Vanadium Species Research Articles

Dopant-Induced Surface Self-Etching of Cobalt Carbonate Hydroxide Boosts Efficient Water Splitting.

Herein, vanadium-doped cobalt carbonate hydroxide, V-CoCH, was synthesized as efficient catalyst for water splitting. Vanadium species were partially dissolved in the early stages of the oxygen-evolution reaction (OER), inducing self-etching of the catalyst surface, which is helpful for catalyst surface reconstruction and resulted in a higher number of active sites and oxygen vacancies. The synergy between V-doping and oxygen vacancies improved the catalytic activity: V-CoCH showed an exceptional OER catalytic performance with an overpotential of 183 mV at 10 mA cm-2 . The water-splitting cell consisting of V-CoCH only required 1.52 V to reach 10 mA cm-2 . Theoretical calculations revealed that vanadium in V-CoCH played an important role in electron regulation of active sites. The oxygen vacancies had an important effect on improvement of the OER performance through not only the exposure of more active sites but also through modulation of the electronic structure. This work provides an effective strategy for constructing high-performance electrocatalysts.

The antihyperglycemic and hypolipidemic activities of a sulfur-oxidovanadium(IV) complex

This study describes the synthesis, characterization, and biological activity of a new class of antidiabetic oxidovanadium(IV)-complexes with S2O2 coordination mode. The target complex 3,6-dithio-1,8-octanediolatooxidovanadium(IV), abbreviated as ([VIVO(octd)]), where octd = 3,6-dithio-1,8-octanediol, is formed from the reaction between the 3,6-dithio-1,8-octanediol and vanadyl sulfate (VIVOSO4). The effects of treatment with ([VIVO(octd)] on blood glucose, lipidic profile, body weight, food intake, water intake, urinary volume, glycogen levels, and biomarkers for liver toxicity were investigated using a streptozotocin (STZ)-induced diabetic Wistar rats model. The results have shown that the [VIVO(octd)] complex caused a significant decrease in blood glucose (247.6 ± 19.3 mg/dL vs 430.1 ± 37.6 mg/dL diabetic group, p < 0.05), triglycerides (TG, 50%) and very low-density cholesterol (VLDL-C, 50%) levels in STZ-diabetic rats after 3 weeks of treatment. The [VIVO(octd)] has shown antihyperglycemic activity in diabetic rats as well as a reduction in elevated lipid levels. Time-dependent studies using EPR and 51V NMR spectroscopy of [VIVO(octd)] were done in aqueous solutions to determine the complex stability and species present in the oral gavage solution used for complex administration. The spectroscopic studies have shown that the antidiabetic/hypolipidemic activity could be attributed to [VIVO(octd)], vanadium species resulting from redox processes, the hydrolysis of [VIVO(octd)] and its decomposition products, or some combination of these factors. In summary, the oxidovanadium(IV) complex containing the S2O2 donor ligand has desirable antidiabetic properties eliminating the symptoms of Diabetes mellitus and its comorbidities.

Visible Light‐Driven Degradation of Trichloroethylene in Aqueous Phase with Vanadium‐Doped TiO2 Photocatalysts

The development of photocatalyzed water remediation strategies using visible (solar) light to mineralize volatile chlorinated organic compounds (VCOCs) is a long standing, not yet fully achieved goal. Herewith, a facile route is presented to synthesize vanadium‐doped TiO2 photocatalysts using a one‐step hydrothermal method. Different characterization methods are employed to investigate the physicochemical properties of as‐prepared V‐doped TiO2 samples, indicating the mixed phases of anatase, rutile, and brookite in the crystal structure addition to the mesoporous framework. The nature of the vanadium species at the TiO2 surface is assessed by X‐ray photoelectron and emission spectroscopy. The aerobic photodegradation of a common VCOC, trichloroethylene, using V‐doped catalysts is demonstrated to be much more effectively than with undoped TiO2. Importantly, the herein described V‐doped photocatalysts show high activity both under ultraviolett and visible light irradiation. Moreover, these V‐doped TiO2 photocatalysts are robust under the reaction conditions, being recyclable for at least four consecutive runs without any activity loss.

The significance of charge and discharge current densities in the performance of vanadium redox flow battery

In this study, the effects of charge current density (CDChg), discharge current density (CDDchg), and the simultaneous change of both have been investigated on the performance parameters of the vanadium redox flow battery (VRFB). In addition, the crossover and ohmic polarization have been studied from a mechanism point of view to understand how the current density affects the characteristics of VRFB. Generally, increasing CDChg, CDDchg, or both of them simultaneously, leads to a decrease in the parameters of charge and discharge capacities, charge and discharge energies, as well as voltage efficiency. While the discharge current is constant, the energy efficiency does not change significantly with increasing CDChg. However, as CDDchg or both of CDChg and CDDchg increase, the energy efficiency decreases. In addition, increasing the current density generally increases the coulombic efficiency. Increasing CDChg has no major impact on the discharge voltage. Similarly, increasing CDDchg does not change the charge voltage significantly. From a mechanism view, low currents cause more crossover of vanadium ions because there are more opportunities for ions to diffuse across the membrane, which lowers the coulombic efficiency. The high charging current causes a reduction in the crossover of vanadium ions because there is not enough time for more diffusion of vanadium ions. On the other hand, because of the high current, electrons transfer more quickly while there are not enough vanadium species to react with all the electrons. This leads to a high ohmic polarization, which causes a reduction in the capacity and voltage efficiency.

Vanadium as co-catalyst for exceptionally boosted Fenton and Fenton-like oxidation: Vanadium species mediated direct and indirect routes

In this study, vanadium powder (V) was employed as a cocatalyst to enhance the Fenton-like system. The V-Fe(III)/H2O2 system can rapidly produce hydroxyl radicals and completely oxidize chloramphenicol with exceptionally high stability for long-term operation. The low-valent vanadium sites on the surface during the stepwise oxidation of vanadium from V0 to V(IV) can donate electrons for direct H2O2 activation and indirect Fenton reaction by reducing Fe(III) to produce hydroxyl radicals. Meanwhile, density functional theory (DFT) calculation unveils that low-valent vanadium sites of vanadium can lengthen Fe-O bonds of FeOH2+ to elevate the oxidation potential of Fe(III) and promote Fe(III) reduction induced by H2O2. The self-cleaning effect of vanadium under acidic conditions can maintain reactive sites for sustainable electron donation and long-lasting enhanced Fenton oxidation. This study provides a novel enhanced Fenton oxidation for water remediation and the first mechanistic insights into the origins of V-based advanced oxidation technologies, it may also be beneficial to treat vanadium-contained wastewater.

Active vanadium(iv) species synthesized at low-temperature facilitate excellent performance in low-temperature NOx-catalytic removal

V4+ species in a series of bulk vanadium oxide catalysts is more conducive to NH3 and O2 activation.

Water in the ball-milling process affects the dispersion of vanadia species on V2O5/TiO2 catalysts for NH3-SCR

Water in the ball-milling process increased polymeric vanadyl species and enhanced the redox capability, resulting in high NH3-SCR activity of V2O5/TiO2.

Comparative study on N2O formation pathways over bulk MoO3 and MoO3-x nanosheets decorated Fe2O3-containing solid waste NH3-SCR catalysts

NH3-SCR technology with commercialized V2O5-WO3(MoO3)/TiO2 catalysts has become the most efficient technology for the removal of NOx from coal-fired power plants. However, the weaknesses of V2O5-WO3(MoO3)/TiO2 catalysts such as the biotoxicity of vanadium species and high cost restrict their increased applicability. Fe2O3-based NH3-SCR catalysts show potential in placing traditional catalysts due to their good N2 selectivity, excellent environmentally friendly performance, high thermal stability, and low cost. In this work, low cost Fe2O3-containing solid waste was exploited as the base material for NH3-SCR catalyst preparing. Moreover, bulk MoO3 and MoO3-x nanosheets decorated Fe2O3 composite NH3-SCR catalysts were synthesized and both revealed conspicuously improved NOx removal efficiency compared with bare-Fe2O3 catalyst. However, the N2 selectivity of these two catalysts showed significant differences. Therefore, comprehensive characterizations, NH3 oxidation experiments, and in-situ diffusion Fourier transform infrared spectroscopy (DRIFTS) experiments were performed to determine the N2O formation pathways of the above two catalysts. The redox properties were highly related to the N2O generated from NH3 oxidation. Moreover, the huge difference in NH3 and NO adsorption ability led to disparate reaction mechanisms over the two catalysts. This new understanding of the N2O formation mechanism has the potential to guide the rational design of improved NH3-SCR catalysts suffering from low N2 selectivity.

Highly stable VSi-beta zeolite synthesized by a post-synthesis strategy for efficiently catalyzing styrene epoxidation

To enhance the doping of vanadium in zeolites and achieve high stability, the selection of vanadium precursors containing specific vanadium species can effectively overcome this crucial problem. Two series of VxSi-Beta(A) and VxSi-Beta(N) zeolites have been prepared by a two-step post-synthesis method at pH = 1 and pH = 7. The properties and environments of vanadium in samples are investigated by UV–vis, XPS, EPR, H2-TPR and 51V MAS NMR. The bonding between vanadium and framework in VSi-Beta(A) is stronger than that of VSi-Beta(N). After the two are calcined or hydrated, the vanadium species in the former are relatively stable, while the pseudo-tetrahedral V(V) species and pseudo-octahedral V(V) species in the latter are interconverted. The changes of vanadium species in the supernatant during the preparation have been investigated by 51V static NMR. At low concentration and pH = 1, there is a unique mononuclear cation (VO2+) in the aqueous NH4VO3 solution, which is favorable for the interaction with the negatively charged hydroxyl nests generated after the nitric acid dealumination, and enables the V atoms to be tightly inserted into the framework. In styrene epoxidation, the type of V(V) species in the catalyst could significantly affect its catalytic performance, and the catalytic activity and stability of VxSi-Beta(A) are superior than that of VxSi-Beta(N).

Stability optimization of orthovanadate nanoparticles in biocompatible media

Rare-earth orthovanadate nanoparticles (NPs) demonstrate unique combination of physicochemical characteristics and biological activity. The redox properties and low toxicity of orthovanadates in nanoform allow considering them as perspective nanomedicine modalities. The local microenvironment in biological media and the way NPs enter the organism determine their biological efficiency. Numerous studies deal with interaction of vanadium species and bio-molecules in serum, however, the interplay between orthovanadate NPs and serum compounds is still under debates. Here we investigate the effect of serum proteins on aggregative stability of three types of negatively charged orthovanadate NPs (spherical, spindle-like, and rod-like). Size of NPs was estimated by light-scattering methods in solutions, biologically relevant buffers and media. Some geometry- and size-dependent peculiarities of NPs behavior in different solutions were found. Modeling the proteins–NPs interactions for main serum proteins at threshold Ca2+ and Mg2+ concentrations revealed nonlinear aggregative behavior depending on protein concentrations. In Krebs-Ringer buffer the behavior of the rod-like NPs differs strongly on the behavior of more isometric NPs (spherical and spindle-like). The hydrodynamic diameter changes are non-linear and rod-like NPs have specific behavior in serum-like protein mixtures. These effects are associated with shape-specific involvement of different forces (including electosteric, hydrophobic, osmotic and recoil ones) in stabilization process.

Flexible and free-standing electrode for high-performance vanadium redox flow battery: Bamboo-like carbon fiber skeleton from textile fabric

Developing the free-standing and flexible electrodes with high current density and cycle stability is still under debate towards the extensive application of vanadium redox flow batteries (VRFBs). So far, carbon felts, carbon fibers and carbon papers are used which mostly prepared from fossil precursors make them unsustainable. Herein, we first sought to prepare a mechanically flexible and free-standing carbon cloth from terry cloth towel fabric (100% cotton) by using a simple pyrolysis method (TCC). Interestingly, we obtained a bamboo-like carbon fiber structure with a well-balanced micro, -meso, and -macro porosity. Moreover, a low-cost Polyethyleneimine (PEI) is used for Nitrogen doping on carbon cloth skeleton (N-TCC) to improve its electrochemical performance. The as-prepared N-TCC were utilized as efficient electrodes for the VRFBs with higher electrochemical activity towards vanadium species VO2+/VO2+ than TCC and commercial graphite felt (GF) in a 3 electrode electrochemical cell i.e. half-cell. Interestingly, the VRFBs constructed with N-TCCs electrodes (both +ve and –ve half cells) in a full cell configuration at varied current densities from 40 to 160 mA cm−2, we achieved an increased energy efficiency (EE), voltage efficiency (VE), and columbic efficiency (CE) compared to pristine CFs, and TCC based VRFBs. The newly designed cotton based electrodes establishes a unique opportunity for constructing a low-cost, metal-free VRFBs towards a large-scale commercialization of sustainable energy storage system.

Amorphous Nitrogen-Doped Vanadium Oxide on Graphene for Enhanced Aerobic Oxidative Desulfurization of Fuels

Aerobic oxidative desulfurization (AODS) promises an emerging method for deep sulfur removal of fuel oil, which requires high-performance catalysts to cost-effectively convert thiophenes into sulfones. In this paper, we report the fabrication of a highly efficient and durable AODS catalyst by loading N-doped amorphous vanadium oxide on reduced graphene oxide via high-temperature ammonia (NH3) treatment. The morphology, phase state, element electronic state, and catalytic performance of the catalysts at different calcination temperatures were systematically studied. The phase transition principle of vanadium species at different ammoniation temperatures as well as its effect on the catalytic performance was revealed. The optimal catalyst ammoniated at 400 °C achieved rapid and full conversion of various thiophenes under the reaction condition of 90–120 °C and normal pressure using air as the oxygen source, showing excellent activity. Moreover, the catalyst maintained its activity after six repeated uses and is expected to act as a cost-efficient and robust catalyst for AODS.

Application of Dithiocarbamate Chitosan Modified SBA-15 for Catalytic Reductive Removal of Vanadium(V)

We have successfully synthesized dithiocarbamate chitosan modified SBA-15 (CS2C@SBA) composites, with promise in vanadium (V(V)) elimination. Among the three composites using different mass ratios of dithiocarbamate chitosan to SBA-15, CS2C@SBA−3, which had the highest CS2 substitution, showed the best performance on V(V) removal of which the maximum adsorption capacity could achieve 218.00 mg/g at pH 3.0. The adsorption kinetics were best fitted with a pseudo−second order reaction model, suggesting a chemisorption mechanism. Meanwhile, the Langmuir model fitted better with the adsorption isotherm, revealing a monolayer adsorption behavior. Through FTIR and XPS analysis, the functional group −SH was identified as dominating reduction sites on this composite, which reduced 73.1% of V(V) into V(IV) and V(III). The functional group −NH− was the main adsorption site for vanadium species. This reaction followed a catalytic reduction coupled adsorption mechanism reducing most of V(V) into less toxic vanadium species. Furthermore, CS2C@SBA−3 showed great selectivity towards V(V) in the presence of various co−existing ions in synthetic wastewater and real water samples. Moreover, CS2C@SBA−3 could retain a removal efficiency over 90% after five adsorption−desorption cycles. Based on the aforementioned results, we can conclude that CS2C@SBA−3 has great potential to be applied in efficient remediation of vanadium water−pollution.

Synergistic effect of copper and vanadium species on Hg0 removal of Cu-SCR catalyst: A DFT and experimental study

The synergistic effect of Cu and V species on the improved Hg0 removal performance of Cu-SCR catalyst was analyzed in depth by experiments and theoretical calculations based on density functional theory (DFT). Possible CuVOx/TiO2(001) surface models were constructed for Hg adsorption and oxidation calculations in the presence of O2. According to the results of partial density of states (PDOS) and charge populations, Cu transfers electrons to V through bridge O, and the strong hybridization of Cu 3d and O 2p orbitals facilitate the generation of O−. Although copper doping slightly promotes the Hg adsorption and oxidation ability of VOx species, the O− bonded with Cu provides the optimal adsorption sites and active centers. Strongly hybridized with CuO, Hg easily transfers charge to O− and generate HgO to desorb from the surface, and the oxygen vacancy thus formed can be supplemented by gaseous O2. Characterizations including Raman, fourier transform infrared spectroscopy (FTIR), H2 temperature program reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) verifies the formation of Cu-O-V structure and the higher involvement of CuOx in Hg0 oxidation, and Hg0 temperature program desorption (Hg0-TPD) were conducted to verify the reaction mechanism. This study reveals the good potential of copper species in Hg0 removal, and provides a reference for designing new materials for mercury control.

Interface sites on vanadia-based catalysts are highly active for NOx removal under realistic conditions

TiO2-supported V2O5 catalysts are commonly used in NOx reduction with ammonia due to their robust catalytic performance. Over these catalysts, it is generally considered that the active species are mainly derived from the vanadia species rather than the intrinsic structure of V-O-Ti entities, namely the interface sites. To reveal the role of V-O-Ti entities in NH3-SCR, herein, we prepared TiO2/V2O5 catalysts and demonstrated that V-O-Ti entities were more active for NOx reduction under wet conditions than the V sites (V=O) working alone. On the V-O-Ti entities, kinetic measurements and first principles calculations revealed that NH3 activation exhibited a much lower energy barrier than that on V=O sites. Under wet conditions, the V-O-Ti interface significantly inhibited the transformation of V=O to V-OH sites thus benefiting NH3 activation. Under wet conditions, meanwhile, the migration of NH4+ from Ti site neighboring the V-O-Ti interface to Ti site of the V-O-Ti interface was exothermic; thus, V-O-Ti entities together with neighboring Ti sites could serve as channels linking NH3 pool and active centers for activation of NH4+. This finding reveals that the V-O-Ti interface sites on V-based catalysts play a crucial role in NOx removal under realistic conditions, providing a new perspective on NH3-SCR mechanism.

Vanadium-density-dependent reactivity for simultaneous removal of NOx and Hg0 over V2O5/TiO2 catalyst

Vanadium-based catalysts have been widely used in the simultaneous removal of NOx and Hg0. However, how vanadium species affect the reactivity of Hg0 oxidation and coverage-dependent behaviors of vanadium species are still unknown. Herein, we synthesized a series of V2O5/TiO2 catalysts with different V loadings and investigated the reaction characteristics of vanadium species (i.e., sub-monolayer, monolayer, and crystalline) for the catalytically simultaneous abatement of NOx and Hg0. At low V loading, the ratio of Oads/Olatt decreased gradually due to the VOx species occupying the defect sites of TiO2. The reaction rate of Hg0 oxidation is proportional to the square of the VOx density up to monolayer coverage. A maximum amount of V5+ is achieved at monolayer coverage and the TOF shows a volcanic trend with the increase of V loading. This study is an in-depth attempt to explore the effects of different vanadium species on the simultaneous removal of NOx and Hg0, and it is expected to provide theoretical guidance for the effective design of state-of-the-art vanadium-based catalysts for multipollutant control.

Ultramicroelectrode Based Approaches to Diagnose Utility of Redox Electrolytes in Flow Batteries

Redox flow batteries are of potential importance to both large scale energy storage and powering the electrical vehicle. Among critical challenges are low volumetric energy density of redox electrolytes, high cost and the maintenance limitations that greatly impede the wide application of conventional flow batteries. In this respect, the redox-active charge-storage material has a significant impact on the performance of a flow battery. The concentration of redox centers and their reaction kinetics have an influence on the available current densities and, thus, the power of the device.Many inorganic and organic electroactive systems have been proposed as alternatives to vanadium species in redox flow batteries. In the study, we explore the concept of highly concentrated solutions of such redox systems as iodine/iodide and poloxometallates of molybdenum and tungsten, and the possibility of optimizing their performance to exhibit high rates of charge propagation. While the iodine/iodide system can be prepared at high concentrations, the polyoxometallates of molybdenum and tungsten can serve as model examples of multi-electron systems for all-liquid redox flow batteries and related fundamental investigations. Reactions in the zinc/iodine (polyiodide) redox flow battery are as follows: Zn → Zn2+ + 2e- (E = −0.76 V vs SHE) at the negative electrode (anode), and 3I- → I3 − + 2e− (E = 0.54 V vs SHE) at the positive electrode (cathode) thus yielding a total theoretical potential output as high as ∼1.3 V. The increase of current density could be achieved not only by reducing the viscosity of the electrolyte, thus accelerating charge-carrier transport, but also – by referencing to our experience with the iodine/iodide couple as charge relay for dye-sensitized solar cells – through improvement of the dynamics of charge propagation in highly concentrated iodine/iodide solution via the catalyzed enhancement of rates of electron self-exchange (hopping) between iodine/iodide (polyiodide) redox species as well as by accelerating the interfacial kinetics at electrodes. This can be realized by choosing appropriate electrode materials and through their activation or modification. The electrochemical activities of the redox couples are usually significantly increased through application of nanostructured functionalized carbons. While dispersed in solutions they can improve electron transfers to the redox sites. The proposed chemistry has been first tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation, heterogeneous and homogeneous (electron self-exchange) rates of electron transfers. Unless catalyzed, both interfacial and bulk (self-exchange) electron transfers involving the iodine/iodide redox system are somewhat complicated; there is a need to break the I-I bond in the I3 -or I2 molecule; it has also been well-established that platinum (e.g. when deposited on the counter electrode) induces electron transfers within the iodine/iodide redox system. As far as heteropolyacids are concerned, they exhibit very strong Brønsted acidity, act as proton conductors, and undergo fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (e.g. tungsten(VI,V) or molybdenum(VI,V) heteropoly blue) compounds. The polyoxometallate-based redox electrolytes have different chemical identities, and they could be considered as anolytes or catholytes, depending on their redox potentials but, typically, their use would require formation of an asymmetric system with different-type redox species.While dynamics of electrochemical processes has an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the choice of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic criteria, we are going to extend the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence redox polymers and polynuclear materials to the development of redox electrolytes. Fundamental electroanalytical approaches utilizing ultramicrodisk electrodes and interdigitated arrays will be adapted to characterization of redox electrolytes.

(Invited) State of Charge Monitoring of Vanadium Flow Batteries Using Spectroscopic and Electrochemical Methods

In this paper we demonstrate our ability to make accurate in- situ measurements of both the state-of-charge and the concentration of individual vanadium species in a lab scale vanadium flow battery. The analysis is based on our previously published characterization of the spectroscopy of mixed solutions of VII/VIII and VIV/VV. Measurements of volume changes of the electrolyte in each half-cell are also shown and used to estimate the true value of concentration for each vanadium species as the cell is charged. The feasibility of optically monitoring the state-of-charge is clearly demonstrated and the unique ability of our data processing techniques to determine actual concentrations in- situ is revealed.

A new vanadium species in black shales: Updated burial pathways and implications

Examining vanadium (V) geochemistry in organic-rich rocks might provide new insights into the redox evolution of paleo ocean and atmosphere through Earth’s history. Previous work, mainly based on experiments and thermodynamic predictions, suggested that V is mainly bound to oxygen (O) atoms and/or ON (nitrogen) groups with oxidation states ranging from +III to +V, when removed from the water column. This conceptual model represented our understanding of the burial processes of V in sedimentary archives. However, until our study, the speciation of V had not been investigated in ancient sediments. For the first time, micro-focused X-ray Absorption Near Edge Structure (µ-XANES) analysis is applied to characterize V speciation in the late Cambrian – Early Ordovician, organic-rich Alum Shale of the Scandinavian region. The result shows the presence of a new V(+IV)–S structure that largely dominates the V speciation (>80%), subordinated by a V(+III)–O structure (<20%) in our samples deposited under euxinic conditions. The V(+IV)–S/∑V ratio seems to be influenced by the intensity of euxinic conditions. We suggest that the new V(+IV)–S structure may have been formed under strongly sulfidic conditions. Organic matter is most likely to be the dominant host phase for this newly identified species. Additionally, we propose an updated model describing the processes involved during the burial of V under a wide range of redox conditions. This model shows that the V speciation has the potential to provide a more nuanced picture of the redox conditions that prevailed at the time of deposition.

Synthesis of Vanadia-Mayenite Nanocomposites and Characterization of Their Structure, Morphology and Surface Sites

Calcium aluminates (CA) with a mayenite structure have attracted a growing interest during the last decades. The present paper reports the preparation of vanadia-mayenite composites performed via an impregnation of pure CA with ammonium vanadate solution. The properties of the prepared materials were explored by a low-temperature nitrogen adsorption/desorption technique, X-ray diffraction analysis, transmission electron microscopy, and spin probe method. As revealed, the addition of vanadium significantly affects the textural properties and the porous structure of mayenite. The blockage of micropores by vanadium species is supposed. The spin probe electron paramagnetic resonance technique based on the adsorption of 1,3,5-trinitrobenzene, phenothiazine, and diphenylamine has been applied to study the active sites on the surface of the composite samples. The results demonstrated an increase in the concentration of weak electron-acceptor sites when the vanadium loading was 10 wt%. X-ray diffraction analysis and transmission electron microscopy studies showed that the composites consist of few phases including mayenite, CaO, and calcium vanadates.