Zeolite-Based Catalysts: A Valuable Approach toward Ester Bond Formation

Single-site ruthenium catalyst supported on zeolite for CO2 hydrogenation to methyl formate

Technologies for the transformation of atmospheric CO2 to useful chemicals, such as formic acid (FA), are essential to combatting excessive fossil fuel use and will need to be implemented on large scale. However, hydrogenation of CO2 to (base-free) FA is challenging for heterogeneous catalysts, due to the requirement for low temperatures enforced by the entropically unfavorable reaction of gases. By coupling CO2 hydrogenation to esterification, methyl formate (MF) can be prepared as a promising alternative platform chemical. Herein, a robust, heterogeneous single-metal-site catalyst was prepared and shown to achieve methanol hydrocarboxylation rates superior to nanoparticle catalysts (up to 18.3 ± 0.6 mmol hour-1 [Formula: see text]) while maintaining very high selectivity to MF (≥95%). Characterization reveals isolated, monodisperse Ru-nitrosyl complexes bound to three O-atoms of the zeolite framework, and the robust catalyst formed achieves a cumulative turnover number of more than 3500 over eight cycles. This work pushes the boundaries of supported single-site catalysts in CO2 utilization.

Unveiling the mechanisms of carboxylic acid esterification on acid zeolites for biomass-to-energy: A review of the catalytic process through experimental and computational studies

In recent years, there has been significant interest from industrial and academic areas in the esterification of carboxylic acids catalyzed by acidic zeolites, as it represents a sustainable and economically viable approach to producing a wide range of high-value-added products. However, there is a lack of comprehensive reviews that address the intricate reaction mechanisms occurring at the catalyst interface at both the experimental and atomistic levels. Therefore, in this review, we provide an overview of the esterification reaction on acidic zeolites based on experimental and theoretical studies. The combination of infrared spectroscopy with atomistic calculations and experimental strategies using modulation excitation spectroscopy techniques combined with phase-sensitive detection is presented as an approach to detecting short-lived intermediates at the interface of zeolitic frameworks under realistic reaction conditions. To achieve this goal, this review has been divided into four sections: The first is a brief introduction highlighting the distinctive features of this review. The second addresses questions about the topology and activity of different zeolitic systems, since these properties are closely correlated in the esterification process. The third section deals with the mechanisms proposed in the literature. The fourth section presents advances in IR techniques and theoretical calculations that can be applied to gain new insights into reaction mechanisms. Finally, this review concludes with a subtle approach, highlighting the main aspects and perspectives of combining experimental and theoretical techniques to elucidate different reaction mechanisms in zeolitic systems.

Tin(II) Chloride-Catalyzed Direct Esterification and Amidation of tert-Butyl Esters Using α,α-Dichlorodiphenylmethane Under Mild Conditions

A practical one-pot synthesis of esters and amides from tert-butyl esters via acid chloride was developed. Reactions of tert-butyl esters with α,α-dichlorodiphenylmethane as the chlorinating agent and SnCl2 as catalyst-generated acid chloride intermediates in situ were subsequently used in reactions with a variety of alcohols and amines to afford the corresponding esters and amides in high yields under mild reaction conditions. This catalytic synthetic procedure offers an effective strategy for the facile esterification and amidation of tert-butyl esters.

Catalytic Characterization of Synthetic K+ and Na+ Sodalite Phases by Low Temperature Alkali Fusion of Kaolinite during the Transesterification of Spent Cooking Oil: Kinetic and Thermodynamic Properties

The mineral raw Egyptian kaolinite was used as a precursor in the synthesis of two sodalite phases (sodium sodalite (Na.SD) and potassium sodalite (K.SD)) according to the low alkali fusion technique. The synthesized Na.SD phase demonstrates enhanced total basicity (6.3 mmol OH/g), surface area (232.4 m2/g), and ion exchange capacity (126.4 meq/100 g) compared to the K.SD phase (217.6 m2/g (surface area), 96.8 meq/100 g (ion exchange capacity), 5.4 mmol OH/g (total basicity). The catalytic performance of the two sodalite phases validates the higher activity of the sodium phase (Na.SD) than the potassium phase (K.SD). The application of Na.SD resulted in biodiesel yields of 97.3% and 96.4% after 90 min and 60 min, respectively, while the maximum yield using K.SD (95.7%) was detected after 75 min. Robust base-catalyzed reactions using Na.SD and K.SD as catalysts were suggested as part of an operated transesterification mechanism. Moreover, these reactions exhibit pseudo-first order kinetics, and the rate constant values were estimated with consideration of the change in temperature. The estimated activation energies of Na.SD (27.9 kJ.mol−1) and K.SD (28.27 kJ.mol−1) reflected the suitability of these catalysts to be applied effectively under mild conditions. The essential thermodynamic functions, such as Gibb’s free energy (65.16 kJ.mol−1 (Na.SD) and 65.26 kJ.mol−1 (K.SD)), enthalpy (25.23 kJ.mol−1 (Na.SD) and 25.55 kJ.mol−1 (K.SD)), and entropy (−197.7 J.K−1.mol−1 (Na.SD) and −197.8 J.K−1.mol−1 (K.SD)), display the endothermic and spontaneous nature of the two transesterification systems.

Synthesis of K+ and Na+ Synthetic Sodalite Phases by Low-Temperature Alkali Fusion of Kaolinite for Effective Remediation of Phosphate Ions: The Impact of the Alkali Ions and Realistic Studies

Two sodalite phases (potassium sodalite (K.SD) and sodium sodalite (Na.SD)) were prepared using alkali fusion of kaolinite followed by a hydrothermal treatment step for 4 h at 90 °C. The synthetic phases were characterized as potential adsorbents for PO43− from the aqueous solutions and real water from the Rákos stream (0.52 mg/L) taking into consideration the impact of the structural alkali ions (K+ and Na+). The synthetic Na.SD phase exhibited enhanced surface area (232.4 m2/g) and ion-exchange capacity (126.4 meq/100 g) as compared to the K.SD phase. Moreover, the Na.SD phase exhibited higher PO43− sequestration capacity (Qmax = 261.6 mg g−1 and Qsat = 175.3 mg g−1) than K.SD phase (Qmax = 201.9 mg g−1 and Qsat = 127.4 mg g−1). The PO43− sequestration processes of both Na.SD and K.SD are spontaneous, homogenous, and exothermic reactions that follow the Langmuir isotherm and pseudo-first-order kinetics. Estimation of the occupied active site density validates the enrichment of the Na.SD phase with high quantities of active sites (Nm = 86.1 mg g−1) as compared to K.SD particles (Nm = 44.4 mg g−1). Moreover, the sequestration and Gaussian energies validate the cooperation of physisorption and weak chemisorption processes including zeolitic ion exchange reactions. Both Na.SD and K.SD exhibit significant selectivity for PO43− in the coexisting of other common anions (Cl−, SO42−, HCO3−, and NO3−) and strong stability properties. Their realistic application results in the complete adsorption of PO43- from Rákos stream water after 20 min (Na. SD) and 60 min (K.SD).

Autocatalyzed and heterogeneously catalyzed esterification kinetics of glycolic acid with ethanol

In this study, the kinetics of the esterification of glycolic acid with ethanol homogeneously autocatalyzed and heterogeneously catalyzed are investigated.

Silica Coating of Metal-Loaded H-ZSM-22 to Form the Core-Shell Nanostructures: Characterization, Textural Properties, and Catalytic Potency in the Esterification of Oleic Acid

In this study, ZSM-22 was synthesized using N,N-diethylaniline as a template through a hydrothermal method. The proton and various metals such as zirconium, strontium, and iron were immobilized on the surface of obtained zeolites through the ion exchange method. The catalysts were studied by Fourier-Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) adsorption isotherms, Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) elemental analysis, and Temperature-Programmed Desorption of ammonia (TPD-NH3) technique for determining the number of acid sites. In the esterification reaction of oleic acid, the operating conditions such as catalyst dosage, temperature, molar ratio of methanol to oil, and reaction time were optimized and adjusted at 11 wt%, 70°C, 10 : 1, and 48 h subsequently. The maximum yield% of 48.07% was achieved in the presence of Zr-H-ZSM-22 at optimum conditions. In order to improve the efficiency of three zeolites Zr-H-ZSM-22, Fe-H-ZSM-22, and Sr-H-ZSM-22, the core-shell structures with SiO2 coating were prepared. Zr-H-ZSM-22@SiO2 was less active than Zr-H-ZSM-22 due to the SiO2 coverage of Lewis active sites.

Synthesis of Mesoporous Zeolites and Their Opportunities in Heterogeneous Catalysis

Currently, zeolites are one of the most important classes of heterogeneous catalysts in chemical industries owing to their unique structural characteristics such as molecular-scale size/shape-selectivity, heterogenized single catalytic sites in the framework, and excellent stability in harsh industrial processes. However, the microporous structure of conventional zeolite materials limits their applications to small-molecule reactions. To alleviate this problem, mesoporous zeolitic frameworks were developed. In the last few decades, several methods have been developed for the synthesis of mesoporous zeolites; these zeolites have demonstrated greater lifetime and better performance than their bulk microporous counterparts in many catalytic processes, which can be explained by the rapid diffusion of reactant species into the zeolite framework and facile accessibility to bulky molecules through the mesopores. Mesoporous zeolites provide versatile opportunities not only in conventional chemical industries but also in emerging catalysis fields. This review presents many state-of-the-art mesoporous zeolites, discusses various strategies for their synthesis, and details their contributions to catalytic reactions including catalytic cracking, isomerization, alkylation and acylation, alternative fuel synthesis via methanol-to-hydrocarbon (MTH) and Fischer–Tropsch synthesis (FTS) routes, and different fine-chemical syntheses.

Use of NaNO3/SiAl as Heterogeneous Catalyst for Fatty Acid Methyl Ester Production from Rapeseed Oil

The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction takes place. For this purpose, different catalysts are used, including a wide range of possibilities. In this research the use of NaNO3/SiAl as a heterogeneous catalyst for FAME production through transesterification of rapeseed oil with methanol is considered. A thorough characterization of the catalyst (including XDR and XPS analysis, SEM microscopy, lixiviation and reusability tests, among others), specific optimization of transesterification by using the final catalyst (considering catalyst amount, stirring rate, methanol/oil ratio, and temperature), and quality determination of the final biodiesel (following the UNE-EN 14214 standard) were carried out. In conclusion, 20 mmolNa·gsupport−1 (that is, NaNO3/SiAl 20/1) offered the best results, with a high activity (exceeding 99% w/w of FAMEs) without requiring higher impregnation amounts. The best chemical conditions for this heterogeneous catalyst were 5% w/w catalyst, 700 rpm, 9:1 methanol/oil ratio, and 65 °C, obtaining Ea = 73.3 kJ·mol−1 and a high-quality biodiesel, similar to those obtained through homogeneous catalysis. Consequently, this catalyst could be a suitable precursor for FAME production.

Role of Chain Length and Degree of Unsaturation of Fatty Acids in the Physicochemical and Pharmacological Behavior of Drug-Fatty Acid Conjugates in Diabetes

Several drug-fatty acid (FA) prodrugs have been reported to exhibit desirable physicochemical and pharmacological profile; however, comparative beneficial effects rendered by different FAs have not been explored. In the present study, four different FAs (linoleic acid, oleic acid, palmitic acid, and α-lipoic acid) were selected based on their chain length and degree of unsaturation and conjugated to Lisofylline (LSF), an antidiabetic molecule to obtain different drug-FA prodrugs and characterized for molecular weight, hydrophobicity, purity, self-assembly, and efficacy in vitro and in vivo in type 1 diabetes model. Prodrugs demonstrated a 2- to 6-fold increase in the plasma half-life of LSF. Diabetic animals treated with prodrugs, once daily for 5 weeks, maintained a steady fasting blood glucose level with a significant increase in insulin level, considerable restoration of biochemical parameters, and preserved β-cells integrity. Among the different LSF-FA prodrugs, LSF-OA and LSF-PA demonstrated the most favorable physicochemical, systemic pharmacokinetic, and pharmacodynamic profiles.

Emerging insights on drug delivery by fatty acid mediated synthesis of lipophilic prodrugs as novel nanomedicines

Many drug molecules that are currently in the market suffer from short half-life, poor absorption, low specificity, rapid degradation, and resistance development. The design and development of lipophilic prodrugs can provide numerous benefits to overcome these challenges. Fatty acids (FAs), which are lipophilic biomolecules constituted of essential components of the living cells, carry out many necessary functions required for the development of efficient prodrugs. Chemical conjugation of FAs to drug molecules may change their pharmacodynamics/pharmacokinetics in vivo and even their toxicity profile. Well-designed FA-based prodrugs can also present other benefits, such as improved oral bioavailability, promoted tumor targeting efficiency, controlled drug release, and enhanced cellular penetration, leading to improved therapeutic efficacy. In this review, we discuss diverse drug molecules conjugated to various unsaturated FAs. Furthermore, various drug-FA conjugates loaded into various nanostructure delivery systems, including liposomes, solid lipid nanoparticles, emulsions, nano-assemblies, micelles, and polymeric nanoparticles, are reviewed. The present review aims to inspire readers to explore new avenues in prodrug design based on the various FAs with or without nanostructured delivery systems.

Catalytic performance of cerium-modified ZSM-5 zeolite as a catalyst for the esterification of glycerol with acetic acid

Esterification of glycerol with acetic acid was carried out over cerium-modified ZSM-5 zeolites to synthesize monoacetin (MA) and diacetin (DA). The modified zeolite catalyst was characterized. The effect of reaction process parameters such as acetic acid to glycerol mole ratio (1–11), reaction temperature (30–120 °C), and catalyst weight (2–8 wt %) on the selectivity of the product was investigated. At 120 °C reaction temperature, 8 wt % catalyst, and 9:1 acetic acid to glycerol mole ratio, about 98.32% conversion of glycerol were obtained. This reaction follows pseudo-first-order reaction kinetics and the activation energy was found to be 63.72 kJ mol−1.