Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including V_xO_y ^n– and V_xO_yCl^n– ions (x = 1–14, y = 2–36, n = 1–3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V₁₄O₃₆Cl(L)₅ (L = Et₄N⁺, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged V_xO_yCl^n– and V_xO_yCl(L)^(n–1)– clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller V_xO_yCl^(1–2)– and V_xO_y ^(1–2)– anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged V_xO_yCl and V_xO_y species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of V_xO_yCl and V_xO_y anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.      

Hydrothermal syntheses of materials constructed from vanadium oxide and secondary metal-tetrapyridylpyrazine subunits. Structural consequences of the identity of the secondary metal

Hydrothermal reactions of V₂O₅, tetra-2-pyridylpyrazine (tpyprz) and an appropriate M(II) starting material yield a series of oxides of general composition [{M_x(tpyprz)}_yV₄O₁₂] [x=1, y=2, M=Co(II), Ni(II); x=2, y=2, M=Cu(I); x=2, y=1, M=Zn(II)]. The Co(II) and Ni(II) analogues (1 and 2) are isostructural and consist of one-dimensional ribbons constructed from {V₄O₁₂}⁴⁻ clusters linked through {M(tpyprz)}₂⁴⁺ binuclear units of edge sharing {MO₃N₃} octahedra. In contrast, the structure of [{Cu₂(tpyprz)}₂V₄O₁₂] (3) is two-dimensional and constructed of {Cu₂(tpyprz)}_n²ⁿ⁺ chains linked in the second dimension through the {V₄O₁₂}⁴⁻ clusters. The structure of [{Zn₂(tpyprz)V₄O₁₂] (4) is also two-dimensional but may be described as {Zn₂V₄O₁₂} chains interconnected through the binucleating tpyprz ligands. The roles of the coordination preferences of the secondary metal cations as well as the nature of the organic components are discussed.     

Complete oxidation of ethanol over vanadium based catalysts

V2O5/γ-Al2O3-TiO2 catalysts were prepared by the mixing sol-gel and co-impregnation method. The performance of the catalysts for complete oxidation of ethanol was performed in a conventional fixed-bed quartz reactor. And the effects of support, preparation methods and vanadium content have been investigated. The results showed that 5% V2O5 catalyst supported on γ-Al2O3-TiO2 possessed the best ethanol conversion under the considered temperature. This may be ascribed to the highly dispersible active component, mutual function between the active component and the carriers. The nature of the best performance for 5%V/γ-Al2O3-TiO2 catalyst may be related to the high V4+ amounts on the surface. And the surface V4+ species may play an important role in the formation of active site for the total ethanol oxidation.     

纳米复合材料Ag/MxOy-TiO2(MxOy=ZnO、Al2O3和Fe2O3)的制备及其微波辅助光催化降解甲基橙

采用溶胶-凝胶-程序升温溶剂热一步法,利用表面活性剂EO₂₀PO₇₀EO₂₀(P123)作为模板剂,分别制备了三元纳米复合材料Ag/ZnO-TiO₂、Ag/Al₂O₃-TiO₂和Ag/Fe₂O₃-TiO₂。通过XRD、氮气吸附-脱附测定、TEM以及扫描电子显微镜配合X-射线能量色散谱仪(SEM-EDS)等对合成的3种催化剂进行了对比表征分析。结果表明,复合材料Ag/M_xO_y-TiO₂中Ag以单质形式存在并较好地分布在M_xO_y-TiO₂表面上。所合成产物颗粒尺寸较小(约10 nm左右),形貌较好。其中,Ag/ZnO-TiO₂的比表面积与Ag/Al₂O₃-TiO₂十分相近,略大于Ag/Fe₂O₃-TiO₂。光催化活性研究中,以甲基橙为模型分子且辅以微波场作用。结果显示,上述三元复合材料的活性均明显高于未掺杂银的二元复合材料,其中Ag/ZnO-TiO₂的光催化活性最好,在90 min内对甲基橙的降解率高达86%。     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.     

Vapor-phase oxidation of β-picoline to nicotinic acid on V2O5 and modified vanadium oxide catalysts

Modification of V₂O₅ with Ti, Sn, Zr, Nb, and Al oxides improves the activity and selectivity of the vanadium oxide catalyst in vapor-phase oxidation of β-picoline to give nicotinic acid. It is shown that the conversion of β-picoline and the yield of nicotinic acid on two-component V₂O₅-TiO₂, V₂O₅-SnO₂, V₂O₅-ZtrO₂, V₂O₅-Nb₂O₅, and V₂O₅-Al₂O₃ catalysts may be several times those on the V₂O₅ catalyst. It was found that, on passing from V₂O₅ to double-component vanadium-containing catalysts, the proton affinity of active oxygen bonded to vanadium, calculated by the quantum-chemical method, grows simultaneously with the increase in the activity of the catalysts in the oxidation reaction.     

Thermoanalytical characterization of vanadium-chromium oxide compounds prepared by 'soft chemistry' method

Summary Hydrated microcrystalline compound, V_1-xCr_xO_y·nH₂O, where x<0.063 and 4.4<n<8 and hydrated amorphous phases, CrVO₄·H₂O and Cr₂V₄O₁₃·4H₂O have been prepared using peroxo-polyacids of vanadium and chromium. The transformations of these hydrated phases upon heating were studied by TG-DTA and XRD techniques and led to three crystalline anhydrous compounds: (i) phase V_1-xCr_xO_y, which is closely related to the orthorhombic V₂O₅, (ii) Cr₂V₄O₁₃ and (iii) monoclinic CrVO₄-M. The ranges of coexistence of phases in equilibrium were also determined.     

掺杂钒和硅对TiO2薄膜超亲水性的影响

0引言 TiO2薄膜是众多氧化物半导体薄膜中研究最为广泛的一种材料．其表面的超亲水性和表面自清洁效应开辟了光催化薄膜功能材料的新的研究领域，已成为众多研究者研究的对象。但是如果薄膜仅由TiO2组成，当光照停止，水在TiO2薄膜表面的润湿角逐渐升高．并恢复原始状态。TiO2的禁带较宽，普通光线如太阳光等都不能将其激发．限制了其实际应用。因此如何使TiO2材料的光谱响应范围由紫外光反扩展到可见．光区一日如何更长时间地保持薄膜良好的亲水性是目前研究的重点。     

Effect of platinum and palladium additives on the surface state and catalytic activity of vanadium oxides in the oxidation of carbon monoxide

The Pt/V₂O₅ and Pd/V₂O₅ systems formed upon hydrogen reduction have catalytic activity in the oxidation of carbon monoxide exceeding the activity of Pt/Al₂O₃ and Pd/Al₂O₃. The transition from the low-activity to high-activity state on the Pt/V₂O₅ and Pd/V₂O₅ catalysts is characterized by temperature hysteresis and change in the kinetic equation. X-ray phase analysis (XPA), X-ray photoelectron spectroscopy (XPES), and X-ray spectral microanalysis were used to establish that prior reduction of V₂O₅ by hydrogen gives VO₂, V₆O₁₃, a-H _x V₂O₅, and b-H _x V₂O₅, which facilitates the formation of an active catalyst surface.     

Synthesis and characterization of new borate-vanadate mixed glasses

Summary It has been found that a series of M_xO_y-V₂O₅-B₂O₃glasses (M_xO_y=Li₂O, Na₂O, K₂O and MgO) containing 10 mol%<span style='font-size:12.0pt;font-family: Symbol;mso-bidi-font-family:Symbol'>a-Fe₂O₃exhibited glass-forming regions that shifted with the content of network modifier (NWM) compared to B₂O₃and V₂O₅glasses. The M?ssbauer spectra of a series of M_xO_y-V₂O₅-B₂O₃glasses showed increased quadrupole splitting (D) with increasing NWM content. This suggests that the coordination numbers of the V⁴⁺and V⁵⁺are fixed and that the formation number of non-bridging oxygens (NBO) is considered to increase with increasing NWM content, and with increasing formation number of NBO, the Fe³⁺ion site changes from VO₄to BO₄tetrahedra. Consequently, the quadrupole splitting increases with increasing NWM content.     

Reactivity Control of C?H Bond Activation over Vanadium–Silver Bimetallic Oxide Cluster Cations

Vanadium–silver bimetallic oxide cluster ions (V_xAg_yO_z⁺; x=1–4, y=1–4, z=3–11) are produced by laser ablation and reacted with ethane in a fast‐flow reactor. A reflectron time of flight (Re‐TOF) mass spectrometer is used to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) reactions are identified over VAgO₃⁺, V₂Ag₂O₆⁺, V₂Ag₄O₇⁺, V₃AgO₈⁺, V₃Ag₃O₉⁺, and V₄Ag₂O₁₁⁺ ions, in which the oxygen‐centered radicals terminally bonded on V atoms are active sites for the facile HAA reactions. DFT calculations are performed to study the structures, bonding, and reactivity. The reaction mechanisms of V₂Ag₂O₆⁺+C₂H₆ are also given. The doped Ag atoms with a valence state of +1 are highly dispersed at the periphery of the V_xAg_yO_z⁺ cluster ions. The reactivity can be well‐tuned gradually by controlling the number of Ag atoms. The steric protection due to the peripherally bonded Ag atoms greatly enhances the selectivity of the V–Ag bimetallic oxide clusters with respect to the corresponding pure vanadium oxide systems.     

Synthesis of VO2 Nanopowders. Part II. Hydrolysis of Vanadium Alkoxide/Citric Acid Premixes: VO2 Nanostructures of Controlled Shape

Reaction of VO(OiPr)₃/citric acid premixes with excess water produces stable, blue dispersions of V_xO_y gel nanoparticles (5–100 nm in diameter) that can be isolated via acetone precipitation. Annealing under reducing conditions transforms these gel particles into crystalline, faceted VO₂ nanoparticles of similar size. Larger V_xO_y gel particles (75–200 nm in diameter) form when V_xO_y nanogel dispersions are aged with aqueous ammonia. Upon annealing, these larger gel particles transform into crystalline VO₂ rods of 50 nm–10 μm in length. Hysteresis loops confirming a semiconductor-to-metal phase transition near 68 °C expected for crystalline VO₂ particles are recorded by variable-temperature electrical resistance and powder X-ray diffraction measurements.     

Photocatalytic degradation of organophosphate flame retardant TBEP: kinetics and identification of transformation products by orbitrap mass spectrometry

The photocatalytic degradation of tris (2–butoxyethyl) phosphate (TBEP) flame retardant using visible light response catalysts TiO₂/V₂O₅, (N,F-doped)-TiO₂/V₂O₅, and N-doped-SrTiO₃ has been studied by high-resolution orbitrap mass spectrometry. TBEP degradation followed first-order kinetics with half-life values ranging between 9.8 and 83.5 min. N-doped-SrTiO₃ was the catalyst with better photocatalytic performance while activity for TiO₂/V₂O₅ composites followed the trend: N, F- TiO₂/V₂O₅ > N-TiO₂/V₂O₅> TiO₂/V₂O₅. The identified degradation products (DPs) revealed hydroxylation, further oxidation and dealkylation as major degradation pathways. Based on the identified DPs and scavenging experiments, ^?OH radical-mediated reactions can be considered for the degradation of TBEP using TiO₂ and SrTiO₃-based photocatalytic materials.     

Recent advances of transition metal oxalate-based micro- and nanomaterials for electrochemical energy storage: a review

A key challenge in the development of electrochemical energy storage (EES) is the design and engineering of electrode materials for electrochemical reactions. Transition metal oxalates (TMOxs) have been widely used in various EES applications due to their low cost, simple synthesis, and excellent electrochemical performance. In this review, the recent advances in the design and engineering of transition metal oxalate-based micro- and nanomaterials for EES are summarized. Specifically, the survey will focus on three types of micro- and nano-scale TMOxs (monometallic, bimetallic, and trimetallic TMOxs), their composites (TMOx-metal oxide, TMOx-hydroxide, TMOx-GO, and TMOx-MOFs composites), and derivatives, including transition metal oxides (TiO₂, V₂O₅, Mn_xO_y, Co₃O₄, NiO, CuO, and Nb₂O₅), multi-transition metal oxides (MCo₂O₄ (M = Ni, Cu, and Zn), NiMn₂O₄, and N_xO_y-M_xO_y), transition metal sulfide (NiS₂), and carbon materials (ordinary carbon, GO and their composites), within the context of their intrinsic structure and corresponding electrochemical performance. A range of experimental variables will be carefully analyzed, such as sample synthesis, crystal structure, and electrochemical reaction mechanism. The applications of these materials as EES electrodes are then featured for supercapacitors (SCs) and lithium-ion batteries (LIBs). We conclude the review with a perspective of future research prospects and challenges.     

Mechanism of the Formation of Molybdenum Metallocarbene Complexes in the Gas Phase

The reactions of Mo⁺ ions and Mo _x O _y ⁺ oxygen-containing molybdenum cluster ions (x = 1-3; y = 1-9) with methane, ethylene oxide, and cyclopropane were studied using ion cyclotron resonance. The formation of a number of organometallic ions, including the metallocarbene MoCH₂ ⁺ , as well as molybdenum oxometallocarbenes Mo _x O _y CH₂ ⁺ (x = 1-3; y = 2, 4, 5, or 8) and Mo _x O _y (CH₄)⁺ ions (x = 1-3; y = 2, 5, or 8), was detected. The upper and lower limits of bond energies in oxometallocarbene complexes were evaluated: 111 > D ⁰ (Mo _x O _y ⁺-CH₂) > 82 kcal/mol (x = 1-3; y = 2, 5, 8).     

The oxidation of toluene on transition metal oxides

The oxidation of toluene on pure vanadium and molybdenum oxides was found to follow independent paths; it was benzene ring oxidation on V₂O₅ and side chain oxidation on MoO₃. On mixed xV₂O₅ · yMoO₃ oxides, the main reaction was the addition at the double bond preferably positioned meta rather than one-electron oxidation.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Weitere magnetische Untersuchungen an Ti3−xMxO5-Phasen (M = Al3+, Fe2+, Mn2+, Mg2+) mit einem Beitrag über CrTi2O5

Additional Magnetic Examinations of Ti_3?xM_xO₅-Phases (M = Al³⁺, Fe²⁺, Mn²⁺, Mg²⁺) with a Contribution about CrTi₂O₅ Ti_3?xM_xO₅ was prepared with M = Al³⁺, Fe²⁺, Mn²⁺, and Mg²⁺. Die magnetic properties of this phases were examinated by the Faraday method in respect to the temperature. The well known magnetic effect of Ti₃O₅ near 450 K is shifted to lower degrees if Ti is replaced by Al, Fe, Mn, or Mg. Compared to Ti_3?xV_xO₅ and Ti_3?xCr_xO₅ the stability of the low temperature-form of Ti₃O₅ is much more reduced in Ti_3?xM_xO₅ (M = Al, Fe, Mn, Mg). The crystal structure investigation of CrTi₂O₅ explained the anomalous behaviour of the Cr³⁺ and V³⁺ doped Ti₃O₅.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Regenerating Spent Solutions of Vanadium‐containing Heteropoly Acids in the Presence of Additives

Vanadium‐containing heteropoly acid solutions of Keggin H_3+xPMo_12–xV_xO₄₀ and modified H_aP_zMo_yV_xO_b types (P‐Mo‐V HPAs) are promising nanosized inorganic metal‐oxygen cluster compounds with the property of reversible oxidability (V^V ↔ V^IV). The oxidation of reduced P‐Mo‐V HPAs at a temperature of 130–170 °C and an oxygen pressure of 4 atm is a convenient method for their regeneration, but results in regeneration degree of only 75–88 %. Various materials with electron transfer or oxidative properties, such as nitrogen doped carbon nanofibers (N‐CNFs), Sibunit‐4, HNO₃, and MoO₂, were investigated as additives to facilitate and accelerate the regeneration of HPA solutions. Among the studied additives HNO₃ was found to show the best efficiency, resulting in regeneration degree of higher 95 %. Rapid and efficient regeneration of spent HPA catalysts is an important criterion for achieving high productivity and sustainability of oxidative processes on their basis.