Catalyst For Condensation Research Articles

Synthesis, characterization, and novel reactivity of nano CeO2 catalyst for solvent-free Knoevenagel condensation

We synthesized the nano CeO2 using the sol-gel method and characterized the material using different techniques, including XRD, FT-IR, BET surface area, SEM, and TEM analysis. We tested the catalytic functionalities of nano CeO2 catalyst for Knoevengel condensation of different substituted benzaldehydes with malononitrile, which offered exceptional 95 % conversion and yield. The results support that nano CeO2 material significantly boosted the yield of the desired product compared to the bulk material. The low-angle XRD profile showed that the regenerated nanomaterial fully retained the porous nature and cubic structure of ceria. FT-IR results reveal that the characteristic vibrational IR band is at 720 cm−1, which is attributed to Ce–O–Ce stretching. The BET surface area result indicates that nano-ceria possesses a higher surface area than bulk CeO2 material. The SEM analysis illustrates cube-like morphology and TEM data show the nanorod-like appearance of ceria. The nanocatalyst exhibited stable and sustainable activity during regeneration up to 5 cycles.

Polyethylene glycol promoted Cs/Zr-SiO2 bifunctional catalyst for aldol condensation of methyl propionate and formaldehyde to methyl methacrylate

The production of methyl methacrylate (MMA) via one-step gaseous aldol condensation of methyl propionate (MP) and formaldehyde (FA) has received wide attention. Herein, series of polyethylene glycol (PEG) promoted Cs-Zr/SiO2 catalysts were developed and characterized by XRD, FT-IR, HR-TEM, BET, NH3–/CO2-TPD and Py-IR etc. The dispersion of active acid and base sites and their balance in catalyst could be significantly improved with the addition of PEG, which facilitated the activation of reactants and conversion towards product MMA. Furthermore, the relationship between the acid-base properties and catalytic performance was revealed, the acid and base sites were responsible for the decomposition of trioxane, which was used as the source of FA, and transformation of MP, respectively. The in-situ DRIFTS experiments unraveled two catalytic pathways through the synergistic effects between the acid and base sites during the aldol condensation of MP with FA to MMA. Kinetic studies revealed that the activation energy of this aldol condensation on the optimal catalyst is 97.9 kJ/mol, with the reaction order of 0.98 and 1.18 corresponding to MP and FA. Deactivation behavior studies demonstrated that the decrease of catalytic activity as a function of time-on-stream was resulting from the deposition of predominant amorphous carbon instead of the loss of active components.

PEG-assisted synthesis of highly dispersed Cs/Zr-SiO2 catalyst for aldol condensation of methyl acetate with formaldehyde

The dispersion of active sites plays an imperative role in the promotion of catalytic performance on methyl acrylate synthesis via direct vaporous aldol condensation. Herein, a novel PEG-assisted impregnation method was proposed to synthesize Cs/Zr-SiO2 catalyst with high dispersion of acid and base sites. A series of characterization techniques including NMR, TEM, physical N2 adsorption isotherms, XRD, XPS, NH3-/CO2-TPD, and Py-IR were used to investigate the physico-chemical properties of these prepared catalyst series. The introduction of PEG improved the specific surface area, dispersion of active sites, and density of acid and base sites, resulting in superior catalytic performance of Cs/PEG@Zr-SiO2 by comparison with that of Cs/SiO2 and Cs/Zr-SiO2. The kinetic experiments revealed that the activation energy of aldol condensation was 80.8 kJ/mol over the Cs/PEG@Zr-SiO2 catalyst. The deactivation behavior derived from carbon deposition was discovered, and the spent catalyst could be regenerated by simple thermal treatment.

Renewable biomass based jet fuel: Aldol condensation of furfural with 3-pentanone over calcium zirconium mixed oxide catalyst

Furfural is a biomass-derived chemical that can be converted into different valuable chemicals using green processes. The current study deals with a highly efficient, robust, and selective solid catalyst for the aldol condensation of furfural and 3-pentanone to synthesize 1-furan-2-yl-2-methylpent-1-en-3-one under environmentally benign conditions. CaZr (different molar ratios of Ca and Zr) mixed oxide (MO) catalysts along with reference CaO and ZrO2 catalysts were prepared by the hydrothermal technique and investigated for the current reaction. Among all, CaZr (1:2) MO catalyst was found to be the best for the conversion of furfural due to its desirable basic strength with good surface area and reusability characteristics. Furfural conversion and 1-furan-2-yl-2-methylpent-1-en-3-one selectivity were found to be 94 % and 98 %, respectively, under optimized reaction conditions. Effect of various reaction parameters was studied carefully to achieve the maximum yield of the required product. Reaction mechanism and kinetics were developed. The reaction aligns with the LHHW mechanism, and the activation energy was determined to be 10.40 kcal/mol.

Zeolite-encaged gold catalysts for the oxidative condensation of furfural

Zeolite-encaged gold catalysts for the oxidative condensation of furfural

Coriandrum Sativum-Derived Catalysts for Eco-Friendly Knoevenagel Condensation: Experimental Investigation and Central Composite Design

Coriandrum Sativum-Derived Catalysts for Eco-Friendly Knoevenagel Condensation: Experimental Investigation and Central Composite Design

Highly efficient CdS/CeO2/Ag3PO4 nanocomposite as novel heterogenous catalyst for Knoevenagel condensation and acetylation reactions

In light of environmental and economic concerns, the use of heterogeneous catalysts that can function under gentler reaction conditions has recently become popular. In this study by using the precipitation method, CdS/CeO2/Ag3PO4 ternary nanocomposites with varied molar proportions of CdS:CeO2/Ag3PO4 were produced. The catalysts' surface functional groups; morphology and crystal structures were examined using FTIR, SEM-EDX and XRD respectively. The catalytic efficiency of all synthesized nanomaterials was tested on a model Knoevenagel condensation reaction. For the best catalyst, selected from the screening, the optimization of reaction conditions such as the solvent, catalyst load, concentration of reagents such as malononitrile/acetic anhydride, and temperature. The ternary nanocomposite CdS/CeO2/Ag3PO4 (4:1) displayed higher catalytic activity (95.4 ± 3.2 %) than the rest of the nanomaterials prepared. Thus, the ternary nanocomposite CdS/CeO2/Ag3PO4 with 4:1 mol ratio with optimized reaction conditions was used to check the substrate scope of Knoevenagel condensation and acetylation reaction. The synthesized Knoevenagel condensation and acetylation reaction products were also characterized by proton and carbon NMR for their structure determination. The nanocomposite's reusability was carried out and only 7.5 ± 2 % decrement was witnessed after four runs and 23.3 % after the fifth run. and this indicates the potential application of the catalyst to organic reactions. Furthermore, we have proposed the possible catalytic mechanisms for both organic reactions.

Carbon-supported hydroxyapatite hybrid catalysts for butan-1-ol conversion: Effect of the nature of carbon support on process selectivity

Hybrid systems of hydroxyapatite supported on carbonaceous materials of different nature (activated charcoals, acetylene black, carbon black, graphite flake, synthesized microporous and mesoporous carbons) are investigated as catalysts for vapor-phase Guerbet condensation of butan-1-ol. The structure, morphology, and acid–base characteristics of hydroxyapatite, carbon supports, and the hybrid systems have been characterized by XRD, SEM-EDX, low-temperature (77 K) nitrogen ad(de)sorption, NMR, XPS, EPR, Raman spectroscopy, and TPD-NH3/CO2 techniques. The butan-1-ol conversion and selectivity towards the reaction products are found to be highly dependent on carbonaceous supports of the hybrid catalysts. The important role of acid–base capacity ratio is highlighted to achieve high selectivity in vapor-phase Guerbet condensation of butan-1-ol to 2-ethylhexan-1-ol. In particular, the surface’s strong basic sites are preferable for elongating the carbon chain. The high selectivity towards 2-ethylhexan-1-ol of about 75% is achieved over HAP/graphite flake and up to 57% over HAP/activated coconut charcoal. Compared to the bulk hydroxyapatite, the enhanced performance of the hybrid catalysts (initial activity and target product yield) is associated with the redistribution of active sites over carbon supports by strength and location.

An overview of the chemistry of condensation curing silicone sealants and adhesives

Condensation curing silicone sealants and adhesives are materials that are used to connect substrates to each other in various industries, especially where harsh conditions are limiting the use of organic materials. Chemistry of condensation curing silicones is reviewed in this publication through an historical perspective, which provides an insight into the challenges faced by the early formulators. The impact of the formulation ingredients can be very significant on the uncured, curing and/or cured properties of the material. Their main influence is described with a special focus on the main curing systems, i.e., acetoxy, alkoxy, oxime, amine, acetone, and amide. Cure characteristics are summarized and compared across their chemistries. Alkyl tin carboxylates and alkoxy titanium catalysts are the most used condensation catalysts. They are acting through a different mechanism, which is compared briefly. Typical features and principles about one-part and two-part silicones are described and related to their physicochemical properties. Finally, a brief review of the latest developments and trends is depicted.

Highly scalable and robust ribbon-like coordination polymer as green catalyst for Hantzsch condensation in synthesis of DHPs and bioactive drug molecule

Ribbon-like coordination polymers (CP) represents a highly unexplored innovative class of metal-coordination network. Herein, we have developed a highly scalable and chemically robust (pH = 3–10 stable) ribbon-like CP [{Cu(Pim)(L)(H2O)·H2O}]n(1) following a complete environment-friendly green synthesis route. Considering the presence of surface flanked labile coordinated water molecules and their appealing correlation with one-dimensional structural characteristics, such sort of ribbon-like CP was explored for the first time as excellent heterogeneous surface catalyst for largely unexplored three-component Hantzsch condensation for synthesis of different classes of dihydropyridine (DHP). Moreover, 1 is employed to synthesize bio-responsive drug ‘Ethidine’ (possessing high anti-oxidant and anticarcinogenic properties) characterized with Single Crystal X-ray Diffraction (SCXRD) analysis. Several DHP-based products are also analysed through in-depth SCXRD analysis. This report inaugurates the usage of a Cu(II) based ribbon-like CPs as heterogeneous surface catalyst following environmentally benign manner for synthesis of bioactive DHPs and Drugs.

UiO-66 metal-organic frameworks as aldol condensation catalyst: Impact of defects, solvent, functionality on the catalytic activity and selectivity

Defected and amine-loaded zirconium-based metal–organic frameworks (MOF) UiO-66(Zr) have been characterized and chemically assessed in a condensation reaction of acetone and 4-nitrobenzaldehyde. The present work focuses primarily on the production of the aldol adduct as the main product while minimizing the formation of the enone adduct as a side product. Four analogues with varying numbers of missing linkers in the hexanuclear secondary building units, from one to four out of a total of 12, were synthesized. Thorough characterization showed that an increased number of defects results in an enhanced acidity, a higher internal surface area, and an increased accessibility of coordinatively unsaturated Zr-sites. The catalytic performance assessment revealed that defects, to a certain extent, positively affect the selectivity towards the aldol adduct, i,e. the catalyst, which is missing 3 of the 12 linkers, exhibits the highest activity in a solvent-free environment with a turnover frequency (TOF) amounting to 8.03 10-3 s−1. This TOF value is approximately double of the catalyst with 1.4 defects, which exhibited a TOF of only 4.41 10-3 s−1. Excluding more than three linkers more likely leads to 'missing cluster defects' and causes a decrease in the reaction rate towards the aldol adduct. A reduction in overall catalytic activity was observed upon functionalization with amine groups (UiO-66-NH2). Functionalization with L-proline (UiO-66Lpr) resulted in a shift from an acid to a basic reaction mechanism which was reflected by an improved selectivity towards the aldol adduct while maintaining a reasonable overall activity level. The best performances were obtained working solvent-free or with hexane as a solvent, while polar/semi-polar solvents hindered the catalyst performance. An 18-hour stability test demonstrated the robustness of defected and functionalized UiO-66.

Green Method Synthesis of Magnetic Nanoparticles and its Functionalized MNPs for Knoevenagel Condensation Reaction

Background: Knoevenagel condensation is an important C-C bond formation reaction catalyzed by various homogeneous and heterogeneous acid-base catalysts. background: Knoevenagel condensation is an important C-C bond formation reaction, and employs various acid and base-catalyzed reactions of both homogeneous and heterogeneous catalysts. Method: The present work describes the eco-friendly preparation of magnetic nanoparticles Fe3O4 (MNPs) and its functionalization to Fe3O4@SiO2@SO3H. The prepared MNPs and their functionalized materials were fully characterized by FT-IR, XRD, FE-SEM, HR-TEM, and VSM. Further demonstrated application of these catalysts for the C-C bond formation reactions of Knoevenagel condensation employing special aldehyde derivatives with malononitrile at room temperature gave excellent product isolation. Results: The application of the prepared functionalized MNPs for the Knoevenagel condensation was demonstrated by the reaction of various aryl/heterocyclic and cholesterol aldehyde with malononitrile at room temperature stirring for about 30 min in ethanol solvent. The final product isolated is confirmed by various spectroscopic techniques such as FT-IR, 1H-, & 13C-NMR, and mass spectrometry. Furthermore, the selected compounds are screened for their photophysical properties, and interestingly compound 3j showed good fluorescent properties. Conclusion: Overall the present work described a greener method preparation of MNPs, and its functionalized employed as a heterogeneous catalyst for the Knoevenagel condensation of various aryl/heterocyclic and cholesterol aldehyde with malononitrile. The method developed is simple, easily separated catalyst by an external magnet, and recycled up to five cycles without any noticeable change in the final product isolation. Further, the prepared derivatives screened for their photophysical properties, and interestingly compound 3j showed good fluorescent properties.

Magnetite nanoparticles immobilized on hydrophilic polyelectrolyte-grafted carbon nanotube as efficient organic–inorganic hybrid heterogeneous catalyst for Knoevenagel condensation in aqueous medium

In this work, a novel organic–inorganic hybrid heterogeneous catalyst was fabricated for Knoevenagel condensation. First, the surface of carbon nanotube (CNT) was covalently functionalized with poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) polyelectrolyte (i.e., organic polybase) through the surface-initiated atom transfer radical polymerization (SI-ATRP) method. Subsequently, magnetic iron oxide nanoparticles (Fe3O4 NPs) (i.e., inorganic Lewis acid) are densely and homogeneously grown on the CNT surface using the CNT-g-PDMAEMA template. The as-prepared acid–base bifunctional catalyst (i.e., CNT-g-PDMAEMA/Fe3O4NPs) was investigated in the model reaction, i.e., Knoevenagel condensation between naphthol, malononitrile and benzaldehyde. The CNT-g-PDMAEMA/Fe3O4NPs catalyst shows high catalytic activity in the Knoevenagel condensation between naphthol, malononitrile and benzaldehyde due to its unique structure and specific chemical constitution. In addition, this acid–base bifunctional catalyst can be readily recovered with an applied magnetic field and reused with negligible loss in the catalytic activity even after six cycles.

Revealing the roles of the dual active-sites on a polyoxometalate-based metal–organic framework in catalyzing Knoevenagel condensations

The efficient catalysis of Knoevenagel condensations under mild conditions is a significant way for obtaining olefin compounds, which can be used to produce a wide range of biologically active heterocyclic chemicals and fine chemical raw materials. Herein, a novel polyoxometalate-based metal–organic framework (POMOF), [Co(bix)(H2O)]{V2O6} (VMOF-1, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), is synthesized and structurally characterized. After removal of the coordinated water molecules of CoII ions by vacuum drying, VMOF-1a with both Lewis acid and Lewis base catalytic active-centers is achieved. VMOF-1a as the heterogeneous catalyst for the conversion of benzaldehyde and malononitrile to high value-added olefinic compounds under mild conditions, exhibits excellent conversion and selectivity, good recyclability and broad substrate applicability. Experimental and theoretical studies have revealed that CoII ion and {V2O6}2− unit in VMOF-1a synergistically catalyze the Knoevenagel condensation reaction: (1) {V2O6}2− is used as a Lewis base to pull out the proton of the active methylene group on malononitrile; (2) CoII ion acts as a Lewis acid to activate the carbonyl oxygen on benzaldehyde. Furthermore, it is demonstrated for the first time that the Lewis acid sites in POMOF can play the role of stabilize the alcohol hydroxyl anion intermediates generated during the reaction process, which further elucidates the reason for the high catalytic activity of VMOF-1a in the Knoevenagel condensation. This study provides theoretical guidance for the design of efficient and sustainable catalysts for Knoevenagel condensation.

Metal–organic frameworks constructed using acid–base mixed ligands, carboxylic acids and N-containing chalcone, and their catalytic performance for Knoevenagel condensation

Metal–organic frameworks constructed using acid–base mixed ligands, carboxylic acids and N-containing chalcone, and their catalytic performance for Knoevenagel condensation

Supported H8PV5Mo7O40 on activated carbon: Synthesis and Investigation of influencing factors for catalytic performance.

Polyoxometalates (POMs), in particular the Keggin-type HPA-5 (H8PV5Mo7O40) are widely established as effective catalysts for acid- and redox-catalyzed reactions. Yet, they are mainly used as homogeneous catalysts, which poses challenges regarding catalyst separation. This study explores the synthesis of supported HPA-5, and its application as a heterogeneous catalyst for biomass conversion, focusing on activated carbons with diverse chemical and physical properties as support materials. Characterization of these carbons gives insights into the influence of surface area, oxygen content, and acidity on HPA adsorption and stability. Activated carbon CW20, was found to be the best support due to its high vanadium loading and effective preservation of the HPA-5 structure. It underwent various pre- and post-treatments, and the obtained supported catalysts were evaluated for their catalytic performance in converting glucose under both oxidative (OxFA process) and inert (Retro-Aldol condensation) conditions. Notably, HPA-5 supported on CW20 emerged as an exceptional catalyst for the retro-aldol condensation of glucose to lactic acid, achieving a selectivity of 15% and a conversion rate of 71%, with only minimal vanadium leaching.

Dual-active Hf(iv)–organic framework for the detection of FOX-7 and as a heterogeneous catalyst for Knoevenagel condensation

A dual-active MOF (CSMCRI-KNC′) was successfully employed for the detection of the explosive FOX-7 and as a heterogeneous catalyst for the synthesis of barbituric acid and its derivatives under mild conditions.

Surface-Immobilized ZnNx Sites as High-Performance Catalysts for Continuous Flow Knoevenagel Condensation in Water.

By immobilizing the metal complex on the substrate surface, our previous results have demonstrated that heterogeneous catalysts with well-dispersed active MNC (metal-nitrogen-carbon) sites can be prepared in a rational and efficient manner. In this study, we employed agarose aerogel (AA) as the substrate to illustrate a straightforward strategy for immobilizing ZnNx sites on the surface. Under relatively low temperatures, the amine group of the ligand condenses with the surface carbonyl group generated in situ, resulting in the surface immobilized Zn sites. This can be supported by the IR, PXRD, and XPS data. Comprehensive characterization methods, including synchrotron powder XRD and spherical aberration-corrected TEM, confirmed the absence of ZnNx site aggregation in the surface immobilization process, even with a high Zn content (up to 8 wt %). The immobilized ZnNx sites exhibited high catalytic performance in Knoevenagel condensation, and α,β-unsaturated compounds were obtained with high yield in both batch and continuous flow reactions. AA-ZnNx-200 showed the best catalytic activity, which was processed under 200 °C with a Zn content of 4.62 wt %. The immobilized ZnNx sites activated both the aldehyde and nitrile substrates, which were quantitatively converted into the corresponding α,β-unsaturated compounds, with water as the solvent at room temperature. In continuous flow reaction conditions, a conversion rate up to 99% can be achieved with malononitrile. This heterogeneous catalyst can be facilely produced with quantitative yield in a large scale from cheap starting material under mild conditions. No catalyst deactivation was observed after seven batch reaction cycles or 80 h of continuous flow reaction, indicating its high robustness under catalytic reaction conditions. This catalyst enables a separation-free, energy-saving, and environment-friendly production process, offering a practical way for the industrial production.

Three Double-Layered {Ni8}@{Bn}2 (n = 3, 4, 6) Cluster Sandwiched Polyoxometalates.

The reaction of [A-α-GeW9O34]10- with Ni2+ in the presence of inorganic boron sources yielded three unprecedented sandwiched Ni-added polyoxometalates (NiAPs): K6Na7H7[({Ni8(μ6-O)(OH)2}@{B3O6(OH)3}2)@(B-α-GeW9O34)2]·16H2O (1), K4Na4H12[({Ni8(μ6-O)}@{B4O8(OH)3}2)@(B-α-GeW9O34)2]·16H2O (2), and K10Na6[({Ni8(μ6-O)}@ {B6O9(OH)5}2)@(B-α-GeW9O34)2]·12H2O (3). The common feature of 1-3 is that a rare double-layered {Ni8}@{Bn}2 (n = 3,4,6) cluster is inlaid in their sandwich belts. The {Ni8} cluster is composed of two cubane {Ni4} clusters by six bridging oxygen atoms and sharing a μ6-O atom. The numbers of boron atoms in the {Ni8}@{Bn}2 (n = 3,4,6) clusters of 1-3 are different, namely, {Ni8}@{B3}2, {Ni8}@{B4}2, and {Ni8}@{B6}2 clusters. To the best of our knowledge, such architectures containing a double-layered {Ni8}@{Bn}2 (n = 3,4,6) cluster in the sandwich belts are the first observed in POM chemistry. Furthermore, 2 was investigated as an efficient heterogeneous catalyst for the Knoevenagel condensation of various aldehydes with malononitrile at room temperature.

Synthesis, characterization and application of nano-silica@[DPSSP][Cl]2 as a novel organic–inorganic hybrid catalyst for the rapid condensation of aldehyde, ammonium acetate and thiobarbituric acid

Synthesis, characterization and application of nano-silica@[DPSSP][Cl]2 as a novel organic–inorganic hybrid catalyst for the rapid condensation of aldehyde, ammonium acetate and thiobarbituric acid