Valence State Of Vanadium Research Articles

Polyaniline-Coated Na3V2(PO4)2F3 Cathode Enables Fast Sodium Ion Diffusion and Structural Stability in Rechargeable Batteries.

Na3V2(PO4)2F3 (NVPF), a typical sodium superionic conductor (NASICON) type structure, has attracted much interest as a potential positive electrode in sodium-ion battery. However, the inherently poor electronic conductivity of phosphates compromises the electrochemical properties of this material. Here, we develop a general strategy to improve the electrochemical performance by preparing a new composite material "polyaniline (PANI)@NVPF" using a Pickering emulsion method. The X-ray diffraction and Raman results indicated a successful PANI coating without affecting the NASICON-type structure of NVPF, and they enhanced the interfacial bonding between the two components. Also, thermogravimetric analysis and scanning electron microscopy analyses revealed that the PANI content influenced the thermal stability and morphology of the nanocomposites. As a result, the sodium test cells exhibited multielectron reactions and a better rate performance for PANI@NVPF nanocomposites as compared to NVPF. Specifically, 2%PANI@NVPF maintained 70% of its initial capacity at 5C. Ex-situ electron paramagnetic resonance revealed the existence of mixed valence states of vanadium (V4+/V3+) in both discharge and charge processes. Consequently, the successful PANI coating into the sodium superionic conductor framework improved the sodium diffusion channels with a measurable increase of diffusion coefficients with cycling (ca. 3.25 × 10-11 cm2 s-1). Therefore, PANI@NVPF nanocomposites are promising cathode candidates for high-rate sodium-ion battery applications.

Sustainable Cathodic Performances of VS4 in Rechargeable Magnesium Batteries by Cobalt Substitution.

Vanadium tetrasulfide (VS4) is one of the most promising cathodic materials for rechargeable magnesium battery systems (RMBSs). Elemental substitution to expand layers, creation of sulfur vacancies, and reduction of particle sizes of VS4 are undoubtedly effective strategies to enhance cathodic performances. Experimental and DFT analysis revealed that valence states of vanadium and cobalt have been elevated from V2+ to V3+ and Co2+ to Co3+ in VS4 and that the Co-S bond length shortened due to cobalt substitution, which resulted in enhanced overall internal polarization in the layered atomic structure of VS4 by increasing cobalt concentrations. This phenomenon of charge accumulation contributes toward regulated magnesiation and accommodated volume expansion while cycling, resulting in the enormous structural stability of VS4 and sustainable battery performance during a long and stable cycling at a cost of 20% capacity diminution as compared to pristine VS4 in RMBS. Hence, 9% CoVS4 demonstrated a capacity of 158 mAh g-1 at a current density of 500 mA g-1 with approximately 98% capacity retention after 1000 cycles. Sustainable cathodic performance is the most desirous feature for commercialization. This work provides insight realization regarding structural limitations and opportunities of VS4 for sustainable cathodic performances in RMBS with non-nucleophilic 0.25 mol/L (R-PhOMgCI)2-A1Cl3/THF (PMC) electrolyte and has laid a theoretical plus experimental foundation for future developments.

The magnetic modulation by the valence transition of polyoxometalate

Three novel vanadoborates with crown-shaped V12B32 cluster cages were successfully synthesized, differing only in their countercation. X-ray photoelectron spectroscopy (XPS) and Bond valence sum (BVS) analyses revealed distinct V4+/V5+ ratios (11:1, 10:2, and 10:2) in the cluster cage of the three compounds. Structural analyses indicated that the valence state ratio was modulated by the countercation. The magnetic properties of these compounds were examined using variable-temperature magnetic susceptibilities and two-dimensional correlation infrared spectroscopy (2D-COS-IR) under magnetic perturbation. This approach elucidated the origin and variability of their magnetic properties, demonstrating that the vanadium valence ratio and countercation significantly influence the magnetic behaviour of vanadoborates. The present study highlights the effectiveness of the transition of the vanadium valence state in the cluster cage by altering the countercation, providing a new avenue for the study of magnetically modulated materials.

V2O3/VO2@NC@GO ultrathin nanosheets as a high-performance cathode for aqueous zinc-ion batteries

Recently, vanadium oxides have attracted much attention as advanced cathodes for aqueous zinc-ion batteries on account of their high theoretical specific capacity, multi-electron transfer and easy synthesis; however, structural instability and poor conductivity of the materials limit their practical application. Herein, N-doped carbon-coated V2O3/VO2 hybrid nanosheets were encapsulated into graphene oxide (V2O3/VO2@NC@GO) as an advanced cathode for aqueous zinc-ion batteries by the combined process of hydrothermal treatment, high-temperature annealing and freeze drying. The multi-valence of vanadium element activates diverse redox reactions and thus results in high specific capacity, while graphene oxide and N-doped carbon layer derived from polyvinyl pyrrolidone establish an efficient conductive network for electronic transfer and provide a rigid skeleton for enhancing the structural stability of the hybrid nanosheets. Benefiting from the above unique advantages of composition and micromorphology, the V2O3/VO2@NC@GO cathode exhibits excellent reaction dynamics and rapid electron transfer, generating high specific capacities of 493.0 mAh g−1 at 0.5 A g−1 and 411.9 mAh g−1 at 5 A g−1 and outstanding long-term cycling performance with a retention of 92.4 % after 1000 cycles at 5 A g−1. This work offers a viable approach for developing high-performance vanadium oxide-based cathodes for aqueous zinc-ion batteries by enriching the valence states of vanadium and encapsulating active materials into highly conductive carbon materials.

Enhanced vanadium bioleaching from stone coal employing Aspergillus niger: Optimization of stone coal pretreatment method

Vanadium is a rare metal with excellent properties. The recovery of vanadium from low-grade stone coal and vanadium-containing solid wastes using microbial leaching, has become an increasingly popular technology. In this paper, Vanadium was obtained from stone coal using Aspergillus niger as the leaching strain, and the process of vanadium bioleaching was strengthened. Compared with plasma treatment and ultrasonic pretreatment of stone coal, the leaching effect of stone coal after roasting at 900 °C was the best, and the leaching rate of vanadium was as high as 94.52 %. The vanadium bioleaching mechanism was explored by SEM-EDS, XRD, XPS and FTIR analysis. The findings indicated that Aspergillus niger has the ability to adhere to the surface of stone coal, resulting in subsequent corrosion and degradation. The roasting treatment of stone coal and bioleaching of Aspergillus niger jointly lead to the decrease of crystallinity, the increase of interplanar spacing and the decrease of stability of stone coal. Meanwhile, the valence state and binding form of vanadium changed, and V (III) was oxidized to V (IV) and V (V). The mineral structure may be distorted as a result of the distinctive peak's vibratory stretching and the influence of functional categories that include oxygen, which in turn causes the change of the coordination form of the internal metal ions, which affects the symmetry of the mineral and facilitates the dissolution of vanadium from the stone coal. Research indicates that roasting and Aspergillus niger bioleaching have a great deal of promise to increase vanadium recovery from stone coal.

High efficiency triethylamine gas sensor based on SmVO4 nano octahedron granules

Triethylamine (TEA) is typical hazardous volatile organic gas (VOCs), it is particularly important for us to effectively detect triethylamine in complex places. In this work, high efficiency triethylamine gas sensor based on SmVO4 was successfully obtained by means of hydrothermal reaction and assisted calcination. Characterization of analytical materials, SmVO4 octahedral nanoparticles formed clusters similar to pomegranate fruits. There is a trace +4 valence state of vanadium in the material, which contributes to the oxidation-reduction reaction between the target gas and the surface of the material. Gas sensitive test results found that the SmVO4 sensor still has a 2.45 response to the target gas (triethylamine) at low concentrations (1 ppm). SmVO4 shows excellent selectivity for triethylamine, with a response value more than three times that of other gases. In 25 days, it shows excellent stability and fast response recovery time (15 s/40 s). In addition, the gas sensing mechanism is analyzed.

VO2 nano-rod coated mica composite pearlescent pigment for temperature control packaging

A temperature control mica/VO2 functional pearlescent pigment was designed for the packaging industry. Firstly, a layer of VO2 nanorod film was coated on the surface of flake mica powder by hydrothermal method. Then, the surface of pure mica was modified by silane coupling agent KH-570 and sandwiched between inorganic powders to strengthen the combination. Secondly, the mica/VO2 composite pearlescent powder with gray-green pearlescent effect were successfully obtained by thermal annealing. The crystal structure of the VO2 coating and the chemical valence state of vanadium were verified by X-ray diffraction and X-ray photoelectron spectroscopy. Finally, powders were mixed with polyurethane resin to obtain a functional film. The infrared transmittance of film at 28 °C and 70 °C showed that the composite film with mica content of 3 g had greater temperature control properties, and the difference between high and low temperature transmittance was about 16%. Most importantly, the shiny decorative effect of pearlescent pigment can be still be maintained after being endowed with temperature control property. This work proposes the preparation of functional mica/VO2 composite with pearlescent effect and temperature control property.

VOx@ graphene electro-catalysts for water splitting and dopamine sensing

Vanadium oxide@graphene (VOG) composites were synthesized using facile hydrothermal method by varying the synthesis time from 6 to 24 h. The samples with best catalytic characteristics were reprepared by replacing graphene oxide with N-doped graphene in the initial hydrothermal reaction. The role of graphene/N-doped graphene in determining the catalytic properties of vanadium oxide was effectively studied using various characterizations viz. X-ray diffraction, Fourier Transform Infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Maximum hydrogen evolution reaction (HER) activity with high current density of –31.07 mA/cm2 (Tafel slope = 162 mVdec−1) has been achieved for VONG-24 sample, indicating Volmer reaction as rate determining step. The high electrochemical surface area (ECSA) of VOG-24 sample in 1 M KOH corroborated the enhanced current density of 144.90 mA/cm2 (Tafel slope = 83 mVdec−1) for maximum oxygen evolution reaction (OER) activity. The VOG12/GCE sample with a 0.29 μM limit of detection (LOD) proved to be the best electrochemical sensor for dopamine (DA) in a wide linear detection range i.e., 1–150 μM. Both catalytic as well as sensor responses of VOG samples were deeply influenced by the amount of O-species along with relative ratios of the V3+, V4+ and V5+. The nature of the graphene in the initial mixture emerged as a crucial parameter in tailoring the vanadium valence state content in the composites.

Phase Separation Prevents the Synthesis of VBi2Te4 by Molecular Beam Epitaxy.

Intrinsic magnetic topological insulators (IMTIs) have a non-trivial band topology in combination with magnetic order. This potentially leads to fascinating states of matter, such as quantum anomalous Hall (QAH) insulators and axion insulators. One of the theoretically predicted IMTIs is VBi2Te4, but experimental evidence of this material is lacking so far. Here, we report on our attempts to synthesise VBi2Te4 by molecular beam epitaxy (MBE). X-ray diffraction reveals that in the thermodynamic phase space reachable by MBE, there is no region where VBi2Te4 is stably synthesised. Moreover, scanning transmission electron microscopy shows a clear phase separation to Bi2Te3 and VTe2 instead of the formation of VBi2Te4. We suggest the phase instability to be due to either the large lattice mismatch between VTe2 and Bi2Te3 or the unfavourable valence state of vanadium.

Investigation of Transition Metal Oxides & Phosphates for Zn-Ion/Zn-Air Batteries

Being a champion in a portable electronics world, lithium-ion batteries (LIBs) are irreplaceable, but the scarcity of Li, high cost, and the inclusion of non-aqueous electrolytes make them relatively perilous and inefficient for grid-scale energy storage. Recently, the blooming aqueous Zn-ion batteries (ZIBs) have emerged as one of the pioneer candidates featuring the inherently safe nature of metallic Zn anode and its unique properties.[1] Vanadium-based compounds show fast ion diffusion and excellent reversible capacity because of their rich valence state of vanadium, facile distortion of V-O polyhedrons, and tuneable composition, which offers an excellent treasure house. Moreover, the different oxidation states of vanadium allow a higher degree of structural change and greater functional flexibility while incorporating multivalent cations into vanadium-based compounds. [2] The present work focuses on one V-based oxide cathode. The cathode, ZnV2O4, synthesized by a simple solid-state route, showed a reversible capacity of around 200 mAh/g at a current density of 500 mA/g. Ex-situ XAS suggested that there is a drastic change in V and Zn local environment, confirming that there is a structural transformation taking place. Further, we have pursued ex-situ TEM where segregation of the conversion product phases was seen, confirmed by the small crystalline domains present at the nanoscale regime. A detailed analysis will be discussed to verify that a phase transformation is happening and is getting amorphized in subsequent cycles using ex-situ TEM and XAS.Also, metal-air batteries are widely discussed and studied because of their high energy density. In this pursuit, highly efficient bifunctional electrocatalysts, non-noble such as Co metal-based phosphates/oxides, have been studied vividly.[3,4] Herein, we present a thorough study of three-dimensional ZnCo2(PO4)2 (ZCP), which showed excellent bifunctional activity compared to the benchmark catalysts, denoting the presence of many catalytically active Co sites in ZCP. The presence of asymmetric edge-sharing CoO5/CoO6 polyhedra enhances the net catalytic activity.[5] ZCP exhibited robust oxygen reduction and evolution (ORR and OER) activity with the onset of 0.87 and 1.50 V vs. RHE for ORR and OER, respectively. The ORR saturated current density for ZCP was 6.38 mA/cm2, close to the 20% Pt/C catalyst benchmark. It also showed an OER exchange current density of 16.7 mA/cm2, closer to RuO2 ( j= 17.6 mA/cm2). This bifunctional electrocatalytic activity will be elaborated using analytical tools and DFT, along with the demonstration of Zn-air batteries. A detailed structural characterization using synchrotron refinement, TEM analysis, magnetic studies, and electrocatalysis performance will be discussed. Reference s : [1] M. Song et al., Adv. Funct. Mater. 2018, 28, 1802564.[2] Yao. Zhang et al., Chem. Front. 2021, 5 744-762.[3] J. L. Jung et al., Energy Environ. Sci. 2016, 9176-183.[4] W. Liu et al., Acc. Chem. Res . 2018,51,1858.[5] A. Baby et al., Chem. Comm. 2020, 56, 8400-8403.

Boosting activity of γ-alumina-supported vanadium catalyst for isobutane non-oxidative dehydrogenation via pure V3+

The vanadium-based dehydrogenation (DH) catalyst is becoming a promise alternative to the industrial used Pt- and Cr-based catalysts, due to lower cost and less environmental threat. However, the low DH activity hampered the industrial application of vanadium-based catalysts. Herein, for the first time, we introduce a method to prepare high-efficiency vanadium-based catalyst by constructing pure V3+ species on γ-Al2O3 through treatment of as-prepared thiovanadate. The V3+ species contributes to not only enhancing the DH activity, but also fabricating the V3+-O/S acid-base pair with ideal strength and stability. The isobutene yield can reach as high as 56.9 wt%. Only Lewis acid is recognized on V3+/Al2O3 catalyst, while no Brønsted acid remains. The side-reactions are consequently inhibited, and the selectivity to isobutene is improved. Besides, with the increase of vanadium loadings, the Lewis acid content increases at first and then decreases, and the content of acid sites in middle strength keeps decreasing. Though the deposited coke on V3+/Al2O3 was just 2.5 wt% during 8.5 h consecutive DH reaction, the valence state of vanadium was still influenced and the fraction of inert V4+ species increased steadily. This study will improve the potential for industrial application of vanadium-based DH catalyst, and offer theoretical guidance for optimization of ideal DH catalysts.

Defect regulation in bimetallic oxide cathodes for significantly improving the performance of flexible aqueous Zn-ion batteries

Bimetallic oxides have received extensive attention as cathode materials in aqueous zinc-ion batteries (AZIBs) due to their effective multi-electron storage mechanism. However, their capacity still falls short of the current demand. In this study, through reasonable structural design, we synthesized spherical glucose-derived carbon-regulated defect state Zn3V3O8 (ZVO) bimetallic oxide (CS@ZVO) cathode. Such a design avoids the layered accumulation of electrode materials, which prevents the structural collapse during the cycle process, leading to a significant improvement in the cycle stability of AZIBs. Additionally, the introduction of glucose-derived carbon can shift the valence state of vanadium in the ZVO bimetallic oxide cathode towards reduction, thereby significantly improving its Zn-ion storage capacity. The resulting CS@ZVO cathode manifests a high discharge capacity of 154 mAh g−1 at 1 A g−1 after 100 cycles and a stable lifespan of 2000 cycles at 5 A g−1. We also constructed a flexible and foldable AZIB using a hydrogel electrolyte, which operates with a specific capacity of up to 230 mAh g−1 at 0.5 A g−1 and can be bent and folded arbitrarily when working. This strategy for regulating the valence state of bimetallic oxides offers a promising path for the development of cathode materials in flexible AZIBs.

Selective sulfuric acid cyclic leaching of vanadium from the calcification roasting pellets of vanadium titanomagnetite

Here, a new method of sulfuric acid cyclic leaching was proposed to selectively leach vanadium from the calcification roasting pellets of vanadium titanomagnetite. Cyclic leaching and conventional heap leaching were compared. The results showed that under the optimal conditions, the leaching rate of vanadium was higher and those of iron and titanium were lower than when using conventional heap leaching. Under the optimal cyclic leaching conditions (acid concentration 3.0 mol/L, liquid: solid ratio 4: 1, temperature 90 °C, and leaching time 100 h), the leaching rate of vanadium reached 80.28%, while the leaching rates of iron and titanium were 1.39% and 1.72%, respectively. After secondary roasting, the crushing strength of the leached pellets reached 2200 N, which meets the requirements for pellets used in blast furnace smelting. In addition, the valence states of vanadium and iron in the pellets before and after leaching and the main phases in the pellets were analyzed and characterized. Most V5+ and Fe2+ leached, while Fe3+ was hardly leached, and main phases in the pellet were unchanged. Furthermore, the leaching kinetics of vanadium during cyclic leaching showed that the reaction rate of vanadium was controlled by solid product diffusion during acid leaching. In this study, vanadium was selectively leached, and iron was obtained by secondary roasting of the pellets, followed by blast furnace ironmaking. This paper provides a new method for the comprehensive utilization of valuable metals in vanadium titanomagnetite.

Achieving high performance in aqueous iron-ion batteries using tunnel-like VO2 as a cathode material.

The research on aqueous iron-ion batteries (AIIBs) is still in its early stages and highly limited by the lack of suitable cathode materials. In this study, we propose using tunnel-like VO2 as a cathode material, which delivers a high capacity of 198 mA h g-1 at 0.2 A g-1. Besides, the AIIB exhibits appreciable cycling performance, retaining 78.9% of its initial capacity after 200 cycles. The unique structure of VO2 and the multiple valence states of vanadium in VO2 enable the reversible storage of Fe2+ during cycling. This work presents a new choice for the cathode and considerable development prospects in AIIBs.

A flexible zinc ion hybrid capacitor integrated system with layers-dependent V2CTx MXene

Ti3C2Tx MXene with unique physical and chemical properties are recently sparked tremendous interest in the energy storage field. Compared to Ti3C2Tx, V2CTx MXene is a more promising candidate for energy storage due to a low number of atomic layers in the V2CTx structure and varied valence states of vanadium. Herein, we report a flexible V2CTx electrode with different layers (named accordion-like V2CTx, multi-layer V2CTx, and few-layer V2CTx, respectively) fabricated by using electrophoretic deposition, then assembled a flexible zinc ion hybrid capacitor (ZIHC) by virtue of zinc anode and gel electrolyte. The areal capacitance of few-layer V2CTx based ZIHC is 54.12 mF cm−2 at 0.1 mA cm−2, which is greater than those of accordion-like V2CTx and multi-layer V2CTx based ZIHC. The outstanding electrochemical performance of few-layer V2CTx based ZIHC is attributed to its richer active sites and shorter ion transport routes. Additionally, the few-layer V2CTx based ZIHC also owns well cycling stability, with 81.48 % capacity retention after 8000 cycles, and a low self-discharge rate of 6.4 mV h−1, making it suitable for wearable devices. So, the V2CTx based ZIHC is integrated with a Ti3C2Tx based pressure sensor to monitor diverse human activities, demonstrating its steady and long-term power supply capacity as the energy storage device.

The valance state of vanadium-key factor in the flexibility of potassium vanadates structure as cathode materials in Li-ion batteries

Potassium hexavanadate (K2V6O16·nH2O) nanobelts have been synthesized by the LPE-IonEx method, which is dedicated to synthesis of transition metal oxide bronzes with controlled morphology and structure. The electrochemical performance of K2V6O16·nH2O as a cathode material for lithium-ion batteries has been evaluated. The KVO nanobelts demonstrated a high discharge capacity of 260 mAh g−1, and long-term cyclic stability up to 100 cycles at 1 A g−1. The effect of the vanadium valence state and unusual construction of the nanobelts, composed of crystalline and amorphous domains arranged alternately were also discussed in this work. The ex-situ measurements of discharged electrode materials by XRD, MP-AES, XAS and XPS show that during the subsequent charge/discharge cycle the potassium in the K2V6O16·nH2O structure are replacing by lithium. The structural stability of the potassium hexavandate during cycling depends on the initial vanadium valence state on the sample surface and the presence of the “fringe free” domains in the K2V6O16·nH2O nanobelts.

Adjusting the V5+ content of vanadium oxide cathodes for high-performance Zn-ion batteries by aging

Vanadium oxides are promising cathode materials with great potential. Here, we present a simple, safe, and environmentally friendly aging treatment to change the content of V5+ in vanadium oxides. The influence of different V5+ contents in vanadium oxides cathodes on the properties of Zn-ion batteries (ZIBs) is studied. V6O13 and V3O7/V6O13 nanosheets are synthesized by aging VO2 precursors for different periods of time. V6O13 is found to exhibit higher specific capacity and excellent cycling performance compared to VO2 and V3O7/V6O13. It is also characterized by an extremely high capacity of 300 mA h g−1 at a high current density of 5 A g−1. At 0.3 A g−1, it maintains a capacity of 421 mA h g−1 during 100 cycles with a high capacity retention rate of 95%. Changes in the vanadium valence state, structure, and morphology of electrodes during charging and discharging are also investigated for a better understanding of the underlying electrochemical processes.

Synergistic interlayer and defect engineering of hydrated vanadium oxide toward stable Zn-ion batteries

Layered hydrated vanadium oxides are considered as promising cathode materials for aqueous Zn-ion batteries because of their open layered frameworks and multiple valence states of vanadium. However, they usually exhibit poor electrochemical performance due to the instability of layered frameworks. Herein, Ca-intercalated hydrated vanadium oxide (CaVO) nanobelts have been synthesized by a simple hydrothermal method, accompanied with the formation of cationic V vacancies. The intercalated Ca ions and induced V vacancies can not only synergistically enhance the Zn-ion storage capability by offering numerous active sites, but also effectively stabilize the crystal structure over long-term cycling because of the pinning effect of Ca ions, leading to the enhanced electrochemical performance of hydrated vanadium oxide. Consequently, the CaVO nanobelts deliver a high reversible capacity of 310 mAh g−1 at a current rate of 0.5 A g−1, a superior rate performance of 88 mAh g−1 at 15 A g−1, and an impressive cycling stability with a capacity retention of 91.7% at 10 A g−1 over 3000 cycles. Our present study demonstrates that the synergistic interlayer and defect engineering is a promising strategy to construct advanced layered cathode materials for practical Zn-ion batteries.

Revealing excess Al3+ preinsertion on altering diffusion paths of aluminum vanadate for zinc-ion batteries

Layered metal vanadates have been extensively investigated for aqueous zinc-ion batteries (AZIBs) due to their low cost, crystal structure, and a wide diversity of vanadium valence states. However, research on the number of cationic pre-intercalation layers is almost empty and the effect of Al atomic numbers in H11Al2V6O23.2 (HAVO) on the diffusion path has not been studied even more. The systematic investigation into pre-intercalated ions in electrode materials is fundamental but vital for the further development of high-performance batteries of both the point of academic and industry. In this contribution, we designed and synthesized HAVO with four different layer spacings by simply modulating aluminum content for the first time and combined a range of ex-situ and in-situ complementary techniques to reveal the reaction mechanism of zinc ion storage and its intrinsic relationship with electrochemical performance. The “pillar” effects of stable Al3+ between the interlayers protects the laminate structures from collapse during electrochemical process and effectively widens the layer spacing at the same time. However, based on experiments and calculations we have demonstrated that the appropriate aluminum content can significantly improve the electrochemical properties of the material, while excessive ion intercalation can block the zinc ions diffusion channels. As a result, HAVO with a suitable Al atomic number displays extraordinary electrochemical performance. This work provides further insights into the design and construction of cathodes for pre-inserted ion batteries, and facilitates the exploitation of low-cost and high-safety cathodes.

Rare earth metal based DES assisted the VPO synthesis for n-butane selective oxidation toward maleic anhydride

Deep eutectic solvents (DESs) are now considered a new class of ionic liquid analogs that have been generously used in various fields. Herein, vanadium phosphorus oxide (VPO) catalysts are synthesized in combination with a deep eutectic solvent containing rare earth metal (rE-DES), and their catalytic performance in n-butane selective oxidation to produce maleic anhydride (MA) is evaluated. The rE-DES is produced from the interaction of choline chloride (ChCl) and rare earth metal salts (Cerium, Europium, Lanthanum, and Samarium metal salt) (ChCl:rE = 1:0.5–1:3) under mild conditions. It was found that DESs served as structural modifiers and electronic promoters during VPO synthesis. It regulated the chemical state of the catalyst surface, such as the vanadium valence state, acid-base properties, and ratios of V4+/V5+, Lat–O/Sur–O and P/V. Various characterization techniques, such as FT-IR, DSC, XRD, SEM, EDS, TEM, Raman, TGA, NH3-TPD, and XPS, were used to examine its physical and chemical characteristics. These characteristics were correlated with the catalytic performance. The VPO catalyst modified by rE-DES showed a significant enhancement of n-butane conversion and MA selectivity while suppressing the selectivity of CO and CO2 as well as the CO/CO2 ratio compared to the unpromoted VPO catalyst. Especially for Ce-DES-VPO, it increased the n-butane conversion and MA mass yield up to approximately 11% and 10%, respectively. In addition, we evaluated the catalytic performance under different activation atmospheres.