Catalytic Oxygen Research Articles

Microflower-like Fe-Co-MOF with enhanced catalytic performance for decomposition of ammonium perchlorate and combustion of ammonium perchlorate-based composite propellants

Ammonium perchlorate (AP) serves as a crucial component in solid propellants. Enhancing its thermal decomposition with catalysts improves the combustion performance of solid propellants significantly. To enhance the catalytic performance of metal-organic frameworks (MOFs) on AP, this study controlled the morphology of MOFs by adding metal atoms, resulting in a Fe-Co-MOF catalyst with higher specific surface area and dual-metal synergistic effect. The catalytic effect of the catalyst on AP was investigated using DSC and TG-IR, followed by studying its influence on the combustion performance of AP-based composite propellants. The results show that the introduction of 5% Fe-Co-MOF reduced the decomposition temperature of AP to 298.6 °C, decreased the activation energy to 151.6 kJ mol-1, and increased the heat release by 110.6%. Additionally, the ignition delay of the propellant decreased by 71 ms, and the combustion rate increased by 43.8%. Mechanistic studies demonstrate that the abundant catalytic sites and oxygen vacancies of Fe-Co-MOF facilitate the charge transfer rate during the AP thermal decomposition process and promote the increase in AP heat release by suppressing the high-temperature conversion of N2O. This research paves the way for enhancing the application of MOF materials in AP-based solid propellants.

Regulating atomic Fe/Cu dual sites with unsymmetrical Fe-N6 and Cu-N1S2 coordination for promoting bifunctional oxygen electrocatalysis in advanced zinc-air batteries

Dual-metal single-atom catalysts with heteronuclear active sites exhibit superior oxygen catalysis performance than their single-atom counterparts, facilitating the practical applications in advanced electrochemical energy devices. Herein, a Fe-Cu dual-metal single-atom catalyst with Fe-N6 and Cu-N1S2 coordination environment (FeCu-DSAs/NSC) is reported. Due to the synergism of bimetallic active sites and asymmetric heteroatom coordination, the resultant FeCu-DSAs/NSC displays better bifunctional catalytic performance (a small potential gap between the Eη10 and E1/2, ΔE=0.647 V) when compared with the counterparts (Pt/C+IrO2 and Cu-ISAs/NSC), as well as surpassing most of bifunctional metal atom-based catalysts reported to date. As expected, FeCu-DSAs/NSC based rechargeable zinc-air battery shows remarkable superiority than commercial Pt/C+IrO2 benchmark, resulting in a high peak power density (230.66 mW cm−2), open-circuit voltage (1.464 V) and long-term cycling stability (up to 350 h at 10 mA cm−2).

Delocalization Engineering of Heme‐Mimetic Artificial Enzymes for Augmented Reactive Oxygen Catalysis

AbstractDeveloping artificial enzymes based on organic molecules or polymers for reactive oxygen species (ROS)‐related catalysis has broad applicability. Herein, inspired by porphyrin‐based heme mimics, we report the synthesis of polyphthalocyanine‐based conjugated polymers (Fe‐PPc‐AE) as a new porphyrin‐evolving structure to serve as efficient and versatile artificial enzymes for augmented reactive oxygen catalysis. Owing to the structural advantages, such as enhanced π‐conjugation networks and π‐electron delocalization, promoted electron transfer, and unique Fe−N coordination centers, Fe‐PPc‐AE showed more efficient ROS‐production activity in terms of Vmax and turnover numbers as compared with porphyrin‐based conjugated polymers (Fe‐PPor‐AE), which also surpassed reported state‐of‐the‐art artificial enzymes in their activity. More interestingly, by changing the reaction medium and substrates, Fe‐PPc‐AE also revealed significantly improved activity and environmental adaptivity in many other ROS‐related biocatalytic processes, validating the potential of Fe‐PPc‐AE to replace conventional (poly)porphyrin‐based heme mimics for ROS‐related catalysis, biosensors, or biotherapeutics. It is suggested that this study will offer essential guidance for designing artificial enzymes based on organic molecules or polymers.

Delocalization Engineering of Heme-Mimetic Artificial Enzymes for Augmented Reactive Oxygen Catalysis.

Developing artificial enzymes based on organic molecules or polymers for reactive oxygen species (ROS)-related catalysis has broad applicability. Herein, inspired by porphyrin-based heme mimics, we report the synthesis of polyphthalocyanine-based conjugated polymers (Fe-PPc-AE) as a new porphyrin-evolving structure to serve as efficient and versatile artificial enzymes for augmented reactive oxygen catalysis. Owing to the structural advantages, such as enhanced π-conjugation networks and π-electron delocalization, promoted electron transfer, and unique Fe-N coordination centers, Fe-PPc-AE showed more efficient ROS-production activity in terms of Vmax and turnover numbers as compared with porphyrin-based conjugated polymers (Fe-PPor-AE), which also surpassed reported state-of-the-art artificial enzymes in their activity. More interestingly, by changing the reaction medium and substrates, Fe-PPc-AE also revealed significantly improved activity and environmental adaptivity in many other ROS-related biocatalytic processes, validating the potential of Fe-PPc-AE to replace conventional (poly)porphyrin-based heme mimics for ROS-related catalysis, biosensors, or biotherapeutics. It is suggested that this study will offer essential guidance for designing artificial enzymes based on organic molecules or polymers.

From Synthesis to Mechanisms: In-Depth Exploration of the Dual-Atom Catalytic Mechanisms Toward Oxygen Electrocatalysis.

Dual-atom catalysts (DACs) hold a higher metal atom loading and provide greater flexibility in terms of the structural characteristics of their active sites in comparison to single-atom catalysts. Consequently, DACs hold great promise for achieving improved catalytic performance. This article aims to provide a focused overview of the latest advancements in DACs, covering their synthesis and mechanisms in reversible oxygen electrocatalysis, which plays a key role in sustainable energy conversion and storage technologies. The discussion starts by highlighting the structures of DACs and the differences in diatomic coordination induced by various substrates. Subsequently, the state-of-the-art fabrication strategies of DACs for oxygen electrocatalysis are discussed from several different perspectives. It particularly highlights the challenges of increasing the diatomic loading capacity. More importantly, the main focus of this overview is to investigate the correlation between the configuration and activity in DACs in order to gain a deeper understanding of their active roles in oxygen electrocatalysis. This will be achieved through density functional theory calculations and sophisticated in situ characterization technologies. The aim is to provide guidelines for optimizing and upgrading DACs in oxygen electrocatalysis. Additionally, the overview discusses the current challenges and future prospects in this rapidly evolving area of research.

Suppressing the Hypoxia‐Adenosinergic Axis by a Tailored Nanoreactor for Enhanced Photothermal Immunotherapy

Cell metabolite adenosine can induce extensive and persistent immunosuppression by binding to adenosine receptors on immune cells. Seriously, the hypoxia‐driven adenosinergic axis aggravates adenosine accumulation via dephosphorizing immune‐activating adenosine triphosphate (ATP) released during immunogenic cell death (ICD). Different from direct adenosine clearance or adenosine receptor blockade or directly using ecto‐enzyme (CD39/CD73) antagonist, it is hoped to use an innovative small science engineering to regulate the upstream hypoxia/HIF‐1α signal of the hypoxia‐adenosinergic axis, thereby reducing the immunosuppressive extracellular adenosine and enhancing ICD‐triggered antitumor immunity. PM@Mn is constructed by gradually integrating metformin and MnO2 on polydopamine (PDA) nanoparticles. PM@Mn can effectively suppress hypoxia‐adenosinergic axis via combining catalytic oxygen production with reduced endogenous oxygen consumption. Such motif of hypoxia relief suppresses the metabolism of ATP to adenosine via down‐regulating the expression of HIF‐1α, CD39, and CD73. Meanwhile, PDA in PM@Mn can induce local tumor ablation and trigger the “vaccine effect” of ICD under near‐infrared radiation. In a mouse breast cancer model with low immunogenicity, our strategy can effectively reduce adenosine accumulation, PM@Mn group exhibits 4.51‐fold cytotoxic T lymphocyte infiltration and tumor inhibition rate of 75.4%. This study provides a new strategy to advance ICD‐triggered antitumor immunity through supressing hypoxia‐adenosinergic axis.

Red emissive carbon dots Self-Cascading antioxidant nanozymes combine with anti-miRNA-155 for accurate monitoring and ameliorating rheumatoid arthritis

Accurate monitoring and effective antioxidant treatment strategies are highly desirable in rheumatoid arthritis (RA) amelioration. Herein, cerium (Ce) and selenium (Se) co-doped carbon dots (CS-CDs) integrated superoxide dismutase (SOD)-like and glutathione peroxidase (GPx)-like self-cascading catalytic activity are engineered. In this self-cascading nanozymes system, Ce active center catalyzes ·O2− to H2O2 by mimicking SOD, and the adjacent Se component sequentially decomposes the H2O2 by mimicking GPx, achieving enhanced catalytic and superior reactive oxygen species (ROS)-scavenging activities. CS-CDs further load cyanine-5 (Cy5)-labeled anti-miRNA-155 to realize macrophage subphenotype identification via miRNA-155 ratiometric imaging for RA accurate monitoring, and regulate the polarization of pro-inflammatory macrophages for synergistic RA amelioration. Comprehensive in vitro and in vivo experiments validate the advanced RA monitoring and therapy performance of the self-cascading nanozymes. This work not only offers a rationally designed self-cascading nanozyme with simple structures and intriguing ROS-scavenging capacity, but also opens up a strategy for accurate RA monitoring and synergistic amelioration.

Recent advances on COF-based single-atom and dual-atom sites for oxygen catalysis.

Covalent organic frameworks (COFs) have emerged as promising platforms for the construction of single-atom and dual-atom catalysts (SACs and DACs), owing to their well-defined structures, tunable pore sizes, and abundant active sites. In recent years, the development of COF-based SACs and DACs as highly efficient catalysts has witnessed a remarkable surge. The synergistic interplay between the metal active sites and the COF has established the design and fabrication of COF-based SACs and DACs as a prominent research area in electrocatalysis. These catalytic materials exhibit promising prospects for applications in energy storage and conversion devices. This review summarizes recent advances in the design, synthesis, and applications of COF-based SACs and DACs for oxygen catalysis. The catalytic mechanisms of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are comprehensively explored, providing a comparative analysis to elucidate the correlation between the structure and performance, as well as their functional attributes in battery devices. This review highlights a promising approach for future research, emphasizing the necessity of rational design, breakthroughs, and in-situ characterization to further advance the development of high-performance COF-based SACs and DACs for sustainable energy applications.

Cu-Fe-Ni layered hydroxides / magnetic biochar composite as peroxymonosulfate activator for removal of enrofloxacin

In this research, an economical peroxymonosulfate (PMS) was employed as the oxidizing agent, while a sophisticated Cu-Fe-Ni layered hydroxides/magnetic biochar composite (MBC/CuFeNi LDHs, succinctly termed MC-1) functioned as a catalyst to mitigate the presence of enrofloxacin (ENR), a notably toxic contaminant discerned in water. The stratified architecture and intricate surface functional groups of the composite played pivotal roles in ENR's degradation. Metal oxides containing Cu, Fe, and Ni particularly exhibit excellent catalytic performance and oxygen storage capacity. The introduction of magnetic biochar (MBC) can reduce the aggregation of CuFeNi, and the rich functional groups on the surface of MBC can increase the content of functional groups on the surface of the composite, which helps to activate PMS. To be more precise, an impressive 91.6% of ENR was abated by the MC-1&PMS ensemble within a mere 20 min. Moreover, the catalytic dynamism of the MC-1&PMS synergy was predominantly ascribed to the production of hydroxyl (∙OH) radicals, complemented by sulfate (SO4∙-), singlet oxygen (1O2), and superoxide radicals (∙O2-). In the ensuing discourse, a conceivable degradation trajectory for ENR was postulated. Overall, this investigation furnishes novel perspectives in the conceptualization of heterogeneous carbon catalysts within the realm of advanced oxidation techniques.

A self-cleaning window for high-efficiency photodegradation of indoor formaldehyde

Formaldehyde (HCHO) as an indoor air pollutant released by new furniture and decorative materials is of great concern. Developing a self-cleaning device to remove HCHO is an ideal way to improve indoor air quality. In this study, a self-cleaning window with a multilayered structure constructed from fluorine-doped tin oxide/bismuth tungstate/resorcinol-formaldehyde resin (FTO/Bi2WO6/RF) has been fabricated, which is capable of degrading HCHO in natural indoor condition. The as-fabricated device could utilize the natural room light and promote the generation and transfer of the photocatalytic carriers in Bi2WO6, which subsequently delivers a good catalytic oxygen reduction efficiency in RF to produce hydrogen peroxide (H2O2). The as-synthesized H2O2 could further split into hydroxyl radicals (•OH), then oxide the HCHO molecules in the air. The present study demonstrates a novel and efficient strategy to fabricate a transparent multifunctional window for self-cleaning indoor gaseous pollutants, the concept is of great importance to be expanded in a broad range of indoor furniture for in-house air pollution control.

High Sucrose Diet-Induced Subunit I Tyrosine 304 Phosphorylation of Cytochrome c Oxidase Leads to Liver Mitochondrial Respiratory Dysfunction in the Cohen Diabetic Rat Model.

The mitochondrial oxidative phosphorylation process generates most of the cellular energy and free radicals in mammalian tissues. Both factors play a critical role in numerous human diseases that could be affected by reversible phosphorylation events that regulate the function and activity of the oxidative phosphorylation complexes. In this study, we analyzed liver mitochondria of Cohen diabetes-sensitive (CDs) and Cohen diabetes-resistant (CDr) rats, using blue native gel electrophoresis (BN-PAGE) in combination with mitochondrial activity measurements and a site-specific tyrosine phosphorylation implicated in inflammation, a known driver of diabetes pathology. We uncovered the presence of a specific inhibitory phosphorylation on tyrosine 304 of catalytic subunit I of dimeric cytochrome c oxidase (CcO, complex IV). Driven by a high sucrose diet in both CDr and CDs rats, Y304 phosphorylation, which occurs close to the catalytic oxygen binding site, correlates with a decrease in CcO activity and respiratory dysfunction in rat liver tissue under hyperglycemic conditions. We propose that this phosphorylation, specifically seen in dimeric CcO and induced by high sucrose diet-mediated inflammatory signaling, triggers enzymatic activity decline of complex IV dimers and the assembly of supercomplexes in liver tissue as a molecular mechanism underlying a (pre-)diabetic phenotype.

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Construction of Warped Graphitic Layers from Fullerene Soot and Study of Their Catalytic Oxygen Reduction Activity

Photothermal-promoted O2/[rad]OH generation of gold nanotetrapod @ platinum nano-islands for enhanced catalytic/photodynamic therapy

Ultrasmall platinum (Pt) nanozymes are used for catalytic therapy and oxygen (O2)-dependent photodynamic therapy (PDT) by harnessing the dual-enzyme activities of catalase (CAT) and peroxidase (POD). However, their applications as nanocatalysts are limited due to their low catalytic activity. Herein, we constructed a photothermal-promoted bimetallic nanoplatform (AuNTP@Pt-IR808) by depositing ultrasmall Pt nano-islands and modifying 1-(5-Carboxypentyl)-2-(2-(3-(2-(1-(5-carboxypentyl)-3,3-dimethylindolin-2-ylidene)ethylidene)-2-chlorocyclohex-1-en-1-yl)vinyl)-3,3-dimethyl-3H-indol-1-ium bromide (IR808) on gold nanotetrapod (AuNTP) with CAT/POD activities to enhance PDT/catalytic therapy. In the tumor microenvironment, the ultrasmall Pt can catalyze endogenous hydrogen peroxide (H2O2) to produce O2, relieving tumor hypoxia and enhancing the PDT performance. Moreover, AuNTP integration into the bimetallic nanoplatform showed good electron transfer properties and promoted the POD activity of ultrasmall Pt. Importantly, AuNTP@Pt-IR808 possessed higher photothermal conversion performance than single AuNTPs, which enhanced photothermal therapy (PTT). It also accelerated the CAT/POD dual-enzyme activities, and promoted the generation of singlet oxygen (1O2) and hydroxyl radical (OH). By enhancing the performances of PTT/PDT/catalytic therapy, the developed AuNTP@Pt-IR808 nanoplatform demonstrated good antitumor efficacy against breast cancer.

Fe-Nx sites coupled with core-shell FeS@C nanoparticles to boost the oxygen catalysis for rechargeable Zn-air batteries

The development of efficient single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) remains a formidable challenge, primarily due to the symmetric charge distribution of metal single-atom sites (M-N4). To address such issue, herein, Fe-Nx sites coupled synergistic catalysts fabrication strategy is presented to break the uniform electronic distribution, thus enhancing the intrinsic catalytic activity. Precisely, atomically dispersed Fe-Nx sites supported on N/S-doped mesoporous carbon (NSC) coupled with FeS@C core-shell nanoparticles (FAS-NSC@950) is synthesized by a facile hydrothermal reaction and subsequent pyrolysis. Due to the presence of an in situ-grown conductive graphitic layer (shell), the FeS nanoparticles (core) effectively adjust the electronic structure of single-atom Fe sites and facilitate the ORR kinetics via short/long-range coupling interactions. Consequently, FAS-NSC@950 displays a more positive half-wave potential (E1/2) of 0.871 V with a significantly boosted ORR kinetics (Tafel slope = 52.2 mV dec−1), outpacing the commercial Pt/C (E1/2 = 0.84 V and Tafel slope = 54.6 mV dec−1). As a bifunctional electrocatalyst, it displays a smaller bifunctional activity parameter (ΔE) of 0.673 V, surpassing the Pt/C-RuO2 combination (ΔE = 0.724 V). Besides, the FAS-NSC@950-based zinc-air battery (ZAB) displays superior power density, specific capacity, and long-term cycling performance to the Pt/C-Ir/C-based ZAB. This work significantly contributes to the field by offering a promising strategy to enhance the catalytic activity of SACs for ORR, with potential implications for energy conversion and storage technologies.

Construction of n-type homogeneous to improve interfacial carrier transfer for enhanced photoelectrocatalytic hydrolysis

Photoelectrocatalyzed hydrogen production plays an important role in the path to carbon neutrality. The construction of heterojunctions provides an ideal example of an oxygen precipitation reaction. In this work, the performance of the n-n type heterojunction CeBTC@FeBTC/NIF in the photoelectronically coupled catalytic oxygen evolution reaction (OER) reaction is presented. The efficient transfer of carriers between components enhances the catalytic activity. Besides, the construction of heterojunctions optimizes the energy level structure and increases the absorption of light, and the microstructure forms holes with a blackbody effect that also enhances light absorption. Consequently, CeBTC@FeBTC/NIF has excellent photoelectric coupling catalytic properties and requires an overpotential of only 300 mV to drive a current density of 100 mA cm−2 under illumination. More importantly, the n-n heterojunction was found to be effective in enhancing charge and photogenerated electron migration by examining the carrier density of each component and carrier diffusion at the interface.

Understanding the Super-Theoretical Capacity Behavior of VO2 in Aqueous Zn Batteries.

VO2 material, as a promising intercalation host, is widely investigated not only in aqueous lithium-ion batteries, but also in aqueous zinc-ion batteries (AZIBs) owing to its stable tunnel-like framework and multivalence of vanadium. Different from lithium-ion storage, VO2 can provide higher capacity when storing zinc ions, even exceeding its theoretical capacity (323mAhg-1), but the specific reason for this unconventional performance in AZIBs is still unclear. The present study proposes a catalytic oxygen evolution reaction (OER) coupled with an interface oxidation mechanism of VO2 during the initial charging to a high voltage. This coupling induces a phase transformation of VO2 into a high oxidation state of V5O12∙6H2O, enabling a nearly two-electron reaction and providing additional zinc storage sites to achieve super-theoretical capacity. Furthermore, it is demonstrated that these vanadium oxide cathodes (V2O3, VO2, and V2O5) will all undergo phase change after the first charge or short cycle. Notably, water molecules participate in the final formation of layered vanadium-based hydrate, highlighting their crucial role as "pillars" for stabilizing the structure. This work significantly enhances the understanding of vanadium-based oxide cathodes.

Transformation of Waste Agarwood Leaves into Heteroatom-Doped Microporous Carbon for Highly Active Metal-Free Catalytic Oxygen Reduction Reaction and Efficient Capacitive Energy Storage Application

Transformation of Waste Agarwood Leaves into Heteroatom-Doped Microporous Carbon for Highly Active Metal-Free Catalytic Oxygen Reduction Reaction and Efficient Capacitive Energy Storage Application

MnF2 Surface Modulated Hollow Carbon Nanorods on Porous Carbon Nanofibers as Efficient Bi-Functional Oxygen Catalysis for Rechargeable Zinc-Air Batteries.

Developing highly efficient bi-functional noble-metal-free oxygen electrocatalysts with low-cost and scalable synthesis approach is challenging for zinc-air batteries (ZABs). Due to the flexible valence state of manganese, MnF2 is expected to provide efficient OER. However, its insulating properties may inhibit its OER process to a certain degree. Herein, during the process of converting the manganese source in the precursor of porous carbon nanofibers (PCNFs) to manganese fluoride, the manganese source is changed to manganese acetate, which allows PCNFs to grow a large number of hollow carbon nanorods (HCNRs). Meanwhile, manganese fluoride will transform from the aggregation state into uniformly dispersed MnF2 nanodots, thereby achieving highly efficient OER catalytic activity. Furthermore, the intrinsic ORR catalytic activity of the HCNRs/MnF2@PCNFs can be enhanced due to the charge modulation effect of MnF2 nanodots inside HCNR. In addition, the HCNRs stretched toward the liquid electrolyte can increase the capture capacity of dissolved oxygen and protect the inner MnF2, thereby enhancing the stability of HCNRs/MnF2@PCNFs for the oxygen electrocatalytic process. MnF2 surface-modulated HCNRs can strongly enhance ORR activity, and the uniformly dispersed MnF2 can also provide higher OER activity. Thus, the prepared HCNRs/MnF2@PCNFs obtain efficient bifunctional oxygen catalytic ability and high-performance rechargeable ZABs.

Well‐defined N3C1‐anchored Single‐Metal‐Sites for Oxygen Reduction Reaction

AbstractN‐, C‐, O‐, S‐coordinated single‐metal‐sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well‐defined such SMSs, and the fundamental comprehension has long been impeded in case‐by‐case reports using carbon materials as investigation targets. In this work, the well‐defined molecular catalysts with N3C1‐anchored SMSs, i.e., N‐confused metalloporphyrins (NCPor‐Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor‐Ms with corresponding N4‐anchored SMSs (metalloporphyrins, Por‐Ms), are synthesized for catalytic activity evaluation. Among all, NCPor‐Co reaches the top in established volcano plots. NCPor‐Co also shows the highest half‐wave potential of 0.83 V vs. RHE, which is much better than that of Por‐Co (0.77 V vs. RHE). Electron‐rich, low band gap and regulated d‐band center contribute to the high activity of NCPor‐Co. This study delves into the examination of well‐defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high‐performance asymmetric SMS catalysts.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction.

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.