Concept Of Catalysis Research Articles

Chalcogen Bonding Catalysis with Phosphonium Chalcogenide (PCH).

ConspectusThe exploration of new catalysis concepts and strategies to drive chemical reactions is of vital importance for the sustainable development of organic synthesis. Recently, chalcogen bonding catalysis has emerged as a new concept for organic synthesis and has been demonstrated to be an important synthetic tool capable of addressing elusive reactivity and selectivity issues. This Account describes our progress in the research field of chalcogen bonding catalysis, including (1) the discovery of phosphonium chalcogenide (PCH) as highly efficient chalcogen bonding catalyst; (2) the development of "chalcogen-chalcogen bonding catalysis" and "chalcogen···π bonding catalysis" modes; (3) the demonstration that chalcogen bonding catalysis with PCH can activate hydrocarbons to achieve cyclization and coupling reactions of alkenes; (4) the discovery of unusual results that chalcogen bonding catalysis with PCH can solve elusive reactivity and selectivity issues that are inaccessible by classic catalysis approaches; and (5) the elucidation of chalcogen bonding mechanisms.With PCH catalysts, we systematically studied their chalcogen bonding properties, the relationship between structure and catalysis, and their application in facilitating a diverse array of reactions. Enabled by chalcogen-chalcogen bonding catalysis, an efficient assembly reaction of three molecules of β-ketoaldehyde and one indole derivative in a single operation was realized, delivering heterocycles with a newly constructed seven-membered ring. In addition, a Se···O bonding catalysis approach achieved an efficient synthesis of calix[4]pyrroles. We developed a "dual chalcogen bonding catalysis" strategy to solve reactivity and selectivity issues in the Rauhut-Currier-type reactions and related cascade cyclizations, thus shifting conventionally covalent Lewis base catalysis to a cooperative Se···O bonding catalysis approach. This strategy enables the cyanosilylation of ketones to take place in the presence of a ppm-level amount of PCH catalyst loading. Furthermore, we established chalcogen···π bonding catalysis for catalytic transformation of alkenes. In the research field of supramolecular catalysis, the activation of hydrocarbons such as alkenes by weak interactions is a highly interesting unresolved topic. We showed that the Se···π bonding catalysis approach could efficiently activate alkenes to achieve both coupling and cyclization reactions. Chalcogen···π bonding catalysis with PCH catalysts is particularly highlighted by the capability of facilitating strong Lewis-acid inaccessible transformations, such as the controlled cross coupling of triple alkenes. Overall, this Account presents a panoramic view of our research on chalcogen bonding catalysis with PCH catalysts. The works described in this Account provide a significant platform to solve synthetic problems.

Visible-light photoredox catalysis with organic polymers

The development of photocatalysts to drive organic reactions is a frontier research topic. Organic polymers can be well tuned in terms of structural and photophysical properties and, therefore, constitute a promising class of photocatalysts in photoredox catalysis for organic synthesis. In this review article, we provide an overview of the concept of photoredox catalysis and recent developments in organic polymers as photocatalysts including porous organic polymers, graphitic carbon nitride, carbon dots, and polymer dots with adjustable reactivity that have undergone state-of-the-art advancement in different photoredox catalytic organic reactions.

Strong phosphide-metaphosphate interaction in RuP/CoNiP4O12 for enhanced electrocatalytic water splitting

Strong metal-support interaction (SMSI) is a crucial concept in heterogeneous catalysis, which has been utilized to design efficient catalysts for electrocatalytic overall water splitting. Herein, a novel strong phosphide-metaphosphate interaction (SPmPI) is discovered in the RuP/CoNiP4O12 catalyst for the first time. The SPmPI leads to efficient electron transfer from RuP to CoNiP4O12 support, endowing the catalyst with a unique coordination environment of Ru-P and Ru-O, which is demonstrated to greatly facilitate the rate-determining water dissociation step. As a result, the RuP/CoNiP4O12 catalyst with proper Ru-P and Ru-O coordination numbers requires an ultralow overpotential of 27 mV to deliver a current density of 10 mA cm-2 for hydrogen evolution reaction (HER) in alkaline media. Moreover, the catalyst inherits the remarkable catalytic activity from the CoNiP4O12 support for oxygen evolution reaction (OER), and therefore is also effective for overall water splitting (requiring 1.56 V to achieve 10 mA cm-2 current density). This work not only reports a highly efficient catalyst for electrocatalytic overall water splitting, but also provides a novel concept of SPmPI for designing supported catalyst in heterogeneous catalysis.

In Situ Non‐Topotactic Reconstruction‐Induced Synergistic Active Centers for Polysulfide Cascade Catalysis

AbstractMost reported catalysts for lithium‐sulfur battery can work for only one of the multiple elementary reactions, thereby resulting in the gradual enrichment of unconverted polysulfides at the catalytic centers and aggravating the shuttle effect. Herein, the concept of cascade catalysis based on a ternary heterostructure, which divides sulfur redox reactions into distinct steps by multiple catalytic centers, is proposed to realize the tandem reduction of Li2S8 to Li2S. As a proof of concept, the ternary heterostructure Na0.67Ni0.25Mn0.75O2(NNMO)‐MnS2‐Ni3S4 achieved by in situ non‐topotactic electrochemical reconstruction successfully integrates three types of active centers into one structure to achieve cascade catalysis. More specifically, NNMO acts as an adsorption mediator to effectively capture polysulfides, MnS2 functions better in catalyzing the conversion of polysulfides into Li2S4 and Ni3S4 demonstrates an enhanced catalytic effect for Li2S precipitation. This synergistic cascade catalysis originates primarily from the dynamic energy‐level matching between the metal d‐band center and the lowest unoccupied molecular orbital of the polysulfides, affording appropriate molecular orbital hybridization and facile interfacial electron transition and thus endowing favorable sulfur reduction kinetics. Eventually, the NNMO‐MnS2‐Ni3S4/S composite electrode exhibits excellent rate performance and high restraining ability toward the polysulfide shuttle under long cycling, high sulfur loading and low electrolyte conditions.

Synthetic Application of Bismuth LMCT Photocatalysis in Radical Coupling Reactions

Ligand-to-metal charge transfer (LMCT) photocatalysis allows the activation and synthetic utilization of halides and other heteroatoms in metal complexes. Many metals are known to undergo LMCT but so far remain underutilized in the field of catalysis. A screening assay identifying LMCT activity helped us to expand this catalysis concept to the application of bismuth LMCT in organic radical coupling reactions. We demonstrate its application for the generation of two different radicals (chlorine and carboxyl) in net-oxidative as well as redox-neutral photochemical reactions. Detailed investigation of the model Giese-type coupling revealed BiCl4– and BiCl52– as catalytically active bismuth species under 385 nm irradiation. Combined cyclic voltammetry and UV–vis studies gave insight into the reactivity of the highly reactive bismuth(II) catalyst fragment.

Synthesis of Pd–AuAg trimetal nanohybrids with controlled heterostructures and their application in the continuous flow catalytic reduction of Cr(vi)

A novel method that combines the concepts of nanocomposite hydrogels and flow catalysis was developed for the efficient conversion of Cr(vi) to Cr(iii) in water.

Bidirectional manipulation of iodine redox kinetics in aqueous Fe-I2 electrochemistry.

Catalyzing conversion is a promising approach to unlock the theoretical potentials of the I2/I- redox couple in aqueous Fe-I2 electrochemistry. However, most reported results only obtain one-directional efficient iodine conversion and cannot realize a balance of full reduction and reoxidation, thereby resulting in rapid capacity decay and/or low coulombic efficiency. Herein, the concept of bidirectional catalysis based on a core-shell structured composite cathode design, which accelerates the formation and the decomposition of FeI2 simultaneously during battery dynamic cycling, is proposed to regulate the Fe-I2 electrochemical reactions. Notably, the functional matrix integrates N, P co-doping and FeP nanocrystals into a carbon shell to achieve bidirectional catalysis. More specifically, the carbon shell acts as a physical barrier to effectively capture active species within its confined environment, N, P heteroatoms function better in directing the iodine reduction and FeP facilitates the decomposition of FeI2. As confirmed with in situ and ex situ analysis, the Fe-I2 cell operates a one-step but reversible I2/FeI2 pair with enhanced kinetics. Consequently, the composite cathode exhibits a reversible Fe2+ storage capability of 202 mA h g-1 with a capacity fading rate of 0.016% per cycle over 500 cycles. Further, a stable pouch cell was fabricated and yielded an energy density of 146 W h kgiodine-1. Moreover, postmortem analysis reveals that the capacity decay of the Fe-I2 cell originates from anodic degradation rather than the accumulation of inactive iodine. This study represents a promising direction to manipulate iodine redox in rechargeable metal-iodine batteries.

Laminar membranes assembled by ultrathin cobalt-copper oxide nanosheets for nanoconfined catalytic degradation of contaminants

• Nanoconfinement catalysis is implemented within Co-Cu ONS membrane nanochannels. • Co-Cu ONS membrane achieves ∼ 100% removal of organic pollutants within 86 ms. • The degradation rate is 10 3−5 times faster compared with the best state-of-the-art. • Oxygen vacancies facilitate electron transfer between metal cations and PMS. • DFT calculations illustrate the mechanism of nanoconfinement catalysis. Practical applications for the degradation of organic contaminants by conventional batch-mode heterogeneous advanced oxidation processes remain elusive due to mass-transfer limitations of short-lived reactive oxygen species (ROS). Nanoconfinement catalysis has received increasing attention because of enhanced reaction efficiency and mass and electron transfer. Here, we implemented the concept of nanoconfinement catalysis using a two-dimensional membrane. Ultrathin cobalt-copper oxide nanosheets (Co-Cu ONS) rich in active sites and oxygen vacancies were prepared through a facile solution reduction method. The assembled Co-Cu ONS membrane with active sites confined within membrane nanochannels spontaneously activates peroxymonosulfate and facilitates the generation of ROS and the redox cycles of metal cations. Therefore, an ultimate degradation efficiency (∼100%), ultrafast (∼86 ms) decomposition of organic pollutants, and excellent catalytic stability (greater than120 h) were achieved. The degradation rate is 10 3−5 times faster than the best state-of-the-art. This approach offers an attractive alternative for water purification with membrane-based nanoconfinement catalysts.

Active and selective reverse water-gas shift reaction over Pt/Na-Zeolite catalysts

The introduction of the frustrated Lewis pair (FLP) concept in heterogeneous catalysis, particularly zeolites, is effective in activating stable molecules, such as CO2. However, regulating the FLP density structure to control the activity and selectivity remains challenging. This study examined the effects of the FLP density and zeolite structure on the reverse water-gas shift reaction using Pt/zeolite catalysts. The reaction results obtained using catalysts with various zeolites showed that the presence of FLP in the zeolite promoted CO2 conversion and CO selectivity, but a high FLP density was not necessarily beneficial. A high density of FLP could delay the intracrystalline diffusion of intermediates and could lower the CO selectivity. Operando infrared spectroscopy and density functional theory calculations suggested that FLP could effectively stabilize the intermediate responsible for CO production through selective hydrogenation of the oxygen atom of CO2 at the initial stage of the reaction.

Combining Cobalt Ferrite Nanozymes with a Natural Enzyme to Reshape the Tumor Microenvironment for Boosted Cascade Enzyme-Like Activities.

Nanozymes with the merits of effective enzyme-mimic activities, tunable catalytic properties, pH/temperature tolerance, and high stability have been consumingly researched for nanocatalytic therapy. Herein, the union nanozymes and a natural enzyme nanoplatform (DMSN@CoFe2O4/GOD-PCM) are elaborately designed by simply depositing an ultrasmall cobalt ferrite (CoFe2O4) bimetallic oxide nanozyme and natural glucose oxidase (GOD) that are loaded into the aperture (∼12 nm) of dendritic mesoporous silica (DMSN) for near-infrared-II-enhanced tumor therapy. Upon irradiation, the hyperthermia generated by CoFe2O4 nanozymes unlocks the "gate" of phase-change material (PCM) for releasing GOD, which reshapes the specific tumor microenvironment (TME) through the glucose metabolism pathway. The resulting strengthened acid condition and a considerable amount of H2O2 efficiently initiate the cascade catalysis reactions. Moreover, highly toxic hydroxyl radicals are generated with a Co/Fe dual-cycle system of ultrasmall CoFe2O4 nanozymes. The in situ glutathione consumption and hypoxia relief further amplify oxidative stress. In addition, chemotherapeutic effects due to the cytotoxicity of cobalt ions enhance the therapeutic performance. Collectively, this study provides a proof of concept for TME-reshaped natural and artificial nanozyme cascade catalysis for combined reactive oxygen species-based therapy and chemotherapy.

Three-center-four-electron halogen bond enables non-metallic complex catalysis for Mukaiyama-Mannich-type reaction

SummaryThe three-center-four-electron halogen bond (3c4e X-bond) presents a fundamental design concept for catalysis. By integrating halogen(I) (X+: I+ or Br+), the bis-pyridyl ligand NN, and a non-nucleophilic counteranion Y, we developed non-metallic complex catalysts, [N···X···N]Ys, that exhibited outstanding activity and facilitated the Mukaiyama-Mannich-type reaction of N-heteroaromatics with parts-per-million-level catalyst loading. The high activity of [N···X···N]SbF6 was clearly demonstrated. NMR titration experiments, CSI-MS, computations, and UV-vis spectroscopic studies suggest that the robust catalytic activity of [N···X···N]Y can be attributed to the unique ability of the 3c4e X-bond for binding chloride: i) the covalent nature transforms the [N···X···N]+ complexation to sp2 CH as a hydrogen-bonding donor site, and ii) the noncovalent property allows for the dissociation of [N···X···N]+ for the formation of [Cl···X···Cl]−. This study introduces the application of 3c4e X-bonds in catalysis via halogen(I) complexes.

I2/TBHP Reagent System: A Modern Paradigm for Organic Transformations**

AbstractMolecular iodine in combination with TBHP offers an advanced concept for organic synthesis and catalysis by improving the selectivity and sustainability of organic transformations. It leads to the development of metal free greener protocols under ambient conditions either as a catalytic duo or as a reagent system in combination with an additive. The advent of this indispensable tool led to formation of complex organic architectures empowering novel reaction pathways through C−H functionalization, cyclization, cycloaddition, rearrangement, sulfonylation/sulfenylation and oxidation reactions in organic synthesis.

Tailoring Ir-FeOx interactions and catalytic performance in preferential oxidation of CO in H2 via the morphology engineering of anatase TiO2 over Ir-FeOx/TiO2 catalysts

Ir-FeOx/TiO2 catalysts with both Ir and Fe contents of ∼1% wt. employing anatase TiO2 nanocrystals predominantly exposing either {100}, {101}, or {001} facets as the support were prepared and a comprehensive study was conducted on their interactions in pairs that are strongly dependent on the TiO2 morphology. The strongest FeOx-TiO2 interactions occurred over TiO2{001} support while TiO2{101} support contributes to the strongest Ir-TiO2 and Ir-FeOx interactions. Catalytic performance of the Ir-FeOx/TiO2 catalysts in preferential oxidation of CO in H2 is not only affected by the CO reactivity, but also determined by the Ir-FeOx interfaces. Ir-FeOx/TiO2{101} catalyst exhibits the highest CO conversion and best O2 selectivity over the three Ir-FeOx/TiO2 catalysts, which could be ascribed to stronger Ir-FeOx interactions that contribute to the enhancement of a H-spillover effect and subsequently facilitate the transformation of surface carbonaceous intermediates into CO2. These results add the versatility of the morphology engineering strategy in tailoring the structures and catalytic performance of oxide-based catalysts, and broaden the concept of morphology-dependent catalysis of oxide-based nanocrystal catalysts.

Metal-ligand cooperation in the catalytic oxidation of (R)-carvone by Ga(NO3)3/H2O2

In this work, the catalytic epoxidation of (R)-carvone by the Ga(NO3)3/H2O2 system was studied alongside the metal-ligand cooperation by exploring 17 different ligands. It was observed that the acidic ligands such as acetic acid mostly favor the epoxidation of the endocyclic double bond of (R)-carvone (22% yield, 1 h), while nitrogen heterocycles direct the epoxidation to the exocyclic double bond, especially the ones that are unsubstituted or have electron-donating groups, such as pyrazine (28% yield, 5 h), 4-dimethylaminopyridine (28% yield, 8 h), and 1-methyimidazole (43% yield, 8 h). Pyrazinecaboxylic acid favored the epoxidation of the exocyclic double bond (25%, 3 h). EPR analysis of both Ga(NO3)3/H2O2 and Ga(NO3)3/PCA/H2O2 systems indicates the presence of hydroxyl radicals in the reaction medium, although these do not determine the epoxidation rate that is likely regulated by the interaction of Ga-peroxo complexes with (R)-carvone. This study contributes to widening the application of the cooperating ligand concept in molecular catalysis toward further development of more selective and efficient epoxidation reactions catalyzed by non-transition metal centers.

Short-Range Diffusion Enables General Synthesis of Medium-Entropy Alloy Aerogels.

Medium-entropy alloy aerogels (MEAAs) with the advantages of both multimetallic alloys and aerogels are promising new materials in catalytic applications. However, limited by the immiscible behavior of different metals, achieving single-phase MEAAs is still a grand challenge. Herein, a general strategy for preparing ultralight 3D porous MEAAs with the lowest density of 39.3 mg cm-3 among the metal materials is reported, through combining auto-combustion and subsequent low-temperature reduction procedures. The homogenous mixing of precursors at the ionic level makes the short-range diffusion of metal atoms possible to drive the formation of single-phase MEAAs. As a proof of concept in catalysis, as-synthesized Ni50 Co15 Fe30 Cu5 MEAAs exhibit a high mass activity of 1.62 A mg-1 and specific activity of 132.24 mA cm-2 toward methanol oxidation reactions, much higher than those of the low-entropy counterparts. In situ Fourier transform infrared and NMR spectroscopies reveal that MEAAs can enable highly selective conversion of methanol to formate. Most importantly, a methanol-oxidation-assisted MEAAs-based water electrolyzer can achieve a low cell voltage of 1.476 V at 10 mA cm-2 for making value-added formate at the anode and H2 at the cathode, 173 mV lower than that of traditional alkaline water electrolyzers.

Frustrated Lewis Pairs in Heterogeneous Catalysis: Theoretical Insights.

Frustrated Lewis pair (FLP) catalysts have attracted much recent interest because of their exceptional ability to activate small molecules in homogeneous catalysis. In the past ten years, this unique catalysis concept has been extended to heterogeneous catalysis, with much success. Herein, we review the recent theoretical advances in understanding FLP-based heterogeneous catalysis in several applications, including metal oxides, functionalized surfaces, and two-dimensional materials. A better understanding of the details of the catalytic mechanism can help in the experimental design of novel heterogeneous FLP catalysts.

In Situ Infrared Spectroscopy of NOx Reduction Catalysts: A Laboratory Exercise for In-Person and Virtual Learning

Infrared (IR) spectroscopy and catalysis represent two of the most practically relevant topics in chemistry, but they are normally taught in separate contexts at the undergraduate level. Although IR spectroscopy is introduced to students as a tool for organic compound characterization, it also finds wide applicability in the investigation of catalytic reactions. Here we present a laboratory exercise that binds the concepts of IR spectroscopy and catalysis together in the study of nitrogen oxide abatement by selective catalytic reduction─a reaction that is of industrial relevance and environmental importance. We originally designed the practical course for in-person instruction, but we adapted it into a virtual learning experience during the COVID-19 pandemic. Our analysis revealed that there was no significant difference between the performance of the in-person and virtual participants, suggesting that the online offering of the course could be a viable alternative to face-to-face instruction in case of extraordinary circumstances.

Rapidly regenerated CNC/TiO2/MnO2 porous microspheres for high-efficient dye removal

The cellulose nanocrystal (CNC)/transition metal oxide hybrid porous microspheres usually have high adsorption performance and degradability, and show promising applications in the field of wastewater treatment. However, single metal oxides are limited by the forbidden band width and electron-hole complexation, and often fail to achieve good effluent treatment. Herein, a CNC/manganese dioxide/titanium dioxide porous microspheres are prepared by the combination of bubble template and ionic crosslinking between sodium alginate and Ca2+ ions as a matrix. Based on the synergistic effect of two kinds of transition metal oxide, the degradation efficiency of CNC/MnO2/TiO2 porous microspheres for methylene blue is as high as 97.0%, showing easy recovery process and rapid regeneration of this material. Besides, its maximum removal of dyes reaches up to 310.2 mg/g, which is much higher than most CNC based adsorption materials. The concept of concerted catalysis can to explain the origin for excellent performance of as-prepared hybrid microspheres.

Modifying the Electrocatalytic Selectivity of Oxidation Reactions with Ionic Liquids.

The “solid catalyst with ionic liquid layer” (SCILL) is an extremely successful new concept in heterogeneous catalysis. The idea is to boost the selectivity of a catalyst by its modification with an ionic liquid (IL). Here, we show that it is possible to use the same concept in electrocatalysis for the selective transformation of organic compounds. We scrutinize the electrooxidation of 2,3‐butanediol, a reaction which yields two products, singly oxidized acetoin and doubly oxidized diacetyl. When adding the IL (1‐ethyl‐3‐methyl‐imidazolium trifluormethanesulfonate, [C2C1Im][OTf]), the selectivity for acetoin increases drastically. By in situ spectroscopy, we analyze the underlying mechanism: Specific adsorption of the IL anions suppresses the activation of water for the second oxidation step and, thus, enhances the selectivity for acetoin. Our study demonstrates the great potential of this approach for selective transformation of organic compounds.

Lab at home in distance learning: A case study

Lab work is a basic pillar, especially in engineering and science. It promotes problem solving and discovery and it has proven to enhance student learning. Transversal competences such as autonomy or effective oral and written communication are also enhanced. E-learning is currently increasing and requires a redesign of practical work. Several virtual laboratories can be found to cover different areas. This, however, does not replace the face-to-face laboratories in the field of chemistry, where students need to perform hands-on experiments to acquire the required skills. An alternative is experimentation at home. Most existing references in this regard describe qualitative experiences. In this work we have designed a home practical work in which some fundamental concepts of chemical kinetics and catalysis are developed quantitatively. Students are introduced here to wastewater treatment using an advanced oxidation process; the Fenton reaction. From the results of a preactivity survey, students showed motivation and high expectations with the activity proposal. From a post-activity survey, we concluded that the perception of students towards the activity did not change after completing it. The learning objectives were met both for the students that participated in the take-home experiment and for those who did the experiment in the laboratory.