Transition Metal-based Catalysts Research Articles

Recent Advances in Transition Metal-Based Catalysts for Ethylene Copolymerization with Polar Comonomer.

The synthesis of polar functionalized polyolefin (PFP) offers improvement in mixing properties, polymer surface, and rheological properties with the potential of upgraded polyolefins for modern and ingenious applications. The synthesis of PFP from metal-based catalyzed olefin (non-polar in nature) copolymerization with polar comonomers embodies energy-efficient, atom-efficient, and apparently an upfront methodology. Despite their outstanding success during conventional polymerization of olefin, 3rd and 4th group (early transition metal)-based catalysts, owing to their electrophilic nature, face challenges mainly due to Lewis basic sites of the polar monomers. On the contrary, late transition metal-based catalysts have also made progress, in recent years, for PFP synthesis. The recent past has also witnessed several advancements in the development of dominating palladium-based catalysts while their lower resistance towards ligand functional groups has limited the practical application of abundant and cheaper nickel-based catalysts. However, the relentless efforts of the scientific community, during the past half-decade, have indicated rigorous progress in the development of nickel-based catalysts for PFP synthesis. In this review, we have abridged the recent research trends in both early as well as late transition metal-based catalyst development. Furthermore, we have highlighted the role of transition metal-based catalysts in influencing the polymer properties.

A facile aqueous-phase synthesis of Co-based nanostructures composed of cobalt hydroxide and cobalt oxide for enhanced photocatalytic activity of dye-sensitized H2 production

Transition metal catalysts are more cost competitive than noble metal catalysts, but there is a drawback in that catalyst activity must be greatly increased for industrial use. In this research, we report the formation of cobalt-based mixture nanostructures composed of cobalt hydroxide having high photoelectron attracting force, electron transfer ability, and easy access and cobalt oxide having facile charge transfer based on the interchangeability to significantly increase the activity of transition metal-based catalysts. Furthermore, the Co-based nanostructures (CNS) were easily synthesized via an aqueous-phase synthesis, and the molar ratio of α-Co(OH)2/Co3O4 was controlled by simply varying the reaction time. Due to the well-mixed structure of α-Co(OH)2 and Co3O4, which could have a beneficial effect on each other in a photocatalytic reaction, the CNS exhibited 11 times superior hydrogen production than the commercial α-Co(OH)2 in a photocatalytic hydrogen production reaction.

CoCuAlOx mixed oxides for the CO2 purification from oxycombustion process exhaust feed

To produce CO2 rich effluents, oxyfuel combustion is a promising technology. Nevertheless, storage as well as valorization steps require the removal CO and NOx produced during combustion process to reach a CO2 as purest as possible. In view of development of transition metal-based catalyst for this application, CoCuAlOx mixed oxide derived from hydrotalcite like preparation way were used as catalyst for NO-CO abatement in a gas stream similar to those obtained in oxyfuel combustion. Materials characterization was explored by several techniques (XRD, Surface area analysis, TPR, HAADF-STEM coupled with EDX, in-situ XPS) that show good catalyst homogeneity and copper surface species modification. The best catalytic performances for the NO-CO abatement are obtained with the ratio Co/Cu= 2 mixed oxide catalyst. The impact of water was also investigated and following trends were obtained: (i) a shift towards CO oxidation higher temperature; (ii) a decrease of NO reduction yield due to copper surface species modification.

Construction of Fe/N/C nano-clusters anchored on porous diatomite for efficient removal of norfloxacin via the adsorption-PMS activation

In this study, natural porous diatomite was utilized as a conciliatory carrier for the fabrication of Fe/N/C nano-clusters with assistance of binary molten salt of NaCl-ZnCl2 under different annealing temperature and used to removal of norfloxacin (NFA). The sample Fe/Dm900 (prepared at 900 °C) exhibited a high surface area and great catalytic performance for antibiotics in the presence of PMS. Over 97% NFA can be decomposed within 5 min and the final degradation rate reached 98%. Meaningfully, high-efficiency Fe/Dm900-PMS system was nearly impervious to pH values and inorganic cations in aqueous solution and could be a likely candidate for degradation of multiple contaminants in pharmaceutical outlet water. Furthermore, the other impacting variables such as catalyst dosage, PMS dosage, NFA concentration and initial pH were moreover explored towards debasement, and conceivable degradation pathways of NFA were presented through LC-MS. This work builds up a compelling procedure to synthesize super-dispersed Fe clusters, which may be amplified to other transition metal-based catalyst via molten salt.

The S-Fe(Ni) sub-surface active sites for efficient and stable overall water splitting

Balancing catalytic efficiency and stability is always a critical and challenge issue for energy related research. Here we propose a reaction reconstruction strategy to create active sites in the sub-layer of sulfur-modified transition metal-based catalysts, which can both achieve a high efficiency and exhibit an excellent stability for overall water splitting. The sub-layer active sites of S-Fe and S-Ni are evidenced by the bulk-sensitive X-ray absorption spectroscopy (XAS), while they cannot be observed by the surface-sensitive X-ray photoelectron spectroscopy. Theoretical calculations reveal that the sub-layer active sites can promote the water dissociation and accelerate the formation of high-energy peroxyl groups in anodes to achieve a high efficiency, while the surface layer can protect the sub-layer sites for excellent stability. The high stability is also confirmed by in-situ XAS. As a result, the obtained bi-functional catalyst as both cathode and anode can achieve a current density of 10 mA cm−2 for overall water splitting at a low cell voltage of 1.53 V (1.81 V for 100 mA cm−2), with an excellent stability over 200 h, which outperforms the benchmark Pt/C-RuO2/NF electrodes.

Iron nickel sulphide embedded on multi-walled carbon nanotubes as efficient electrocatalysts for oxygen evolution reaction in alkaline medium

Oxygen evolution reaction (OER) plays a vital role in clean energy production such as water splitting and metal-air batteries to achieve renewable energy technologies. In this regard, electrocatalysts play a major role in the oxidative half-cell reaction of water splitting. Among various transition metal-based catalysts, FeNi-based electrocatalysts are of particular interest owing to their low-cost, non-toxic, non-precious metal, high stability, and enhanced electrocatalytic performance of OER. Herein, we report the preparation of iron-nickel sulphide-based catalysts (a mixed phase of Fe5Ni4S8 and Ni9S8, or FeNiS) and their composite with MWCNTs using a facile hydrothermal method for electrocatalytic water oxidation. The physicochemical properties of the prepared composite of FeNiS-MWCNT were analyzed through various characterization techniques. The FeNiS-MWCNT composite exhibits enhanced electrochemical performance of OER with the current density of 10 mA cm−2 at a lower overpotential of 260 mV vs RHE and lower Tafel slope of 50 mV dec−1 as compared to FeNiS (10 mA cm−2 at an overpotential of 370 mV vs RHE; Tafel slope of 82 mV dec−1). The superior electrocatalytic performance of the FeNiS-MWCNT composite over the FeNiS catalyst is attributed to the higher surface area, conductivity of the MWCNT and the synergistic effect of FeNiS and MWCNTs. This work also paves the way for the development of highly efficient and promising non-precious metal catalysts for electrocatalytic water oxidation as an alternative to traditional noble-metal catalysts.

Si Doping-Induced Electronic Structure Regulation of Single-Atom Fe Sites for Boosted CO2 Electroreduction at Low Overpotentials.

Transition metal-based single-atom catalysts (TM-SACs) are promising alternatives to Au- and Ag-based electrocatalysts for CO production through CO2 reduction reaction. However, developing TM-SACs with high activity and selectivity at low overpotentials is challenging. Herein, a novel Fe-based SAC with Si doping (Fe-N-C-Si) was prepared, which shows a record-high electrocatalytic performance toward the CO2-to-CO conversion with exceptional current density (>350.0mAcm-2) and~100% Faradaic efficiency (FE) at the overpotential of <400mV, far superior to the reported Fe-based SACs. Further assembling Fe-N-C-Si as the cathode in a rechargeable Zn-CO2 battery delivers an outstanding performance with a maximal power density of 2.44mWcm-2 at an output voltage of 0.30V, as well as high cycling stability and FE (>90%) for CO production. Experimental combined with theoretical analysis unraveled that the nearby Si dopants in the form of Si-C/N bonds modulate the electronic structure of the atomic Fe sites in Fe-N-C-Si to markedly accelerate the key pathway involving *CO intermediate desorption, inhibiting the poisoning of the Fe sites under high CO coverage and thus boosting the CO2RR performance. This work provides an efficient strategy to tune the adsorption/desorption behaviors of intermediates on single-atom sites to improve their electrocatalytic performance.

Recent developments and prospects for engineering first-row transition metal-based catalysts for electrocatalytic NOx− reduction to ammonia

First-row transition metal-based electrocatalysts, including Cu, Fe, Co, Ni, and Ti-based electrocatalysts, for high-efficiency NOx− reduction are reviewed. These electrocatalysts should possess three advantages indicated in the figure above.

Recent progress of transition metal-based catalysts as cathodes in O2/H2O-involved and pure Li–CO2batteries

The composition, structure, reaction mechanism of transition metal-based catalysts and their effects on the electrochemical performance of Li-CO2cells were summarized, and some perspectives for the development of Li-CO2cells were put forward.

MOF-derived transition metal-based catalysts for the electrochemical reduction of CO2 to CO: a mini review.

The excessive emission of CO2 derived from the consumption of fossil fuels has caused severe energy and environmental crises. The electrochemical reduction of CO2 into value-added products such as CO not only reduces the CO2 concentration in the atmosphere but also promotes sustainable development in chemical engineering. Thus, tremendous work has been devoted to developing highly efficient catalysts for the selective CO2 reduction reaction (CO2RR). Recently, MOF-derived transition metal-based catalysts have shown great potential for the CO2RR due to their various compositions, adjustable structures, competitive ability, and acceptable cost. Herein, based on our work, a mini-review is proposed for an MOF-derived transition metal-based catalyst for the electrochemical reduction of CO2 to CO. The catalytic mechanism of the CO2RR was first introduced, and then we summarized and analyzed the MOF-derived transition metal-based catalysts in terms of MOF-derived single atomic metal-based catalysts and MOF-derived metal nanoparticle-based catalysts. Finally, we present the challenges and perspectives for the subject topic. Hopefully, this review could be helpful and instructive for the design and application of MOF-derived transition metal-based catalysts for the selective CO2RR to CO.

A-site defective La2-xCuO4 perovskite-type oxides for efficient oxidation of cyclohexylbenzene.

Phenol production through the oxidation of cyclohexylbenzene (CHB) and the subsequent decomposition of tertiary hydroperoxide has attracted more and more attention. In this study, defective La2-xCuO4 perovskite-type oxide catalysts with tunable A-site deficient structures and abundant surface oxygen vacancies were developed for the liquid phase oxidation of CHB to produce cyclohexylbenzene-1-hydroperoxide (CHBHP). By tuning the amount of A-site La ions in the perovskite structure, more surface oxygen vacancies and Cu+ species were formed in catalysts. The A-site-deficient La1.9CuO4 catalyst achieved significant catalytic efficiency along with a high CHBHP yield of 27.6% at 48.6% CHB conversion under reaction conditions (i.e., 120 °C and 12 h), outperforming those of other transition metal-based catalysts previously reported in the literature. A series of structural characterization methods and catalytic reactions highlighted the crucial roles of surface oxygen vacancies and metal La and Cu ions in the oxidation process. It was revealed that metal ions favored CHB adsorption and activation, while surface oxygen vacancies facilitated the creation of active adsorbed oxygen species. The present study offers an opportunity for the future design of new high-efficiency heterogeneous catalyst systems for CHB oxidation to obtain phenol.

Reusable nano-catalyzed green protocols for the synthesis of quinoxalines: an overview.

Heterocyclic compounds are very widely distributed in nature and are essential for life activities. They play a vital role in the metabolism of all living cells, for example, vitamins and co-enzyme precursors thiamine, riboflavin etc. Quinoxalines are a class of N-heterocycles that are present in a variety of natural and synthetic compounds. The distinct pharmacological activities of quinoxalines have attracted medicinal chemists considerably over the past few decades. Quinoxaline-based compounds possess extensive potential applications as medicinal drugs, presently; more than fifteen drugs are available for the treatment of different diseases. Diverse synthetic protocols have been developed via a one-pot approach using efficient catalysts, reagents, and nano-composites/nanocatalysts etc. But the use of homogeneous and transition metal-based catalysts suffers some demerits such as low atom economy, recovery of catalysts, harsh reaction conditions, extended reaction period, expensive catalysts, the formation of by-products, and unsatisfactory yield of products as well as toxic solvents. These drawbacks have shifted the attention of chemists/researchers to develop green and efficient protocols for synthesizing quinoxaline derivatives. In this context, many efficient methods have been developed for the synthesis of quinoxalines using nanocatalysts or nanostructures. In this review, we have summarized the recent progress (till 2023) in the nano-catalyzed synthesis of quinoxalines using condensation of o-phenylenediamine with diketone/other reagents with plausible mechanistic details. With this review, we hope that some more efficient ways of synthesizing quinoxalines can be developed by synthetic chemists.

Alloying Pt into Ni partially amorphous for promoted alkaline hydrogen production

Aiming at the sluggish water dissociation step in alkaline hydrogen evolution reaction (HER), the platinum-nickel alloy material (PtNi10/C) featuring unique crystalline/amorphous structure supported on carbon black is deliberately designed and fabricated via a reversely rapid co-precipitation and mild thermal reduction strategy. Electrochemical results show that only 66 mV of overpotential is needed for PtNi10/C to drive a current density of 10 mA cm−2 at a lower platinum loading (8.3 μgPt cm-2 geo), which is much lower than that of other catalysts with a single metal source(S-Ni/C and S-Pt/C) and even the commercial Pt/C catalyst (20 wt%). The target catalyst also exhibits smaller tafel slope value (16.73 mV dec−1) and electrochemical impedance value, enabling a fast kinetics rate for water dissociation. Partial crystallization facilitates moderate adsorption of intermediates, while the high-valence Ni(II) and Pt(II) species serve as pivotal driving force for the kinetic dissociation of water. The unique microstructure of PtNi10/C shows a remarkable advantage toward HER in alkaline but acidic medium. In addition, other transition metal-based catalysts following the similar protocol are also fabricated and present varying degrees of HER performance. Hence, the facile and rapid co-precipitation/thermal reduction strategy proposed in this study provides some guidelines for designing high-efficiency alkaline HER catalysts.

Mechanism of formic acid dehydrogenation catalysed by Cp*Co(III) and Cp*Rh(III) complexes with N,N’-bidentate imidazoline-based ligands: A DFT exploration

Homogenous formic acid dehydrogenation (FAD) is largely accomplished with the aid of Ir and Rh based catalysts. The use of earth-abundant transition-metal based catalysts for FAD are rather scarcely reported. This work computationally explores the mechanistic aspects of FAD catalysed by Cp*Co(III) and Cp*Rh(III) -based catalysts with pyridyl-imidazoline (L1) and 2,2’-biimidazoline (L2) ligand architectures. The computed free energy profiles substantiate that the β-hydride elimination is the slowest step in the FAD process. Further mechanistic analysis revealed that H3O+ is the energetically favoured proton source compared to formic acid (FA) for generating H2. NBO analysis signified that the proton from H3O+ ion is relatively more electrophilic than FA and that the metal-hydride bond in the transition state is more negatively charged in the transition state involving H3O+ ion. These factors make the protonation process easier and decreases the barrier for hydronium ion mediated protonation process. All the four designed catalysts were found to possess a moderate range of computed activation barrier (13.5 kcal/mol to 16.2 kcal/mol) at the rate-determining step which are comparable with their corresponding iridium analogues reported in the earlier studies. The Co and Rh catalysts designed in the present work with L1 ligand system were found to be relatively better candidates than L2. Particularly, the Co catalysts and the mechanistic details derived there in would help in the development of efficient earth-abundant transition metal-based catalysts for FAD.

Current Progress on Methods and Technologies for Catalytic Methane Activation at Low Temperatures.

Methane (CH4 ) is an attractive energy source and important greenhouse gas. Therefore, from the economic and environmental point of view, scientists are working hard to activate and convert CH4 into various products or less harmful gas at low-temperature. Although the inert nature of CH bonds requires high dissociation energy at high temperatures, the efforts of researchers have demonstrated the feasibility of catalysts to activate CH4 at low temperatures. In this review, the efficient catalysts designed to reduce the CH4 oxidation temperature and improve conversion efficiencies are described. First, noble metals and transition metal-based catalysts are summarized for activating CH4 in temperatures ranging from 50 to 500°C. After that, the partial oxidation of CH4 at relatively low temperatures, including thermocatalysis in the liquid phase, photocatalysis, electrocatalysis, and nonthermal plasma technologies, is briefly discussed. Finally, the challenges and perspectives are presented to provide a systematic guideline for designing and synthesizing the highly efficient catalysts in the complete/partial oxidation of CH4 at low temperatures.

Three-dimensional carbon nanofiber networks encapsulated in cobalt–molybdenum metal clusters on nitrogen-doped carbon as ultra-efficient electrocatalysts for hydrogen evolution reactions

Efficient and cost-effective catalysts have been developed for the production of hydrogen via water electrolysis. In this study, we develop a strategy for the fabrication of carbon nanofiber catalysts loaded with CoMo clusters covered by a nitrogen-doped carbon network (CoMo/CN@CNFs/MEL). The surface of two-dimensional carbon fibers was coated with a nitrogen-doped carbon network via melamine pyrolysis, thereby forming three-dimensional (3D) networks. These 3D network catalysts exhibited excellent catalytic performance in the hydrogen evolution reaction with 1 M KOH, requiring an overpotential of only 148 mV to reach a current density of 10 mA cm−2 owing to synergistic effects resulting from their structure and composition. The catalytic performance of the CoMo/CN@CNFs/MEL catalysts was comparable to that of commercial Pt/C at high current densities owing to their unique structural features, including restricted Co–Mo clusters, porous nitrogen-doped carbon frameworks, continuous conducting carbon nanofibers, and carbon nitride networks. This work provides a promising approach to transition metal-based catalysts with improved stability and atom utilization efficiency.

Design and synthesis of TiO2/ZnO nanocomposite with enhanced oxygen vacancy: Better photocatalytic removal of MB dye under visible light-driven condition

• TiO 2 /ZnO nanocomposite was synthesized by a facile hydrothermal route. • C. verum leaf extract was utilized as a bio-reducing and templating agent. • TiO 2 /ZnO (0.5mol) exhibited superior photocatalytic activity against MB dye removal. • TiO 2 /ZnO increases surface oxygen vacancy supressing recombination of e - -h + pair. • Excellent catalytic performance is owing to controlled surface oxygen vacancy and small particle size. Construction of capable, affordable, transition metal-based catalysts featuring photocatalytic behaviour is urgently required and important. Herein, for the first time we have synthesized an eco-friendly, capsule shaped ZnO nanoparticles (NPs) anchored upon TiO 2 nanoplates, by utilizing bio-active components available in Cinnamon verum leaf extract. The bio-active components, linalool and phytol served as a self-reducing and gapping agent that enrich the surface with oxygen vacancy without disrupting lattice arrangement. The XRD results confirms presence of wurtzite ZnO, anatase and rutile TiO 2 NPs. Anatase TiO 2 with ZnO supress the electron-hole pair recombination effect. The delayed luminescence behaviour is consistent with the UV-DRS results and suggests that the band gap of TiO 2 /ZnO has been widened. SEM with EDX results justifies that TiO 2 /ZnO nanocomposite mounted oxygen vacancy in a controlled phenomenon, which can boost the separation efficacy of photogenerated carriers and is in good agreement with the PL results. Under visible light irradiation for 60 minutes, TiO 2 /ZnO significantly improves photocatalytic degradation for aqueous organic dye pollutants. The k value of the TiO 2 /ZnO (0.5 mol) nanocomposite is 2.5x10 -2 mint -1 which is comparably higher. The unusual nanoarchitecture, high surface area, and wide band gap of TiO 2 /ZnO are primarily responsible for its noticeably improved photodegradation performance.

Spin-Enhanced C–C Coupling in CO 2 Electroreduction with Oxide-Derived Copper

Spin-Enhanced C–C Coupling in CO ₂ Electroreduction with Oxide-Derived Copper

Cu-Ce Bimetallic Metal-Organic Framework-Derived, Oxygen Vacancy-Boosted Visible Light-Active Cu2O-CeO2/C Heterojunction: An Efficient Photocatalyst for the Sonogashira Coupling Reaction.

The development of an economical transition metal-based catalyst for photocatalytic carbon-carbon coupling reactions is aspiring. Herein, a Cu-Ce metal-organic framework (MOF) was synthesized and carbonized to produce bimetallic Cu2O-CeO2/C, which was utilized in the Sonogashira cross-coupling reaction. The defects and oxygen vacancies in the catalyst were characterized by X-ray photoelectron spectroscopy and Raman spectroscopy, while the nature of Cu was characterized by H2-TPR analysis. The defect-induced MOF-derived Cu-Ce heterojunction created more oxygen vacancies (OV) in CeO2, revealing the high photocatalytic activity. The Cu-Ce heterojunction (Cu2O-CeO2/C) formed a Cu(I)-phenylacetylide active complex and exhibited higher catalytic activity for the visible light-induced Sonogashira cross-coupling reaction. 25%Cu2O-CeO2/C offered 93.8% phenylacetylene conversion with a 94.2% Sonogashira product selectivity by using household light-emitting diodes. No discernible activity loss was observed from the recycling of the catalyst. Based on catalytic activity, control reactions, and physicochemical and optoelectronic characterization, the structure-activity relationship was established and a reaction mechanism was proposed. Replacement of the costly Pd metal-based catalyst with a cheap Cu2O-CeO2-based catalyst for the synthesis of commercially important compounds with a sustainable visible light-induced catalytic process will be highly attractive to chemists and industrialists.

Synergistic effect of Fe/Cu[sbnd]N[sbnd]C dual single-atom catalyst for C[sbnd]H bond oxidation

Transition metal-based (Fe, Co, Cu, etc.) single-atom catalysts (SAC) have been widely used in the direct oxidation of ethylbenzene and benzene. However, their catalytic performance is limited by the low metal loading. Compared with traditional SAC, dual site single-atom catalysts (DSAC) show the advantages of abundant active sites, high metal loading, and excellent catalytic performance. Herein, a novel Fe/CuNC DSAC was prepared by facile one-pot pyrolysis of formaldehyde, dicyandiamide, and metal salts. Dicyandiamide acted as the carbon source with advantage of high nitrogen content, which promoted the formation of metal centers and increased the metal loading. Meanwhile, the synergistic effect between Fe and Cu active centers was revealed to adjust the coordination environment, thus improving the catalytic activity of oxygen activation. The synthesized Fe/CuNC DSAC demonstrated superior catalytic performance in ethylbenzene oxidation reaction with O2 as a green oxidant under mild reaction conditions, with a 99 % conversion of acetophenone and no significant degradation of activity after 10 circles. In addition, NaCl was added into the synthesis as a template to adjust the pore structure, and the modified Fe/CuNC DSAC showed excellent performance in benzene oxidation reaction with high product conversion. In conclusion, this work paves the way for the construction of efficient, green, and cost-effective catalysts for the direct oxidation of ethylbenzene and benzene.