Heterogeneous Catalyst Research Articles

Integrated Ziegler-Natta/Brookhart-Ni Catalysts for the Synthesis of Sutured Polar High-Impact Polypropylenes.

The direct synthesis of polar high-impact polypropylenes using industrially-preferred heterogeneous catalysts is challenging due to the poisoning of polar functional groups towards metal center and the high stereo-selectivity requirement. In this work, dual-site catalysts combining Ziegler-Natta and Brookhart-Ni catalysts were used to produce polar polyolefin ionomers, followed by polar high-impact polypropylenes containing isotactic polypropylene and branched polyethylene as toughening agents. Three combination modes between these catalysts were investigated, including mixed, core-shell, and integrated types. The integrated dual-site catalyst achieved the optimal material properties because the polyolefin ionomer acted as a suture molecule that stitched different components into a whole network. This produced sutured polar high-impact polypropylenes with excellent mechanical properties and compatibility with polar substances. The restraining effect of the suture molecules greatly reduced the release of microplastic particles after aging. Moreover, the obtained polar high-impact polypropylene can serve as an efficient compatibilizer to recycle polyethylene/polypropylene mixed-waste plastics. This work provides an appealing and potentially practical strategy to upgrade the widely used polypropylenes and to alleviate the ever-growing plastic pollution issue.

Vitalizing Perovskite Oxide-Based Acetone Sensors with Metal-Organic Framework-Derived Heterogeneous Oxide Catalysts.

Perovskite oxides are promising candidates for chemiresistive-type gas sensors owing to their exceptional thermal and chemical stability during solid-gas reactions. However, perovskites suffer from critical issues such as low surface area and poor surface activity, which negatively influence the sensing characteristics. While metal nanoparticles can be incorporated in perovskites to improve their reactivity, the fundamental incompatibility between catalytic metals and perovskite oxides often leads to substantial structural degradation as well as phase instability. Herein, we overcome this challenge through the introduction of an intermediary phase that forms coherent interfaces with both the perovskite phase and catalyst metals. Specifically, we present the case study of p-type La0.8Ca0.2Fe0.98Pt0.02O3 perovskite, whose hole accumulation layer was modulated by the incorporation of metal-organic framework (MOF)-derived n-type α-Fe2O3 nanoparticles decorated with highly dispersed Pt catalysts. The resulting composite exhibited significantly improved surface activity over the nonmodified La0.8Ca0.2FeO3 perovskite, leading to exceptional chemiresistive sensing performance toward acetone gas (Rg/Ra = 39.8 toward 10 ppm of acetone at 250 °C) with high cross-sensitivity against interfering gases. Importantly, our findings reaffirm the critical influence of interfacial engineering in facilitating surface chemical reactions on perovskite oxides and, by doing so, effectively provide a general synthetic guideline to the design of perovskite-based chemiresistors.

Advancing Hybrid Nanocatalyst Research: A Python-based Visualization of Similarity Analysis for Interdisciplinary and Sustainable Development

Background: This study presents a comprehensive analysis of hybrid nanocatalysts, which amalgamate attributes of both heterogeneous and homogeneous catalysts. Aim: To achieve a holistic understanding of the topic, we embarked on a meticulous exploration across multiple databases. Methods: The Web of Science repository yielded 239 pertinent documents, while the Scopus database offered a more exhaustive collection of 1,887 documents. Although Google Scholar suggested a staggering 25,000 articles, its unclear selection criteria raised questions about the precision and dependability of its data. Hence, our study primarily relied on the Scopus database to ensure an extensive sample and analytical rigor. Using the Python-boosted visualization of Similarities methodology, we illuminated interconnections among various terminologies, identifying burgeoning areas within hybrid nanocatalyst research. Results: Our findings emphasized the ascending trajectory toward innovating materials with superior properties in hybrid nanocatalysis. This trajectory accentuated the pivotal role of interdisciplinary collaboration and sustainable methodologies. Advanced analytical techniques, notably X-ray diffraction, emerged as quintessential in delineating the nuanced relationship between hybrid nanocatalysts' structural and functional attributes. We also spotlighted Energy-Dispersive X-ray Spectroscopy's capability in fine-tuning hybrid nanocatalysts' properties, enhancing their catalytic efficacy and selectivity. An intriguing trend our study unearthed was the surge in interest toward integrating natural enzymes as potential catalysts within hybrid nanocatalysts, positioning them as beacons for sustainable and cost-efficient catalyst development. Conclusion: By synthesizing these insights, this research underlines the significance of diverse characterization techniques and the ethos of interdisciplinary collaboration. The derived knowledge offers a repository for fellow researchers, guiding further inquiries, especially regarding integrating natural enzymes in hybrid nanocatalyst innovation.

Efficient activation of peroxyacetic acid by cobalt-iron alloy/oxide heterojunctions anchored in defect-rich biochar for pesticide degradation in water: Unravelling the radical-unradical mechanism

The activation processes of peracetic acid (PAA-AOPs) have garnered significant attention in wastewater treatment. In this study, an amorphous carbon-modified bimetallic CoFe alloy/oxide catalyst (CoFe@DBCx-y, where x represents biomass mass and y represents pyrolysis temperature) was developed to activate PAA for the degradation of organochlorine pesticides (OCPs). Due to the size effect, biochar dynamically regulates the particle size of metal species, which is influenced by the pyrolysis temperature. Among these systems, the CoFeDBC2.0–700/PAA oxidation system effectively removed 95.7 % of 2,4-dichlorophenoxyacetic acid (2,4-D), exhibiting a kinetic constant 1.7 times higher than that of the Nano/PAA system. Furthermore, quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that high-valent metal oxides (MIV = O) and singlet oxygen (1O2) are the primary active species responsible for the removal of 2,4-D, whereas organic radicals (RO·) and hydroxyl radicals (·OH) play a secondary role. Electrochemical and Raman spectroscopy tests revealed the formation of a metastable surface complex (≡Co(III)–OO(O)CCH3) between PAA and the catalyst, which acted as an intermediate oxidant to generate reactive oxygen species (ROS) through a chain reaction. Carbon defects in the biochar functioned as an electron source, continuously replenishing the electrons consumed in the reaction and facilitating the valence cycling between Co and Fe. This study provides new insights into the remediation of pesticide-contaminated wastewater using PAA-AOPs with heterogeneous bimetallic carbon-based catalysts.

Efficient degradation of Enrofloxacin with novel magnetic MnFe2O4/NiS2 composite as an activator of peroxymonosulfate

The development of highly active and recoverable heterogeneous catalysts for peroxymonosulfate (PMS) activation to remove the persistent presence of antibiotics in aquatic environments, such as Enrofloxacin (ENR), remains a significant challenge. Here, we introduce a pioneering magnetic nanocomposite catalyst, MnFe2O4-NiS2, synthesized via a two-step hydrothermal process, which activates PMS to efficiently degrade ENR. The optimized 0.25MnFe2O4-NiS2/PMS system reached an ENR removal efficiency of 89.9 % within 90 min, outperforming both NiS2/PMS and MnFe2O4/PMS by 5.6 and 2.5 times, respectively. Quenching experiments and electron spin response analysis confirmed SO4•- and •O2– as the primary reactive oxygen species. The enhanced mediated electron transfer capability of the 0.25MnFe2O4-NiS2 nanocomposite improved the redox cycling of Ni (Ⅱ), Mn (Ⅱ) and Fe (Ⅲ) on its surface, as verified by Density Functional Theory calculations. Furthermore, the activation of surface PMS complexes (PMS*) played a crucial role in ENR degradation. The proposed degradation pathways of ENR were confirmed, and toxicity analysis indicated a decrease in intermediate toxicity with the 0.25MnFe2O4-NiS2/PMS system. This study presents an innovative magnetically recoverable, multifunctional catalyst with easy reusability for potential applications in the degradation of organic pollutants.

Kinetics of continuously catalyzed peroxymonosulfate in a fixed-bed reactor

Most studies have been conducted in batch reactors. Therefore, understanding the catalytic reaction kinetics and mass transfer in continuous catalytic reactors is essential for the design of heterogeneous catalysts and optimisation of catalytic degradation processes in heterogeneous systems. In this research, granular catalysts (Co-600/AlSi-0.25/AP) is used to investigate the kinetic constants and mass transfer resistance for the continuous catalytic decomposition of peroxymonosulfate (PMS) and degradation of p-nitrophenol (PNP) in a fixed bed reactor. The flow rate is 5 mL/min and reaction temperature is 30 °C, intrinsic kinetic constants of PMS decomposition and PNP degradation are 48 and 195 kg−1·min−1·L, respectively, which are 20–30 times of the apparent kinetic constants of PMS decomposition and PNP degradation in fixed bed reactors, respectively. The decomposition rates of PMS and PNP are controlled by mass transfer, and the reaction takes place in the diffusion-controlled regime. The mass transfer kinetic model based on the plug-flow model shows a good agreement between the calculated data and the experimental data. Which indicate that PMS decomposition and pollutant degradation in a fixed-bed reactor can be predicted by mass transfer kinetic modelling, guide the design of catalysts and the optimisation of heterogeneous catalytic reaction system in a fixed-bed reactor.

Natural Surface Frustrated Lewis Pairs: The Concept and Beyond.

The reusable and separable surface frustrated Lewis pairs (SFLPs) open up a novel approach to efficient small-molecule activation and conversion in heterogeneous catalysis. However, SFLPs have only been reported on limited systems due to the difficulty in the design and synthesis process. The inherent Lewis pairs on various solid materials offer promising opportunities for finding natural SFLPs, providing a straightforward and efficient strategy to overcome the current limitations. In this concept, we retrospect the concept of natural SFLPs proposed on wurtzite crystal surfaces and identify other natural SFLPs that probably exist on solid materials, including reduced oxide surfaces, corrugated graphene, and perovskite quantum dots. Having focused on the reactivity of natural SFLPs in small-molecule activation, we discuss the current challenges, propose possible research directions, and highlight potential applications of natural SFLPs in heterogeneous catalysis.

Emission Library and Applications of 2,1,3‐Benzothiadiazole and Its Derivative‐Based Luminescent Metal–Organic Frameworks

AbstractOrganic linker‐based luminescent metal–organic frameworks (LMOFs) have received extensive attention due to their promising applications in chemical sensing, energy transfer, solid‐state‐lighting and heterogeneous catalysis. Benefiting from the virtually unlimited emissive organic linkers and the intrinsic advantages of MOFs, significant progress has been made in constructing LMOFs with specific emission behaviors and outstanding performances. Among these reported organic linkers, 2,1,3‐benzothiadiazole and its derivatives, as unique building units with tunable electron‐withdrawing abilities, can be used to synthesize numerous emissive linkers with a donor‐bridge‐acceptor‐bridge‐donor type structure. These linkers were utilized to coordinate with different metal nodes, forming LMOFs with diverse underlying nets and optical properties. In this Minireview, 2,1,3‐benzothiadiazole and its derivative‐based organic linkers and their corresponding LMOFs are summarized with which an emission library is built between the linker structures and the emission behaviors of constructed LMOFs. In particular, the preparation of LMOFs with customized emission properties ranging from deep‐blue to near‐infrared and sizes from dozens to hundreds of nanometers is discussed in detail. The applications of these LMOFs, including chemical sensing, energy harvesting and transfer, and catalysis, are then highlighted. Key perspectives and challenges for the future development of LMOFs are also addressed.

Emission Library and Applications of 2,1,3-Benzothiadiazole and Its Derivative-Based Luminescent Metal-Organic Frameworks.

Organic linker-based luminescent metal-organic frameworks (LMOFs) have received extensive attention due to their promising applications in chemical sensing, energy transfer, solid-state-lighting and heterogeneous catalysis. Benefiting from the virtually unlimited emissive organic linkers and the intrinsic advantages of MOFs, significant progress has been made in constructing LMOFs with specific emission behaviors and outstanding performances. Among these reported organic linkers, 2,1,3-benzothiadiazole and its derivatives, as unique building units with tunable electron-withdrawing abilities, can be used to synthesize numerous emissive linkers with a donor-bridge-acceptor-bridge-donor type structure. These linkers were utilized to coordinate with different metal nodes, forming LMOFs with diverse underlying nets and optical properties. In this Minireview, 2,1,3-benzothiadiazole and its derivative-based organic linkers and their corresponding LMOFs are summarized with which an emission library is built between the linker structures and the emission behaviors of constructed LMOFs. In particular, the preparation of LMOFs with customized emission properties ranging from deep-blue to near-infrared and sizes from dozens to hundreds of nanometers is discussed in detail. The applications of these LMOFs, including chemical sensing, energy harvesting and transfer, and catalysis, are then highlighted. Key perspectives and challenges for the future development of LMOFs are also addressed.

Hydrogen Spillover-Bridged Interfacial Water Activation of WCx and Hydrogen Recombination of Ru as Dual Active Sites for Accelerating Electrocatalytic Hydrogen Evolution.

Tungsten carbide (WCx) is a promising alternative to platinum catalysts for hydrogen evolution reaction (HER). However, strong tungsten-hydrogen bond hinders hydrogen desorption while favoring H+ reduction, thus limiting HER kinetics. Inspired by the phenomenon of hydrogen spillover in heterogeneous catalysis, a ruthenium (Ru) doped-driven activated hydrogen migration from WCx surface to Ru is reported. This approach achieved high activity with an ultralow overpotential of 9.0mV at 10 mA·cm-2 and superior stability at an industrial-grade current density of 1.0 A·cm-2 @ 1.65V. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS)and operando electrochemical impedance spectra revealed that this exceptional hydrogen production-which surpasses that of previously reported Pt/C catalysts-is attributable to the outstanding ability of WCx to induce water dissociation and hydrogen spillover from WCx to Ru surface. During the HER process, the rigid interfacial water network negatively affected the HER efficiency under alkaline conditions. The WCx sites disrupted this rigid structure, facilitating the contact between activated hydrogen (H*) and WCx sites. Subsequently, H* migrates to Ru surface, where hydrogen recombination occurs to produce H2. This work paves a new avenue for the construction of coupled catalysts at the atomic scale to facilitate HER electrocatalysis.

Deciphering the Ce3+to Ce4+Evolution: Insight from X-ray Raman Scattering Spectroscopy at Ce N4,5Edges.

Cerium oxide, or ceria, (CeO2) is one of the most studied materials for its wide range of applications in heterogeneous catalysis and energy conversion technologies. The key feature of ceria is the remarkable oxygen storage capacity linked to the switch between Ce4+ and Ce3+ states, in turn creating oxygen vacancies. Changes in the electronic structure occur with oxygen removal from the lattice. Accordingly, the two valence electrons can be accommodated by the reduction of support cations where the electrons can be localized in empty f states of Ce4+ ions nearby.Quantifying the different oxidation states in situ is crucial to understand and model the reaction mechanism. Beside the different techniques to quantify Ce3+ and Ce4+ states, we discuss the use of X-ray Raman Scattering (XRS) spectroscopy as an alternative method. In particular, we show that XRS can observe the oxidation state changes of cerium directly in the bulk of the materials under realistic environmental conditions. The Hilbert++ code is used to simulate the XRS spectra and quantify accurately the Ce3+ and Ce4+ content. These results are compared to those obtained from in situ X-ray Diffraction (XRD) collected in parallel and the differences arising from the two different probes are discussed.

Designing Sustainable Copper‐Based Hybrid Framework Catalysts for One‐Pot Multicomponent Organic Reactions

AbstractThe recent breakthroughs in heterogeneous catalysis emphasize the need for novel materials capable of driving organic transformations. The present study explores two copper phosphonate hybrid framework materials, 2D Cu3[(Hhedp)2(C4H4N2)].2H2O (Cu(II)Pyz‐P) and 3D Cu3[(H3hedp)2(C4H4N2)4(SO4)].2H2O (Cu(I/II)Pyz‐P), as single crystals isolated via hydrothermal synthetic strategy using H4hedp (1‐hydroxyethane 1,1‐diphosphonic acid) and N‐donor secondary ligand (Pyrazine; C4H4N2). Cu(II)Pyz‐P contains exclusively +2 oxidation state of copper, while Cu(I/II)Pyz‐P is characterized by a mixed oxidation state, where copper +2 phosphonate is embedded within the network formed by copper +1 state. Moreover, magnetic study elucidates the distinct oxidation states of both compounds by showing deviations from each other. The aforementioned compounds are exceedingly effective for catalyzing multicomponent reactions, that is, A3 coupling reaction and click reaction. Cu(I/II)Pyz‐P ensures the regioselective synthesis of triazole with high purity, while A3 coupling reaction is facilitated by both the compounds. Solvent‐ and additive‐free efficient multicomponent reactions are explored for the first time in the copper phosphonate hybrid framework structures. The present study reveals the promise of copper‐based hybrid phosphonate frameworks as durable and efficient catalysts for organic synthesis, providing cost‐effective and sustainable ways for advanced catalytic transformations.

Transesterification reaction time impacts on oxidation stability and acid number of biodiesel production from waste cooking oil

The scarcity of fossil fuels, environmental concerns, and the sharp rise in fossil fuel prices have driven scientists to search for alternative fuels. The characteristics of biodiesel have made the quest for high-quality biodiesel production particularly appealing. The use of waste cooking oil is a key component in reducing biodiesel production costs by 60-90%. Researchers have employed various types of transesterification reactions with both homogeneous and heterogeneous catalysts for biodiesel production; in this study, a 0.5% NaOH catalyst is used. The objectives of this study are to produce biodiesel fuel based on waste cooking oil, evaluate the impact of reaction time variation on the oxidation value and acid value of biodiesel produced from waste cooking oil, and statistically test the effects of reaction time on the oxidation value and acid value of biodiesel produced from waste cooking oil using analysis of variance (ANOVA). The optimum yield was obtained at a reaction time of 90 minutes, achieving 97%. The results for acid number and oxidation value for various reaction times complied with ASTM, EN, and SNI standards. Linear regression analysis of ANOVA for the acid number concluded that the P-value t3 is 0.399, which is greater than Alpha = 0.05, indicating that the variation in reaction time does not have a significant effect on the acid number. Linear regression analysis of ANOVA for the oxidation number concluded that the P-value t3 is less than Alpha (0.047 < 0.05), indicating that reaction time has a significant effect on the oxidation number.

Practical Considerations for Understanding Surface Reaction Mechanisms Involved in Heterogeneous Catalysis

Practical Considerations for Understanding Surface Reaction Mechanisms Involved in Heterogeneous Catalysis

Promotion of Single-Electron Transfer by Low-Coordinated Co Single Atoms to Facilitate Advanced Oxidation Processes in Wastewater Treatment.

Heterogeneous catalysts are fascinating for advanced oxidation processes (AOPs) in wastewater treatment to reduce cost, metal contamination, and pH operation limitations. However, they usually encounter low catalytic efficiency because of the difficult single-electron-transfer (SET) pathway during AOPs. Herein, an efficient heterogeneous catalyst for AOPs is realized through the rational regulation of N coordination around Co single-atom (SA) centers in favor of SET. As guided by calculations, low N coordination enables a high density of electronic states at the Fermi energy level of SA Co to facilitate SET activation of peroxomonosulfate (PMS). A special oxide-compounding method is further applied to decrease the N coordination of SA Co on the carbon carriers from common Co1-N3/4 to the desired Co1-N2. Co1-N2 shows a delightful activity for AOP degradation of various organic pollutants with kinetic rate and turnover frequency values up to 0.862 min-1 and 389 h-1, respectively, greatly outperforming those of Co1-N3/4. It is also superior in a wide pH operation range and has strong resistance to environmental disturbances. Detailed mechanistic investigations confirm the generation of singlet oxygen (1O2) instead of common radical O species from the SET between PMS and Co1-N2, corroborating the calculated results and accounting for the enhanced AOP activity.

Study of Electron Beam Irradiated Palladium on Carbon Catalysts for Transfer Hydrogenation Reactions of Nitroarenes Compounds

Palladium-catalyzed hydrogenation is considered a crucial stage in the entire synthesis of difficult natural products as well as a crucial step in the manufacturing of fine compounds used in pharmaceuticals. When it comes to the reaction rate and simplicity of work-up, using Pd/C as heterogeneous catalyst is one of the best choice for process efficiency. In this study, nitroarenes compounds viz. 3-bromo nitrobenzene, 4-fluoro nitrobenzene, 3-methyl nitrobenzene, 4-hydroxy nitrobenzene reduced by using macro 10% Pd/C and micro 10% Pd/C to 3-bromo aniline, 4-fluoro aniline, 3-methyl aniline, 4-hydroxy aniline respectively and verified from 1H NMR studies. The reduction reactions were similar conditions using electron beam irradiated 250 kGy macro and micro 10% Pd/C catalyst. The effectiveness of commercial sources of palladium on carbon (Pd/C) varies widely, leading to the appreciable variations in the reaction times. The decrease in reaction time has been attributed to the higher dispersion of Pd particles upon irradiation. The physico-chemical characteristics of effective hydrogenation catalysts were determined to be: (i) small Pd particle size and (ii) homogeneous distribution of Pd on the carbon support. With no significant loss of catalytic activity, the electron beam-irradiated catalyst can be used again for five runs. These days, chemists can determine as well as forecast the effectiveness of catalysts before investing time and money in expensive synthetic materials.

Water-promoted oxidative coupling of aromatics with subnanometer palladium clusters confined in zeolites

A fundamental understanding of the active sites in working catalysts can guide the rational design of new catalysts with improved performances. In this work, we have followed the evolution of homogeneous and heterogeneous Pd catalysts under the reaction conditions for aerobic oxidative coupling of toluene for the production of 4,4′-bitolyl. We have found that subnanometer Pd clusters made with a few Pd atoms are the working active sites in both homogeneous and heterogeneous catalytic systems. Moreover, water can promote the activity of Pd clusters by nearly one-order magnitude for oxidative coupling reaction by facilitating the activation of O2. These new insights lead to the preparation of a catalyst made with Pd clusters supported on a two-dimensional zeolite, which expands the scope of the oxidative coupling of aromatics to larger substrates.

Magnetic extract of iron ore-derived goethite microparticles as a promising heterogeneous Fenton-like catalyst for brilliant green dye discolorization

Magnetic extract of iron ore-derived goethite microparticles as a promising heterogeneous Fenton-like catalyst for brilliant green dye discolorization

Copper Catalysts Anchored on Cysteine-Functionalized Polydopamine-Coated Magnetite Particles: A Versatile Platform for Enhanced Coupling Reactions

Cysteine plays a crucial role in the development of an efficient copper-catalyst system, where its thiol group serves as a strong anchoring site for metal coordination. By immobilizing copper onto cysteine-modified, polydopamine-coated magnetite particles, this advanced catalytic platform exhibits exceptional stability and catalytic activity. Chemical modification of the polydopamine (PDA) surface with cysteine enhances copper salt immobilization, leading to the formation of the Fe3O4@PDA-Cys@Cu platform. This system was evaluated in palladium-free, copper-catalyzed Sonogashira coupling reactions, effectively catalyzing the coupling of terminal acetylenes with aryl halides. Additionally, the Fe3O4@PDA-Cys@Cu platform was employed in click reactions, confirming the enhanced catalytic efficiency due to increased copper content. The reusability of the platform was further investigated, demonstrating improved performance, especially in recyclability tests in click reaction, making it a promising candidate for sustainable heterogeneous catalysis.

Potassium Carbonate as a Low-Cost and Highly Active Solid Base Catalyst for Low-Temperature Methanolysis of Polycarbonate.

As the demand for polycarbonate (PC) plastic increases over the years, the development of a chemical recycling system to produce virgin-like-quality monomers is indispensable not only to attain completely sustainable cycles but also to contribute to the decrease in global plastic pollution. Herein, potassium carbonate (K2CO3) was used as a low-cost, readily available, and highly active solid base catalyst for low-temperature PC methanolysis in the presence of THF as a solvent, producing highly pure and crystalline bisphenol A (BPA) and with a catalytic performance higher than group IIA metal oxides (MgO, CaO, and SrO) and some group IA metal carbonates (NaHCO3, KHCO3, and Na2CO3). THF was the best solvent in aiding the reaction owing to it having a similar polar parameter (δp) to that of PC according to Hansen solubility parameters. By the reaction over the catalyst, 100% PC conversion, 97% BPA yield, and 86% dimethyl carbonate yield were achieved within just 20 min at 60 °C. The catalyst possessed an apparent activation energy (Ea) of 52.3 kJ mol-1, which is the lowest value so far for heterogeneous catalysts, while the mechanistic study revealed that the reaction proceeded via the methoxide pathway. The reusability test demonstrated that the catalyst was reusable at least four times. Furthermore, this catalytic system was successfully applied to actual post-consumerPC wastes and polyesters, including polyethylene terephthalate (PET) and polylactic acid (PLA).