Iron-Modified Mesoporous Silica as an Efficient Solid Lewis Acid Catalyst for the Mukaiyama Aldol Reaction

When the Study of the Post-Synthetic Modification Method on a 1D Spin Crossover Coordination Polymer Highlights its Catalytic Activity

We are interested in studying the catalytic activity of the spin crossover (SCO) complex ([Fe(NH2trz)3](NO3)2). In this work, we demonstrate that, by adapting the experimental conditions, we can switch from a quantitative post-synthetic modification (PSM) reaction to the use of this complex as a catalyst for the formation of imine from 4-amino-1,2,4-triazole. During the catalytic reaction, the iron complex undergoes two different PSM reactions: the first is the action of the aldehyde on the NH2 groups present on the complex, whereas the second PSM reaction occurs between the imine complex and aminotriazole, leading back to the starting complex. These two PSM reactions are at least partially involved in the catalytic mechanism. Furthermore, the combination of these two PSM reactions enables us to modulate the particle size and shape of the final amine complex without altering its excellent SCO properties. This result is of interest in the field of heterogeneous catalysis, where particle size has a strong influence on the catalytic activity, and for the proper integration in devices for different applications.

Reaction Thermodynamic and Kinetics for Esterification of 1-Methoxy-2-Propanol and Acetic Acid over Ion-Exchange Resin

The esterification of 1-methoxy-2-propanol (PM) and acetic acid (AA) is an important reaction for the production of 1-methoxy-2-propyl acetate (PMA). Herein, we used the macroporous ion-exchange resin Amberlyst-35 as a catalyst to explore the effects of reaction conditions on the reaction rate and equilibrium yield of PMA. Under the optimized conditions of a reaction temperature of 353 K, using the initial reactant PM/AA with a molar ratio of 1:3, and a catalyst loading of 10 wt%, the PMA equilibrium yield reached 78%, which is the highest equilibrium yield so far. The reaction equilibrium constants and activity coefficients were estimated to obtain reaction thermodynamic properties, indicating the exothermicity of the reaction. Furthermore, pseudo-homogeneous (PH), Eley-Rideal (ER), and Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models were fitted based on experimental reaction kinetic data. The results demonstrate that the LHHW model is the most consistent with experimental data, indicating a surface reaction-controlled process and exhibiting an apparent activation energy of 62.0 ± 0.2 kJ/mol. This work represents a valuable example of calculating reaction thermodynamics and kinetics, which are particularly essential for promising industrial reactor designs.

Controlling the Fe2O3-SiO2 interaction: The effect on the H2S selective catalytic oxidation and catalyst deactivation

Biogas utilization is one of the most promising options for reducing the consumption of fossil fuels for energy production, but the presence of H₂S represents a serious industrial and environmental problem. In this work, two different synthesis methods (sol-gel and incipient wetness impregnation) were used to synthesize iron oxide supported on silica catalysts (Fe₂O₃/SiO₂) with metal loadings ranging from 0.5 to 10 %wt. The catalysts were tested for the selective oxidation of H₂S, changing the operating conditions like O₂/H₂S (0.5-2.5), temperature (170-250°C), and water content (0-50%). The optimum condition was O₂/H₂S = 0.5 and no water at 230 °C with the conversion of approximately 100%, the selectivity of 97%, and the deactivation of 0.6%. A detailed characterization of the fresh and spent catalysts' surface revealed the presence of four deactivation mechanisms: metal surface reduction, oxygen vacancy loss, pore plugging, and sintering. Among the observed deactivation mechanisms, the sintering showed the highest impact on catalytic activity and deactivation. The sol-gel catalysts (SG) showed the highest metal-oxide/support interaction, which reduced the metal-oxide nanoparticles sintering compared with the incipient wetness impregnation method (IWI), reporting a lower sintering, higher activity, and selectivity, lower deactivation rates and lower sensitivity to the operating conditions. A catalytic cycle representing the possible surface intermediate states of the catalyst is proposed based on the performance and characterization results obtained.

On the importance of physicochemical parameters of copper and aminosilane functionalized mesoporous silica for hydroxychloroquine release

Recently, great attention has been paid to hydroxychloroquine which after promising in vitro studies has been proposed to treat the severe acute respiratory syndrome caused by SARS-CoV-2. The clinical trials have shown that hydroxychloroquine was not as effective as was expected and additionally, several side effects were observed in patients cured with this medicament. In order to reduce them, it is suggested to deliver hydroxychloroquine in a controlled manner. Therefore, in this study non-modified (SBA-15, SBA-16) and modified with copper and aminosilane mesoporous silica materials were applied as novel nanocarriers for hydroxychloroquine. First, pristine and functionalized samples were synthesized and characterized by X-ray diffraction, low-temperature nitrogen sorption, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, laser diffraction. Then the influence of physicochemical parameters of materials obtained on the adsorption and release processes of hydroxychloroquine was analyzed. The mechanism of hydroxychloroquine binding to non-modified silicas was based on the formation of hydrogen bonds, while in the case of copper and aminosilane functionalized materials the complexes with drug molecules were generated. The release behavior of hydroxychloroquine from silica samples obtained was determined by different factors including pH conditions, textural parameters, surface charge, and presence of surface functional groups. The greatest differences in hydroxychloroquine release profiles between materials were observed at pH 7.2. The amount of drug desorbed from silica decreased in the following order: functionalized SBA-15 (84%) > functionalized SBA-16 (79%) > SBA-15 (59%) > SBA-16 (33%). It proved that a higher amount of drug was released from materials of hexagonal structure.

The impact of environmental water on the potential application of core-shell titania-silica nanospheres as photocatalysts

In this study, the core-shell silica nanospheres modified with titanium dioxide were tested in the photocatalytic decomposition of dyes. The presented data underlines the advantages and shortcomings in the potential application of silica-based catalysts to neutralize organic pollutants. During the photocatalytic reaction in distilled water, catalysts showed decreased efficiency due to a carbon layer deposited on its surface. This finding set an additional goal to investigate the possibility of regenerating the photocatalyst. Studies have shown that the catalyst could be successfully reused following the thermal removal of deposited carbon.Furthermore, the reactivated silica-titania catalysts exhibited comparable photocatalytic performance to the newly made nanomaterial. Surprisingly, catalyst application in the river water eventually resulted in the permanent deactivation of silica-titania nanospheres, which was caused by the interchangeable silica dissolution/precipitation process on the surface of the studied nanomaterial. In environmental water, silica dissolves and precipitates on titanium dioxide's surface, blocking the interaction between organic compounds and TiO₂. The deactivation occurring in the environmental samples is irreversible. In distilled water, the decomposition of organic compounds leads to photocatalysts' deactivation by forming a carbon layer on their surface. Reactivation of the silica-based photocatalyst after distilled water is achievable by annealing at a high temperature. In light of our findings, the combination of the photocatalytic properties of TiO₂and the silica template shows no prospects in the purification of polluted waste or environmental water.

Oxygen vacancies and Lewis sites activating O3/H2O2 at wide pH range via surface electron transfer over CeOx@SiO2 for nitrobenzene mineralization

The low efficiency of peroxone (O₃/H₂O₂) at acidic and neutral pH restrained its application in water purification. To overcome this shortcoming, CeO_X@SiO₂ with large surface area, abundant surface oxygen vacancies (V_o), Lewis sites (L sites) and high Ce(III)/Ce(IV) ratio were synthesized to change the traditional electron transfer pathway between O₃ and H₂O₂. V_o was facile in absorbing H₂O₂ to form V_o-H₂O₂ and L sites were capable of absorbing O₃ to form L-O₃. The electron at V_o could be donated to V_o-H₂O₂ and generate V_o-HO₂^-, which then effectively triggered the decomposition of L-O₃ at CeO_X@SiO₂'s interface and O₃ in bulk solution. The electron transfer at the solid-liquid interface with the help of Ce³⁺/Ce⁴⁺ redox cycle and V_o was pH independent and different from the traditional electron transfer of peroxone reaction. Nitrobenzene (NB) mineralization was promoted to 92.5% in CeO_X@SiO₂-peroxone, but only 63.8% TOC was removed in tradition peroxone process. Moreover, CeO_X@SiO₂-peroxone had a wide pH application range. NB's degradation in CeO_X@SiO₂-peroxone process followed the co-oxidation mechanism of superoxide free (•O₂^-) and hydroxyl radical (•OH). The finding of this study could broaden the popularization of peroxone in water treatment and provided a strategy for catalyst design.

Efficient stereoselective synthesis of chiral 3,3′-dimethyl-(2,2′-bipyridine)-diol ligand and applications in FeII-catalysis

A seven step synthesis of a chiral 2,2′-bipyridinediol ligand with 3,3′-dimethyl substituents was achieved starting from commercially available materials.

Silica Mesoporous Structures: Effective Nanocarriers in Drug Delivery and Nanocatalysts

The application of silica mesoporous structures in drug delivery and the removal of pollutants and organic compounds through catalytic reactions is increasing due to their unique characteristics, including high loading capacities, tunable pores, large surface areas, sustainability, and so on. This review focuses on very well-studied class of different construction mesoporous silica nano(particles), such as MCM-41, SBA-15, and SBA-16. We discuss the essential parameters involved in the synthesis of these materials with providing a diverse set of examples. In addition, the recent advances in silica mesoporous structures for drug delivery and catalytic applications are presented to fill the existing gap in the literature with providing some promising examples on this topic for the scientists in both industry and academia active in the field. Regarding the catalytic applications, mesoporous silica particles have shown some promises to remove the organic pollutants and to synthesize final products with high yields due to the ease with which their surfaces can be modified with various ligands to create appropriate interactions with target molecules. In the drug delivery process, as nanocarriers, they have also shown very good performance thanks to the easy surface functionalization but also adjustability of their porosities to providing in-vivo and in-vitro cargo delivery at the target site with appropriate rate.

Simultaneous determination of seven compounds in Chinese patent medicines Chenxiangqu by matrix solid-phase dispersion coupled with ultra high performance liquid chromatography and quadrupole time-of-flight mass spectrometry

A simple, efficient, and sensitive strategy by coupling matrix solid-phase dispersion with ultra high performance liquid chromatography quadrupole time-of-flight mass spectrometry was proposed to extract and determine three types of components (including seven analytes) in Chinese patent medicines Chenxiangqu. The highly ordered mesoporous material Fe-SBA-15 synthesized under weakly acidic conditions was selected as a dispersant in matrix solid phase dispersion extraction for the first time. Several parameters including the mass ratio of sample to dispersant, the type of dispersant, the grinding time, and the elution condition were investigated in this work. Under the optimized conditions, 20 compounds were identified by quadrupole time-of-flight mass spectrometry and seven analytes were quantified. The results demonstrated that the developed method has good linearity (r > 0.9995), and the limits of detection of the analytes were as low as 0.55 ng/mL. The recoveries of all seven analytes ranged from 97.6 to 104.6% (relative standard deviation < 3.4%). Finally, the improved method was successfully applied to determination of five batches of Chenxiangqu samples, which provided a robust method in quality control of Chinese patent medicines Chenxiangqu. The developed strategy also shows its great potential in analysis of complex matrix samples.

Formaldehyde-Controlled Synthesis of Multishelled Hollow Mesoporous SiO2 Microspheres

We developed a facile one-pot method to synthesize multishelled hollow mesoporous SiO₂ microspheres (HMSs) with controllable interior structures including one-shell, double-shell, and yolk-shell. Single reagent formaldehyde could fully control the morphology of HMSs, in that formaldehyde was crucial to the SiO₂ precursor's hydrolysis rate and the template pore size.

Iron(III) Complexes for Highly Efficient and Sustainable Ketalization of Glycerol: A Combined Experimental and Theoretical Study

The growing production of biodiesel as a promising alternative and renewable fuel led as the main problem the dramatic increase of its by-product: glycerol. Different strategies for glycerol derivatization have been reported so far, some more efficient or sustainable than others. Herein, we report a very promising and eco-friendly transformation of glycerol in nontoxic solvents and chemicals (i.e., solketal, ketals), proposing three new families of Fe(III) compounds capable of catalysing glycerol acetalization with unpublished turn over frequencies (TOFs), and adhering most of the principles of green chemistry. The comparison between the activity of complexes of formula [FeCl₃(1-R)] (1-R = substituted pyridinimine), [FeCl(2-R,R')] (2-R,R' = substituted O,O'-deprotonated salens) and their corresponding simple salts reveals that the former are extremely convenient because they are able to promote solketal formation with excellent TOFs, up to 10⁵ h^-1. Satisfactory performances were shown with respect to the entire range of substrates, with results being competitive to those reported in the literature so far. Moreover, the experimental activity was supported by an accurate and complete ab initio study, which disclosed the fundamental role of iron(III) as Lewis acid in promoting the catalytic activity. The unprecedented high activity and the low loading of the catalyst, combined with the great availability and the good eco-toxicological profile of iron, foster future applications of this catalytic process for the sustainable transformation of an abundant by-product in a variety of chemicals.

Can Hammett indicators accurately measure the acidity of zeolite catalysts with confined space? Insights into the mechanism of coloration

The acidic properties of zeolite catalysts play a crucial role in governing catalytic performances, which makes the acidity characterization an important subject in the field of zeolite catalysis.

FeII-catalysed insertion reaction of α-diazocarbonyls into X–H bonds (X = Si, S, N, and O) in dimethyl carbonate as a suitable solvent alternative

The insertion reaction of a broad range of diazo compounds into Si–H bonds was found to be efficiently catalysed by Fe(OTf)₂ in an emerging green solvent i.e. dimethyl carbonate (DMC).