Niobium Phosphate Research Articles

Hydrodeoxygenation of Glycerol to Propene Over Molybdenum and Niobium Phosphate Catalysts

AbstractIn single‐step conversion of glycerol to propene, the intricate catalytic pathways with molybdenum and niobium catalysts remain elusive. While these catalysts can effectively accelerate the hydrogenolytic cleavage of the glycerol CO bonds, resulting in a high selectivity to propene, the routes have not been thoroughly studied. This study explores the reaction routes and the role hydrogen plays in determining the product distribution. The hydrodeoxygenation (HDO) of glycerol was investigated using various glycerol purities in both batch and continuous reaction modes. Remarkably, Mo(PO4)x and Nb(PO4)x demonstrated catalytic performance with raw glycerol, indicating that impurities had no detrimental effect on the catalyst's activity. In batch mode, a propene selectivity of 53% was achieved over Mo(PO4)x as the catalyst, highlighting the catalyst's stability under these conditions. In continuous operation, the highest product selectivity to propene (12%) was observed at low temperatures (573 K), while more C2 to C6 alkanes were formed at increased temperatures (623 and 673 K). Whereas a hydrogen atmosphere promotes formation of 2‐propenol, as primary precursor to propene, an inert atmosphere leads to increased formation of propanal and dissociation products. Our work has elucidated new routes to upcycle biorenewable glycerol to propene over Mo(PO4)x and Nb(PO4)x catalysts.

Thermochemical and structural study of sodium, iron, and niobium phosphate NASICON solid solutions

Solid solutions NaxFe0.5+0.5xNb1.5-0.5x(PO4)3 (0 ≤ x ≤ 1; x = 2) of NASICON structure (sp.gr. R3-c) and NbOPO4 were prepared via solid-state reaction and characterized by electron microprobe analysis, powder X-ray and neutron diffraction, and differential thermal analysis. The decrease of the a- and b-unit cell parameter prevails over the increase in c-parameters, resulting in nonlinear decrease of the unit cell volume with Na content. Enthalpies of drop solution in molten sodium molybdate solvent at 700 °C were measured by high temperature oxide melt solution calorimetry and were used to derive the enthalpies of formation. Strongly negative enthalpies of formation from elements and from constituent oxides indicate high thermodynamic stability. The mixing enthalpies of solid solutions show negative deviation from the ideality. Negative mixing enthalpies and negative mixing volumes indicate short-range ordering of cations in the structure.

Structural and interfacial microenvironment modulation of two-dimensional layered niobium phosphate to enhance uranium adsorption

To address the environmental and resource challenges arising from the advancement of the nuclear power industry, it becomes imperative to foster the development of efficient and expeditious materials for uranium adsorption. Here, for the first time, a kind of niobium phosphate with improvement of interlayer spacing and hydrophilicity (NbP-8) is employed by crystal phase modulation for uranium adsorption, which synergistically realizes structural and interfacial microenvironment modulation. Characterizations demonstrate that the expanded interlayer spacing contributes to accommodation of uranyl which increases adsorption capacity, and the enhanced hydrophilicity reduces infiltration time and greatly accelerates the adsorption rate. Consequently, NbP-8 possesses exceptional adsorption capacity of 1470.4 mg g−1, ultra-fast adsorption rate with an equilibrium time of 1 min and high selectivity, delivering one of the best phosphate uranium adsorbents. Moreover, this work opens a new venue for optimizing performance of phosphate by changing the crystal phase to modulate structure and interfacial microenvironment for uranium adsorption.

Polymorphism of Niobium Phosphate Bronze Na4Nb8P4O32 Deduced by the Packings of Structural Units: A Centrosymmetric Phase.

Herein, a new centrosymmetric phase Na4Nb8P4O32 (referred to as CS-Na4Nb8P4O32) was obtained by a molten salt method, which is a polymorph of niobium phosphate bronze Na4Nb8P4O32. CS-Na4Nb8P4O32 displays high structural similarity to the noncentrosymmetric Na4Nb8P4O32 phase (referred to as NCS-Na4Nb8P4O32): Distorted NbO6 octahedra are corner-coordinated to form ReO3-type layers, which are further joined together by isolated PO4 tetrahedra. However, two polymorphous phases adopt different packings of structural units, resulting in distinct symmetries. NbO3 layers and PO4 tetrahedra are reversely arranged along the crystallographic a direction in CS-Na4Nb8P4O32, thereby producing a centrosymmetric structure. The reverse packing cancels out all contributions of dipole moments originating from the distorted NbO6 octahedra; NCS-Na4Nb8P4O32 exhibits the C2-rotation distribution of NbO3 layers and PO4 tetrahedra, thus generating a noncentrosymmetric and polar structure. The C2-rotation packing of structural units brings a constructive addition of the dipole moments, further obtaining large calculated independent second harmonic generation susceptibilities. The study of structural evolution deduced by the packings of structural units in polymorphous Na4Nb8P4O32 might provide valuable insights into polymorphism and structural regulation.

Na12(NbO)3(PO4)7: A Congruent Melting Nonlinear Optical Crystal with Large NbO6 Distortion and High Laser-Induced Damage Threshold.

A new noncentrosymmetric crystal Na12(NbO)3(PO4)7 was successfully synthesized in the niobium phosphate system. Its structure characterizes isolated and highly distorted NbO6 octahedra joining with isolated PO4 groups to form a unit of a (Nb6P6O12) hexagonal star by sharing O atoms. In (Nb6P6O12) hexagonal stars, all Nb and P atoms are in a hexagonal star-like arrangement and all Na atoms are also in a hexagonal star-like arrangement, except for Na(3) and Na(10) atoms. Notably, it exhibits a strong phase-matched second harmonic response: 3 × KDP, which is rare in known niobium phosphate systems. Meanwhile, it also has a wide optically transparent window (0.29-4.44 μm) and a high laser-induced damage threshold (3.5 GW/cm2). More importantly, Na12(NbO)3(PO4)7 is a congruent melting compound that has the potential to be grown into large-sized single crystals by the Czochralski method. These excellent properties make it a promising candidate as a mid-infrared nonlinear optical crystal.

One-pot solvent-free sequential synthesis of high-density polycycloalkanes fuels from lignin-derivatives over laminated NbOPO4 catalyst

Upgrading lignocellulose biomass to renewable fuels is essential to achieve carbon neutrality. However, the multiple synthetic, and purification steps as well as the employment of solvents in the production of renewable fuel inhibit the overall yields and cause the waste of energy and resources. Herein, a new catalytic strategy for one-pot solvent-free sequential synthesis (OSS) of perhydrofluorene and dicyclohexylmethane was developed from lignin-derivatives. A two-dimensional layered nanosheet niobium phosphate (NbOPO4-IB) catalyst was fabricated to efficiently integrate the alkylation of phenol and benzyl alcohol and sequential hydrodeoxygenation with a cocatalyst of Ru/C. The high crystalline NbOPO4 phase and the lamellar morphology contributes to the large specific surface area to expose more active sites, especially more Brønsted acid sites. The NbOPO4-IB catalyst with a suitable Brønsted/Lewis acid ratio of 1.49 favors the selectivity of fuel precursors benzyl phenol in the alkylation and also provides the appropriate acid strength to promote hydrodeoxygenation activity. NbOPO4-IB also shows good reusability. Excessive phenol plays a vital role in promoting the alkylation reaction by dissolving the intermediates, and then into cyclohexane to enhance the H2 dissolution in the hydrodeoxygenation. A possible mechanism of OSS from lignin-derivatives into polycycloalkanes over the cocatalysts was proposed.

Influence of CeO2 on glass formation, structural and thermal properties of sodium niobium phosphate glass

Cerium is a well-known surrogate to trivalent and tetravalent actinides and has been investigated to explore the structural and thermal characteristics of simulated radwaste-loaded material systems. The solubility and distribution of CeO2 into a sodium niobium phosphate glass have been explored with the objective of developing a host matrix for radioactive waste immobilization. Niobium phosphate glasses of (100-x) (40Na2O–20Nb2O5–40P2O5)-xCeO2 (x = 0, 1, 3, 5, 8, and 10 mol%) compositions are prepared by melt-quenching method and are characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). This study summarises the influence of cerium ion incorporation on the structure, thermal stability, and formation of crystalline phases of the niobium phosphate glass. The various glass stability parameters, such as Hruby (KH), Weinberg (KW), and Lu–Liu (KLL) parameters are estimated to assess the stability of the glass melt against devitrification in the supercooled region. The spectroscopic analysis ascertains the presence of metaphosphate and pyrophosphate networks as primary structural building units in the glass. However, the Raman analysis demonstrates the influence of CeO2 on the network linkages arising from the corner-sharing of NbO6 octahedrons and Nb–O–P bonding in the glass. The CeO2 loading is optimized up to 8 mol% into the base 40Na2O–20Nb2O5–40P2O5 glass matrix without precipitation of any crystalline phase. The glasses are heat treated to obtain glass-ceramics embedded with the crystalline phases, namely, monazite CePO4, NbOPO4, NaNbO3, and niobium phosphate bronze Na6Nb8(PO4)5O15. The microanalysis of these glass ceramics shows that the CeO2 is more aggregated inside the niobium phosphate bronze framework than in the bulk at a higher temperature. It is also observed that the surface crystallization process is a prevalent mechanism for the crystallization of glasses on heating at crystallization onset temperature.

Methyl Esters Production from Degummed Soybean Oil Catalyzed by Niobium Phosphate

Methyl Esters Production from Degummed Soybean Oil Catalyzed by Niobium Phosphate

Exploring the electrochemical performance of niobium phosphate electrode for supercapacitor application

This study assessed the suitability of niobium phosphate (NbPO5) thin films for energy storage applications. The NbPO5 thin films were synthesized using a hydrothermal technique for various deposition times. The structural, morphological, elemental, and electrochemical characteristics of the NbPO5 thin films were analyzed. The NbPO5 thin films had an orthorhombic crystal structure with a unique surface morphology consisting of tetragonal-shaped micro-rods surrounded by nanostructured spheres. X-ray photoelectron spectroscopy and energy dispersive spectroscopy confirmed the NbPO5 composition. The micro-rods and nanospheres morphology of NbPO5 samples at 6 h deposition time (NbP-6) exhibited a high areal capacitance (CA) of 3542.4 mF cm−2 at a current density of 10 mA cm−2. The excellent energy storage performance of the NbP-6 sample was attributed to the high diffusion coefficient, enhanced charge transfer, and carrier mobility. Moreover, the NbP-6 sample displayed excellent long-term cycling stability, maintaining 85.4% of its total capacitance and 98.7% of coulombic efficiency over 10,000 consecutive galvanostatic charge-discharge cycles. The present study suggests that an NbPO5 electrode is a promising candidate for supercapacitor applications owing to the synergistic effects of niobium and phosphate.

Apical Sealing and Bioactivity of an Experimental Gutta-Percha Containing Niobium Phosphate Bioglass.

This study evaluated the apical sealing ability and bioactivity of an experimental gutta-percha containing niobium phosphate bioglass. Thirty-six human premolars were endodontically prepared and divided into three groups: GPC-filling with conventional gutta-percha; GBC-filling with bioceramic gutta-percha (EndoSequence BC); GNB-filling with experimental gutta-percha containing niobophosphate. Teeth were stored in tubes containing 2 mL of simulated body fluid (SBF) solution in an oven for 30 days. Then, the samples were immersed in lanthanum nitrate solution and analyzed for apical nanoleakage (NI) with a scanning electron microscope (SEM/EDS) and transmission electron microscope (TEM). Gutta-percha specimens were immersed for 28 days (SBF) and analyzed in SEM/EDS and X-ray diffraction (XRD) to assess bioactivity. NI data originated from the SEM/EDS were analyzed using the Kruskal-Wallis test (α = 5%). NI data originated from TEM and bioactivity were descriptively reported. Statistical analysis did not detect a significant difference between groups (p = 0.13) for NI. In the bioactivity analysis, an abundant layer of hydroxyapatite was identified only in the surface of the GNB group samples. The gutta-percha containing niobophosphate bioglass promoted an apical sealing similar to EndoSequence BC, in addition to demonstrating bioactivity through the deposition of hydroxyapatite on the surface of the material after immersion in SBF.

Effect of Bioactive Filler Addition on the Mechanical and Biological Properties of Resin-Modified Glass Ionomer.

The maintenance of affected dentin can promote the greater conservation of tooth structure. The development of materials that have properties capable of reducing the demineralizing potential and/or even helping in dental remineralization is important for conservative dentistry. This study aimed to evaluate, in vitro, the alkalizing potential, fluoride as well as calcium ion release ability, antimicrobial activity, and dentin remineralization properties of resin-modified glass ionomer cement (RMGIC) incorporated with a bioactive filler (niobium phosphate (NbG) and bioglass (45S5)). The study samples were grouped into RMGIC, NbG, and 45S5. The materials' alkalizing potential, ability to release calcium as well as fluoride ions, and antimicrobial properties concerning Streptococcus mutans UA159 biofilms were analyzed. The remineralization potential was evaluated using the Knoop microhardness test, which was performed at different depths. The alkalizing and fluoride release potential was higher for the 45S5 group (p < 0.001) over time. An increase in the microhardness of demineralized dentin was observed in the 45S5 and NbG groups (p < 0.001). No differences in biofilm formation were observed between the bioactive materials, although 45S5 exhibited lower biofilm acidogenicity at different time points (p < 0.001) and greater calcium ion release in the microbial environment. A resin-modified glass ionomer cement enriched with bioactive glasses, particularly 45S5, is a promising alternative for the treatment of demineralized dentin.

Non-isothermal crystallization kinetics study of sodium niobium phosphate glasses

Sodium niobium phosphate (SNP) glasses of composition xNb2O5–(50-x/2)Na2O–(50-x/2) P2O5 (x = 20, 30, 40 mol. %) are prepared by the conventional melt–quench technique. The non-isothermal kinetics of glass transition & crystallization of SNP glasses are studied by a differential scanning calorimeter (DSC). The dependence of glass transition temperature on the heating rate is used to deduce the activation energy of glass transition. The average activation energies of crystallization are calculated by model-free peak kinetic methods (Kissinger, Boswell, Augis-Bennet, and Ozawa). The local activation energies for crystallization with the volume fraction crystallized is estimated by linear iso-conversional methods (Kissinger-Akahira-Sunose, Starink, Tang, Flynn-Wall-Ozawa, and Various heating rates (VHR)) and by Friedman differential method. Avrami exponents are deduced to understand the nucleation and growth of various crystalline phases formed on heat treatment of SNP glasses. The change in the local Avrami exponent with the crystallized volume fraction confirms that the crystallization process occurs through volume nucleation, mainly with 3D growth. SEM analysis explored the crystalline morphologies and revealed the evolution of sheaf-like crystals.

Hydrodeoxygenation of oleic acid over NiMo bimetallic catalysts supported on niobium phosphate

The properties of the support have profound effects on the catalytic performance of the supported catalyst.

Unexpected High-Substrate-Dependent Ketonization of Aldose on Niobium Phosphate-Supported Magnesia: An Emphasis on Surface Chemisorption

A water-tolerant magnesia-based solid base was prepared by combining the use of a non-equilibrium and highly structured dual-porous niobium phosphate (NbP) as the support and high-temperature thermal treatment. The crystal growth of MgO changed, and the bond length of Mg–O was longer than that of pure MgO after it was supported on NbP, which led to the higher basic property of O2– on the surface of MgO/NbP to act as a solid base catalyst toward aldose ketonization. It was revealed that the prepared solid base MgO/NbP exhibited high substrate dependence for ketonization of saccharides, facilitating the use of glucose and glucose-containing aldo-disaccharides─including maltose, cellobiose, lactose, and melibiose─due to their lower free energy after chemisorption than that of pentose, and a moderate reverse reaction barrier in aqueous solution. It was demonstrated that ketonization mainly occurred on the solid surface, especially in the case of high substrate concentration, which was different from the conventional opinion. The type of glycosidic bond and the constituent monosaccharides also affected the yield and selectivity of rare keto-disaccharides. The high performance of the MgO/NbP catalyst toward ketonization of disaccharides was realized as the typical yield and the productivity of maltulose reached 14.2% and 42.6 g·kg-solution–1·h–1, respectively, when treated with 30.0 wt % maltose solution at 130 °C. Although deactivation issues, such as leaching of ions and coke deposition, still remain to be solved, the catalyst has potential to be used in synthesizing high-value rare keto-disaccharides.

Tunable Production of Diesel Bio-Blendstock by Rhenium-Catalyzed Hydrogenation of Crude Hexanoic Acid from Grape Pomace Fermentation

The transition from fossil resources to renewable ones represents a pressing need. The acidogenic fermentation of biomass-derived ethanol to carboxylic acids represents a novel and smart possibility, opening the way for the production of further value-added bio-products through cascade chemical approaches. In this work, the hydrogenation of commercial hexanoic acid to give 1-hexanol/hexyl hexanoate mixtures was preliminary studied in the presence of commercial rhenium catalysts (Re2O7 and 5 wt% Re/C), which resulted as mainly active and selective towards 1-hexanol. On the other hand, the use of niobium phosphate as the acid co-catalyst markedly shifted the selectivity towards hexyl hexanoate. Moreover, 5 wt% Re/C and physical mixtures of (5 wt% Re/C + niobium phosphate) were further tested for the hydrogenation of crude hexanoic acid obtained through fermentation of white grape pomace, confirming the promising performance of these catalytic systems and their recyclability. For the first time, the employment of 1-hexanol/hexyl hexanoate mixtures as a diesel blendstock was evaluated, highlighting a significant reduction of soot and CO emissions, without any significant change in the engine performance. The promising properties of these oxygenated additives are favorable for the partial replacement of traditional fossil fuels, in accordance with the short-term goals of EU countries.

Studies on synthesis, structural and thermal properties of sodium niobium phosphate glasses for nuclear waste immobilization applications

Studies on synthesis, structural and thermal properties of sodium niobium phosphate glasses for nuclear waste immobilization applications

Niobium and Zirconium Phosphates as Green and Water-Tolerant Catalysts for the Acid-Catalyzed Valorization of Bio-Based Chemicals and Real Lignocellulosic Biomasses

Commercial niobium and synthesized zirconium phosphates were tested as water-tolerant heterogeneous acid catalysts in the hydrothermal conversion of different bio-based substrates. Different acid-catalyzed reactions were performed using biomass-derived model compounds and more complex real lignocellulosic biomasses as the substrate. The conversion of glucose and cellulose was preliminarily investigated. Then, a wide plethora of raw lignocellulosic biomasses, such as conifer wood sawdust, Jerusalem artichoke, sorghum, miscanthus, foxtail millet, hemp and Arundo donax, were valorized towards the production of water-soluble saccharides, 5-hydroxymethylfurfural (HMF), levulinic acid (LA) and furfural. The different catalytic performances of the two phosphates were explained on the basis of their acid features, total acidity, Brønsted/Lewis acid sites ratio and strength. Moreover, a better insight into their structure–acidity relationship was proposed. The different acid properties of niobium and zirconium phosphates enabled us to tune the reaction towards target products, achieving from glucose maximum HMF and LA yields of 24.4 and 24.0 mol%, respectively. Remarkably, when real Jerusalem artichoke biomass was adopted in the presence of niobium and zirconium phosphate, maximum yields of furanic compounds and cellulose-derived sugars of 12.7 and 50.0 mol%, respectively, were obtained, after only 1 h of reaction. The synthesized hydrolysates, which were found to be rich in C5 and C6 carbohydrates, can be better exploited for the cascade production of more added-value bio-products.

Carbon-coated monoclinic NbOPO4 with polyanionic framework for rechargeable aqueous lithium-ion batteries beyond 2 V

The choice of anode materials for high-voltage aqueous batteries beyond 1.5 V is still far from satisfactory, due to the narrow electrochemical stability window of aqueous electrolytes. With the inherent advantages of low working voltage and fast ionic diffusion, niobium phosphates with polyanionic framework groups built of NbO6 octahedra and PO4 tetrahedra are very promising anode materials for high-voltage aqueous batteries. Herein, carbon-coated NbOPO4 (NPO/C) materials with monoclinic structure has been prepared by the solid-state reaction & chemical vapor deposition method. Between -1.34 V and 0.6 V vs. standard hydrogen electrode, it could deliver a specific capacity of 116 mAh/g with a high coulombic efficiency of 92.0% at a low current rate of 0.33C in aqueous electrolytes based on methylsulfonylmethane, LiClO4 and H2O (DES). The diffusion-controlled process dominates the electrochemical reaction of NPO/C. Upon the reversible insertion/extraction of lithium ion into/from NPO/C, it maintains the monoclinic structure with a small lattice expansion, which is a characteristic of zero-strain effect. Finally, the full cell based on NPO/C anode, LiMn2O4 cathode and DES electrolytes with a high specific energy 101.6 Wh/kg and a high voltage output beyond 2 V has been validated. It also shows excellent cycling performance with the capacity retention of 94.3% after 1000 times at 2C rate, which suggests that monoclinic β-NbOPO4 can be used as a promising electrode material for aqueous lithium-ion batteries with high voltage output for energy storage in the future.

Microwave-assisted hydrothermal synthesis of three-dimensional NbOPO4-reduced graphene oxide-carbon nanotube composite for high performance sodium-ion battery anode

Sodium-ion batteries (SIBs) have aroused more and more academic and industrial interest due to their decent electrochemical performance and the cost-effectiveness of sodium (Na) resource. However, fabricating an appropriate anode material with high specific capacity, long-term cycle stability and superior rate capability remains a great challenge. Here, we adopt an efficient microwave-assisted hydrothermal method to prepare layered niobium oxyphosphate (NbOPO4) nanosheets, which grows on the single-walled carbon nanotubes (SWCNT) and reduced graphene oxide (rGO) (NbOPO4-rGO-SWCNT). Benefiting from three-dimensional hierarchical architecture combining NbOPO4 nanosheets with rGO-SWCNT framework with excellent electrical conductivity, NbOPO4-rGO-SWCNT electrode delivers a higher reversible specific capacity (323.2 mAh g−1 at 0.1 A g−1) and superior rate capability (147.9 mAh g−1 at 5 A g−1) than that of NbOPO4 (143.1/43.5 mAh g−1). Ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements further reveal the electrochemical mechanism that reversible reaction between niobium phosphate (NbPO4) and niobium (Nb) occurs after the initial intercalation-conversion reaction, which contributes to the stable reversibility and high-rate capability in the following cycling. This work not only indicates that NbOPO4-rGO-SWCNT can act as a desirable anode material for SIBs, but also provide new insights to material design for niobium oxyphosphate composite.

Metal-Supported Niobium Catalysts Investigation for Conversion of Bio-Renewable Glycerol to Organic Compounds

The glycerol oxidative dehydration to organic compounds, especially acrolein and acrylic acid, was studied over vanadium, molybdenum, and cobalt oxides supported on niobium oxide and niobium phosphate catalysts. At 300 °C, the glycerol conversion was 100% over all catalysts tested, and acrolein was the main product observed, without significant deactivation within the time on stream studied. Except for Co/V/Nb2O5, acrylic acid was formed over all catalysts, but the selectivity was not higher than 10%. Acetaldehyde and acetic acid were the other organic oxygenated products formed. Although the catalysts supported over Nb2O5 presented significantly lower acidity than the catalysts supported over NbOPO4, they showed 100% glycerol conversion, indicating that the dehydration of glycerol does not require strong acidity. These data indicate the potential of niobium-based supports in the development of an active and selective catalyst for the glycerol oxidehydration to acrolein and acrylic acid, chemicals of great importance in the industry.