Heterogeneous Catalyst Research Articles

CO2-Based Stable Porous Metal-Organic Frameworks for CO2 Utilization.

The transformation of carbon dioxide (CO2) into functional materials has garnered considerable worldwide interest. Metal-organic frameworks (MOFs), as a distinctive class of materials, have made great contributions to CO2 capture and conversion. However, facile conversion of CO2 to stable porous MOFs for CO2 utilization remains unexplored. Herein, we present a facile methodology of using CO2 to synthesize stable zirconium-based MOFs. Two zirconium-based MOFs CO2-Zr-DEP and CO2-Zr-DEDP with face-centered cubic topology were obtained via a sequential desilylation-carboxylation-coordination reaction. The MOFs exhibit excellent crystallinity, as verified through powder X-ray diffraction and high-resolution transmission electron microscopy analyses. They also have notable porosity with high surface area (SBET up to 3688 m2 g-1) and good CO2 adsorption capacity (up to 12.5 wt %). The resulting MOFs have abundant alkyne functional moieties, confirmed through 13C cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectra. Leveraging the catalytic prowess of Ag(I) in diverse CO2-involved reactions, we incorporated Ag(I) into zirconium-based MOFs, capitalizing on their interactions with carbon-carbon π-bonds of alkynes, thereby forming a heterogeneous catalyst. This catalyst demonstrates outstanding efficiency in catalyzing the conversion of CO2 and propargylic alcohols into cyclic carbonates, achieving >99% yield at room temperature and atmospheric pressure conditions. Thus, this work provides a dual CO2 utilization strategy, encompassing the synthesis of CO2-based MOFs (20-24 wt % from CO2) and their subsequent application in CO2 capture and conversion processes. This approach significantly enhances overall CO2 utilization.

Interface reconfiguration of MnCO3/Mn3O4 heterostructure enhances the ozone decomposition in the entire humidity range

The catalytic efficiency of manganese-based catalysts in practical ozone decomposition applications is limited by challenging desorption of intermediate oxygen species and competitive adsorption of H2O molecules in humid environments. In this work, MnCO3/Mn3O4 composites with heterogeneous structures were synthesized through a facile one-step strategy. The obtained MnCO3/Mn3O4-1/2 catalyst exhibited high content of oxygen vacancies, fast electron mobility rate and obvious advantages in catalytic ozone decomposition performance at a space velocity of 600 L g−1 h−1 and 95% RH. In-situ DRIFT spectra indicated that the rate-determining steps for ozone decomposition of MnCO3 and Mn3O4 are the reaction of atomic oxygen with ozone to form O22- and desorption of O22-, respectively. MnCO3/Mn3O4 heterogeneous catalyst undergoes reconfiguration under ozone atmosphere, inducing discontinuous MnOx coatings on the MnCO3 surface, which form a potential difference with Mn3O4. MnCO3/Mn3O4 heterogeneous structure modulates the electronic state of active site, and the synergistic effect of MnCO3 and Mn3O4 improves catalytic performance.

Metal–Organic Framework Fe-BTC as Heterogeneous Catalyst for Electro-Fenton Treatment of Tetracycline

This study explores the use of the iron-containing metal–organic framework (MOF), Basolite®F300, as a heterogeneous catalyst for electrochemically-driven Fenton processes. Electrochemical advanced oxidation processes (EAOPs) have shown promise on the abatement of recalcitrant organic pollutants such as pharmaceuticals. Tetracyclines (TC) are a frequently used class of antibiotics that are now polluting surface water and groundwater sources worldwide. Acknowledging the fast capability of EAOPs to treat persistent pharmaceutical pollutants, we propose an electrochemical Fenton treatment process that is catalyzed by the use of a commercially available MOF material to degrade TC. The efficiency of H2O2 generation in the IrO2/carbon felt setup is highlighted. However, electrochemical oxidation with H2O2 production (ECO-H2O2) alone is not enough to achieve complete TC removal, attributed to the formation of weak oxidant species. Incorporating Basolite®F300 in the heterogeneous electro-Fenton (HEF) process results in complete TC removal within 40 min, showcasing its efficacy. Additionally, this study explores the effect of varying MOF concentrations, indicating optimal removal rates at 100 mg L−1 due to a balance of kinetics and limitation of active sites of the catalysts. Furthermore, the impact of the applied current on TC removal is investigated, revealing a proportional relationship between current and removal rates. The analysis of energy efficiency emphasizes 50 mA as the optimal current, however, balancing removal efficiency with electrical energy consumption. This work highlights the potential of Basolite®F300 as an effective catalyst in the HEF process for pollutant abatement, providing valuable insights into optimizing electrified water treatment applications with MOF nanomaterials to treat organic pollutants.

Production and testing of mahua oil-based biodiesel synthesized through heterogeneous catalyst using experimental and numerical method.

A two-step treatment of mahua oil was conducted to synthesize mahua biodiesel using heterogeneous biomass-based catalyst derived from mahua shell. Mahua oil having higher free fatty acid (FFA) content (about 19%) was esterified to reduce the FFA content up to 1%. The esterification process was carried out using 200mL mahua oil, 5:1 molar ratio (methanol:oil), and 2.25 weight% of H2SO4 at a temperature of 60°C for 3h. Post esterification, a set of 16 experiments were created using a Box-Behnken design (BBD)-based response surface methodology (RSM) approach to conduct the transesterification of the esterified oil. Molar ratio, catalyst loading, reaction temperature, and reaction time were the four input variables chosen for the design of experiments. The optimized conditions for maximum biodiesel yield (87.7%) were found to be 14.88 molar ratio, 3.578% catalyst loading, 69.7°C reaction temperature, and 81.9min reaction time. The Diesel RK engine simulation tool which was experimentally validated for baseline diesel fuel was used for numerical simulation of mahua biodiesel. The performance, combustion, and emission behavior of mahua biodiesel analyzed using numerical simulation presented the sustainability of mahua biodiesel as an alternate fuel.

Copper-bonded polyoxomolybdates-based framework as a heterogeneous catalyst for the cascade click reaction and bromination

The selective conversion of alkynes into bromotriazoles over a single-component catalyst is highly desirable but presents significant challenges. In this study, we developed a robust copper-bonded polyoxomolybdates-based framework [Cu2(Mo6O20)]·2H2O (CPF-1), and it integrates the catalytic ability of Cu(I) site with the multielectron-transfer ability of polyoxometalates. As a result, CPF-1 exhibits favorable bifunctional catalytic activity for click chemistry and achieves 99% yield in the conversion of corresponding products to bromotriazoles. To our knowledge, CPF-1 represents the first heterogeneous catalyst that significantly enhances cascade reaction with excellent efficiency and sustainable recyclability. Additionally, the possible cascade catalytic mechanisms of these two reactions are also proposed.

Controlled synthesis of defective MOF-808 and its application in levulinic acid esterification

Defective MOF-808 (Def. MOF-808) plays a pivotal role in catalysis, offering the potential for optimizing catalytic reactions and enhancing reactivity. Through precise control of MOF-808 synthesis conditions, including time, temperature, zirconium (Zr) source, ligand ratio, defect agent type, and content, we systematically studied their effect on material properties. The results showed that by adjusting these conditions, we synthesized a series of MOF-808 materials with varying defect concentrations, referred to as Def. MOF-808. Shorter synthesis times, lower temperatures, defect agents with stronger coordination capabilities, and increased defect agent concentration or reduced organic ligand concentration effectively enhance Def. MOF-808’s defect concentration. The presence of defect sites facilitates the effective binding of the sulfate group, thereby amplifying the level of sulfation and augmenting its acid catalytic potential. Furthermore, this study unveiled a direct link between defect concentration and the catalytic activity observed in the levulinic acid esterification reaction. The Defect-engineered MOF-808 optimized through response surface design demonstrates exceptional heterogeneous acid catalysis performance, achieving impressive conversion rates of 97.5% and selectivity of 96.2%, coupled with remarkable catalytic stability. This study highlights defect engineering as a successful strategy to improve MOF-808 catalyst performance, offering insights for future enhancements.

Development Trends in Selective Hydrogenation Upgrading of 5-Hydroxymethylfurfural Catalyzed by Heterogeneous Metal Catalysts

Development Trends in Selective Hydrogenation Upgrading of 5-Hydroxymethylfurfural Catalyzed by Heterogeneous Metal Catalysts

Utilizing Recycled Expanded Polystyrene Plastics to Stabilize Metal–Organic Frameworks for Heterogeneous Catalysis

Polystyrene plastics present significant environmental and human health threats due to their poor recyclability and degradability. However, leveraging their properties to enhance material performance stands out as one of the most effective strategies for mitigating these issues. Here, we have employed recycled expanded polystyrene plastics to manufacture metal–organic framework/expanded polystyrene plastic composites (MOF@EPP) using an adverse solvent precipitation method. This method simultaneously recycles EPPs and safeguards moisture-sensitive MOFs. Due to the exceptional hydrophobic properties of EPPs, HKUST−1@EPP can maintain structural integrity even when immersed in water for 30 days. This method is applicable to other moisture-sensitive MOFs, such as MOF−74(Zn) and MIL−53(Al). The HKUST−1@EPP composite also exhibits desirable heterogeneous catalytic activity in the Knoevenagel condensation reaction between benzaldehyde and acrylonitrile. The conversion rate can reach 94.9% within 4 h at 90 °C and does not exhibit a significant decrease even after six cycles, even in the presence of water. This study not only introduces a novel concept for recycling polystyrene plastics, but also offers a practical strategy for safeguarding moisture-sensitive MOFs.

Effect of crystal facets in plasmonic catalysis

While the role of crystal facets is well known in traditional heterogeneous catalysis, this effect has not yet been thoroughly studied in plasmon-assisted catalysis, where attention has primarily focused on plasmon-derived mechanisms. Here, we investigate plasmon-assisted electrocatalytic CO2 reduction using different shapes of plasmonic Au nanoparticles - nanocube (NC), rhombic dodecahedron (RD), and octahedron (OC) - exposing {100}, {110}, and {111} facets, respectively. Upon plasmon excitation, Au OCs doubled CO Faradaic efficiency (FECO) and tripled CO partial current density (jCO) compared to a dark condition, with NCs also improving under illumination. In contrast, Au RDs maintained consistent performance irrespective of light exposure, suggesting minimal influence of light on the reaction. Temperature experiments ruled out heat as the main factor to explain such differences. Atomistic simulations and electromagnetic modeling revealed higher hot carrier abundance and electric field enhancement on Au OCs and NCs than RDs. These effects now dominate the reaction landscape over the crystal facets, thus shifting the reaction sites when comparing dark and plasmon-activated processes. Plasmon-assisted H2 evolution reaction experiments also support these findings. The dominance of low-coordinated sites over facets in plasmonic catalysis suggests key insights for designing efficient photocatalysts for energy conversion and carbon neutralization.

A Robust Pyrazolate Metal-Organic Framework for Efficient Catalysis of Dehydrogenative C-O Cross Coupling Reaction.

Construction of robust heterogeneous catalysts with atomic precision is a long-sought pursuit in the catalysis field due to its fundamental significance in taming chemical transformations. Herein, we present the synthesis of a single-crystalline pyrazolate metal-organic framework (MOF) named PCN-300, bearing a lamellar structure with two distinct Cu centers and one-dimensional (1D) open channels when stacked. PCN-300 exhibits exceptional stability in aqueous solutions across a broad pH range from 1 to 14. In contrast, its monomeric counterpart assembled through hydrogen bonding displays limited stability, emphasizing the role of Cu-pyrazolate coordination bonds in framework robustness. Remarkably, the synergy of the 1D open channels, excellent stability, and the active Cu-porphyrin sites endows PCN-300 with outstanding catalytic activity in the cross dehydrogenative coupling reaction to form the C-O bond without the "compulsory" ortho-position directing groups (yields up to 96%), outperforming homogeneous Cu-porphyrin catalysts. Moreover, PCN-300 exhibits superior recyclability and compatibility with various phenol substrates. Control experiments reveal the synergy between the Cu-porphyrin center and framework in PCN-300 and computations unveil the free radical pathway of the reaction. This study highlights the power of robust pyrazolate MOFs in directly activating C-H bonds and catalyzing challenging chemical transformations in an environmentally friendly manner.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction.

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

A review of process of methanol carbonylation to produce acetic acid

Acidic corrosion plays a significant part in the compound business, particularly in the production of new substance fiber. As of now, the primary technique for creating acidic corrosive is the carbonylation of methanol utilizing iridium or rhodium organometallic edifices. The delegate techniques and the most recent advancement of methanol carbonylation to deliver acidic corrosion from two parts of homogeneous catalysis and heterogeneous catalysis are explored efficiently. The present homogeneous catalytic method and heterogeneous catalytic synthesis method using two different catalytic systems are introduced, followed in chronological order by the traditional method of producing acetic acid by carbonylation of methanol in the history of the chemical industry. The primary issues with producing acetic acid using conventional techniques are examined, including the product separation and the costly catalyst recovery. These issues can be resolved by developing and perfecting heterogeneous catalytic systems. The benefits and drawbacks of conventional techniques are broken down, the comprehensive summary and critical analysis of previous research provide comprehensive background knowledge, and the future exploration bearing is to work on the heterogeneous synergist framework to accomplish higher selectivity and preservation rate and work on financial proficiency.

P-modified Pt/Al2O3 catalysts for selective propane dehydrogenation

The rigorous operating conditions required for propane dehydrogenation result in undesired side reactions on Pt catalysts. Herein, we present the successful suppression of structure-sensitive side reactions by modifying Pt/Al2O3 catalysts with P. The characterization of the P-modified Pt/Al2O3 catalysts revealed the coexistence of metallic Pt and Pt–P alloys on the surfaces of the Pt nanoparticles. At a reaction temperature of 600 °C, the Pt catalyst modified with an optimal amount of P exhibited a notably higher propylene selectivity (95%) than that of the unmodified Pt/Al2O3 catalyst (typically ∼83%), without any loss of activity. A detailed investigation revealed that the geometric effect resulting from the formation of the Pt–P alloy, which reduced the size of the Pt ensembles, was mainly responsible for the enhanced performance of P-modified Pt/Al2O3. This study offers vital insights into the formation of noble metal–P alloys on nanoparticle surfaces and their advantageous effects on heterogeneous catalysis.

Three-dimensional ordered FeTe-SmCoO3 nanocomposite: As efficient electrocatalyst for water oxidation

In this work, FeTe-SmCoO3 is fabricated through a hydrothermal method and then coated on a stainless steel (SS) substrate to enhance the electrocatalytic performance. The crystal structure, surface chemical state, and morphological features of pure (FeTe and SmCoO3) and heterogeneous catalysts (FeTe-SmCoO3) are determined via XRD, XPS, and TEM/EDX techniques. The fabricated FeTe-SmCoO3 electrocatalyst is attributed to the particular morphological design resulting from the synergistic effect of FeTe and SmCoO3 phases. The as-developed high exposure level of active sites with structural transformation greatly promoted the oxidation property with an overpotential only of 199 mV to derive a current density of 10 mA/cm2, also observed a small Tafel slope of 72 mVdec−1 with extraordinary stability of 90 h. The modified heterogeneous catalyst provides outstanding catalytic behavior toward OER in the alkaline solution, due to flexibility and multiple accessible oxidation states of samarium, cobalt, and iron ions. The catalyst not only acquires additional reaction sites and opens up new channels through the dispersion of the metal centers, but also achieves quick electron transfer in FeTe-SmCoO3 nanocomposite through the interconnection between two phases.

Non-radical activation of peroxymonosulfate by modified activated carbon for efficient degradation of oxytetracycline: Mechanisms and applications

The application of heterogeneous metal-free catalysis for non-radical peroxymonosulfate (PMS) oxidation is of great significance because of its low environmental effects and mild oxidant dosage. The purpose of this study was to investigate the activation mechanism of PMS using acid-modified activated carbon and oxytetracycline (OTC) as a representative pollutant. Modified activated carbon (MAC)/PMS system was capable of achieving 100 % degradation efficiency of OTC within 60 min, with an observed rate constant (kobs) of 0.0414 min−1. The degradation of OTC is dominated by non-radical oxidation pathways involved in mediated singlet oxygen (1O2) and electron-transfer process through electron paramagnetic resonance (EPR) and radicals quenching studies. The activation of PMS is attributed to the structural defects of MAC, persistent free radicals, and oxygen functional groups such as C-OOH. Moreover, the MAC/PMS system consistently demonstrates high and reliable contaminant removal in various water matrices. A continuous-flow device utilizing MAC shows excellent performance in purifying micro-polluted water. Additionally, the degradation pathways of pollutants and changes in toxicity during the degradation process were identified through density functional theory (DFT) calculations, liquid chromatography-mass spectrometry (LC-MS), and toxicological analysis. Finally, the cultivation of green beans, peas, and wheat was found to significantly decrease the toxicity of contaminated water through degradation. This study proposes a low-cost method to enhance the activation pathway of non-radical PMS by utilizing modified activated carbon materials for pollutant remediation.

Barium Alginate Gel Beads: A Homochiral Porous Material from Brown Algae for Heterogeneous Asymmetric Catalysis

Barium Alginate Gel Beads: A Homochiral Porous Material from Brown Algae for Heterogeneous Asymmetric Catalysis

Preview of CO2 utilization in converting to methanol process

Carbon dioxide, a greenhouse gas, has contributed to environmental issues on the planet in the past few years. Thus, it would be helpful to mitigate the impact that caused by carbon footprint, which is trying to reduce the carbon dioxide emission to the atmosphere and utilize it to generate green products for usage. It has been reported that CO_2 reduction could be converted to a valuable fuel source and thus it could be a potential solution to mitigate the impact of CO_2. In this paper, it illustrates three underlying approaches which are conventional heterogeneous catalysis, photocatalysis and electrochemical, and flaws existed inCO_2 converted to CH_3 OH production. Approach mechanism, principles and barriers are included in the following with detailed product selectivity/yield comparison between different catalysts under various conditions. Studies on different approaches have made substantial information focusing on various aspects and recommending the appropriate catalyst for the technique under the specific scenario. Finally, the overview of the research aims to provide feedback on progress made in CH_3 OH production from CO_2 in a large scale along with a summary regarding the future expectations on the research of the methanol conversion approaches developed.

Homogenous Oxidizing Oligomerization Coupled with Coagulation for Water Purification

Natural manganese oxides could induce the intermolecular coupling reactions among small-molecule organics in aqueous environments, which is one of the fundamental processes contributing to natural humification. These processes could be simulated to design novel advanced oxidation technology for water purification. In this study, periodate (PI) was selected as the supplementary electron-acceptor for colloidal manganese oxides (Mn(IV)aq) to remove phenolic contaminants from water. By introducing polyferric sulfate (PFS) into the Mn(IV)aq/PI system and exploiting the flocculation potential of Mn(IV)aq, a post-coagulation process was triggered to eliminate soluble manganese after oxidation. Under acidic conditions, periodate exists in the H4IO6− form as an octahedral oxyacid capable of coordinating with Mn(IV)aq to form bidentate complexes or oligomers (Mn(IV)-PI*) as reactive oxidants. The Mn(IV)-PI* complex could induce cross-coupling process between phenolic contaminants, resulting in the formation of oligomerized products ranging from dimers to hexamers. These oligomerized products participate in the coagulation process and become stored within the nascent floc due to their catenulate nature and strong hydrophobicity. Through coordination between Mn(IV)aq and H4IO6−, residual periodate is firmly connected with manganese oxides in the floc after coagulation and could be simultaneously separated from the aqueous phase. This study achieves oxidizing oligomerization through a homogeneous process under mild conditions without additional energy input or heterogeneous catalyst preparation. Compared to traditional mineralization-driven oxidation techniques, the proposed novel cascade processes realize transformation, convergence, and separation of phenolic contaminants with high oxidant utilization efficiency for low-carbon purification.

Semiconductor Catalyst: Investigation for the Degradation of BB9 Azo Dye by Sonophotocatalytic Process

AbstractThe degradability of an azo dye, Basic Blue 9 (BB9), by heterogeneous sonocatalytic, photocatalytic, and sonophotocatalytic oxidation process was examined using simultaneous irradiation of UV‐C at 254 nm and power ultrasound at 20 kHz accompanied with a heterogeneous catalyst zinc oxide (ZnO) in the study. The effect of ZnO dose and initial dye concentration was investigated on the dye degradation in sonocatalytic, photocatalytic, and sonophotocatalytic processes at pH 5.5 (natural pH). The results obtained from the experimental studies were evaluated with the parameters of color removal, pseudo‐first‐order rate constant, and half‐life time. It was observed that the degradation of BB9 dye by the sonophotocatalytic process was higher compared to both sonocatalytic and photocatalytic degradation. as follows: 97.46, 48.64 and 56.88 %. The combination of sono and photocatalytic showed a remarkable synergistic effect in BB9 degradation. The kinetics of sonophotocatalytic oxidations, depending on the initial BB9 dye concentration, were found to follow the Langmuir‐Hinshelwood model. In addition, the effect of ZnO on the sonophotocatalytic oxidation process was higher compared to titanium dioxide and zero‐valent iron as follows: 97.47, 80.77 and 80.62 %.

Ultrafast catalytic reduction of organic pollutants using ternary zinc–copper–nickel layered double hydroxide

Water is the utmost essential commodity for the support of life process in animals. In recent decades, rapid industrialization and uncontrolled agricultural practices have led to increased level of toxic pollutants in groundwater, including organic pollutants (dyes, nitroarene compounds, antibiotics, etc.), inorganic pollutants (heavy metals, nanoparticles, etc.), and pesticides, posing a serious threat to human health and the environment. Although various technologies such as adsorption, photocatalysis, reverse osmosis, filtration, sedimentation, flocculation, and precipitation are available for the elimination of toxic pollutants from wastewater, issues such as their cost and efficacy limit their usage. Recently, catalysis has been found to be the most effective approach since it exhibits significant capability to eliminate almost all the pollutants and offers the benefit of simple design and low initial cost. In the present study, ternary zinc–copper–nickel layered double hydroxide (ZnCuNi‐LDH) synthesized using facile acid hydrolysis method was employed as an efficacious heterogeneous catalyst for the reduction of NACs (para‐nitrophenol and para‐nitroaniline) and degradation of organic azo dyes (methyl orange, amaranth, and brilliant black). ZnCuNi‐LDH exhibited superior catalytic activity for the reduction of all five model pollutants with reduction efficiency of more than 95% within a short time span of 5 min. Therefore, keeping in view the layered structure, high specific surface area, and remarkable catalytic performance, ZnCuNi‐LDH holds immense potential for the large‐scale catalytic degradation of refractory pollutants.