Stereoselective Research Articles

Engineering a PtCu Alloy to Improve N2 Selectivity of NH3-SCO over the Pt/SSZ-13 Catalyst.

Improving the N2 selectivity is always a great challenge for the selective catalytic oxidation of ammonia (NH3-SCO) over noble-metal-based (especially Pt) catalysts. In this work, Cu as an efficient promoter was introduced into the Pt/SSZ-13 catalyst to significantly improve the N2 selectivity of the NH3-SCO reaction. A PtCu alloy was formed in the PtCu/SSZ-13 catalyst, as confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive spectrometry mapping, and X-ray absorption spectroscopy results. As indicated by the X-ray photoelectron spectroscopy analysis, the Pt species in the alloyed PtCu nanoparticle was mainly present in the electron-rich state on PtCu/SSZ-13, while the electron-deficient Cu and isolated Cu2+ species were both present on the surface of PtCu/SSZ-13. Due to such a unique alloyed structure with an altered oxidation state, the N2 selectivity of NH3-SCO on the PtCu/SSZ-13 catalyst was remarkably improved, while the NH3-SCO activity was kept comparable to that on Pt/SSZ-13. The reaction path was changed from the NH mechanism on Pt/SSZ-13 to both NH and internal selective catalytic reduction mechanisms on the PtCu/SSZ-13 catalyst, which was considered the main reason for the enhanced N2 selectivity. This work provides a new route to synthesize efficient alloy catalysts for optimizing the N2 selectivity of NH3-SCO for NH3 slip control in diesel exhaust purification.

Polyoxometalate‐Based Frameworks: Construction Strategies and Photocatalytic Applications

AbstractPolyoxometalate‐based frameworks, as a kind of material constructed by polyoxometalates (POMs), metal ions or clusters, organic ligands, are combined both the advantages of oxygen‐rich POMs and porous metal‐organic frameworks (MOFs) within one single system. This integration greatly expands their potential applications compared to the individual POMs or MOFs. Particularly for photocatalysis, the narrow light absorption range of the typical POMs units in the ultraviolet region hinders their extensive uses as visible‐light‐driven photocatalysts. However, the incorporation of photoactive units into POMs‐based frameworks can be considered as an effective approach to overcome this limitation. In this paper, we review selected examples of recent progress based on the POM‐based frameworks along with their construction strategies and applications in various areas of photocatalysis, mainly including water splitting, CO2 reduction, organic synthesis and also the selective coupling reactions.

Improving the stability of an unstable lipase by applying different immobilization strategies for the selective hydrolysis of fish oil

AbstractRhizopus oryzae lipase (ROL) is known to present high selectivity in chemical reactions. However, the poor stability of ROL effectively limits its industrial applications. In this study, several immobilization protocols, such as hydrophobic adsorption, covalent immobilization, multi‐point covalent attachment, ionic adsorption/cross‐linking, and ionic interaction, were applied to improve the stability of ROL. Heterogeneous modification of aspartic and glutamic acid residues on the surface of ROL was carried out by 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC) to introduce new amine groups with lower pKb. The highest immobilization yield of 89% was achieved for octyl‐agarose, producing specific activity of 45 U/mg, which is 15 folds higher than the specific activity of the soluble enzyme. Improved stability of ROL was observed, in particular for those derivatives obtained by multi‐point covalent attachment of ROL on glyoxyl‐agarose (Gx‐ROL) and aminated ROL on glyoxyl‐agarose (Gx‐NH2‐ROL) by retaining 28%–36% of their initial activities after 24 h incubation at 60°C. Immobilization also altered the co‐solvent stability profile of the immobilized derivatives producing biocatalysts with varied co‐solvent stabilities. Furthermore, utilization of the immobilized preparations in fish oil hydrolysis revealed the selective release of cis‐5,8,11,14,17‐eicosapentaenoic acid (EPA) and cis‐4,7,10,13,16,19‐docosahexaenoic acid (DHA) in favor of EPA. The highest EPA/DHA selectivity of 33 was observed for the hydrophobically immobilized ROL on octyl‐sepharose.

Air-Stable and Highly Active Transition Metal Phosphide Catalysts for Reductive Molecular Transformations

This review introduces transition metal phosphide nanoparticle catalysts as highly efficient and reusable heterogeneous catalysts for various reductive molecular transformations. These transformations include the hydrogenation of nitriles to primary amines, reductive amination of carbonyl compounds, and biomass conversion, specifically, the aqueous hydrogenation reaction of mono- and disaccharides to sugar alcohols. Unlike traditional air-unstable non-precious metal catalysts, these are stable in air, eliminating the need for strict anaerobic conditions or pre-reduction. Moreover, when combined with supports, metal phosphides exhibit significantly enhanced activity, demonstrating high activity, selectivity, and durability in these hydrogenation reactions.

Mechanistic Insights into Surfactant-Modulated Electrode-Electrolyte Interface for Steering H2O2 Electrosynthesis.

Electrocatalytic reactions taking place at the electrified electrode-electrolyte interface involve processes of proton-coupled electron transfer. Interfacial protons are delivered to the electrode surface via a H2O-dominated hydrogen-bond network. Less efforts are made to regulate the interfacial proton transfer from the perspective of interfacial hydrogen-bond network. Here, we present quaternary ammonium salt cationic surfactants as electrolyte additives for enhancing the H2O2 selectivity of the oxygen reduction reaction (ORR). Through in situ vibrational spectroscopy and molecular dynamics calculation, it is revealed that the surfactants are irreversibly adsorbed on the electrode surface in response to a given bias potential range, leading to the weakening of the interfacial hydrogen-bond network. This decreases interfacial proton transfer kinetics, particularly at high bias potentials, thus suppressing the 4-electron ORR pathway and achieving a highly selective 2-electron pathway toward H2O2. These results highlight the opportunity for steering H2O-involved electrochemical reactions via modulating the interfacial hydrogen-bond network.

Self‐Supported Fe‐Based Nanostructured Electrocatalysts for Water Splitting and Selective Oxidation Reactions: Past, Present, and Future

AbstractElectrochemical water splitting plays a vital role in facilitating the transition towards a sustainable energy future by enabling renewable hydrogen (H2) production, energy storage, and emission‐free transportation. Developing earth‐abundant electrocatalysts with outstanding overall water‐splitting performance, excellent catalytic activity, and robust long‐term stability is highly important in the practical application of water electrolysis. Self‐supported electrocatalysts have emerged as the most appealing candidate for practical H2 production due to their increased active site loading, rapid mass and charge transfer, and strong interaction with the underneath conducting support. Additionally, these electrocatalysts also provide enhanced reaction kinetics and stability. Here, a comprehensive review of recent progress in developing self‐supported Fe‐based electrocatalysts for water splitting and selective oxidation reactions is presented with examples of oxyhydroxides, layered double hydroxides, oxides, chalcogenides, phosphides, nitrides, and other Fe‐containing electrocatalysts. A comprehensive historical development in the synthesis of self‐supported Fe‐based electrocatalysts is provided, with an emphasis on the various deposition methods and the choice of self‐supported conducting substrates considering large‐scale commercial applications. An overview of mechanistic understanding and approaches for enhanced H2 production are also presented. Finally, the challenges and opportunities associated with developing Fe‐based electrocatalysts for practical applications in water splitting and alternative oxidation reactions are discussed.

Oxygen vacancy based WO3/SnO2-x promote electrochemical H2O2 accumulation by two-electron water oxidation reaction and toxic uniform dimethylhydrazine degradation

The key to constructing an anodic electro-Fenton system hinges on two pivotal criteria: enhancing the catalyst activity and selectivity in water oxidation reaction (WOR), while simultaneously inhibiting the decomposition of hydrogen peroxide (H2O2) which is on-site electrosynthesized at the anode. To address the issues, we synthesized novel WO3/SnO2-x electrocatalysts, enriched with oxygen vacancies, capitalize on the combined activity and selectivity advantages of both WO3 and SnO2-x for the two-electron pathway electrocatalytic production of H2O2. Moreover, the introduction of oxygen vacancies plays a critical role in impeding the decomposition of H2O2. This innovative design ensures that the Faraday efficiency and yield of H2O2 are maintained at over 80 %, with a noteworthy production rate of 0.2 mmol h−1 cm−2. We constructed a novel electro-Fenton system that operates using only H2O as its feedstock and applied it to treat highly toxic uniform dimethylhydrazine (UDMH) from rocket launch effluent. Our experiments revealed a substantial total organic carbon (TOC) removal, achieving approximately 90 % after 120 mins of treatment. Additionally, the toxicity of N-nitrosodimethylamine (NDMA), a byproduct of great concern, was shown to be effectively mitigated, as evidenced by acute toxicity evaluations using zebrafish embryos. The degradation mechanism of UDMH is predominantly characterized by the advanced oxidative action of H2O2 and hydroxyl radicals, as well as by complex electron transfer processes that warrant further investigation.

Electrochemical CO2 Reduction by Urea Hangman Mn Terpyridine species.

Based on our previous study in chemical subtleties of the proton tunneling distance for metal hydride formation (PTD-MH) to regulate the selectivity of CO2 reduction reaction (CO2RR), we have developed a family of Mn terpyridine derivatives, in which urea groups functions as multipoint hydrogen-bonding hangman to accelerate the reaction rate. We found that such changes to the second coordination sphere significantly increased the turnover frequency (TOF) for CO2 reduction to ca. 360 with this family of molecular catalysts while maintaining high selectivity (ca. 100 %±3) for CO even in the presence of a large amount of phenol as proton source. Notably, the compounds studied in this manuscript all exhibit large value for as that achieved by Fe porphyrins derivates, while saving up to 0.55 V in overpotential with respect to the latter.

Tailoring the Electronic Metal-Support Interactions in Supported Silver Catalysts through Al modification for Efficient Ethylene Epoxidation.

Metal-modified catalysts have attracted extraordinary research attention in heterogeneous catalysis due to their enhanced geometric and electronic structures and outstanding catalytic performances. Silver (Ag) possesses necessary active sites for ethylene epoxidation, but the catalyst activity is usually sacrificed to obtain high selectivity towards ethylene oxide (EO). Herein, we report that using Al can help in tailoring the unoccupied 3d state of Ag on the MnO2 support through strong electronic metal-support interactions (EMSIs), overcoming the activity-selectivity trade-off for ethylene epoxidation and resulting in a very high ethylene conversion rate (~100 %) with 90 % selectivity for EO under mild conditions (170 °C and atmospheric pressure). Structural characterization and theoretical calculations revealed that the EMSIs obtained by the Al modification tailor the unoccupied 3d state of Ag, modulating the adsorption of ethylene (C2H4) and oxygen (O2) and facilitating EO desorption, resulting in high C2H4 conversion. Meanwhile, the increased number of positively charge Ag+ lowers the energy barrier for C2H4(ads) oxidation to produce oxametallacycle (OMC), inducing the unexpectedly high EO selectivity. Such an extraordinary electronic promotion provides new promising pathways for designing advanced metal catalysts with high activity and selectivity in selective oxidation reactions.

Tailoring the Electronic Metal‐Support Interactions in Supported Silver Catalysts through Al modification for Efficient Ethylene Epoxidation

AbstractMetal‐modified catalysts have attracted extraordinary research attention in heterogeneous catalysis due to their enhanced geometric and electronic structures and outstanding catalytic performances. Silver (Ag) possesses necessary active sites for ethylene epoxidation, but the catalyst activity is usually sacrificed to obtain high selectivity towards ethylene oxide (EO). Herein, we report that using Al can help in tailoring the unoccupied 3d state of Ag on the MnO2 support through strong electronic metal‐support interactions (EMSIs), overcoming the activity‐selectivity trade‐off for ethylene epoxidation and resulting in a very high ethylene conversion rate (~100 %) with 90 % selectivity for EO under mild conditions (170 °C and atmospheric pressure). Structural characterization and theoretical calculations revealed that the EMSIs obtained by the Al modification tailor the unoccupied 3d state of Ag, modulating the adsorption of ethylene (C2H4) and oxygen (O2) and facilitating EO desorption, resulting in high C2H4 conversion. Meanwhile, the increased number of positively charge Ag+ lowers the energy barrier for C2H4(ads) oxidation to produce oxametallacycle (OMC), inducing the unexpectedly high EO selectivity. Such an extraordinary electronic promotion provides new promising pathways for designing advanced metal catalysts with high activity and selectivity in selective oxidation reactions.

Enhanced Electrocatalytic Performances by Spatially Confined Aqueous Electrolytes

AbstractElectrocatalysis is an important energy conversion and storage technology that has made significant progress in areas such as fuel cells, hydrogen production from electrolyzed water and electrochemical synthesis. In practical applications, the efficiency and stability of electrocatalytic processes remain challenging. Spatially confined (or called domain‐limited) water refers to the immobilization of water molecules in a limited region near the catalyst surface to form a specific aqueous phase environment. This domain‐limited aqueous phase environment can greatly influence the electrocatalytic efficacy by enhancing adsorption and lowering the proton transport and solvent diffusion energy barriers in the reaction. In recent years, the goal of improving electrocatalytic performance has been successfully achieved through interfacial domain‐limited, microporous domain‐limited and nanoreactor domain‐limited. Spatially domain‐limited water as a novel strategy can significantly enhance the activity and selectivity of electrocatalytic reactions, but understanding its mechanism of action remains a challenge. With a deeper understanding of domain‐limited water and further development of the technology, it is believed that it will bring greater breakthroughs and application prospects in the field of electrocatalysis.

Tailoring the aluminum nanocrystal surface oxide for all-aluminum-based antenna-reactor plasmonic photocatalysts

Aluminum nanocrystals (AlNCs) are of increasing interest as sustainable, earth-abundant nanoparticles for visible wavelength plasmonics and as versatile nanoantennas for energy-efficient plasmonic photocatalysis. Here, we show that annealing AlNCs under various gases and thermal conditions induces substantial, systematic changes in their surface oxide, modifying crystalline phase, surface morphology, density, and defect type and concentration. Tailoring the surface oxide properties enables AlNCs to function as all-aluminum-based antenna-reactor plasmonic photocatalysts, with the modified surface oxides providing varying reactivities and selectivities for several chemical reactions.

Effect of I- ligand and surface oxygen-containing groups on catalytic activity and stability of activated carbon-supported Pd catalysts in acetylene dicarbonylation

The support and ligand play a crucial role in regulating the catalytic performance, selectivity, and stability of heterogeneous catalysis. Herein, activated carbon (AC) supported palladium (Pd) catalysts (2.0 wt%) were prepared by impregnation for acetylene dicarbonylation. The oxygen-containing groups on the surface of the AC support were modulated by nitric acid (HNO3) to investigate metal–support interactions on the catalytic performance and stability of the Pd/AC. The characterization of the chemical composition and structure of the supports and catalysts demonstrates that high concentrations of oxygen-containing groups on the surface of the carbon support lead to the fine dispersion of Pd nanoparticles. Notably, the finely dispersed Pd/AC70 catalyst exhibited good activity and stability for acetylene dicarbonylation under high-pressure CO conditions after several rounds of regeneration. Furthermore, operational parameters including the type of support, co-catalyst (KI), and reaction time and temperature were identified for their impact on the reaction. It was found that I- anions serve as a co-catalyst and can ligate with Pd species, thereby preventing the leaching of Pd and improving reaction selectivity. This study presents a straightforward and sustainable modulation strategy to improve the dispersion of active metals, as well as to prevent the leaching and sintering of these metals during high-pressure CO reactions.

Solar‐Driven Selective Oxidation Over Bismuth‐Based Semiconductors: From Prolific Catalysts to Diverse Reactions

AbstractSynthesis of organic compounds often necessitates rigorous reaction conditions or the involvement of hazardous oxidants, resulting in substantial energy consumption and considerable environmental damage. Photocatalytic selective oxidation represents a green and environmentally friendly way to obtain high‐value chemicals, which has developed rapidly in recent years. Bismuth‐based (Bi‐based) semiconductor materials have gained intense interest in selective organic synthesis due to their diverse crystal structures and compositions, tunable band structure, and outstanding photocatalytic performance. Herein, a systematic summary of the solar‐driven selective oxidation over varieties of Bi‐based semiconductors is provided. Initially, the reactive species involved in selective oxidation, Bi‐based materials widely used in photocatalytic selective oxidation, and the methods for synthesizing these Bi‐based materials are meticulously classified. Concerning their selective oxidation reactions, a variety of modification strategies, with a focus on the separation of photogenerated carriers and the regulation of reactive species is extensively documented. Highlights are the diverse applications and mechanism discussions of Bi‐based photocatalysts in the oxidation reactions, including alcohol oxidation, C─H bond activation, amine oxidation, and sulfide oxidation, as well as the coupling reactions with photoreduction. Finally, the future development prospects and challenges of Bi‐based photocatalysts in the field of selective oxidation is proposed, hoping to provide valuable insights and guidance for the design of photocatalysts for selective oxidation.

Polymer-dispersed liquid crystal with low driving voltage utilising reaction selectivity of two-stage polymerisation

ABSTRACT An optimised approach is presented in this study for the fabrication of a polymer-dispersed liquid crystal (PDLC) device with a low driving voltage and high contrast ratio (CR). This method involves a two-step process utilising Michael addition and radical polymerisation, employing a reaction-selective orthogonal photoinitiated system. The impact of incorporating low surface energy monomers on PDLC performance is thoroughly investigated, and the driving voltage is further reduced through selective reaction-induced interface modification. The polymer morphology can be finely tuned by adjusting the thiol content, leading to various PDLC properties. This paper introduces a novel surface modification technique within the polymer-liquid crystal system, presenting a fresh perspective on regulating PDLC performance. By choosing monomer structures, the sequence of reactions can be precisely controlled, allowing for the introduction of structural units with distinct functionalities at the polymer interface. This approach facilitates interfacial functionalization and enables the design of multi-layer structures for synthetic polymers, realising innovative functionalities.

Coupling and electronic synergistic effects of Fe/CeO2 composite to achieve high efficiency and selectivity for RWGS reaction

Transition metal iron, because of its high oxygen mobility, excellent thermal stability and low price, is often used in the study of RWGS reaction. However, the bottleneck problem of iron-based catalysts is the poor CO2 conversion rate. Herein, the Fe/CeO2 composite catalyst with Fe-O-Ce was successfully constructed, which has both high CO2 conversion and high CO selectivity for the low-temperature RWGS reaction. Furthermore, the influence of Fe0 contents is studied, and the result indicated that the CO2 conversion rate and CO selectivity are up to 50.05% and 100% at 500 ºC by the use of 20Fe/CeO2. Moreover, CeO2 is the best catalyst holder than the others. The physical and chemical properties of the catalysts are investigated by in-situ XPS, XRD, low-temperature N2 absorption-desorption (BET) and CO2-TPD. Nano zero-valent iron (Fe0) is the main active center for the RWGS reaction, which easily releases the outer electrons to activate reactant molecules. The introduction of the CeO2 is conducive to the high dispersion of Fe0 nanoparticles and the formation of abundant active centers. With the increase of Fe loading, the electron-rich Fe0 induces a strong electronic effect on the electron-deficient CeO2. The regularity of catalyst are changed by a large amount of zero-valent iron entering into the CeO2 lattice, then formed a lot of Fe-O-Ce solid solution. A large amount of zero-valent iron enter into the CeO2 lattice, inhibiting the grain growth and aggregation of monometallic species, and promoting nano Fe species highly dispersed on CeO2 carriers, leading more active centers exposure. Meanwhile, the abundant oxygen vacancy on xFe/CeO2 surface is advantage for the adsorption and activation of H2 and CO2 molecules. Therefore, the coupling and electronic synergistic effects of the active component Fe0 and the carrier CeO2 make xFe/CeO2 becoming a promising candidate catalyst for RWGS reaction.

Switchable reductive amination of aldehydes over metal-encapsulated S-1 zeolites with tunable acid-base properties

Catalytic reductive amination of aldehydes is a valuable strategy to synthesize nitrogen-containing compounds but often suffers from low selectivity and complex reaction mechanisms. This study aims to develop a selective control method for the syntheses of primary amines and secondary imines, which are widely used in fine and bulk chemicals, materials, and pharmaceuticals. Metal-encapsulated zeolite is a special type of catalyst that combines the advantages of metal nanoparticles and zeolites, such as high activity and selectivity. Herein, metal-encapsulated zeolites (Pd-M@S-1, M=Ni, Mn, Co) were applied as catalysts for the reductive amination of aromatic aldehydes. Results showed that the reductive amination of aldehydes over Pd-M@S-1 catalysts can be selectively switched between primary amines over Pd0.6@S-1 and secondary imines over Pd0.6Ni@S-1 by tuning the acid-base properties of the catalysts. The effect of acid-base properties of catalysts on selectivity control was claimed by conducting control experiments, time-dependent curves, and detailed characterizations.

Robust cooperative of cadmium sulfide with highly ordered hollow microstructure coordination polymers for regulating the photocatalytic performance

Accurately controlling and achieving selective reactivity at difficult-to-access reaction sites in organic molecules is challenging owing to the similar local and electronic environments of multiple reaction sites. In this work, we regulated multiple reaction sites in a highly selective and active manner using cobalt coordination polymers (Co-CP) 1 and 1a with various particle sizes and morphologies ranging from large granular to ordered hollow hemispheres by introducing sodium dodecyl sulfate (SDS) as a surfactant. The size and morphology of the catalysts could be tuned by controlling the amount of SDS. An SDS concentration of 0.03 mmol generated 1a having a highly ordered hollow hemispherical microstructure with a well-defined platform as a pre-made building unit. Cadmium sulfide (CdS), as a typical photocatalyst, was subsequently uniformly anchored in-situ on the premade building unit 1a to produce CdS@1a composites, that inherited the originally ordered hollow hemispherical microstructure while integrating CdS as well-dispersed catalytic active sites. Furthermore, the well-established CdS@1a composites were used as photocatalysts in selective oxidation reactions under air atmosphere with blue irradiation. The CdS0.109@1a composite with unique structural characteristics, including uniformly distributed and easily accessible catalytic sites and excellent photoelectrochemical performance, served as a highly efficient heterogeneous photocatalyst for promoting the selective oxidation of sulfides to sulfoxides as the sole products. This work presents an approach for fabricating CPs as premade building units that function as well-defined platforms for integration with photocatalysts, enabling tuning of the structure-selectivity-activity relationships.

Prospects and challenges of sensor materials: A comprehensive review

Sensor materials have become more important in several industries as they facilitate the development of advanced sensing technologies in the modern day. These materials, specifically engineered to transform physical, chemical, or biological stimuli into quantifiable signals, play a crucial role in gathering vital data for controlling, monitoring, and making informed decisions. It is essential to comprehend the obstacles and prospects linked to sensor materials, given the escalating demand for sensor systems that are both efficient and versatile. The sensing qualities of a material refer to its capacity to detect and quantify alterations in its surroundings. These properties encompass a range of approaches, including optical, chemical, piezoelectric, capacitive, and resistive interactions. Although these materials are utilized in various industries such as transportation, medicine, agriculture, industrial operations, and environmental monitoring, persistent issues are still related to improved reaction speed, selectivity, and sensitivity. Nevertheless, the outlook for sensor materials seems optimistic, as current research and advancements are anticipated to result in materials that exhibit enhanced performance, durability, and energy economy. Developing nanomaterials and sophisticated production processes facilitates the potential for creating highly selective and sensitive sensors with new functionalities. This advancement contributes to the growth of the Internet of Things (IoT) and its applications in massive data collection, leading to enhanced automation and decision-making capabilities. This review article examines the recent advancements, applications, and research in sensor materials while also discussing the obstacles they encounter and the potential opportunities that enable them to significantly impact multiple industries and society.

Stereo Selectivity of Histaminic Receptors Play an Important Role of Anti-histaminic Activity

The histamine is a natural compound derived from histidine and amino acid which act on different histaminic receptors (H1, H2, H3 and H4), each receptor combined with histamine and give the different actions especially H1 and H2 receptors. The action of each depends on the specificity of the receptors, e.g., the compounds which act on H1 receptor are similar to each other but different than the compounds which act on H2 receptor (due to the difference between two receptors from the area and stereo of the receptors).