel that fits the European standard EN 14214 was proposed. It was found that a reduction of FAME LC allows a lower UD while keeping biodiesel specifications under the standard limits.

Application of a new hydrogenated aluminophosphate oxynitride (ALPON) as a catalytic support for the one-step synthesis of methyl isobutyl ketone from acetone

Abstract A new hydrogenated aluminophosphate oxynitride (ALPON) obtained by nitridation of AlPO 4 can be used as a support to prepare a polyfunctional catalyst with both basic and metallic sites. Ni/ ALPON catalyst was effective for the low-pressure one-step methyl isobutyl ketone (MIBK) synthesis from acetone. The selectivity of the process depended on the temperature and time-on-stream of the hydrogen reduction treatment suggesting that selective MIBK production is achieved by a fine balance between basic and metallic sites.

Highly selective one-step formation of methyl isobutyl ketone from acetone with a magnesia supported nickel catalyst

Abstract A new catalyst for the production of methyl isobutyl ketone (MIBK) from acetone and hydrogen in one step at atmospheric pressure has been prepared. The catalyst was obtained by impregnation of MgO with an aqueous solution of nickel nitrate, dried, calcined in air and reduced in hydrogen. This catalyst showed a high selectivity to MIBK, reaching in some experiments between 60 and 80%. A loss of activity with time on stream, probably due to coke deposition was also found. An increase in reduction temperature from 300 to 500 °C gives a decrease in MIBK selectivity that is due to an increase in the yield of 2-propanol.

Effects of various alkali–acid additives on the activity of a manganese oxide in the catalytic combustion of ketones

Abstract The catalytic combustion of acetone and methyl-ethyl-ketone (MEK) has been studied over a manganese oxide, Mn 2 O 3 . The reactant conversion has been followed as a function of the reaction temperature and it has been observed that lower temperatures are required for the combustion of acetone than for MEK. The performance of Mn 2 O 3 in the combustion reactions when alkali and acid ions are added to the oxide has also been investigated. A significant improvement of the catalyst performance is observed when Cs + and Na + are used as additives. The data of the ignition curves have been fitted to a simplified model where both ketone combustion reactions are assumed to have power law rate equations, which are first-order with respect to the corresponding organic molecule and do not depend on the oxygen partial pressure. Differences in the apparent activation energy values estimated with this model for acetone and MEK combustion are significant only when acid ions additives are present.

Effect of the reduction temperature on the selectivity of the high temperature reaction of acetone and hydrogen over alumina and titania supported nickel and cobalt catalysts

Abstract The high-temperature acetone hydrogenation at atmospheric pressure over alumina and titania-supported nickel and cobalt catalysts has been studied. The results obtained during characterization have shown that the preparation steps produced a significant metal—support interaction in the alumina-supported precursors. On the other hand, the high-temperature (500°C) reduced titania-supported catalysts showed catalytic properties which resemble in some aspects those ascribed to the SMSI state. An interesting effect of the previous H 2 reduction temperature on the acetone hydrogenation selectivity has been found. 2-Propanol and methyl isobutyl ketone (MIBK) were the main reaction products. The MIBK selectivity of the alumina-supported catalysts decreased as the temperature of reduction was increased. However, whereas the low-temperature (300°C) reduced titania-supported catalysts did not give any MIBK, a remarkable activity to this product was developed when the temperature of reduction was increased to 500°C. The effect of the temperature of reduction on selectivity has been tentatively explained according to a general model which relates the activation of the carbonyl functional group with specific sites created at the metal—support interface under conditions favourable to the establishment of significant metal—support interactions.

Influence of vegetable oils fatty acid composition on reaction temperature and glycerides conversion to biodiesel during transesterification.

Presence of unreacted glycerides in biodiesel may reduce drastically its quality. This is why conversion of raw material in biodiesel through transesterification needs to readjust reaction parameter values to complete. In the present work, monitoring of glycerides transformation in biodiesel during the transesterification of vegetable oils was carried out. To check the influence of the chemical composition on glycerides conversion, selected vegetable oils covered a wide range of fatty acid composition. Reactions were carried out under alkali-transesterification in the presence of methanol. In addition, a multiple regression model was proposed. Results showed that kinetics depends on chemical and physical properties of the oils. It was found that the optimal reaction temperature depends on both length and unsaturation degree of vegetable oils fatty acid chains. Vegetable oils with higher degree of unsaturation exhibit faster monoglycerides conversion to biodiesel. It can be concluded that fatty acid composition influences reaction parameters and glycerides conversion, hence biodiesel yield and economic viability.