Unraveling the Chemical State of Cobalt in Co-Based Catalysts during Ethanol Steam Reforming: an in Situ Study by Near Ambient Pressure XPS and XANES

Enhanced Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Silica-Coated Pt-CoxOy Hybrid Nanoparticles

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is difficult due to the intrinsic difficulty with thermodynamically easier hydrogenation of C═C bonds. In this work, Pt-CoxOy hybrid nanoparticles encapsulated in mesoporous silica nanospheres (Pt-CoxOy@mSiO2) were synthesized by a sol-gel method, which showed greatly improved COL selectivity for hydrogenation of CAL. At 80 °C and 1.0 MPa of H2, Pt-CoxOy@mSiO2 achieved a CAL conversion of 98.7% with a COL selectivity of 93.5%. In contrast, Pt@mSiO2 yields 3-phenylpropanol (HCOL) as the major product with HCOL selectivity of 67.2%, while PtCo@mSiO2 yields 3-phenylpropionaldehyde with selectivity of 51.8% under the same conditions. The enhanced catalytic performance of Pt-CoxOy@mSiO2 for hydrogenation of CAL to COL is ascribed to the Pt surface electron deficiency induced by metal-oxide interaction, and the protection of active NPs by silica shells results in good catalytic stability.

Cobalt-based MOF-derived carbon electrocatalysts with tunable architecture for enhanced oxygen evolution reaction

Development of the hydrogen economy requires the design of catalysts that increase the rate of the accompanying sluggish kinetic oxygen evolution reaction (OER). This is a key process in electrochemical energy conversion and storage, such as water splitting and metal-air batteries. The OER needs high overpotential and typically expensive precious metal-based catalysts. Therefore, designing low-cost and efficient electrocatalysts for OER is of paramount importance. In addition to focusing on the number of active sites or high specific surface area, the correlation between catalyst particle shape and performance should be considered. This work presents an electrocatalytic activity comparison of cobalt-containing carbons with different morphologies in the OER process. Employing metal-organic frameworks as carbon and metal precursors, the materials in the shape of polyhedrons, needles, unique spherical hedgehogs, and sea urchins were obtained. The effect of MOF template infiltration with additional carbon source on the physicochemical properties of electrocatalysts was also examined. The furfuryl alcohol-impregnated needle-shaped particles were characterized by a high content of cobalt active sites, surrounded by nitrogen-containing graphite layers. Electrochemical tests confirmed their best activity (overpotential 317 mV@10 mA/cm2), long stability (up to 20 h), as well as low reagents diffusion limitations (Tafel slope 57 mV/dec up to 24 mA/cm2). The vertically aligned structure of the catalyst contributed to improved detachment of the oxygen bubbles produced.

UV- and visible-light photocatalysis using Ni-Co bimetallic and monometallic hydrotalcite-like materials for enhanced CO2 methanation in sabatier reaction

The CO2 catalytic reduction activities of four different Co-modified Ni-based catalysts derived from hydrotalcite-like materials (HTCs) prepared by co-precipitation method were investigated under thermal and photocatalytic conditions. All catalysts were tested from 473 to 723 K at 10 bar (abs). The light intensity for photocatalytic reactions was 2.4 W cm-2. The samples were characterized to determine the effect of morphological and physicochemical properties of mono-bimetallic active phases on their methanation activity. The activity toward CO2 methanation followed the next order: Ni > Co-Ni > Co. For the monometallic Ni catalyst an increase of a 72% was achieved in the photo-catalytic activity under UV and vis light irradiation at temperatures lower by > 100 K than those in a conventional reaction. Co-modified Ni based hydrotalcite catalysts performed with stability and no deactivation for the 16 h studied under visible light for methanation at 523 K due to the presence of basic sites.

Highly Efficient Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over CoRe/TiO2 Catalyst

Allylic alcohols typically produced through selective hydrogenation of α,β-unsaturated aldehydes are important intermediates in fine chemical industry, but it is still a challenge to achieve its high selectivity transformation. Herein, we report a series of TiO₂-supported CoRe bimetallic catalysts for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using formic acid (FA) as a hydrogen donor. The resultant catalyst with the optimized Co/Re ratio of 1:1 can achieve an exceptional COL selectivity of 89% with a CAL conversion of 99% under mild conditions of 140 °C for 4 h, and the catalyst can be reused four times without loss of activity. Meanwhile, the Co₁Re₁/TiO₂/FA system was efficient for the selective hydrogenation of various α,β-unsaturated aldehydes to the corresponding α,β-unsaturated alcohols. The presence of ReO_x on the Co₁Re₁/TiO₂ catalyst surface was advantageous to the adsorption of C=O, and the ultrafine Co nanoparticles provided abundant hydrogenation active sites for the selective hydrogenation. Moreover, FA as a hydrogen donor improved the selectivity to α,β-unsaturated alcohols.

Boosting Propane Dehydrogenation by the Regioselective Distribution of Subnanometric CoO Clusters in MFI Zeolite Nanosheets

Direct dehydrogenation of propane (PDH) has already been implemented worldwide in industrial processes to produce value-added propylene. The discovery of earth-abundant and environmentally friendly metal with high activity in C-H cleavage is of great importance. Co species encapsulated within zeolite are highly efficient for catalyzing direct dehydrogenation. However, exploring a promising Co catalyst remains a nontrivial target. Direct control of the regioselective distribution of Co species in the zeolite framework through altering their crystal morphology gives opportunities to modify the metallic Lewis acidic features, thus providing an active and appealing catalyst. Herein, we achieved the regioselective localization of highly active subnanometric CoO clusters in straight channels of siliceous MFI zeolite nanosheets with controllable thickness and aspect ratio. The subnanometric CoO species were identified by different types of spectroscopies, probe measurements, and density functional theory calculations, as the coordination site for the electron-donating propane molecules. The catalyst showed promising catalytic activity for the industrially important PDH with propane conversion of 41.8% and propylene selectivity higher than 95% and was durable during 10 successive regeneration cycles. These findings highlight a green and facile method to synthesize metal-containing zeolitic materials with regioselective metal distribution and also to open up a future perspectives for designing advanced catalysts with integrated advantages of the zeolitic matrix and metal structures.

Recovery of valuable metals from spent lithium-ion batteries by complexation-assisted ammonia leaching from reductive roasting residue

Recycling valuable metals in spent LIBs is not only in line with the purpose of resource recycling but also an important measure for environmental protection. In this article, a process using biomass reduction roasting followed by a unique complexation-assisted ammonia leaching is proposed. Using waste areca powder (WAP) as a biomass reducing agent, the roasted residue is leached in an aqueous solution for the carbonate. The leaching efficiencies of Ni, Co, and Mn reach over 99% under ammonia leaching conditions of 1.5 M ammonium citrate (AC), 3 M ethylenediamine (EDA). The kinetics of ammonia leaching indicates the activation energies of Ni, Co, and Mn are 51.8 kJ mol^-1, 47.7 kJ mol^-1, and 40.8 kJ mol^-1, respectively, which shows the whole duration is controlled by chemical reactions. Most importantly, this study systematically explores the mechanism of ammonia leaching and provided a useful recommendation for selecting the right ammonium salt.

Cobalt-based co-ordination complex-derived nanostructure for efficient oxygen evolution reaction in acidic and alkaline medium

Electrochemical water splitting is one of the most important method for energy conversion and storage. For this, the design and development of a low-cost robust electrocatalyst are highly desirable. In this study, Cobalt-based electrocatalyst for Oxygen Evolution Reaction was synthesized by thermal treatment of Cobalt-dehydroacetic acid (Co-DHA). The as-synthesized Co nanostructures and Co-DHA crystals were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy thermo-gravimetric analysis, and field emission scanning electron microscopy. The electrochemical O₂ evolution study shows the overpotential (at 10 mV/cm⁻²) correspond to 294 mV vs reference hydrogen electrode (RHE) for K-300 (Co₃O₄@300), whereas K-500 (Co₃O₄@500) shows 170 mV vs RHE values in 1 M KOH solution, respectively. Similar trends have been observed for electrochemical O₂ evolution studies in 0.5 M H₂SO₄, where K-300 and K-500 shows the overpotential (at 10mV/cm⁻²) of 234 mV vs RHE, and 199 mV vs RHE, respectively. The outcomes show better catalytic efficiency of K-500 as compared to K-300.

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Simple one pot synthesis for precursor of Co₃O₄.

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Enhanced activity for oxygen evolution reaction.

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Efficient performance and stability in both acidic and alkaline medium.

Synergically engineering defect and interlayer in SnS2 for enhanced room-temperature NO2 sensing

Defect and interlayer engineering are considered as two promising strategies to alter the electronic structures of sensing materials for improved gas sensing properties. Herein, ethylene glycol intercalated Al-doped SnS₂ (EG-Al-SnS₂) featuring Al doping, sulfur (S) vacancies, and an expanded interlayer spacing was prepared and developed as an active NO₂ sensing material. Compared to the pristine SnS₂ with failure in detecting NO₂ at room temperature, the developed EG-Al-SnS₂ exhibited a better conductivity, which was beneficial for realizing the room-temperature NO₂ sensing. As a result, a high sensing response of 410% toward 2 ppm NO₂ was achieved at room temperature by using the 3% EG-Al-SnS₂ as the sensing material. Such outstanding sensing performance was attributed to the enhanced electronic interaction of NO₂ on the surface of SnS₂ induced by the synergistic effect of Al doping, S vacancies, and the expanded interlayer spacing, which is directly revealed by the in-suit measurement based on near-ambient pressure X-ray photoelectronic spectroscopy (NAP-XPS). Furthermore, to identify the role of Al doping, S vacancies, and the expanded interlayer spacing in enhancing the NO₂ sensing properties, a series of comparative experiments and theoretical calculations were performed.

The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)-Oxo Complex

In this paper, we report the preparation, spectroscopic and theoretical characterization, and reactivity studies of a Co(IV)-oxo complex bearing an N4-macrocyclic coligand, 12-TBC (12-TBC = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane). On the basis of the ligand and the structure of the Co(II) precursor, [Co^II(12-TBC)(CF₃SO₃)₂], one would assume that this species corresponds to a tetragonal Co(IV)-oxo complex, but the spectroscopic data do not support this notion. Co K-edge XAS data show that the treatment of the Co(II) precursor with iodosylbenzene (PhIO) as an oxidant at -40 °C in the presence of a proton source leads to a distinct shift in the Co K-edge, in agreement with the formation of a Co(IV) intermediate. The presence of the oxo group is further demonstrated by resonance Raman (rRaman) spectroscopy. Interestingly, the EPR data of this complex show a high degree of rhombicity, indicating structural distortion. This is further supported by the EXAFS data. Using DFT calculations, a structural model is developed for this complex with a ligand-protonated structure that features a Co═O···HN hydrogen bond and a four-coordinate Co center in a seesaw-shaped coordination geometry. Magnetic circular dichroism (MCD) spectroscopy further supports this finding. The hydrogen bond leads to an interesting polarization of the Co-oxo π-bonds, where one O(p) lone-pair is stabilized and leads to a regular Co(d) interaction, whereas the other π-bond shows an inverted ligand field. The reactivity of this complex in hydrogen atom and oxygen atom transfer reactions is discussed as well.

CoFe Nanoparticle-Decorated Reduced Graphene Oxide for the Highly Efficient Reduction of 4-Nitrophenol

High-performance, nonprecious metal catalysts with special morphologies and easy-to-recycle properties are essential for the treatment of environmental pollutants. Herein, CoFe nanoparticle-decorated reduced graphene oxide (RGO) catalysts were designed and successfully fabricated, and the catalyst was then used to reduce 4-nitrophenol into 4-aminophenol. Outstanding catalytic properties with a reduction rate constant of 4.613 min^-1 were achieved due to the synergistic properties of the CoFe metal alloy and the high-conductivity RGO components in the catalysts. In addition, the catalyst was conveniently recovered via magnets due to its inherent magnetic properties. The facile preparation, outstanding catalytic performance, structural stability, and low material costs make the CoFe/RGO nanocatalyst a promising candidate for potential applications in catalysis.

Hydrothermal control of the lithium-rich Li2MnO3 phase in lithium manganese oxide nanocomposites and their application as precursors for lithium adsorbents

Lithium manganese oxides (LMOs) are key materials due to their role in Li-ion batteries and lithium recovery from aqueous lithium resources. In the present work, we investigated the effect of the crystallization temperature on the formation by hydrothermal synthesis of LMO nanocomposites with high Li/Mn ratios. It is demonstrated that LMOs with a high Li/Mn ratio can be formed by systematically favoring the lithium-rich layered monoclinic phase (Li₂MnO₃) in a mixture of monoclinic and spinel crystalline phases. LMO nanocomposites have been characterized in terms of morphology, size, crystallinity, chemical composition and surface properties. Moreover, lithium adsorption experiments were conducted using acid-treated LMOs (HMOs) to evaluate the functionality of the nanocomposites as lithium adsorbent materials in a LiCl buffer solution. This study spotlights the structural, compositional, and functional properties of different LMO nanocomposites obtained by the hydrothermal method using the same Li and Mn precursor compounds at slightly different crystallization temperatures. According to our knowledge, this is the first report of the successful application of the lithium-rich Li₂MnO₃ phase in lithium manganese oxide nanocomposites as lithium adsorbent materials. Therefore, specific LMO nanocomposites with controlled amounts of the layered phase can be engineered to optimize lithium recovery from aqueous lithium resources.

Ru-Ni bimetallic catalysts for steam reforming of xylene: effects of active metals and calcination temperature of the support

A series of Ru and Ni supported catalysts were prepared and their catalytic performance was evaluated in the steam reforming of xylenes. The effects of active metals, active metal loading sequence, and the calcination temperature of the support on the catalyst activity and stability were investigated. The bimetallic 2Ru → 15Ni catalyst shows much higher activity and stability than the monometallic 2Ru and 15Ni catalyst owing to the synergic effect of Ni and Ru. The 2Ru → 15Ni catalyst has the least coke deposition owing to its high conversion performance and much less coke precursor being formed on the catalyst surface. After decoking, most of the small-sized pores cannot be recovered because of the pore collapse under severe hydrothermal conditions. o-Xylene has the lowest reactivity due to electronic and steric effects. Besides the steam reforming reaction, demethylation and C–C cracking are also observed, forming benzene and toluene. The catalyst with a loading sequence of 15Ni → 2Ru shows high activity at low temperatures (550–600 °C), but undergoes an activity drop at high temperatures (625–650 °C) because the Ni sintering at high temperatures greatly affects the state of Ru on the catalyst. The catalyst with a loading sequence of 2Ru → 15Ni has an advantage at high temperatures owing to its better sintering resistance. The simultaneously loaded 2Ru ↔ 15Ni catalyst shows the lowest activity. The high calcination temperature of the support enhances the catalyst stability by eliminating the small-sized pores before reaction; on the other hand, the elimination of pores decreases the dispersion of the active metals. The 2Ru → 15Ni catalyst calcined at 1000 °C balances the active metal dispersion and resistance to sintering under severe hydrothermal conditions, showing the best activity and stability. The catalyst calcined at 1000 °C has the best coke resistance with only 0.166 g g_cat⁻¹ of coke formation after the 24 h durability test. The DTG results indicate that the carbon formed on the catalysts is mainly graphitic carbon.

The performance of the bimetallic 2Ru15Ni/La₂O₃–MgO–Al₂O₃ catalyst in the steam reforming of xylene greatly depends on the metal loading sequence and support calcination temperature.

Taming the butterfly effect: modulating catalyst nanostructures for better selectivity control of the catalytic hydrogenation of biomass-derived furan platform chemicals

This minireview highlights versatile routes for catalyst nanostructure modulation for better hydrogenation selectivity control of typical biomass-derived furan platform chemicals to tame the butterfly effect on the catalytic selectivity.

Effect of Metal Content on Ethanol Decomposition over Ni-Co Catalysts Supported on La-Ce Oxides

The search for catalysts with features that can improve coke resistance and decrease byproduct formation is a current goal in H₂ production from renewable sources. In this work, the effect of the presence of Ni nanoparticles over Co/La-Ce oxides on the ethanol decomposition reaction was studied. Catalysts were synthetized using as precursor a La_0.8Ce_0.2Ni_xCo_1-xO₃ perovskite-type material to ensure a low segregation of phases and a high dispersion of metals. After reduction at 873 K, the perovskite structure was destroyed, and metal Co-Ni particles were supported over a lanthanum-cerium oxide. The materials were characterized by different techniques before and after reaction. Solids exhibited metal particle sizes between 5 and 15 nm demonstrating the advantages of the preparation method to obtain Ni-Co alloys. Although the results of adsorption of ethanol followed by diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) showed acetate species strongly adsorbed on the catalyst's surface, the material (Ni_0.7Co_0.3/La_0.8Ce_0.2) with the lowest particle size was the most stable system leading to the lowest amount of carbon deposits during ethanol decomposition. This catalyst showed the better performance, with a higher ethanol conversion (98.4%) and hydrogen selectivity (75%). All catalysts exhibited carbonaceous deposits, which were an ordered and disordered carbon phase mixture.

Cooperative Co0 /CoII Sites Stabilized by a Perovskite Matrix Enable Selective C-O and C-C bond Hydrogenolysis of Oxygenated Arenes

Strontium-substituted lanthanum cobaltite (La_0.8 Sr_0.2 CoO₃ ) matrix-stabilized Co⁰ /Co^II catalytic sites were prepared, which present tunable C-O and C-C hydrogenolysis activity for the vapor-phase upgrading of oxygenated arenes. Co^II sites associated with oxygen vacancies were favored at low temperatures and performed selective C-O hydrogenolysis, in which Sr-substitution facilitated oxygen vacancy formation, leading to approximately 10 times higher reactivity compared to undoped LaCoO₃ . Co⁰ sites were favored at high temperatures and performed extensive C-C bond hydrogenolysis, generating a wide range of alkanes. The lower reaction order with P H 2 (1.1±0.1) for C-C hydrogenolysis than for C-O hydrogenolysis (2.0±0.1) led to a high selectivity towards C-C hydrogenolysis at low P H 2 . The Co₃ O₄ surfaces featured a narrower temperature window for obtaining the respective optimal Co^II and Co⁰ pairs compared to analogous perovskite surfaces; whereas, the perovskite matrix stabilizes these pairs for selective C-O and C-C hydrogenolysis. This stabilization effect offers an additional handle to control reactivity in oxide catalysts.

A mini review of in situ near-ambient pressure XPS studies on non-noble, late transition metal catalysts

The rich surface chemistry of Fe, Co, Ni and Cu during heterogeneous catalytic reactions from the perspective of NAP-XPS studies.