This review of the use of clay minerals and clay mineral nanocomposites as catalysts for reactions begins by considering the structural characteristics responsible for activity, specificity and selectivity. Examples of catalytic activity described include Bronsted and Lewis acidity, redox activity, formation of reactive intermediates and catalysis of cycloaddition reactions. Clay minerals are also useful as supports for acids, ionic liquids, reagents and other catalysts, phase transfer agents and reactions initiated by microwaves, ultrasound or gamma irradiation. The review concludes with examples of the use of clay-based catalysts in the synthesis of ‘complex’ organic molecules and a consideration of the industrial situation of clay mineral usage.

Clay Minerals as Catalysts

Publisher Summary This chapter discusses catalysis by clay minerals, including their use as catalyst supports. In most petrochemical processing, such as cracking, solid catalysts were used for decades. Originally, the catalysts were based on acid-treated clays but for many years now framework silicates (zeolites) proved more effective and selective. Clay minerals have a different and interesting set of properties. They are very effective catalysts for a wide variety of organic reactions, often displaying highly sought product-, regio-, or shape-selectivity. In addition, however, soft dimensional constraints are often displayed. They have significant potential in organic chemical processing. The chapter focuses on smectites and their derivatives, which display by far the highest activity levels and range of reactions catalyzed. The chapter summarizes the performance of clay minerals in different types of reaction. The chapter concludes with a discussion on some recent developments and current utilization of these clays in industrial processes and prospects for the future.

Chapter 10.2 Clay Minerals as Catalysts

Bio-derived catalysts for production of biodiesel: A review on feedstock, oil extraction methodologies, reactors and lifecycle assessment of biodiesel

The structural transformation of natural montmorillonite clay with different acids and superacids (hydrochloric, HCl; sulfuric, H2SO4; hydrofluoric, HF; perchloric, HClO4; chlorosulfonic, HSO3Cl; and trifluoromethanesulfonic, HSO3CF3 acids) is evaluated by various techniques, allowing its full characterization. The process involves the modulated digestion of the aluminum and silicon atoms from the original clay without the loss of the original mass in the material from a careful drying methodology. The x-ray diffraction technique suggests that the process is disruptive, causing different magnitudes of modification, depending on the acidic source, taking the material with natural lamellar structure as reference. By 27Al and 29Si magnetic resonance, it is also shown that all the silicon and aluminum atoms were removed from the chemical structure to be physisorbed or dispersed in the interstices of the clay lattice when HF, HSO3Cl, and H2SO4 acid treatments were carried out. However, with treatment of HClO4, the results suggest that only was achieved partial digestion and physisorption of the aluminosilicate core. Treatment with HCl led to a mild digestion that increased the laminar distance of the montmorillonite. Finally, HSO3CF3 acid achieved a total disorder of the lamellar structure of the clay. In addition, by infrared spectrometry, the disappearance of the absorption peaks assigned to Al2OH, AlMgOH, and Al-O-Si are other evidence of the complete digestion of silicon and aluminum atoms caused by the acidic medium. On the other hand, the Brunauer–Emmett–Teller (BET) surface areas of the acidified clays showed a great enlargement in comparison with the unmodified clay. The porosimetry measurements demonstrate the presence of mesopores and hysteresis as observed in the physisorption isotherms, which indeed exhibited a capillary condensation into the porous structures. The present results are the first full characterization research and structural comparison between the acidic and the not-extensively-studied superacidic modified clays of this type.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400093225

Synthesis and characterization of montmorillonite clays with modulable porosity induced with acids and superacids

Biodiesel is eco-friendly, less toxic and one of the most researched biofuels in recent years to reduce our reliance on fossil fuels and minimize emissions. The various problems associated with batch-type reactors are longer residence time, higher operating costs, and energy consumption with low production efficiency. Researchers are now focusing on continuous flow biodiesel production techniques to overcome problems in batch reactors. This paper highlights various reactors used in continuous flow biodiesel synthesis, catalyst mechanism, hybrid reactors technique and separation methods. Various continuous flow reactors used in biodiesel production have been discussed and the microreactor was intensively elaborated. Compared to traditional reactors, microreactor technology exhibits higher efficiency, improved mixing, high heat and mass transfer rates due to a high surface-area-to-volume ratio and short diffusion distance. The parameters that influence the liquid-liquid phase flow patterns in the microreactors include mixer type, channel size, internal configuration reaction time, reaction temperature, and alcohol to oil ratio. Post-treatment techniques help to improve the quality of the biodiesel and utilization of by-products has been discussed. The limitations and practical implications prevailing in the microreactors help improve the reactor techniques forward in large-scale production. Finally, the review addresses future directions in bridging the gap in current research on microreactors for better yield and high biodiesel quality.

A critical review of recent advancements in continuous flow reactors and prominent integrated microreactors for biodiesel production

Continuous biodiesel production: A review of advances in catalysis, microfluidic and cavitation reactors

The deterioration of food quality during food processing has been the subject of intense research. Changes in the secondary metabolites present in foodstuff have been identified during drying (phenolic and anthocyanin compounds). To explain the effect of temperature on the phenolic and anthocyanin content in strawberries during drying, a molecular dynamics simulation study at the Density Functional Theory (DFT) level was performed and validated with experimental data. Solar drying and tray drying at different temperatures were investigated. The total phenolic compounds (TPC), anthocyanins, and antioxidant activity were measured. Aromaticity indexes were obtained to rank the stability during the simulated drying process. The changes observed in the aromatic behavior were related to destabilization of the compounds, which leads to the degradation process observed experimentally. These results are of utility in the selection of the operating conditions to prevent TPC deterioration and to understand the role played by the electronic structure properties of anthocyanin molecules on their degradation.

Understanding the drying kinetics of phenolic compounds in strawberries: An experimental and density functional theory study

The cyclooligomerization of piperonyl alcohol (1) afforded trimethylendioxyorthocyclophane (2), a novel product, which was promoted by the catalytic action of a commercial bentonitic earth, Tonsil Actisil FF, as well as by hydrochloric acid in 1, 4-dioxane. The structure of 2 was established by 1 H , 13 C NMR and HMQC experiments (DMSO-d6 and in the solid state), and by the corresponding mass spectrometric data (EI, CID and HR).

Jorge Escobar

Papers

Continuous biodiesel production: A review of advances in catalysis, microfluidic and cavitation reactors

Understanding the drying kinetics of phenolic compounds in strawberries: An experimental and density functional theory study

Catalytic promotion of piperonyl alcohol to trimethylendioxyorthocyclophane by bentonitic earth, or by hydrochloric acid