Absence Of Catalyst Research Articles

Methanol‐Mediated One‐Pot Transformation of Benzonitriles to Five and Six‐Membered Heterocycles: Synthesis and Mechanistic Approach

AbstractHerein we describe a facile methodology for the synthesis of heterocyclic molecules such as 2‐aryl‐substituted imidazolines, oxazolines and 1,4,5,6‐tetrahydropyrimidines, under one‐pot and metal‐free conditions. A series of electron‐poor substituted benzonitriles were used as starting materials with different available diamines and amino alcohols, producing the desired products in good to high yields within methanol and in the absence of catalyst or additives. This methodology can be easily scaled up to laboratory size of 3 mmol for both five‐ and six‐membered heterocycles. Detailed mechanistic and theoretical studies supported the dual role of methanolic media as solvent and as mediated agent. To shed light on the reaction mechanism, DFT mechanistic studies suggest a distinction in the first step, with the activation of the nitrile by methanol, and the formation of a benzimidamide and/or a benzimidate (observed by NMR) as intermediates. This facile synthetic procedure provides a green, metal‐free, and mild protocol for the synthesis of a series of imidazoline, oxazoline and tetrahydropyrimidine derivatives.

The phosphodiester dissociative hydrolysis of a DNA model promoted by metal dications.

Phosphodiester bonds, which form the backbone of DNA, are highly stable in the absence of catalysts. This stability is crucial for maintaining the integrity of genetic information. However, when exposed to catalytic agents, these bonds become susceptible to cleavage. In this study, we investigated the role of different metal dications (Ca2⁺, Mg2⁺, Zn2⁺, Mn2⁺, and Cu2⁺) in promoting the hydrolysis of phosphodiester bonds. A minimal DNA model was constructed using two pyrimidine nucleobases (cytosine and thymine), two deoxyribose units, one phosphate group, and one metallic dication coordinated by six water molecules. The results highlight that Cu2⁺ is the most efficient in lowering the energy barrier for bond cleavage, with an energy barrier of 183kJ/mol, compared to higher barriers for metals like Zn2⁺ (202kJ/mol), Mn2⁺ (202kJ/mol), Mg2⁺ (210kJ/mol), and Ca2⁺ (223kJ/mol). Understanding the interaction between these metal ions and phosphodiester bonds offers insight into DNA stability and organic data storage systems. DFT calculations were employed using Gaussian 16 software, applying the B3LYP hybrid functional with def2-SVP basis sets and GD3BJ dispersion corrections. Full geometry optimizations were performed for the initial and transition states, followed by identifying energy barriers associated with phosphodiester bond cleavage. The optimization criteria included maximum force, root-mean-square force, displacement, and energy convergence thresholds.

Production of High-Value Green Chemicals via Catalytic Fast Pyrolysis of Eucalyptus urograndis Forest Residues

Lately, pyrolysis has attracted significant attention due to its substantial potential for bio-oil production, with the ability to serve as a renewable energy source and/or facilitate the production of valuable chemical compounds. The chemical compounds generated and their amounts are completely influenced by the traits and chemical makeup of the initial biomass. In this work, the catalytic fast pyrolysis of Eucalyptus urograndis canopy was carried out using a pyrolyzer coupled to gas chromatography/mass spectrometry (Py-GC/MS) at different temperatures and in the presence and absence of catalysts. Elemental composition analysis was employed to characterize the chemical composition of the biomass. The results showed a biomass with a carbon percentage of 50.20%, oxygen of 43.21%, and hydrogen of 6.34%, as well as a lower calorific power of 17.51 MJ/kg. The Py-GC/MS analyses revealed the presence of several noteworthy compounds, including acetic acid (C2H4O2) and, in smaller quantities, hydrogen (H2), furfural (C5H4O2), and levoglucosan (C6H10O5). The technical-economic evaluation revealed that the production of acetic acid, furfural, hydrogen, and levoglucosan commands a high market price. Additionally, a single production cycle is anticipated to yield a favorable technical-economic balance, generating approximately USD 466.10 /ton of processed biomass. This outcome is achieved through the process of catalytic fast pyrolysis, where CuO has been identified as the most suitable catalyst.

Enhancing nanoplastics removal by metal ion-catalyzed ozonation

Nanoplastics (NPs), characterized by sizes < 1 µm, are not completely removed in conventional drinking water treatment plants affecting human health. Catalytic ozonation appears as a promising alternative due to its ability to oxidize emerging pollutants by generating hydroxyl radicals with higher removal rate and mineralization than single ozonation. In this work, catalytic ozonation was investigated for the removal of polystyrene nanoplastics (PSNPs) by employing transition metal ion catalysts, Fe3+, Co2+, Ni2+, and Zn2+. The single ozonation of PSNPs, in the absence of catalyst, led to low turbidity reduction (33 %) and low mineralization rate (16 %) even after 2 h reaction time. Nevertheless, the rapid size reduction of PSNPs by >99 % in less than 5 min of ozonation (TOD: 30 mg L−1) was confirmed. This fact could imply a new issue under the ozone disinfection conditions by the formation of smaller-size particles. However, in the presence of Co2+ (1 mM), the highest PSNPs ozonation performance was achieved, decreasing the turbidity up to 65 % and achieving 70 % of mineralization in the same ozonation time. The scavenger experiments with methanol confirmed that direct ozonation and catalyst role were responsible for PSNPs degradation, with the generation of •OH being the most dominant catalytic mechanism. Therefore, although single ozonation at disinfection doses reduced the particle size of PSNPs, the catalytic process demonstrated greater efficacy in the total removal of PSNPs. These results highlight the need to further investigate ozonation of NPs intermediates, and the synergic improvements of catalytic ozonation for their mineralization.

Diarylformamides as a safe reservoir and room temperature source of ultra-pure CO for a 'green' rWGS reaction.

Diarylformamides are shown to be a safe reservoir and source of CO. Perfectly selective decarbonylation is achieved in solution at room temperature with potassium and cesium diarylamide catalysts. Moreover,solvent-freedecarbonylations may be run either in a diphenylformamide melt at 70 ºC or, when the bisformamide9is used, in thesolid stateat 88 ºC in virtue of its improved atom economy. These These simple and practicaltransition-metal-freereactions afford ultra-pure (i.e.dry and solvent-free) CO at moderate temperatures and the byproduct diarylamines are recycled as pure compounds. In the absence of catalysts, diarylformamides1and9are long-term stable at > 200 ºC.DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph2NC(O)H and a barrier-free CO elimination from Ph2NC(O)-.

Visible‐Light‐Mediated Catalyst and Additive‐Free C(sp3)‐H Phosphorylation of Glycine Ester Derivatives

AbstractWe herein report a visible light induced dehydrogenative phosphonylation reaction of glycine derivatives and di‐aryl phosphine oxides. A diverse range of phosphine‐glycine derivatives were constructed under ambient condition in the absence of catalyst and additives. A plausible mechanism was also proposed.

Tannic Acid-Decorated Bimetallic Copper-Gold Nanoparticles with High Catalytic Activity for the Degradation of 4-Nitrophenol and Rhodamine B.

In this study, tannic acid (TA) was applied as a stabilizing agent for synthesizing bimetallic copper-gold (CuAu) nanoparticles. Cu(NO3)2 and NaAuCl4 were used as the sources of copper and gold ions, respectively, and NaBH4 was employed as a reducing agent. The prepared TA-CuAu nanoparticles were extensively characterized via ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction, and zeta potential analyses. To evaluate their catalytic activity, the TA-CuAu nanoparticles and NaBH4 were applied in the degradation of 4-nitrophenol (4-NP) and rhodamine B (RB) individually and in a mixture. The individual degradation of 4-NP and RB was completed within 10 min, and the apparent rate constants were calculated as 0.3046 and 0.2628 min-1, respectively, emphasizing the efficient catalytic activity of the TA-CuAu nanoparticles. Additionally, controlled experiments were performed for the degradation of 4-NP and RB in the absence of catalysts or NaBH4 to investigate the kinetic feasibility of the catalytic reactions. A mixture of 4-NP and RB was successfully degraded within 10 min using the TA-CuAu nanoparticles as catalysts. Furthermore, the reuse of the catalysts after five successive cycles demonstrates an outstanding performance with no significant loss in the catalytic activity. Finally, the successful treatment of the tap and lake water samples spiked with 4-NP and RB using the TA-CuAu nanoparticles further confirmed their application potential as catalysts in environmental water remediation.

Co–B supported on waxberry-like hierarchical porous carbon microspheres: An efficient catalyst for hydrogen generation via sodium borohydride hydrolysis

Rapid release of hydrogen at ambient condition is highly favorable and is necessary for fuel cell power generation on-demand. Hydrolysis of hydrides offers such advantage with sodium borohydride (NaBH4) as a representative exemplar. Despite with exceptionally high hydrogen content, the hydrolysis kinetics of NaBH4 is sluggish in the absence of catalyst. Co–B alloy has generally been employed as effective catalyst in the hydrolysis of borohydrides. However, Co–B particles are prone to agglomeration during the reaction, reducing the activity and durability of the catalyst. In this work, waxberry-like hierarchical porous carbon microspheres (HPCMs) were successfully prepared and were used as carriers to support Co–B particles to form the Co–B/HPCMs catalyst. The effects of HPCMs with different nitrogen contents in Co–B/HPCMs on the catalytic dehydrogenation rate of NaBH4 hydrolysis were systematically investigated. The experimental results showed that Co–B/HPCM-2 exhibited excellent catalytic activity in the hydrolysis of NaBH4 at 298 K, with a low activation energy of 43.3 kJ ·mol−1 and a high hydrogen generation rate of 3083.1 mlH2·min−1·g−1. Moreover, after five consecutive cycles, its catalytic activity maintained at 91.7 % of the initial catalytic activity, displaying satisfactory cycling performance. The findings obtained from this study are expected to expand a novel path for the development of efficient Co-based catalysts in heterogeneous catalytic reactions.

Studies on catalyst assisted low-temperature curing of benzoxazines

The present study addresses an increasing interest in achieving low-temperature curing of benzoxazines by utilizing chemical substances with acid moieties of varying functionalities as curing catalysts. Specifically, cardanol-furfurylamine (1), card-bisphenol-furfurylamine (2), bisphenol-A-aniline (3) and bisphenol-F-aniline (4) based benzoxazines were chosen for curing studies. The selected catalysts were systematically applied into benzoxazines and its curing behavior was studied with minimum amount of 5 wt%. Catalysts, including those with carboxyl and N,N-dimethyl functionalities, were evaluated based on their performance, with a focus on their substituent effect on curing behavior. The results contribute to the identification of catalysts with optimal potential for achieving the efficient low-temperature curing of benzoxazines with an objective of utilizing them for wide area of applications. Among the catalysts studied, gallic acid was found to be the better catalyst and reduces the curing temperature to 130 °C. The conversion graph for both bisphenol-A-aniline benzoxazine (3) in the absence of catalysts and bisphenol-A-aniline benzoxazine in the presence of catalysts (3 s) have been studied by DSC analysis. The activation energy (Ea) has been calculated using Kissinger-Ozawa method through DSC analysis. Data resulted from different catalysts used for curing of benzoxazines, it was inferred that the pKa values of the catalysts also play a crucial role in the polymerization of benzoxazines. Further, the study aims to meet the growing demand for efficient and economically viable low-temperature curing processes for benzoxazines.

Catalyst-Free Cardanol-Based Epoxy Vitrimers for Self-Healing, Shape Memory, and Recyclable Materials.

Bio-based vitrimers present a promising solution to the issues associated with non-renewable and non-recyclable attributes of traditional thermosetting resins, showcasing extensive potential for diverse applications. However, their broader adoption has been hindered by the requirement for catalyst inclusion during the synthesis process. In this study, a cardanol-based curing agent with poly-hydroxy and tertiary amine structures was prepared by a clean synthetic method under the theory of click chemistry. The reaction of a cardanol-based curing agent with diglycidyl ether of bisphenol A formed catalyst-free, self-healing, and recyclable bio-based vitrimers. The poly-hydroxy and tertiary amine structures in the vitrimers promoted the curing of epoxy-carboxylic acid in the cross-linked network and served as internal catalysts of dynamic transesterification. In the absence of catalysts, the vitrimers network can achieve topological network rearrangement through dynamic transesterification, exhibiting excellent reprocessing performance. Moreover, the vitrimers exhibited faster stress relaxation (1500 s at 180 °C), lower activation energy (92.29 kJ·mol-1) and the tensile strength of the recycled material reached almost 100% of the original sample. This work offers a new method for preparing cardanol-based epoxy vitrimers that be used to make coatings, hydrogels, biomaterials, adhesives, and commodity plastics in the future.

Self-extinguishable, intumescent poly(urethane-triazole)s as halogen-free flame retardant materials via bulk polymerization of azide-alkynes

In the present study, an unexplored class of non-halogenated self-extinguishable and intumescent phosphorous-based poly(urethane-triazole)s (P-PUTs) were achieved through the bulk polymerization of azide-alkynes notably in absence of catalyst. A series of azide-functionalized urethane monomers (tetra azides) were synthesized by the reaction of 1,3-diazido-propan-2-ol with commonly used, but three structurally different diisocyanates, viz, aliphatic, alicyclic, and aromatic. Concurrently, a dialkyne, phenyl di-prop-2-ynyl phosphonate was synthesized and co-polymerized with these urethane tetrazides through bulk polymerization at 80 °C. The curing kinetics of the polymerization was monitored by differential scanning calorimetry (DSC) under non-isothermal conditions with different heating ramps. Thermal behaviour, elemental and morphological properties of the synthesized P-PUTs were comprehensively investigated employing thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX), respectively. The flame retardant properties of P-PUTs were assessed by UL–94 vertical burning test, limiting oxygen index (LOI) and lab-scale flammability test. All the P-PUT compositions were found to self-extinguish immediately after the removal of flame with a V-0 rating of UL-94 V, the LOI value (vol%) are 26.3 %, 28.2 % and 29.0 % for H2P-PUT, I2P-PUT and T2P-PUT, respectively and the corresponding char yields were 26.03 wt%, 25.76 wt% and 39.58 wt% along with significant intumescence. This apart, the films with a transparency of 96.5 %, 96.7 % and 94.3 % in the visible wavelength for H2P-PUT, I2P-PUT and T2P-PUT, respectively, can possibly make these P-PUTs materials attractive as fire retardant top coats on wood substrates.

Electrochemical decarboxylative alkylation of β-ketoacids with phenol derivatives.

An electrochemical method for the decarboxylative alkylation of β-ketoacids with phenol derivatives has been developed. The protocol was carried out in readily available unseparated cells at room temperature in the absence of catalysts and oxidants. The corresponding aryl ketones were obtained in satisfactory yields without additional electrolytes, and were easy to produce in gram-scale synthesis. Based on control experiments and cyclic voltammetry, a plausible reaction mechanism was proposed.

Direct amidation of 1-aryl-2,2,2-trifluoroethanones with isothiocyanates via C–C bond cleavage strategy

A facile synthesis of N-aryl amides through the direct amidation of 1-aryl-2,2,2-trifluoroethanones with isothiocyanates in the absence of catalysts and activating reagents has been developed. This reaction allows for the selective cleavage of the C(O)−C bond in 1-aryl-2,2,2-trifluoroethanones under the promotion of base, and exhibits broad substrate scope and high functional group tolerance.

H2 generation from aqueous ethanol over ZnO nanowires, the photo-transformation of surface species

ZnO nanowires (NWs) with wurzite structure and a very high [0001] preferred orientation were grown on a ZnO thin film, from a gas-solid process, in the absence of catalyst. ZnO NWs were characterized by FESEM, XRD, HRTEM, XPS, PL and Raman spectroscopy and used as photocatalysts for the photo-transformation of ethanol(aq) in the gas phase. The existence of different defects such as oxygen vacancies was evidenced. The photocatalytic process was followed by in-situ diffuse reflectance infrared spectroscopy (DRIFTS) coupled to on-line mass spectrometry (MS) analysis. The surface species determined during the irradiation (λ = 365 nm) of ZnO NWs under ethanol/water vapor flow at room temperature are related with the hydrogen production and carbon-containing products evolved.

Crosslinked poly(hydroxyurethane) films from biobased carbonates: Structure-properties relationships and the influence of moisture in the mechanical properties

In this work, crosslinked poly(hydroxyurethane) (PHU) films were prepared by the reaction of biobased cyclic carbonates (BisCC), with different chain lengths, with hyperbranched poly(ethyleneimine) (PEI) under amenable conditions and in the absence of catalysts. Fourier transform infrared (FTIR) spectroscopy revealed that the carbonate groups were completely consumed in the crosslinking reaction and the gel content of the films was about 99 %. It was shown that the thermal and mechanical properties of the PHU films depended on the length of the carbon chain of the BisCC. In the presence of moist environment, the PHU films absorbed moisture (6–8 %) which is ascribed to the presence of hydroxyl groups. This resulted in a deterioration of the mechanical properties, which were not completely recovered after drying. To counteract this effect, a simple procedure was used in which the hydroxyl groups on the surface were modified by stearate groups. Although FTIR and water contact angle measurements demonstrated that the films of PHU became more hydrophobic after modification, the water absorption capacity was similar to that of the unmodified PHU films. This suggests that the modification process may cause some degradation in the bulk of the material that opens spaces for water molecules penetration.In summary, this work has shed light for the first time on the effects of moisture on the mechanical properties of pure PHU films and has shown that surface modifications are not sufficient to prevent moisture absorption.

CO2 reduction employing MgH2 for CH4–H2 mixtures production through mechano-chemical processes

The CO2 methanation employing MgH2 as a source of hydrogen is investigated via mechano-chemical processes through ball milling at room temperature under different experimental conditions such as the presence/absence of catalyst, the milling duration, the molar ratio between the hydride and CO2 and the pre-milling of Ni–MgH2 mixture. The positive effect of Ni addition is demonstrated. After 5h of milling under CO2, the absence of catalyst causes the CH4 yield to drop from 70.0 to 59.0%, from 73.0 to 33.5% and from 54.0 to 40.1%, considering molar ratios of 4:1, 3:1 and 2:1, respectively. The pre-milling of nickel-catalyzed system or the addition of CNTs do not provide significant improvements. This investigation shows that similar methane yields to those obtained by thermo-chemical methods can be achieved, but involving shorter times (5 h versus 24 h) and lower temperatures (room temperature versus 400 °C). The ball collisions during milling allow overcoming passivation phenomena of MgH2 and Mg, promoting the methanation process but with lower selectivity as contamination with Fe from the milling jar provides a catalytic alternative route for the generation of C2–C3 hydrocarbons.

Synthesis of Two Isomers of pyrido/benzo[b][1,4]selenazines: A Selective Catalyst‐Dependent Formation of C−N and C‐Se Bonds

AbstractThis work describes the selective synthesis of a series of pyrido/benzo‐fused 1,4‐selenazines, through the reaction of bis(3‐amino‐2‐pyridyl) or bis(2‐aminophenyl) diselenides with different β‐dicarbonyl compounds. When molecular I2 was used as catalyst, a series of (Z)‐1‐(1H‐pyrido[2,3‐b][1,4]selenazin‐2(3H)‐ylidene)propan‐2‐ones were obtained. On the other hand, in the absence of catalyst, 1‐(2‐methyl‐1H‐pyrido[2,3‐b][1,4]selenazin‐3‐yl)ethan‐1‐ones could be prepared selectively. The structure of the prepared compounds was elucidated by NMR and HRMS analysis and confirmed by single crystal X‐ray diffraction. The versatility of the protocol was demonstrated not only by the access to a variety of 1,4‐selenazine derivatives, but also by the structural diversity in the 1,3‐dicarbonyl precursors, incorporating multifunctionalities in the synthesized heterocycles.

A comprehensive insight on plasma-catalytic degradation of organic pollutants in water: Comparison between ZnO and TiO2

A novel system combining underwater plasma bubbles and high voltage nanopulses was combined for the first time with ZnO and TiO2 for the degradation of organic pollutants in water. The effect of catalyst loading, discharge power and plasma gas on pollutant degradation was investigated whereas the plasma-catalytic mechanism was explored through the quantification of plasma species, COD/TOC measurements and scavenging experiments in the presence and absence of catalysts. The increased efficiency in the presence of either ZnO or TiO2, especially under plasma gases (air and oxygen) able to produce UV radiation in the range of wavelengths absorbed by both catalysts, lies on the increased concentration of the critical reactive species (e.g. ·O2−, ·ΟΗ, H2O2). Compared to plasma alone process, H2O2 was significantly enhanced in the presence of TiO2 and decreased in the presence of ZnO, whereas ·OH concentration was higher in the plasma-ZnO but lower in the plasma-TiO2 system which supports the overall superior performance of ZnO compared to TiO2. The synergy of plasma-ZnO process compared to that of plasma-TiO2 was ∼2.4 and ∼1.5 times higher for Orange II (OII) and Methylene Blue (MB), respectively, exhibiting a very low electrical energy per order (1.4 kWh m−3 for OII and 0.31 kWh m−3 or MB). The present effort contributes on providing fundamental insights and further expand of plasma-catalysis for water treatment.

LNG 이종연료 운전이 상업용 디젤 엔진의 출력 및 배출가스 특성에 미치는 영향

In order to additionally supply LNG to a heavy-duty commercial diesel engine, a dual fuel system was installed; engine power and exhaust gas emissions while operating in the ‘ND-13 mode’, in accordance with the notice from the Ministry of Environment, were investigated. The feasibility of retrofitting the dual fuel system and plans based on mixture rate, power, and emission reduction to enable commercialization were evaluated. The engine power and torque values were within ±5% of the values for the existing engine; these were within the legal modification range. In case of exhaust gas emissions, the decrease in CO 2 emission due to the increase in load was apparent; it was reduced by 15.3%. NO X emission decreased by 58%; this could be attributed to the decrease in combustion temperature owing to water injection. THC and CO increased significantly, possibly due to the reduced combustibility of natural gas owing to bulk quenching, water injection, and the absence of catalysts. Additional research focused on modification of mapping values and installation of oxidation catalysts to improve the combustion performance of the system, is warranted.

A versatile approach for one-pot synthesis of hybridized quinolines linked to fused N-containing heterocycles in water.

Here, highly efficient one-pot protocols for the synthesis of structurally diverse fused N-containing heterocycles containing 2-chloroquinoline employing 1,1-bis(methylsulfanyl)-2-nitroethene, diamines, 2-chloroquinoline-3-carbaldehydes and dimedone/Meldrum's acid in green media in the absence of catalyst are reported. The current report proposes sustainable, simple, four-component and straightforward strategies for generating interesting N-containing heterocyclic compounds from a range of diamines and 2-chloroquinoline-3-carbaldehydes. The utilization of water as green media furnishes sustainability by preventing the usage of toxic solvent. A range of quinoline-containing aldehydes and diamines can be converted to two types of products with respect to using dimedone or Meldrum's acid via an inexpensive, one-pot and easy route.