Heterogeneous Catalytic System Research Articles

Effect of log Kow on the degradation of pharmaceutically active compounds in a heterogeneous catalytic persulfate activation system

In heterogeneous catalytic advanced oxidation processes (HC-AOP), enhancing the reaction rate is the biggest challenge. To enhance the reaction rate, it is necessary to increase the mass transfer rate of reactants toward the catalyst surface and the number of active sites that will provide better contact with the reactants and higher mass transfer. The hydrophobicity of the reactant is an important parameter that affects the transport of molecules toward solid surfaces. In this study, the effect of log Kow, an indicator of hydrophobicity, on enhancing the catalytic activity in persulfate (PS) activation for pharmaceutic compounds (PCs) degradation was investigated. For this purpose, some PCs with different log Kow were selected and their adsorption and degradation behaviors were investigated depending on the PS concentration, catalyst dosage, contact time, pH, and temperature in HC-AOP. Adsorption percentages increased significantly with increasing log Kow value. PCs with higher log Kow were completely degraded at the end of the shorter contact times in the presence of lower catalyst and PS. PCs were significantly degraded by the triple catalytic effect of AC, Fe, and temperature. The pseudo-first-order kinetic model was the best fit for the degradation reaction for all PCs. The higher apparent rate constants and lower activation energy values of the PCs belonging to high log Kow confirmed that log Kow is an effective parameter in enhancing the catalytic activity.

Polyoxometalate-loaded hyper-crosslinked nanoparticles as a Pickering interfacial catalyst for solvent-free epoxidation of allyl chloride under static conditions

Epoxidation of allyl chloride and hydrogen peroxide (H2O2) carried out in heterogeneous catalytic systems suffer from poor reaction efficiency due to their heavy mass transfer resistance present at the liquid-liquid interface. Pickering interfacial catalysis (PIC) provides an elegant solution by involving the design of amphiphilic heterogeneous catalysts, which can act as emulsifiers simultaneously. In this study, interface-active polyoxometalate-loaded hyper-crosslinked nanoparticles (HCNPs) were designed. The structural properties of materials were characterized in detail by elemental analysis, Zeta potential, ICP-OES, SEM, TEM, BET, FT-IR, TGA, and XPS. The prepared nanoparticles can build efficient W/O PIC systems with allyl chloride and H2O2. Systematic experiments indicate that catalysts' surface properties, catalyst dosage, and water/oil volume ratio significantly affect the PIC system's catalytic activity and emulsion properties. Moreover, this PIC system maintains high stability after the reaction and can be reused for at least 8 cycles. Excitingly, these interface-active HCNPs can also efficiently promote allyl chloride epoxidation in the absence of solvent and external stirring, illustrating that this approach holds great potential for developing catalytic systems suitable for multiphase reactions.

Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks.

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

Palladium(II)-immobilized Triptycene based Hypercrosslinked Polymers: An Efficient, Green, and Reusable Heterogenous Catalyst for Suzuki-Miyaura Cross-coupling Reaction.

The Suzuki-Miyaura cross-coupling (SMCC) involves the coupling of organohalides and organoboron molecules in the presence of Pd(II)-based catalysts. Often SMCC reactions employ homogenous catalysts. However, such homogenous SMCC reactions are associated with certain limitations which has motivated design of effective and sustainable Pd(II)-based heterogeneous catalytic systems. Herein, we report a systematic development of a Pd(II)-immobilized and triptycene based ionic hyper crosslinked polymer (Pd@TP-iHCP) and explored its application as a heterogeneous catalyst for SMCC reaction. Pd@TP-iHCP has ample N-heterocyclic carbene (NHC) pendants that anchor Pd(II) centres on the polymeric matrix. Pd@TP-iHCP was characterized satisfactorily using FT-IR, 13 C CP-MAS NMR, BET surface area analysis, SEM, EDX and HRTEM. The performance of Pd@TP-iHCP as a heterogeneous catalyst for SMCC reactions was explored using various combinations of aryl boronic acids and aryl halides. Experimental results show that Pd@TP-iHCP is associated with a moderately high surface area. It is an efficient catalyst for SMCC (in aqueous media) with a modest loading of 0.8 mol % Pd(II)-catalyst since high yields of the expected products were obtained in shorter time intervals. Pd@TP-iHCP also features excellent stability and catalyst recyclability since it could be re-used for several cycles without any significant decrease in catalytic efficiency.

Rapid oxidation and deep As(III) purification from water using gelatin-supported iron-based metal-organic framework aerogel coupled with H2O2: Preparation, performance and mechanism

Metal-organic frameworks (MOFs) are considered a reliable adsorbent for controlling arsenic contamination. However, developing rapid and efficient MOF adsorbents with the capability of easy recovery is still challenging. Herein, we prepared a three-dimensional porous MIL-88A-Fe/gelatin aerogel (PMGA) with macroscopic size and coupled it with H2O2 to fabricate a heterogeneous catalytic oxidation adsorption system to remove As(III) in water. The green synthesis strategy of this catalyst by foaming and low-temperature carbonization not only avoided the use of toxic chemical crosslinkers but also endowed PMGA with a rich hierarchical porous structure and exposed more active sites. Thus, the PMGA/H2O2 system was able to reduce the concentration of As(III) from 1106 to below 10 µg/L and simultaneously realize the complete oxidation of As(III) to As(V) in only 120 min. Meanwhile, the system exhibited an excellent saturation adsorption capacity (24.863 mg/g) for As(III), superior to most similar bio-based or iron-based materials. Quenching experiments, EPR and DFT calculations showed that the active species (surface •OOH and surface •OH) generated by the Fenton-like interaction between the exposed (100) facet of MIL-88A-Fe in PMGA and H2O2 played an essential role in promoting the oxidative removal of As(III). Moreover, the reaction system could work efficiently for As(III) in a wide pH range and was hardly affected by other substances such as chlorides, sulfates, carbonates, silicates, and humic acids. Simultaneously, the fixed bed column filled with PMGA could stably and continuously treat As(III) in groundwater. Therefore, this study not only broadens the horizon for the development and design of 3D functional materials but also provides a new strategy in water purification to eliminate arsenic pollutants using Fe-MOF aerogels.

Synergistic effect of silver nanoparticle-embedded calcite-rich biochar derived from Tamarindus indica bark on 4-nitrophenol reduction

Calcite-biochar composites are attractive materials with outstanding adsorption capabilities for removing various recalcitrant contaminants in wastewater treatment, however, the complexity of their synthesis limits their practical applications. In this work, we have prepared calcite-rich biochar (Ca-BC) from a single precursor (Tamarindus indica bark), which simplifies the synthetic route for preparing calcite-biochar composite. The as-synthesized composite is utilized to make a heterogeneous catalytic system containing the supported silver nanoparticles (Ag@Ca-BC) formed by the reduction of Ag+ ions on the surface of the composite. The formation of Ag@Ca-BC is confirmed by various characterization techniques such as PXRD, FT-IR, UV–Vis, cyclic voltammetry, impedance measurement, SEM, and TEM analyses. Especially, the TEM analysis confirms the presence of Ag nanoparticles with size ranging between 20 and 50 nm on the surface of Ca-BC composite. The nano-catalyst Ag@Ca-BC efficiently promotes the conversion of 4-nitrophenol to 4-aminophenol using NaBH4 as the reductant in water within 24 minutes at room temperature, suggesting that Ag@Ca-BC can be an efficient catalyst to remove nitroaromatics from the industrial effluents. The straightforward synthesis of Ca-BC from a single precursor along with its utility as a catalytic support presents a compelling proposition for application in the field of materials synthesis, catalysis, and green chemistry.

EcoScale MCR sustainability to impart rapid access to pyrrolo[1,2-b]pyrazoles scaffolds assisted by recyclable HClO4‧SiO2 heterogeneous catalytic system

EcoScale MCR sustainability to impart rapid access to pyrrolo[1,2-b]pyrazoles scaffolds assisted by recyclable HClO4‧SiO2 heterogeneous catalytic system

Efficient Protosilylation of Unsaturated Compounds with Silylboronates over a Heterogeneous Cu3N Nanocube Catalyst

AbstractCopper-catalyzed protosilylation of unsaturated compounds with silylboronates has attracted attention for the production of organosilanes; however, the use of organic ligands or bases is unavoidable. Herein, we report a heterogeneous catalytic system for the protosilylation of unsaturated compounds with silylboronates under mild and additive-free conditions over copper nitride nanocubes (Cu3N NCs). This method can be applied to various substrates (e.g., alkynes, alkenes, or imines) to afford the corresponding organosilicon compounds. The Cu3N NC catalyst can be easily recovered and reused several times. Thus, the active and reusable Cu3N NC catalyst offers a green and sustainable method for efficient organosilane production.

Silica-supported catalyst for the synthesis of low entangled UHMWPE suitable for solid-state processing

Different types of silica (mesoporous, spherical and nano-size particles), pre-activated with methylaluminoxane (MAO), are used to activate and support the bis[N-(3‑tert-butylsalicydene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride (FI) complex with the aim to synthesize low-entangled UHMWPE having controlled particle morphology. Through the porosity analysis, nitrogen adsorption and desorption isotherms, a decreased surfaced area of the chosen silica is observed when supported by MAO. From the bonding energy study by XPS, the bonding energy difference of Si and O, between the nano-size silica and in the MAO-nano silica, suggests the formation of Al-O-Si after chemical activation with MAO. Using elementary analysis, ICP-OES and XPS characterization, the aluminum content grafted on the silica surface is found to match with the anticipated amount of MAO on the MAO-Silica/FI catalytic system, indicating a stable grafting after catalyst supporting. From the rheological studies of the polymers, coupled with DSC results using an isothermal crystallization protocol, the resultant entangled state in the semi-crystalline polymers is estimated. The observations are that the entangled state achieved during polymerization from the investigated heterogeneous catalytic systems, is the lowest in PE-MAO-nano silica/FI, increases in PE-MAO-mesoporous silica/FI and is highest in PE-MAO-spherical silica/FI. Silica modification using two different silanes shows significant influence on the catalytic activity, giving lower polymer yield in MAO-modified-mesoporous silica and MAO-modified-nano silica compared to the unmodified MAO-silica. Whereas, no significant spatial effect is observed in the formation of chain entanglement, showing the increased entanglement density of the nascent polymers. By employing heterogeneous catalytic systems, reactor fouling and wall sheeting problems are resolved and the polymers show good morphology replication of the support. The UHMWPE synthesized using the nano silica as support, having the lowest entangled state and loosely packed crystals, can be uniaxially processed in the solid-state to a thin tape having thickness around 34 μm, showing maximum tensile strength of 3.26 N/tex and tensile modulus of 170 N/tex.

Versatile Heterogeneous Catalytic System for the Selective Synthesis of Limonene Epoxide and Diepoxide

Versatile Heterogeneous Catalytic System for the Selective Synthesis of Limonene Epoxide and Diepoxide

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h−1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Reduced porous 2D Co3O4 enhanced peroxymonosulfate activation to form multi-reactive oxygen species: The key role of oxygen vacancies

The introduction of oxygen vacancies (Ov) into Co-based metal oxides has been considered a promising strategy for activating peroxymonosulfate (PMS) to effectively degrade refractory organic contaminants. However, the types of reactive oxygen species (ROS) generated in Ov-catalyst/PMS systems exhibited variability. Therefore, the effect of the interaction between Ov and PMS on ROS generation required further research. Herein, the Ov-tuned 2D porous Co3O4 catalysts were easily constructed by simply controlling the NaBH4 concentration. The as-prepared 2D Co3O4-1.6 had the highest Ov content (2.88 × 1014 spins/g, δ = 0.726), and its catalytic activity for benzotriazole (BTA) degradation (k = 0.032 min−1) was three times higher than that of pristine 2D Co3O4 (k = 0.011 min−1). A series of characterizations and DFT calculations demonstrated that the major active site was Co(II), with Ov serving as an localized electron-rich co-site. These dual sites synergistically improved the adsorption capacity for PMS, enabling rapidly electrons transfer to PMS while promoting the dissociation of O-O bond in PMS to form multiple ROS. Compared to the pristine 2D Co3O4/PMS system, which was dominated only by SO4−, the key ROS in the 2D Co3O4-1.6/PMS system were found to be 1O2 (3.56 µM) and SO4− (2.53 µM), while both O2– (0.72 µM) and OH (0.65 µM) were involved in the activation reaction, the contributions of these four ROS were as follows: 1O2 (36.8%) > SO4− (25.4%) >O2– (9.5%) >OH (6.3%). Finally, three possible degradation pathways of BTA were proposed, and the toxicity of BTA degradation decreased with time, which was consistent with the toxicity prediction results of eleven intermediates. This study provides new insights into the key role of Ov in the heterogeneous catalytic system of PMS-based advanced oxidation processes.

State-of-the-art for the development of Cu-based heterogeneous catalysts for efficient utilization of furfural to value chemicals via liquid-phase and gas-phase reactions

ABSTRACT In the present review, we aim to provide important insights into copper-based heterogeneous catalytic systems and discuss the conversion of furfural (FF) through hydrogenation. Each discussed catalyst and the support used for the catalytic reactions play a vital role in the reaction mechanism along with different factors enhancing the catalytic activity. Also, the importance of Cu-based materials along with support, the importance of solvent in the liquid-phase reaction, and the importance of pre-reduction of catalysts are explained in detail. In addition, the superior activity of the catalyst and a few reports from the last decade for Cu-based catalytic systems have been summarized along with the tabulation of different synthesis procedures, mechanistic study, and detailed descriptions with tables and figures. Finally, the conclusions with future aspects for the development of the catalytic hydrogenation process via Cu-based catalytic systems are overviewed.

Efficient removal of oxytetracycline hydrochloride by ZIF-67 coated hollow spherical CuS (CuS-PVP@ZIF-67) under the synergistic effect of adsorption and PMS activation

Selective removal of organic pollutants by PMS-activated heterogeneous catalytic system has become one of the commonly used methods, but the adsorption of the catalyst is often ignored in the degradation process. Metal-organic frameworks (MOFs) are often used in the field of environment because of their high porosity and structural diversity/adjustability. However, there are still difficulties in the aggregation and recycling of nanoparticles. This study effectively synthesized the material CuS-PVP@ZIF-67 by using hollow spherical CuS as the carrier of Co-MOF (ZIF-67) to solve these problems. A high concentration of oxytetracycline hydrochloride (OTC) can be successfully adsorbed by electrostatic attraction and π-π interaction, and small amount of PMS may be quickly activated, and the removal rate of OTC is 94.82 % in 20 min. The catalyst used can be easily recovered by suction filtration and has good reusability. In addition, a potential cooperating mechanism for adsorption-PMS activation has additionally been proposed. The degradation pathway of OTC is determined, and the potential harm of intermediate products is analyzed. This work aims to create a heterogeneous catalytic system with significant adsorption and catalytic ability to remove refractory organic contaminants in water.

Reliability analysis of NaN3 as quencher of 1O2 in heterogeneous persulfate catalytic oxidation system

At present, more and more scholars have questioned the reliability of NaN3 as a quench agent of 1O2 in heterogeneous persulfate catalytic oxidation system. In this study, we first compared the decomposition kinetics of PMS in the presence of CuO (CuOMgO), different concentrations of NaN3, and CuO (CuOMgO) with different concentrations of NaN3, respectively. Subsequently, the catalytic performance of common catalysts was compared. These results confirmed that the addition of NaN3 will significantly affect the decomposition process of PMS in heterogeneous persulfate catalytic oxidation system, so it is not suitable to be used as quench agent of 1O2.

Hydroformylation of olefins over a novel active rhodium catalyst supported on a melamine–cyanuric acid co-crystal

Hydroformylation, or oxo synthesis, is one of the most important industrial petrochemical processes involving homogeneous catalysts. The development of efficient and stable phosphorus-free heterogeneous catalytic systems for this process is of great interest because it can solve the problem of separation and recycling of expensive metals and reduce the amount of phosphorus-containing waste. Macromolecular compounds containing triazine rings can be promising candidates for supports for the stabilization of metal nanoparticles and subsequent use in heterogeneous catalytic reactions. Herein, it was shown that the interaction of cyanuric chloride with melamine produces cyanuric acid–melamine (CAM) co-crystal, which was used as a support for stabilizing rhodium nanoparticles. The obtained catalyst (CAM/Rh) exhibits high activity and stability in the hydroformylation of olefins of various structures. After completion of the reaction, the catalyst is easily separated from the reaction mixture and can be used repeatedly with virtually no loss of activity.

Mechanistic insights to drive catalytic hydrogenation of formamide intermediates to methanol via deaminative hydrogenation

Amine-promoted hydrogenation of CO2 to methanol typically proceeds via a formamide intermediate when amines are used as additives or if the hydrogenation is performed in carbon capture solvents. The catalysts used for the hydrogenation of the formamide intermediate dictate the selectivity of the products formed: 1) Deoxygenative hydrogenation (C–O bond cleavage) resulting in N-methylation of amine and deactivation of the solvent, 2) Deaminative hydrogenation (C–N bond cleavage) resulting in formation of methanol and regeneration of the solvent. To date, catalytic reductions of CO2 with amine promoters suffer from poor selectively for methanol which we attribute to the limiting formamide intermediate, though to date, the conditions that favor C–N cleavage have yet to be fully understood. To better understand the reactivity of the formamide intermediates, a range of heterogenous catalysts were used to study the hydrogenation of formamide. Well-known gas phase CO2 hydrogenation catalysts catalyze the hydrogenation of formamide to N-methyl product via C–O bond cleavage. However, the selectivity can be readily shifted to selective C–N bond cleavage by addition of an additive with sufficient basicity for both homogenous and heterogeneous catalytic systems. The base additive shifts the selectivity by deprotonating a hemiaminal intermediate formed in situ during the formamide hydrogenation. This prevents dehydration process leading to N-methylated product, which is a key capture solvent deactivation pathway that hinders amine use in carbon capture, utilization, and storage (CCUS). The findings from this study provide a roadmap on how to improve the selectivity of known heterogenous catalysts, enabling catalytic reduction of captured CO2 to methanol.

Constructing a synergistic catalyst by confining Pd within a MOF using an extended “bottle-around-ship” protocol

Developing confined heterogeneous catalytic systems with diverse and evenly dispersed active sites is a hot research topic for various applications. However, the issues related to the agglomeration of active nanoparticles, spatial distribution uniformity of active nanoparticles, and coverage of active sites with the participation of surfactant or organic ligand restrict the activity or selectivity. In this work, a confined catalyst Pd(PPh3)4@MOF-808-150 was successfully prepared through a host-guest assembling strategy followed by thermal activation to enhance the rigidity of the catalyst. The synthesized catalyst is employed to generate β-ketoenamines in the cascade reaction involving nitro-reduction and sequential condensation. This catalyst effectively resolves the electronic preference conflict of the two catalytic steps by isolating the different active sites, demonstrating excellent activity and high chemoselectivity. It is generally applicable to the synthesis of many β-ketoenamines, with up to 16 kinds of products that have been successfully prepared with conversion and selectivity up to 99%. The extended synthesis method holds significant potential for developing the nanoconfined catalyst without surfactant encapsulation.

Readily separable and stable CoFe2O4 beads for activating peroxymonosulfate to degrade lomefloxacin hydrochloride: Optimization, performance and degradation mechanism

CoFe2O4 is regarded as a star material because of its high catalytic activity and excellent separation performance. However, metal-ion dissolution and collection difficulty of powdery CoFe2O4 in practical applications are still critical scientific issues, which will not only cause new environmental risks but also may result in partial loss of catalysts. In this work, buoyant CoFe2O4-loaded hollow glass microspheres embedded in sodium alginate beads (CHS) for activating peroxymonosulfate (PMS) to degrade lomefloxacin hydrochloride (LMH) were successfully prepared by an impregnation-precipitation-gel method. The experimental results showed that the heterogeneous catalytic system (CHS + PMS) displayed 9.5-, 7.7- and 6.6-times degradation rates (kobs) towards LMH than that of leached Fe + PMS, Co + PMS, and Fe + Co + PMS homogeneous systems, respectively. More importantly, CHS could effectively alleviate the dissolution of metal ions due to the coordination of the carboxylate group on the alginate to the Co and Fe sites on the surface of CoFe2O4, ultimately the leached concentration of Co (0.089 mg/L) and Fe (0.014 mg/L) ions from CHS were only about 11.1% and 16.5% of the powdery CoFe2O4, respectively. Primary radicals involved in the LMH degradation process were ·OH and SO4·- through EPR characterization and quenching experiments. This study offers the possibility to design practical potential heterogeneous catalyst for stable activation of PMS.

Recent Advances and Challenges in the Valorization of α‐Pinene toward Value‐Added Chemicals

AbstractThe transformation of abundantly available bioresources into specialty chemicals, particularly as consumer products, remains an important pursuit in chemical research. In this sense, the valorization of bio‐oil strategies that utilize stable and easy‐to‐handle chemical entity not only creates application‐oriented products but also helps in avoiding the usage of toxic and hazardous chemical sources. Recently, the valorization of α‐pinene (readily/naturally available terpenic compounds) has been explored to prepare a wide range of processes to access perfumery products and remains fast‐growing research for industrial and societal applications. Considering the valorization of α‐pinene, challenges for the synthetic and selective preparation of perfumery chemicals are centered around the design of the catalyst and the setting up of the precise reaction conditions. Extensive research is employed using diverse catalytic approaches to utilize α‐pinene to prepare important perfumery intermediates. In this review, the state‐of‐the‐art, recent advances and challenges in the utilization of α‐pinene are reviewed, emphasizing two main products, i.e., α‐campholenic aldehyde and carveol via α‐pinene oxide isomerization, and discussed the pertinent role of various homogeneous and heterogeneous catalytic systems.