Field Of Catalysis Research Articles

Study of Mesostructured CeO2 Synthesis via Nanocasting Using SBA-15 as a Template: Influence of the Cerium Precursor

Mesoporous materials with high surface area, large pore volume, and adjustable pore size are promising in the fields of adsorption and heterogeneous catalysis. In this work, ordered mesoporous ceria structures were successfully prepared via nanocasting using SBA-15 as a template, with Ce(NO3)3·6H2O or CeCl3·7H2O as ceria precursors. The materials were characterized before and after template removal. The CeO2 crystallite size in the CeO2/SBA-15 composites increases with successive impregnations until it reaches the pore size of the SBA‑15. Upon removal of the SBA-15 template, the synthesized materials exhibit pore diameters corresponding to the wall thickness of the SBA-15, evidencing that the inverted structure was obtained. Mesoporous ceria exhibits increasingly ordered structure up to five successive impregnations with 1.3 mmolCe/gSBA-15. Using cerium chloride as a precursor, highly ordered structures were reached after only three impregnations. The feasibility of this synthesis in fewer steps (1, 3, and 5), employing the same amount of Ce precursor (6.7 mmolCe/gSBA-15), was also studied. Results show a higher ordering degree and oxygen mobility capacity at higher impregnation steps. The mesostructured ceria samples exhibit significantly higher oxygen mobility than commercial bulk ceria, along with high thermal stability, which highlights the usefulness of these structures.

Polysilsesquioxane Open Hollow Spheres for Heavy Metal Ions Adsorption

Hollow microspheres with open windows on the shells have shown significant potential in adsorption, catalysis, and drug delivery fields, owing to their low density, large interior volume, high specific surface area, and abundant availability of adsorption sites. However, creating open hollow spheres with structurally stable and entirely organic‐functionalized surfaces remains a challenge. Herein, we fabricated polysilsesquioxane open hollow spheres using trialkoxysilane containing mercaptopropyl groups under vigorous stirring, employing polystyrene microspheres as template. Various reaction parameters were explored, revealing stirring speed as the key factor influencing the morphology and openness of the microspheres. By examining the morphology of intermediate products at different reaction times, we proposed a step‐growth mechanism for microsphere formation. The resulting materials exhibited high adsorption capacity and selectivity towards Hg2+ and Pb2+, attributed to the presence of thiol groups and the open‐hollow structure. Our approach provides a robust method for producing open hollow materials with functionalized surfaces, offering potential applications in the adsorption field.

Understanding the electrocatalytic role of magnesium doped bismuth copper titanate (BCTO) in oxygen evolution reaction

Designing high-efficiency electrocatalysts for water oxidation has become increasingly important in the catalysis field owing to its implications for renewable energy production and storage. The production of hydrogen (H2) from water is hampered by the very sluggish kinetics of the water-splitting process. Enhancement of effective oxygen evolution reaction (OER) electrocatalysts is also required to understand the primary barrier to OER. This article investigates the electrochemical activity of magnesium-doped bismuth copper titanate (Mg-BCTO) as an efficient catalyst for the OER in water electrolysis, a critical step in hydrogen production for sustainable energy. The synthesized materials, including various stoichiometries of Mg-doped BCTO, undergo thorough physical and electrochemical characterization using XRD, FT-IR, Raman, SEM, TEM, XPS, CV, EIS, and Tafel polarization analyses. Remarkably, Mg0.1 doped BCTO demonstrates superior performance, achieving a current density of 10 mA cm−2 at a very low overpotential (η10) of 265 mV and with a Tafel slope of 92 mV dec−1. This finding not only highlights the electrocatalytic efficiency of Mg doped BCTO but also positions it as a promising model for the development of highly active and stable water oxidizing catalysts, contributing to the advancement of clean energy technologies.

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts.

This review provides an overview of recent progress made in the field of catalysis using metal-free tetrapyrrolic macrocycles, focusing on calix[4]pyrroles, porphyrins and corroles, which are structurally related to porphyrins. Calix[4]pyrroles are versatile receptors in supramolecular chemistry while porphyrins are considered as 'pigment of life' due to their role in vital biological processes. Beyond their natural functions, synthetic porphyrins have been applied in various fields, including organometallic catalysis, dye-sensitized solar cells, sensing, artificial olfactory systems, photodynamic therapy (PDT), anticancer drugs, biochemical probes, and electrochemical devices. Relevant examples of these two pyrrolic macrocycles as metal-free organocatalysts, photocatalysts, and electrocatalysts are presented here. The effect of macrocyclic structural modifications such as their functionalization with different substituents, distortion from planarity, conformational flexibility and rigidity towards catalytic activity are presented, highlighting the potential of these two macrocycles as metal-free catalysts.

Revealing the Critical Role of the Lone Pair Electrons of Bi3+ in Electrocatalytic Oxygen Reduction Reaction on Mn‐Based BiMn2O5 Mullite Surface

AbstractThere is a research gap regarding the role of lone pair electrons of post‐transition metal cations in catalysis field, yet such studies hold significant implications for expanding their applications. Herein, the role of Bi3+ ion lone pair electrons in electrocatalytic oxygen reduction reaction (ORR) is elucidated using ternary mullite oxides as prototype catalysts. Among the three synthesized mullites ((Sm/Y/Bi)Mn2O5), BiMn2O5 exhibits notably superior ORR catalytic activity. Through advanced characterization techniques, including in situ Raman, in situ infrared, and X‐ray absorption spectroscopy, combined with theoretical calculations, it is determined that the superior electrocatalytic performance of BiMn2O5 originates from the lone pair electrons that activate catalytic sites through stereochemical effects. Specifically, the Bi3+ lone pair electrons in the 6s orbital near Fermi level interact with O 2p orbitals, causing a shift of the oxygen ligands, and significant variance in A─O bond lengths. This structural distortion of BiO8 coordination unit directly results in a large Mn─O bond angle at the active center of BiMn2O5 and strong covalent interactions, facilitating charge transfer and refining the adsorption behavior of oxygen intermediates to achieve the overpotential of 0.25 V vs. RHE. This study provides insights into developing next‐generation catalysts by harnessing the lone pair electrons of post‐transition metal cations.

MQMAS spectra of half-integer quadrupolar nuclei enhanced by indirect DNP

The observation of half-integer quadrupolar nuclei, which represent 66 % of the NMR-active isotopes, is essential to understand the atomic-level structure of inorganic materials near the surfaces with applications in the field of catalysis, biomaterials and optoelectronics. For that purpose, we have recently introduced an efficient technique, which combines the sensitivity gain provided by indirect DNP (dynamic nuclear polarization) under MAS (magic-angle spinning) and the high resolution obtained by refocusing the second-order quadrupolar interaction (H. Nagashima et al., J. Phys. Chem. Lett. 15 (2024) 4858). This technique combines (i) a D-RINEPT (dipolar-mediated refocused INEPT) transfer, (ii) an MQMAS (multiple-quantum MAS) filter, and (iii) a QCPMG (quadrupolar Carr-Purcell Meiboom-Gill) detection. We explain the design of several variants of this pulse sequence and notably the selection of the coherence transfer pathways. In particular, the amplitudes of the coherence transfer pathways through the ±3Q coherence orders of the quadrupolar isotope can be equalized using a train of π-pulses selective of the central transition, instead of a z-filter. This equalization method has the advantage to limit the length of the phase cycles and to enhance slightly the signal intensity. Moreover, for spin-3/2 nuclei subject to moderate or large quadrupolar interactions, more efficient excitation and conversion of 3Q coherences are achieved using cosine-modulated long-pulses (cos-lp), instead of fast-amplitude-modulated (FAM) pulses. The performances of the different D-RINEPT-MQMAS-QCPMG variants are compared through the observation of 35Cl and 27Al isotopes without DNP in l-histidine hydrochloride and isopropylamine-templated microporous aluminophosphate (ipa-AlPO4–14), respectively, as well as the acquisition of DNP-enhanced high-resolution spectra of 11B and 17O nuclei near the surface of partially oxidized boron nitride supported on dendritic and fibrous nanosilica and γ-alumina enriched in 17O isotope using a slurrying approach. The spectra recorded for γ-alumina show that the slurrying method produces less disorder than grinding assisted by 17O-enriched water.

Synthesis of Homochiral N-Heterocyclic Carbene-Based Nanosheets for Enhanced Asymmetric Catalysis.

Utilizing ultrathin 2D metal-organic framework nanosheets (2D MONs) as supports for incorporating chiral catalysts represents a highly promising avenue in the field of asymmetric catalysis. In this study, four pairs of isostructural chiral metal-organic layers (MOLs) adorned with N-Heterocyclic carbene (NHC) groups are successfully synthesized. Notably, the obtained bulky (S)-1-Zn crystals can be readily delaminated into ultrathin MONs consisting of 1-2 layers through an ion intercalation-assisted exfoliation process. Subsequent asymmetric catalysis studies revealed that the NHC sites can be effectively activated by a proton sponge while maintaining structural integrity for the subsequent benzoin condensation. Due to their well-exposed catalytic sites, ultrathin morphology, and porous structure, the (S)-1-Zn nanosheets exhibited significantly enhanced yield and enantioselectivity compared to their bulk counterparts and organic precursors. This research highlights an efficient strategy for incorporating chiral NHC species onto 2D MONs, thereby unlocking their immense potential for heterogeneous asymmetric catalysis.

Activation and C-C Coupling of Aryl Iodides via Bismuth Photocatalysis.

Within the emerging field of bismuth redox catalysis, the catalytic formation of C-C bonds using aryl halides would be highly desirable; yet such a process remains a synthetic challenge. Herein, we present a chemoselective bismuth-photocatalyzed activation and subsequent coupling of (hetero)aryl iodides with pyrrole derivatives to access C(sp2)-C(sp2) linkages through C-H functionalization. This unique reactivity is the result of the bismuth complex featuring two redox state-dependent interactions with light, which 1) activates the Bi(I) complex for oxidative addition via MLCT, and 2) promotes the homolytic cleavage of aryl Bi(III) intermediates through a LLCT process.

Activation and C−C Coupling of Aryl Iodides via Bismuth Photocatalysis

AbstractWithin the emerging field of bismuth redox catalysis, the catalytic formation of C−C bonds using aryl halides would be highly desirable; yet such a process remains a synthetic challenge. Herein, we present a chemoselective bismuth‐photocatalyzed activation and subsequent coupling of (hetero)aryl iodides with pyrrole derivatives to access C(sp2)−C(sp2) linkages through C−H functionalization. This unique reactivity is the result of the bismuth complex featuring two redox state‐dependent interactions with light, which 1) activates the Bi(I) complex for oxidative addition via MLCT, and 2) promotes the homolytic cleavage of aryl Bi(III) intermediates through a LLCT process.

Construction of a novel chemiluminescence system based on mixed-ligand metal-organic frameworks

Exploring new materials to enhance chemiluminescence (CL) and constructing novel CL systems are essential for expanding the application range of CL analysis and improving its sensitivity. Metal-organic frameworks (MOFs) have gained popularity in catalysis and other fields due to their unique structural features and properties. However, the research on the application of MOFs in CL is still in its infancy. In this study, one kind of mixed-ligand metal-organic frameworks using Zn as the metal ion (Zn m-MOFs) was successfully synthesized and applied to enhance the CL of NaClO-H2O2 system. The synthesized Zn m-MOFs catalyzed the generation of reactive oxygen species (ROS) (·O2−, 1O2 and ·OH) which injected holes and electrons to Zn m-MOFs to generate hole-injected and electron-injected Zn m-MOFs (Zn m-MOFs⋅+ and Zn m-MOFs⋅−). The subsequent annihilation of these charge carriers led to enhanced CL. At the same time, chemiluminescence resonance energy transfer (CRET) occurred during the process. Compared with the NaClO-H2O2 system without Zn m-MOFs, the CL intensity of the Zn m-MOFs-NaClO-H2O2 system was enhanced by approximately 1000 times. This study aims to provide new insights for the development of innovative CL systems based on MOFs, thereby broadening the application fields of CL analysis.

Metal-organic framework-based hybrids with photon upconversion.

Upconversion materials (UCMs) featuring an anti-Stokes type emission establish them as an important category of photoluminescent materials. Metal-organic frameworks (MOFs) are rapidly gaining prominence as a class of versatile materials with favourable physical and chemical properties, including high porosity, controllable pore size, flexible design, and diverse functional sites. To endow MOFs with upconversion capability and improve the properties and performance of UCMs, the hybrids integrating UCMs and MOFs are proven to be successful. This review focuses on the research advancements of upconverting MOF-based hybrids, encompassing classifications, luminescence mechanisms, designs, properties, and applications in energy, catalysis, and biomedical fields. The analyses on the functions of upconversion and MOFs, as well as the advantages and disadvantages of various upconverting MOF-based hybrids, are included. Future research directions spanning from properties and performance to applications are explored. This review will be valuable in highlighting the research accomplishments, inspiring more ideas, facilitating deeper investigations in diverse avenues, and further advancing the research field.

Heterogeneous Asymmetric Hydrogenation of C═C and C═O Double Bonds

AbstractNowadays, heterogeneous catalysts play a crucial role in the field of asymmetric catalysis to produce enantiopure compounds for various applications. The unique properties of heterogeneous systems, such as high stability, reusability, or ease of separation, allow effective catalysis of asymmetric transformations and their further implementation in industrial processes. In this mini‐review, we address the recent trend in the synthesis of chiral heterogeneous catalysts and their subsequent application in asymmetric hydrogenation reactions. We focus on current advances in asymmetric hydrogenation reactions of C═C and C═O bonds due to their high relevance in the fine chemicals industry. Our main aim is to provide a short overview of this expanding field, its current challenges, and future perspectives.

Polyoxometalates@Metal-Organic Frameworks: Synthesis Strategies, Nanostructure Modulation and Application in Biomass Conversion.

Polyoxometalates@metal-organic frameworks (POMs@MOFs) have attracted much attention as multifunctional materials in biomass catalysis. Individual POMs and MOFs are hindered by their respective defects, such as poor stability and single catalytic active site, which make it difficult to realize large-scale applications. However, the combination of POMs and MOFs can be used to maximize the catalytic advantages of each. MOFs with high specific surface area and rich pore structure can effectively stabilize and uniformly disperse POMs, while the introduction of POMs also provides more catalytic possibilities for POMs@MOFs. Therefore, POMs@MOFs with ultra-high porosity, large specific surface area and excellent acid catalytic activity have unique catalytic advantages in the field of biomass catalytic conversion. In this work, we provide an overview of the current development of POMs@MOFs in the field of biomass catalysis. The synthesis strategies of POMs@MOFs are summarized and discussed, highlighting the in-situ synthesis methods. We focus on the nanostructure engineering of POMs@MOFs, and explore the "structure-property" relationship in depth. In addition, the representative work of POMs@MOFs in the catalysis of biomass derivatives is summarized. Filially, the prospects, and challenges for the future development of POMs@MOFs in the field of biomass catalysis are also presented.

Construction of Z-type heterojunction by depositing CuO nanoparticles on NiO nanosheets for visible-light-enhanced catalytic ammonia borane methanolysis

The development of effective and cost-efficient catalysts for the hydrogen production through methanolysis of ammonia borane (AB) is a hot topic in the field of energy catalysis. In this study, a simple method has been developed to construct a low-cost Z-type heterojunction by depositing CuO nanoparticles on the surface of NiO nanosheets. The as-prepared CuO/NiO composites exhibit prominent activity towards AB methanolysis. The hydrogen generation rate (HGR) is 3.00 Lhydrogen min−1 gcat.−1 when the optimal CuO/NiO sample functions as a catalyst, which is increased to 3.93 Lhydrogen min−1 gcat.−1 with the assistance of visible light illumination. The enhancement of catalytic activity are attributed to the variation of the electronic structure of the catalysts. With the formation of Z-type heterojunction, the valence band electrons of CuO and NiO are excited and transfer to their respective conduction bands under light illumination. Subsequently, the conduction band electrons of CuO recombine with the valence band holes of NiO, leading to an accumulation of electrons at the conduction band of NiO. Consequently, the electron density of the Ni sites is increased, which enhances AB methanolysis. This study can provide new insights for the design and synthesis of cost-effective and highly efficient direct Z-type heterojunction catalysts for hydrogen production through AB methanolysis. Moreover, this study is also helpful for the understanding of how visible light enhances AB methanolysis.

Bipolar Membranes With Controlled, Microscale 3D Junctions Enhance the Rates of Water Dissociation and Formation

AbstractA soft lithographic method is developed for making bipolar membranes (BPMs) with catalytic junctions formed from arrays of vertically oriented microscale cylinders. The membranes are cast from reusable polydimethylsiloxane (PDMS) molds made from silicon masters, which are fabricated on 2″ to 4″ wafer scales by nanosphere lithography. High‐aspect‐ratio junctions are made on a length scale similar to the thickness of optimized catalyst layers for water dissociation, creating a platform for probing the dual effects of catalysis and local electric field at the microscale BPM junction. Optimized polymer materials and nanoscale metal oxide catalysts are used in this study. 3D BPMs are tested under reverse and forward bias conditions, exhibiting superior performance relative to their 2D counterparts. Under forward bias in H2‐O2 fuel cells, 3D BPMs achieve a current density of 1500 mA cm−2, ≈7 times higher than 2D membranes made from the same materials.

Correlating Heterogeneities in Support Fragmentation to Polymer Morphology in Metallocene‐Based Propylene Polymerization Catalysis

AbstractIn the field of olefin polymerization catalysis, metallocenes are heterogenized with methylaluminoxane onto silica supports to yield active catalysts. During olefin polymerization, these silica supports act as a framework to control the fragmentation stage, thereby influencing the final polymer product and preventing reactor fouling and fines formation. This study investigates the influence of different silica supports induced on the final polymer product. To study a broad range of silica supports from an industrial silica database, we utilize a hierarchical clustering method to cluster the supports based on their physical properties. From the clustering method, five supports representing the clusters and an industrial benchmark were analyzed at different polymerization stages using focused ion beam–scanning electron microscopy (FIB–SEM) and microcomputed tomography (microCT). This combined FIB‐SEM/microCT methodology revealed differences in both fragmentation behavior and polymer morphologies based on structural features, including macropores, mesopores, spray‐dried shells, spray‐dried spheres, and denser shells. The heterogeneity and ideal fragmentation behavior was further assessed by calculating the replication factor of each support, indicating that silica materials containing macropores and spray‐dried shells have an almost ideal replication phenomenon. This multiscale analysis revealed new understanding of catalyst fragmentation for different supports. This understanding could in the future be further developed by the addition of more supports or additional analysis of the supports to the industrial database.

Hydrophobic Modification of Halloysite Nanotubes Loaded with a Small Amount of Tungsten Oxide for Efficient Oxidative Desulfurization.

Transition metal oxides can be used as efficient multiphase catalysts in the field of catalysis. In this study, a hydrophobic halloysite nanotube (HNT) catalyst was designed and prepared with a low loading. Tungsten oxide was immobilized on the inner surface of the HNT, through electrostatic adsorption and calcination. Furthermore, a dual-functional W/HMT/M catalyst was prepared by hydrophobic modification of the outer surface of HNT through a harmless and nontoxic method. The catalyst was applied in the oxidative desulfurization (ODS) of dibenzothiophene (DBT), and characterized by inductively coupled plasma (ICP), contact angle tests, and other methods. Systematic characterization further confirmed that W/HNT/M has a low loading (0.48 wt %) and a relatively high contact angle of 92.6°. Oxidative desulfurization experiments demonstrated that the high contact angle corresponds to good hydrophobicity. The low loading and high activity of the catalyst enabled it to achieve a removal efficiency of 100% for DBT under conditions of 60 °C and an O/S = 4. The hydrophobic surface of HNT allowed better dispersion in the oil phase, while its hydrophilic inner cavity could adsorb H2O2 and the converted dibenzothiophene sulfoxide, thereby reducing the subsequent extraction steps after oxidative desulfurization and enhancing the reaction environment for reactants and active oxygen. W/HNT/M maintained high activity for at least 5 cycles. Additionally, the potential mechanism of the catalyst in the aqueous ODS reaction was proposed. This study demonstrates that HNT-supported metal oxides have desulfurization potential and provides ideas for improving ODS catalytic activity of the ODS through low loading, high activity, and unique hydrophobicity design.

ZIF-8 Porous Liquids with Different Sterically Hindered Solvents and Porous Guests for Catalytic Conversion of Carbon Dioxide.

Utilizing carbon dioxide (CO2) as a raw material is an effective way to reduce carbon emissions, and developing catalytic systems with high catalytic activity and stability is crucial for the efficient utilization of CO2. Porous liquids (PLs) with both permanent pores and fluidity have great potential in the fields of catalysis, gas sorption, and storage. Nevertheless, the catalytic performance of PLs is affected by many factors; therefore, further study is needed. Herein, we proposed a general strategy to construct a series of type III PLs with different chemical structures of sterically hindered solvents and different microstructures of porous guests. Benefiting from the unique microstructures, the as-prepared PLs exhibit great potential in catalyzing the reaction of CO2 with propylene oxide under suitable conditions. Moreover, their catalytic activity exceeds that of pure sterically hindered solvents without a porous guest loading. The influences of the nucleophilicity of the anion of the sterically hindered solvent and the microstructure of the porous guests on the catalytic activity and the catalytic stability of the PLs were analyzed. Meanwhile, the mechanism of the catalytic conversion of CO2 was proposed, which is of great significance for the design and development of the subsequent PL catalysts.

Facilitating catalytic research via better data reporting and curation: A case study of propane dehydrogenation on Ga/H-ZSM-5

In the field of experimental heterogeneous catalysis, the generation, analysis, and curation of large-scale, high-quality datasets are crucial yet challenging. This work highlights the significance of proper data reporting and curation through a case study on propane dehydrogenation over Ga/H-ZSM-5 catalysts. We demonstrate the challenges and benefits of analyzing larger datasets across multiple publications in the identification of active structures and elucidation of reaction mechanisms. The findings highlight the need for reporting reliable datasets in accessible format to facilitate integration and comparison of catalytic data across different studies, potentially leading to novel scientific insights.

Novel synthesis of nano-cerium oxide using ultrasonic microreactor: Process optimization and AO7 degradation

Nano-CeO2 has been widely used in catalysis, polishing, coating, biomedicine, and other fields, but controlling particle size and homogeneity using conventional reaction techniques remains a great challenge. In this study, a 20 kHz ultrasonic microreactor (USMR) was applied to enhance precursor mixing, reduce agglomeration, and achieve small nanoparticles with a narrow size distribution. The effects of ultrasonic power, residence time, NH3·H2O concentration, and calcination temperature were investigated in detail. Under optimal conditions, the particle size, Ce3+ concentration and specific surface area of nano-CeO2 obtained using the USMR are averaged to be 6 nm, 25.0 % and 114 m2/g, respectively, which is superior to 32 nm, 22.4 % and 60 m2/g using the traditional precipitation method, as well as 9 nm 24.3 % and 101 m2/g using microreactor. Due to the outstanding feature, the CeO2-USMR showed much better catalytic activity in the oxidative degradation of acid orange 7. This study highlights a new strategy for preparing nano-CeO2, which may provide the USMR technique for the synthesis of small metal oxides and ceramic-based nanocomposites for catalysis and biomedical applications.