Catalytic Medium Research Articles

Catalyst efficiency through the disorder kinetics to identify its nonlinearity in their properties of Ag3PO4@TiO2 catalyst using UV–visible spectroscopy

Abstract Photocatalysis has a significant role in water remediation. During the process of photocatalysis, catalysts face different problems, such as instability and inefficiency. Here, we are introducing a new method, ‘nonlinearity kinetics’, which will help to identify this kind of problem during photocatalytic activity. We are considering Ag3PO4@TiO2 to study nonlinear disorder kinetics. Ag3PO4 is a highly photoactive compound with an inherent photocorrossive nature. Here, it addresses the challenge of pure Ag3PO4 by transforming composite materials to Ag3PO4@TiO2 and by studying its nonlinear kinetics during photocatalysis. The Ag3PO4@TiO2 underwent preliminary characterisation. Increment of crystalline nature studied through XRD. FESEM and TEM analysed morphological alignment and diffraction patterns. The functional behaviour of oxygen, Ag, Ti and P–O–P were identified through the FT-IR spectra. The reduced optical band gap Ag3PO4@TiO2 was 2.9 eV Obtained from the UV–visible spectra. Photocatalysis activity was performed, and newly introduced disorder kinetics were observed. The nonlinear fit of the kinetics shows a shift over time (intercept value of linear fit −0.27) that indicates the corrosive characteristics. For an efficient catalyst, this value must be equivalent to zero. The photocorrossive disorder kinetics study demonstrates the disorder and nonlinearity of the catalyst and catalytic medium when it does not fit with a linear fit. To identify a disorder, it is important to look at the disorder kinetics of analysis.

Revealing a volcano correlation of sulfur reduction catalytic activity and elements doping in cobalt-based sulfides for Li-S batteries

The effective utilization of Li-S batteries still necessitates the incorporation of an efficient catalytic medium to address the challenges posed by shuttle effects and sluggish reaction kinetics. Furthermore, the structure-activity relationship of catalysts for the sulfur reduction reaction remains inadequately understood. In this study, we utilize Co9S8 as a template to investigate the correlation between the doping of co-periodic elements (Fe, Ni, Cu and Zn) and their catalytic effects on the sulfur reduction reaction. There is a “volcano peak” correlation between the catalytic performance and the type of doped elements from Fe to Zn, and research indicates that the Ni-doped Co9S8 (NCS) demonstrates superior performance compared to other samples. The NCS not only maintains the inherent advantages of Co9S8 but also effectively lowers the apparent activation energy necessary for Li-S batteries. Consequently, this enhancement facilitates a more rapid and complete conversion of soluble lithium polysulfides, thereby endowing Li-S batteries with an enhanced reaction kinetics. When the sulfur areal loading is elevated to 5.2 mg cm−2, the maximum areal capacity of the cell can attain 5.2 mAh cm−2 at 0.05 C. This work further substantiates the efficacy of the element doping strategy in enhancing the catalytic performance of reduction reaction catalysts, and it also offers significant insights or considerations for the development of practical catalysts, thereby facilitating the practical application of Li-S batteries.

Enhancing Biocatalysis through Chiral Supramolecular Scaffolds: Insights into the Structural Adaptability of Lipase.

How to maintain high catalytic activity and stability in the process of biocatalysis is crucial, inspiring strategies to construct an appropriate catalytic microenvironment. Considering the lipase's inherent chirality and the necessity for a delicate hydrophilic-hydrophobic equilibrium, we crafted a chiral, nonaqueous catalytic microenvironment via the in situ coassembly of Boc-FLFL-NHNH2 (Bfl) and lipase. Benefiting from the chirality and distinct Bfl-lipase interactions, the lipase@Bfl supramolecular hybrid amplifies biological functionalities and can serve as a versatile and highly efficient catalyst. Kinetic investigations and molecular docking simulations uncover the strong lipase-substrate affinity and lipase-Bfl interactions, explaining the enhanced biological effects, catalytic activity, and stability. Our study establishes a suitable microenvironment to address the chirality and hydrophobicity during catalysis and highlights the potential of artificial chiral scaffolds and catalytic medium for enhancing lipase activity.

Catalytic post-treatment of homogeneous Ag–S2O8 and Cu–H2O2 advanced oxidation processes: Revealing the importance of capacitive-Faradaic electrochemical structure of Pt/AC

Implementation of homogeneous advanced oxidation processes (HAOPs) catalysed by Cu and Ag metals is limited due to high residual concentrations of oxidants and dissolved metals. The proposed post-treatment process starts with recirculation of H2-enriched HAOP-treated water through the Pt-loaded activated carbon (AC). Hydrogen oxidation reaction (HOR) on Pt results in degradation of oxidants while silver and/or copper ions are reduced and deposited on the catalytic media. The subsequent aeration of the catalyst results in oxygen reduction reaction (ORR) and oxidation of the metals back into ionic forms. This allows the homogeneous metal catalysts to be reused in multiple HAOP cycles.The capacitive-Faradaic electrochemical structure of the Pt/AC catalyst with Pt acting as a Faradaic electrode and AC as a capacitive electrode plays an important role in the process. The HOR on Pt/AC results in accumulation of electrons in electrical double layer of AC. These electrons can be effectively used in a subsequent H2-free reduction of metal ions and oxidants. Thus, the degradation of H2O2 and S2O82− and reduction of Cu2+ and Ag + ions proceed much faster if the H2-step of the process is split into two sub-processes: (i) hydrogenation of Pt/AC catalyst in an inert Na2SO4 solution to pre-charge the Pt/AC with electrons originating at HOR, followed by (ii) catalytic reduction of oxidants and metal ions by the capacitively stored electrons.The process was investigated using Ag–S2O82− ([S2O82−]0 = 25 mM; [Ag+]0 = 50 mg/L) and Cu–H2O2 ([H2O2]0 = 100 mM, [Cu]0 = 635 mg/L) solutions. Total degradation of oxidants was achieved within <2 h and complete metals’ recovery was obtained. Several cycles of HAOP experiments were performed for the degradation of 1,4-dioxane (10 mg/L) and phenol (25 mg/L) using Ag– S2O82− and Cu–H2O2 HAOPs, respectively. The residual oxidants were completely degraded in all experiments. The reactivation of Pt/AC catalysts inhibited by phenol derivatives was achieved by hydrogenation in Na2SO4 solution (i.e., using the pre-charge approach).

Methane catalytic cracking by solid materials and molten media for hydrogen production: A review

Excessive emission of carbon dioxide is the leading cause of global warming. Hydrogen has the advantages of high calorific value and zero carbon emissions. It is considered an ideal energy to solve the problem of global warming, so the demand for hydrogen is increasing yearly. Due to economic considerations, methane is the main raw material for hydrogen production. Currently, 48% of the world's hydrogen comes from steam methane reforming. However, this process needs to burn some methane for heating, generating carbon dioxide emissions simultaneously. In order to avoid carbon emissions from hydrogen production, there is an urgent need to develop new methods to produce hydrogen from methane. Because the carbon generated from direct methane cracking exists in solid form while not as carbon dioxide, the direct methane cracking process for hydrogen production has become a hot research topic in recent years. In this paper, a comprehensive review of the research related to catalytic methane cracking for hydrogen production is presented, especially the research on catalytic cracking of methane using solid materials or molten metal media as catalytic media is summarized in detail. Next, a brief overview of the mechanism of catalytic methane cracking for hydrogen production and the characteristics of the generated carbon as a by-product are presented. Finally, the catalytic cracking of methane in molten media or solid materials and the research trend were prospected.

Engineering flower-shaped hierarchical micromotors on a sustainable biotemplate by teamed boronate affinity-based surface imprinting for effective separation of shikimic acid

Self-propelled nano/micromotors are the frontier of separation materials because they are capable of converting external energy in the surrounding environment into kinetic energy for their autonomous movement. In this work, a bioinspired flower-shaped hierarchical teamed boronate affinity (TBA)-imprinted Pt-free micromotor is introduced based on waste rape pollen as a biotemplate due to its merits of sustainability, rich source and low price. Such micromotor, composed of MnO2 nanosheets as a catalytic medium, Mg-Al layered double hydroxides (LDH) nanosheets as large surface area substrate and functional surface imprinted polymers as identification subject, exhibits autonomic motor behavior powdered by oxygen bubbles generated by the decomposition of H2O2 and selective recognition and separation for shikimic acid (SA). The hierarchical flower-shaped structure affords more accessible recognition sites for SA, which thus facilitates the separation process. Moreover, in combination with the TBA strategy, the micromotor can precisely recognize the target via boronate affinity between boronic acids and cis-diols from SA while showing strong binding capacity under neutral conditions. Benefiting from the pluripotent role of pioneering boronate affinity-covalent imprinted technique, hydrogen bonds interaction and nanoconfinement effect, the resulting affinity towards SA is evidently enhanced with maximal adsorption capacity of 129.51 mg g−1 at neutral pH in the presence of H2O2. After five capture/release cycles, the adsorption capacity remains above 85 %. This proposed flower-shaped hierarchical micromotor expands the scope of potential materials for the adsorption of SA and provides a new and promising direction for fabricating adsorbents applied in the separation and purification of natural products.

N2O ADSORPTION OVER FLAT AND DEFECTIVE Cu (110) SURFACES: PURE DFT AND DFT+U STUDIES INCLUDING vdW FORCES

The adsorption of N2O on flat and defective Cu (110) surfaces has been studied using pure density functional theory (DFT) and DFT with Hubbard U, including van der Waals (vdW) corrections of the form vdW-DF. The calculations show that for GGA-PBE, as the exchange-correlation and vdW-DF functionals are considered, N2O molecule interacts very weakly with the flat Cu (110) surface, while the presence of the Cu-adatom results in better stability of adsorbed N2O compared to one on the perfect surface. Also, the inclusion of U parameter to PBE and vdW-DF functionals reduces the values of the adsorption energy relative to the standard PBE and vdW-DF functionals with or without spin-polarization. Finally, the analysis of the projected density of states shows a strong hybridization between the Cu-3d band and N-2p orbital. Our investigation suggests that the Cu (110) surface can serve as a catalytic medium that is able to adsorb the harmful N2O molecule.

Iron porphyrin for selective electrochemical reduction of CO2: Synthesis, characterization and effect of electrolyte

The electrochemical CO2reductionreaction to form valued by-products is a challenging and a sustainable process. In general, CO2 reduction to carbon neutral fuels requires selective and well-designed catalysts. Herein, we report perfluorinated iron porphyrin (FeFPor) for CO2-to-CO electroreduction in different bicarbonate electrolytes, byproducts distribution in lithium, sodium, potassium and cesium were analyzed. The immobilized FeFPor on the carbon microporous layer of the carbon cloth exhibited a high selectivity for carbon monoxide production over a wide range of potentials from −0.5 to −1 V vs. RHE in all bicarbonate solution with the NaHCO3 being the best catalytic medium. The highest conversion efficiency to CO production reached 97% at −0.5 V vs. RHE in 0.5 M NaHCO3 in near neutral aqueous solution (pH = 7.2). The CO electrosynthesis dropped when using lithium, potassium and cesium bicarbonates, which was due to the CO2 concentration and reactions at the inner electrode-solution reactions.

Formation mechanism of Al4SiC4 in Al–SiC composite under flowing nitrogen at 1300 °C

Resin-bonded Al–SiC composite was sintered in an electric heating shuttle kiln to prepare aluminum-carbon sliding gates at 1300 °C with nitrogen gas, which synthesized ternary carbide Al4SiC4 in situ and a three-dimensional space interlocking structure of Al4SiC4rods/SiCparticles grown on the surface of SiC particles. The phase composition and microstructure of sintered sample were characterized by XRD and SEM, combined with thermodynamics to investigate the formation mechanism of Al4SiC4. It was found that as temperature increases, trace O2(g) in N2(g) causes active oxidation of carbon, with the composition of gas in environment as N2(g)+CO(g) +trace O2(g). A dense layer (Al4C3+Al2OC-AlNss) was formed on the outer layer of sample preventing the diffusion of ambient gas into inner. Under high temperature and low oxygen partial pressure conditions, the oxygen partial pressure inside the sample was lowered again by the active oxidation of Al(l), and the low oxygen partial pressure induced the active oxidation of SiC(s) so that N2(g)+CO(g)+trace O2(g) outside the sample was transformed to Al2O(g)+SiO(g)+CO(g) inside. Subsequently, Al4SiC4 nuclei were formed on the highly reactive surface of SiC particles by gas-gas reactions as well as releasing trace amounts of O2(g); surrounding SiC(s) and Al(l) rapidly convert O2(g) into reactive gas to participate a second time in the growth process of Al4SiC4 nuclei. A self-circulating system with O2(g) as a catalytic medium has been established to "catalyze" the nucleation and growth of Al4SiC4, which realizes a refined modification of Al4SiC4 morphology at the micro-scale.

Microwave-accelerated Eco-friendly Performance of the Knoevenagel Condensation Reaction with Various Active Methylene Derivat-ives evaluation of Electrochemical Properties

Background: The present work describes sustainable Knoevenagel condensation reac-tion of aryl/ heterocyclic aldehyde with various active methylene derivatives such as malono-nitrile, dimedone, ethyl cyanoacetate, ethyl acetoacetate, barbituric acid, and thiobarbituric acid is reported. The protocol was developed using water extract of mango peel ash (WEMPA), an agro-waste that emerged as a greener solvent media and in combination with microwave irradiation gave high-yield product isolation. The method noticed added advantages for the reaction faster reaction rate, inexpensive extract media, simple work-up, and not required chromatographic puri-fication. The present method synthesized various Knoevenagel condensation derivatives benzyli-dinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid, and 5,5-dimethylcyclohexane-1,3-diones were character-ized by FT-IR, 1H- &amp; 13C-NMR, and mass spectrometry. Further, selected derivatives were inves-tigated for their electrochemical studies using cyclic voltammetry, and showed comparable oxida-tion and reduction potential properties. Objective: The objective of this work is to develop a green methodology synthesis of various active methylene derivatives via Knoevenagel condensation to give the product of benzylidine-malononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5-dimethylcyclohexane-1,3-diones. Methods: We have demonstrated WEMPA as a greener homogenous agro-waste catalytic medi-um for the economic synthesis of Knoevenagel condensation products. The developed method was found robust, non-toxic and solvent-free with a simple work-up to give the target product. The selected derivatives were investigated for their electrochemical studies using the cyclic volt-ammetry method. Results: The agro-waste-based catalyst developed avoids the use of the external organic or inor-ganic base for the Knoevenagel condensation reaction under microwave irradiation. The de-scribed method found faster, eco-friendly, simple filtration and recrystallization excellent yield, and purity of the Knoevenagel product. Further, the selected compounds (8a-8d, 9a- 9d, 10a-10d, 11a,-11c, 12a, 12b, and 13a-13c) were subjected to electrochemical behavior studies and showed good oxidation and reduction properties. Conclusion: In summary, we have established an efficient, simple, inexpensive agro-waste based catalytic approach for the synthesis of benzylidinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5-dimethylcyclohexane-1,3-diones derivatives under microwave irradiation described. The catalyst is agro-waste derived, which is abundant in nature and recyclable without loss of activity after the four-run of the reaction, thus making the present approach a greener one. The advantages of the approach are inexpensive, chemical base free, requiring no external metal catalyst, short reaction time, and simple work-up isolated excellent yields of the product. For the first time, herein, we reported the electrochemical behavior of the products prepared, and showed good oxidation and reduction properties, and these molecules will emerge as good antioxidant agents. other: NA

Temperature- and Pressure-Reducing Regimes in the Growth Cell of HPHT Diamonds, Optimal for Preserving Crystal Integrity after Growth Completion

With its exceptional strength characteristics, diamond has some mechanical drawbacks, significant brittleness being among them. In particular, some HPHT-grown diamonds crack when the extreme parameters inherent to the diamond growth process gradually decrease. The cracking is caused by excessive stress due to the poor plastic properties of the diamond growth catalytic medium at certain stages of reducing the pressure and the temperature. An insulating container with the growth cell and heating circuit fragment inside can also make a significant contribution to the probability of cracking. This paper considers the possibility of minimizing the mechanical stress in the growth cell and, consequently, in the diamond crystal by choosing the optimal trajectory for the decrease in the pressure and temperature from diamond growth conditions to normal conditions.

High-performance ZnIn2S4/Ni(dmgH)2 for photocatalytic hydrogen evolution: Ion exchange construction, photocorrosion mitigation, and efficiency enhancement by photochromic effect

In this work, a novel photocatalyst of ZnIn2S4/Ni(dmgH)2 was designed by a simple chemical precipitation method and used to enhance hydrogen evolution under visible light irradiation. Along with vigorous discharges of hydrogen bubbles, an optimal rate of 36.3 mmol/g/h was reached under UV–Vis light for hydrogen evolution, nearly 4.9 times of the one from pure ZnIn2S4. The heterojunction exhibits steady hydrogen evolution capability and owns a high apparent quantum efficiency (AQE) of 20.45% under the monochromatic light at 420 nm. By coupling ZnIn2S4 with Ni(dmgH)2, an extraordinary photochromic phenomenon was detected and attributed to the active Ni-S component in situ formed between the nickel and sulfur composites under light irradiation. The emerging sulfide benefits light absorption of the system and separation of photogenerated electron and hole pairs. Besides providing a promising photocatalyst for visible light hydrogen production, the present work is hoped to inspire new trends of catalytic medium designs and investigations.

An Agro-Waste Catalyzed Facile Synthesis of 1H-Pyrazolo[1,2-b]Phthalazine-5,10-Dione Derivatives: Evaluation of Antioxidant and Electrochemical Studies

Rapid and inexpensive one-pot multicomponent synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione through a condensation reaction of aryl aldehyde, malononitrile or ethyl cyanoacetate and phthalhydrazide catalyzed by water extract of papaya bark ash (WEPBA) solvent medium under microwave irradiation is described. The catalytic medium is used environmentally friendly, and provides several benefits of being simple, inexpensive, high yield, simple work-up and not required hazardous solvent for the reaction. Some of the selected derivatives were characterized by FT-IR, 1H-, and 13C-NMR, and mass spectrometry techniques. The oxidation-reduction properties of the synthesized compounds (4b, 4e, 4f, 4i, and 4k and 6f, 6g, 6h, 6i, and 6j) were studied using cyclic voltammetry (CV). The voltammetry peak current for the oxidation-reduction of the compounds examined at different scan rates. Further, some of the selected 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives were evaluated in vitro antioxidant activity using DPPH assay method. The result appears that, compounds 4b, 4e, 4i, 6f, 6g, and 6h possess significant antioxidant properties in comparison with the ascorbic acid reference.

Concise nanotherapeutic modality for cancer involving graphene oxide dots in conjunction with ascorbic acid.

Cancer cells tend to have higher intracellular reactive oxygen species (ROS) levels and are more vulnerable to ROS-generating therapies such as ascorbic acid (H2Asc) therapy, whose potency has been explored by several clinical trials. However, its efficiency is restricted by the requirement of pharmacologically high local H2Asc concentrations. Here, we show that nitrogen-doped graphene oxide dots (NGODs), which are highly crystalline and biocompatible, can serve as a catalytic medium for improving H2Asc cancer therapy at orally achievable physiological H2Asc concentrations. NGODs catalyze H2Asc oxidation for H2O2 and dehydroascorbic acid generation to disrupt cancer cells by consuming intracellular glutathione (GSH) and inducing ROS damage. This is the first study to demonstrate the direct consumption of GSH using a carbon-based nano-catalyst (NGODs), which further expedites tumor killing. In addition, as in our previous study, NGODs can also serve as a highly efficient photosensitizer for photodynamic therapy. Under illumination, NGODs produce a considerable amount of H2O2 in the presence of physiological levels of H2Asc as a hole scavenger and further enhance the therapeutic efficiency. Thus, a concise nanotherapeutic modality could be achieved through the conjunction of multifunctional NGODs and H2Asc to selectively eliminate deep-seated and superficial tumors simultaneously (under 65% of normal cell viability, it kills almost all cancer cells). Note that this level of therapeutic versatility generally requires multiple components and complex manufacturing processes that run into difficulties with FDA regulations and clinical applications. In this study, the concise NGOD-H2Asc nanotherapeutic modality has demonstrated its great potential in cancer therapy.

Investigation of the reaction mechanism regarding thermal treatment of biomass using molten salts: A kinetic study of small molecule gases formation

The conversion of biomass to produce high-valued fuel is an important way to improve the utilization rate of biomass energy. For the coupled utilization of solar energy and biomass, molten salts are used as heat storage and catalytic medium to convert biomass into combustible gases. To balance the supply of energy storage with the energy consumption for biomass conversion, the reaction mechanism regarding thermal treatment of biomass using molten salts is studied in the present research. The thermal treatment reactor combined with an online mass spectrometry is employed to characterize the gases release behavior of typical biomass components and actual biomass. In addition, a kinetic model of gas released from beech wood pyrolysis in molten salts was constructed by pyrolysis unit reactions of three typical components. The experimental results showed that molten salts can enhance the yields of small molecule gases compared to conventional pyrolysis process. For the relevance of gas release kinetics between biomass and three components, the results showed a good agreement between simulated curves and experimental data. The release of CO and H2 was mainly from the pyrolysis of lignin, CO2 was mainly from the pyrolysis of cellulose, and CH4 was mainly from the pyrolysis of both hemicellulose and cellulose. In addition, the gas release characteristics of beech wood were similar to those of the lignin, which played a leading role in the gas release of actual biomass pyrolysis.

Emergent dynamics of light-induced active colloids probed by XPCS

Self-propelled particulate systems manifest certain collective behavior of living matter, which have been the subject of intense research over the past decades. One of the elegant methods for realizing such active motions is by means of custom synthesized Janus particles suspended in a catalytic medium that can be triggered upon illumination by ultraviolet light. In this work, the evolution of the particle dynamics from passive diffusive to active ballistic behavior upon light illumination was probed by multispeckle x-ray photon correlation spectroscopy (XPCS). This technique enables not only studying the emergence of active motions in three dimensions (3D) but also deciphering different contributions to the overall dynamics. Using a combination of homodyne and heterodyne analysis, the ensemble averaged mean velocity, velocity fluctuations and diffusion coefficient of particles were determined in the thermodynamic limit. Results revealed a gradual transition from diffusive to ballistic dynamics with systematic increase of the catalytic activity. At the intermediate region, the dynamics is dominated by Gaussian velocity fluctuations and an enhanced relaxation rate with a weaker wave vector dependence similar to superdiffusive behavior. For the highest activity, the dynamics became purely ballistic with Lorentzian-like distribution of velocity fluctuations. Presented results demonstrate that different aspects of active dynamics can be investigated in 3D over a broad range of Péclet numbers and other control parameters by means of multispeckle XPCS.

H2O2 formation mechanisms on the (1 1 2) and (3 1 0) facets of SnO2 via water oxidation reaction with the participation of Bicarbonate: DFT and experimental Investigations

The H2O2 formation mechanisms on the (112) and (310) facets of SnO2 via the water oxidation reaction (WOR) with participation of bicarbonate are investigated by density functional theory calculations and electrochemical measurements. Both computational and experimental results show that H2O2 generation is hindered on the surfaces of SnO2 in the absence of HCO3 species. In contrast, more H2O2 is detected for SnO2 films tested in HCO3− aqueous solution than those measured in non-bicarbonate electrolyte. Nevertheless, our kinetic simulations suggest that the co-adsorption of HCO3 species adjacent to H2O on the (112) and (310) surfaces of SnO2 do not effectively promote the two-electron WOR to form H2O2. Considering that the H2O2 production scales linearly with the concentration of HCO3−, bicarbonate is likely to directly participate in the process of H2O2 generation as a catalytic medium. That is, the mechanism that H2O2 is formed through the hydrolyzation of HCO4− that is produced by the peroxidation of HCO3− is likely. Our calculations show that H2O2 is formed through this route on both (112) and (310) facets of SnO2. In addition, the (112) surface of SnO2 is kinetically favored for H2O2 generation compared to the (310) facet.

Evaluation of CO2 as an Acid Catalyst Precursor for Promoting a Nitrogen-Generating System

Summary Nitrogen-generating systems (NGSs) are mainly used in the oil industry to fluidize low melting point organic deposits and gas hydrate buildups. They are exothermic reactions between two nitrogenous salts in acidic catalytic media. This work investigates the use of CO2 to promote NGS reactions instead of commonly used acids such as acetic and citric acids, which can be problematic for corrosion control. Sodium nitrite and ammonium chloride were the reactants, and CO2 performance was evaluated for up to 4 hours at 5 and 25°C, and either under autogenous pressure at 10, 25, and 50 bar of CO2 or pressurized at 10 bar of CO2 by adding 40 bar of nitrogen (totaling 50 bar). The nitrite conversion was determined by measuring the concentration of residual nitrite using titration. Thus, it was verified that the CO2 effectively promoted the NGS at various experimental conditions. The nitrite conversion increased with increasing CO2 pressure and increasing temperature. Moreover, the nitrite conversion was enhanced in the pressurized system (PS) because the high pressure enabled the dissolution of CO2 in the aqueous medium, and therefore, the constant formation of carbonic acid, favoring the acidic catalytic medium at the reaction. This advantage was confirmed by carrying out an NGS catalyzed by acetic acid, in which the pH increases as reagents are consumed, and therefore, a lower nitrite conversion is achieved. The use of CO2 also converts the NGS in a process more suitable for flow assurance applications in offshore oil production, particularly in the Brazilian presalt fields where the coproduced CO2 can be used.

Catalytic Methods for the Production of Sugar Esters

Nowadays, Sugar esters (SEs) have become the focus of researchers due to their biocompatibility and extensive industrial applications as surfactants. This trend provides new methods and opportunities for the development of green synthetic chemistry. Taking the above into consideration, a critical review presented in this work emphasized the efficiency of catalyzing the synthesis of SEs with minimal hazardous by-products. These catalytic media have been employed with various impacts involving chemical, biological, and other catalytic materials. Chemical methods have been reported to show limitations in terms of preparation and bio-compatibility. To solve these shortcomings, therefore, other technologies have been adopted; ionic liquids (eutectic solvents), chemo-enzymatic systems and chemo-enzymatic systems on a catalytic surface. The use of chemo-enzymatic systems on catalytic surfaces has proved to be suitable in solving biocompatibility and stability problems and correspondingly increasing the yield of esters formed. Therefore, finding an improved catalytic surface, and the sustainable optimal reaction conditions for enzymes will be vital to improving sugar ester conversion. This study highlights the different catalytic advances employed in the esterification of SEs.

Tomato fruit extract: an environmentally benign catalytic medium for the synthesis of isoxazoles derivatives

One-pot multicomponent reaction between aromatic aldehyde, hydroxylamine hydrochloride and ethyl acetoacetate/methyl acetoacetate for the synthesis of isoxazoles derivatives by employing tomato fruit extract as a catalytic medium has been developed. Tomato fruit extract was found to be a favorable catalytic medium for the synthesis of titled compounds. Mild reaction condition, ease of separation, moderate to high yield of the product, and short reaction time makes this method more attractive over earlier reported methods for the synthesis of isoxazoles derivatives.