Vanadium Loading Research Articles

Effect of vanadium loadings in the textural and structural properties of Mg–Al–V mixed oxides

Effect of vanadium loadings in the textural and structural properties of Mg–Al–V mixed oxides

Enhancing the selectivity of light olefins through synergistic VOx/ZSM-5 composite in the oxidative cracking of hexane

Oxidative-aided cracking of n-hexane is studied in a gas-phase oxygen-free environment over VOx/ZSM-5. The catalysts were prepared by impregnation of VOx on ZSM-5. Characterization of the prepared samples using XRD, SEM, and BET showed smooth, fine, highly crystalline, and highly dispersed VOx on ZSM-5. Raman spectroscopy revealed the presence of isolated moieties on the 1.5 and 2.5 % vanadia loading while a small number of polyvanadate species are detected on the 5 % VOx sample. TPR confirmed the ZSM-5 support contains highly reducible vanadia species. The amount of VOx loading also affected the activity and product distribution. The olefin and COx selectivities are affected by reaction time/temperature and amount/availability of lattice oxygen. VOx/ZSM-5(1.5) showed 99.9 % n-hexane conversion and 91.39 olefin selectivity at 575 °C and 25 s time-on-stream. This superior performance is attributed to the intermittent release of oxygen, optimum acidity, microporosity, and mesoporosity.

Investigation of the CO2 Activation and Regeneration of Reduced VOx/CeO2 Catalysts Using Multiple In Situ Spectroscopies

AbstractCeria‐supported vanadium oxide (VOx/CeO2) is an important catalyst for various oxidation reactions. Recently, vanadia has emerged again as a less toxic alternative to CrOx‐based catalysts for the CO2‐assisted oxidative dehydrogenation (ODH) of alkanes. To establish a mechanistic understanding of catalyst regeneration during CO2 exposure, often described as the rate‐limiting step of these reactions, we investigated the regeneration of VOx/CeO2 catalysts with different vanadia loadings using multiple in situ spectroscopies, that is, multi‐wavelength Raman, UV‐Vis, IR and X‐ray photoelectron spectroscopy. Time‐dependent analysis reveals that ceria is only partially regenerated in the bulk but fully regenerated in the subsurface. At the surface, stable carbonates form at vacancies, which are able to regenerate the lattice and deactivate ceria surface oxygen. The VOx/CeO2 samples show a loading‐dependent behavior, with low‐loaded samples regenerating vanadia only partially, due to the high concentration of monomers, while at higher loadings, vanadia can be almost fully regenerated due to the higher nuclearities being thermodynamically more stable. Ceria is regenerated faster than vanadia, indicating that vanadia regenerates by oxygen spill‐over from the ceria lattice. Our results provide important mechanistic insight into CO2 activation over supported vanadia catalysts, which is of great relevance for CO2‐assisted ODH reactions.

Efficient formation of propylene oxide under low hydrogen concentration in propylene epoxidation over Au nanoparticles supported on V-doped TS-1

The direct epoxidation of propylene to propylene oxide (PO) represents a unique feature of gold nanoparticle catalysts. Different amounts of vanadium were introduced into TS-1 using a hydrothermal method to give V-TS-1, and the effect of various vanadium loadings on the catalytic performance of Au/V-TS-1 was investigated in the epoxidation of propylene under different reaction conditions. The obtained characterization results indicate that the molecular sieve pore structure and crystalline phase structure of TS-1 were maintained after vanadium incorporation, and vanadium was incorporated into the molecular sieve framework. The introduction of an appropriate amount of vanadium resulted in the homogeneous dispersion of gold particles with a small average particle size, which facilitated the epoxidation reaction. When V was introduced into TS-1, the propylene conversion decreased under the condition of 10 % H2 concentration (C3H6/H2 = 1/1) in the reaction atmosphere, but the PO selectivity was maintained. Interestingly, when the H2 concentration in the reaction atmosphere was lowered to 2 % (C3H6/H2 = 3/1), the propylene conversion in Au/TS-1 was significantly decreased compared to 10 % H2 concentration condition, while in Au/V-TS-1, the propylene conversion was maintained in 2 % H2 concentration condition compared to 10 % H2. Au/V-TS-1 also maintained its selectivity for PO even when the H2 concentration was lowered. Therefore, under low hydrogen concentration conditions, the PO formation rate of Au/V-TS-1 was much higher than that of Au/TS-1. More, the same trend was observed when Mo was added in place of V. Our strategy will guide the design of future catalysts as a way to utilize hydrogen more effectively while maintaining PO productivity.

Structure and reactivity of surface vanadia sites in bi-layered supported VOx/AlOx/SiO2 catalysts via solid-state NMR, first-principles calculations, and catalytic studies

By combining multinuclear 1H, 29Si, 27Al and 51V solid-state NMR experimental measurements with reactivity and selectivity data, as well as first-principles calculations, for ternary bi-layered supported VOx/Al2O3/SiO2 catalysts, the structure of the dehydrated surface vanadia species was determined for each combination of supported VOx and AlOx active components. The specific structure of the surface vanadia sites in the ternary bi-layered supported VOx/Al2O3/SiO2 catalyst system have been investigated for the first time.The following vanadia sites are proposed based on the current findings:At low vanadia content, surface VO(OH)(OSi)2 sites form on the alumina-free surface of the SiO2 support in the bi-layered supported VOx/Al2O3/SiO2 catalyst system. In addition, two types of VO(OSi)3 surface species are likely present in this system. On small alumina clusters, weakly bonded surface VO(OH)(OAl)2 sites also form, along with the sites containing mixed Si/Al pods VO(OH)(OAl)(OSi). As the size of alumina clusters increases, strongly bonded VO(OAl)3 centers form, alongside the surface sites containing mixed pods VO(OAl)2(OSi) and VO(OAl)(OSi)2. The content of these sites increases with the loading of vanadia. Comparing supported VOx/SiO2, VOx/Al2O3, and bi-layered VOx/Al2O3/SiO2 catalyst systems revealed differences in catalytic activity due to the presence of new sites with different pods, with OH groups as well as the influence of Al-O-Si bonds on the electronic structure of surface vanadia sites on the alumina clusters. During the formation of dimethyl ether (DME), the turnover frequency (TOFDME) of the catalysts decreases with increasing domain size of the alumina clusters on SiO2. Addition of surface VOx sites, however, slightly decreases the TOFDME with the higher vanadia content weakening the activity of the alumina clusters. When surface VOx exists predominantly as V/Al1 and V/Al2, TOFredox depend on the vanadia content with lower vanadia content resulting in higher the TOFredox values. The 51V NMR spectra show that this decrease in redox TOF value correlates with the appearance of vanadia sites associated with silica pods. The activity of the catalysts was tested in methanol conversion reactions.

Effect of vanadium and tungsten loading order on the denitration performance of F-doped V2O5-WO3/TiO2 catalysts.

F-doped V2O5-WO3/TiO2 catalyst has been confirmed to have excellent denitration activity at low temperatures. Since the V2O5-WO3/TiO2 catalyst is a structure-sensitive catalyst, the loading order of V2O5 and WO3 may affect its denitration performance. In this paper, a series of F-doped V2O5-WO3/TiO2 catalysts with different V2O5 and WO3 loading orders were synthesized to investigate the effect of denitration performance at low temperatures. It was found that the loading orders led to significant gaps in denitration performance in the range of 120-240 °C. The results indicated loading WO3 first better utilized the oxygen vacancies on the TiF carrier promoting the generation of reduced vanadium species. In addition, loading WO3 first facilitated the dispersion of V2O5 thus enhanced the NH3 adsorption capacity of VWTiF. In situ DRIFT verified the rapid reaction between NO2, nitrate, and nitrite species and adsorbed NH3 over the VWTiF, confirming that the NH3 selective catalytic reduction (NH3-SCR) reaction over VWTiF at 240 °C proceeded by the Langmuir-Hinshelwood (L-H) mechanism. This research established the constitutive relationship between the loading order of V2O5 and WO3 and the denitration performance of the F-doped VWTi catalyst providing insights into the catalyst design process.

Impact of Vanadium Loading and Thermal Aging on the Surface Properties of Titania-Supported Vanadium Oxide

Impact of Vanadium Loading and Thermal Aging on the Surface Properties of Titania-Supported Vanadium Oxide

Supported H8PV5Mo7O40 on activated carbon: Synthesis and Investigation of influencing factors for catalytic performance.

Polyoxometalates (POMs), in particular the Keggin-type HPA-5 (H8PV5Mo7O40) are widely established as effective catalysts for acid- and redox-catalyzed reactions. Yet, they are mainly used as homogeneous catalysts, which poses challenges regarding catalyst separation. This study explores the synthesis of supported HPA-5, and its application as a heterogeneous catalyst for biomass conversion, focusing on activated carbons with diverse chemical and physical properties as support materials. Characterization of these carbons gives insights into the influence of surface area, oxygen content, and acidity on HPA adsorption and stability. Activated carbon CW20, was found to be the best support due to its high vanadium loading and effective preservation of the HPA-5 structure. It underwent various pre- and post-treatments, and the obtained supported catalysts were evaluated for their catalytic performance in converting glucose under both oxidative (OxFA process) and inert (Retro-Aldol condensation) conditions. Notably, HPA-5 supported on CW20 emerged as an exceptional catalyst for the retro-aldol condensation of glucose to lactic acid, achieving a selectivity of 15% and a conversion rate of 71%, with only minimal vanadium leaching.

Loss of potentially toxic elements to snowmelt runoff from soils amended with alum, gypsum, and Epsom salt

Soil amendment effects on the mobility of potentially toxic elements (PTEs) have been hardly investigated under snowmelt flooding conditions. This research quantifies and compares the loadings of arsenic (As), copper (Cu), nickel (Ni), selenium (Se), vanadium (V), and zinc (Zn) to snowmelt from unamended, alum-, gypsum-, and Epsom salt-amended soils from a manured agricultural field and a non-manured agricultural field. In the fall of 2020, amendments were surface applied at a rate of 2.5 Mg ha−1 to field plots with four replicates. Runoff boxes were installed at the plots’ edge to collect winter snow. In the spring of 2021, the snowmelt in each box was pumped out, and volume was recorded until all snow in the boxes had melted. Concentrations of PTE and other cations and pH were measured in a subsample of the snowmelt. The snowmelt from the manured field had higher Ni, Se, and V loads than that from the non-manured field. There were no significant differences in snowmelt PTE loads between the amended soils and the unamended controls at each field. Although not statistically significant, the Epsom salt-amended treatment resulted in a 75% reduction in Se loading and a 44% reduction in V loading, while the gypsum-amended treatment showed a 38% reduction in Ni loading compared to the unamended treatment in the manured soil. Overall, our findings from a single season using both manured and non-manured fields suggest that alum, gypsum, and Epsom salt additions did not significantly alter the mobility of the studied PTEs during the spring snowmelt period.

Effect of Particle Size of Rice-Husk Derived Silica on the Pyrolysis of Pomelo Peels

Silica with two different sizes i.e. microsilica (MS) and nanosilica (NS) was used as a catalytic support for vanadium (5-15 wt%) in the pyrolysis of pomelo peels. Besides use of pomelo peels (agricultural residues) as a feedstock for the pyrolysis, to contribute to environmental sustainability, rice husk was used as a silica source for obtaining the silica support. From the result, it was found that non-catalytic pyrolysis of pomelo peels gave a bio-oil yield of 33.3 wt%. The catalytic pyrolysis with vanadium-modified silica decreased the bio-oil yields ranging between 27.2-33.1 wt%. This was due to the occurrence of the second reactions generated from the active sites on the catalysts, which leads to the conversion of bio-oil into gas products. For NS catalyst, increasing the amount of vanadium loading directly decreased the bio-oil yields and increased the gas yield. The variation of product phase distribution was not clearly observed for MS catalyst even with various vanadium loadings. In addition, NS catalyst exhibited higher efficiency in reducing the acid content in the bio-oil, and increasing the phenol content. The distinguished properties of the nanoparticles may be the main reason for these phenomena. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

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.

V2O5 supported on NbTiOx: A novel NH3-SCR catalyst with high performance induced by V-Nb-Ti interaction

The traditional vanadia-based catalysts frequently employed for selective catalytic reduction of NOx with NH3 (NH3-SCR) have been criticized for their restricted operating temperature window and subpar low-temperature activity. In the present work, a series of NbTiOx solid solutions were used as supports to prepare V/NbxTi1-x (1.0 wt% V2O5) catalysts. The novel 1V/Nb0.15Ti0.85 catalyst presented superior catalytic performance and excellent resistance to SO2 in the SCR reaction, reaching above 95% NOx conversion in a wide temperature range from 270 to 485 °C. In comparison to pure TiO2, Nb-Ti-O solid solution support exhibited different pore structures and pore sizes, contributing to much larger specific surface area. Meanwhile, the surface Nb-OH and Nb = O bonds could serve as new acid sites to facilitate more NH3 adsorption. More importantly, there was a strong redox-acid interaction (V-Nb-Ti) for 1V/Nb0.15Ti0.85 catalyst, which induced the formation of highly redox-active V sites and promoted the activation of adsorbed ammonia, facilitating the NH3-SCR reaction. Unlike 1V/Ti, NOx species adsorbed on 1V/Nb0.15Ti0.85 participated in NH3-SCR reaction below 250 °C, further promoting the low-temperature activity. This study provides a novel vanadium-based catalyst with a low vanadium loading and high SCR activity for practical NOx abatement.

Pr-modified vanadia-based catalyst for simultaneous elimination of NOx and chlorobenzene

The V2O5/TiO2 catalyst is the most concerned NH3-SCR catalytic system for simultaneous removal of NOx and chlorinated volatile organic compounds (Cl-VOCs). There is an urgent need to develop a vanadia-based catalyst with low vanadium loading and excellent low-temperature catalytic performance. In this work, the Pr and W co-doped vanadia-based catalysts were prepared by a simple impregnation method. After the doping of Pr and W, the vanadia-based catalyst exhibited the excellent catalytic activity for NOx reduction and chlorobenzene (CB) oxidation. The more abundant polymeric vanadyl species and crystalline V2O5 were observed on the PrV5W/Ti catalyst, which are contributing to NH3-SCR and CB oxidation activity. The redox capability and the amount of surface-active adsorbed oxygen of vanadia-based catalyst were improved markedly, thus promoting NH3-SCR and CB oxidation reaction on PrV5W/Ti. This catalyst is promising to be used in the muti-pollutant control reaction of NOx and VOCs.

The role of vanadium oxide species on the performance of Pd/VOx/SiO2 catalysts for HDO of phenol

This work investigates the effect of vanadia species on the performance of Pd/VOx/SiO2 catalysts containing different vanadia loadings for HDO of phenol in the gas phase. in situ XANES experiments reveal the presence of a mixture of V2O4 and V4O7 species for all catalysts after reduction at 573 K. In situ XRD and XANES demonstrate that Pd particles and VOx species are in close contact, which is likely due to the presence of polymerized vanadate species, regardless of vanadia content, as shown by UV–Vis spectroscopy. This close contact promotes the selective hydrogenation of the C = O bond or the cleavage of the C-O bond, producing benzene. The strong interaction between the oxygen of the tautomer intermediate molecule and the oxygen vacancies associated with the presence of V3+ and V4+ cations is responsible for the deoxygenation activity of Pd/VOx/SiO2 catalysts.

Vanadium substituted AlPO4 as environmentally benevolent cool yellow pigment

In the current exploration, a sequence of AlP1-xVxO4 (x = 0, 0.05, 0.1, 0.15, 0.2) inorganic pigments were synthesised by chemical precipitation method using K3PO4 as a self-precipitation agent. Higher loading of vanadium (x = 0.15) into the P5+ lattice changed the crystal structure from tridymite (x = 0–0.1) to crystobolite which is supported by Powder X-ray diffraction analysis. Strain in the lattice was observed due to the substitution of higher ionic radii V5+ (0.35 Å) element, in the lower ionic radii P5+ (0.17 Å) framework. A drastic shift in the absorption curve to a higher wavelength was observed due to the insertion of vanadium in the AlPO4 system. A steady increase in the yellow hue was observed as a result of the substitution effect and the charge transfer transition occurred between V5+ and O2−. Though serious agglomerations of particles are noticed in the SEM and TEM micrographs, spherical shape particles are noticed after careful analysis of TEM images. The NIR reflectance of all the fabricated materials is found to be R > 75% and the chemical stability test confirmed all the recipes are stable (<2% weight loss and color change) in the harsh chemical conditions proving the materials can be used for metallic coating applications.

Selective Methanol Oxidation to Green Oxygenates—Catalyst Screening, Reaction Kinetics and Performance in Fixed-Bed and Membrane Reactors

Experimental and simulation-based investigations are carried out for the selective oxidation of green methanol to the oxygenates dimethoxymethane (DMM) and methyl formate (MF), including an initial catalyst screening, the derivation of a reaction kinetic model, and a feasibility study of a fixed-bed and a membrane reactor with oxygen distribution. The catalyst screening of different supports and loading of vanadium revealed a 6.6 wt.-% VOx/TiO2 catalyst offering the highest potential to the formation for the target products. Kinetic experiments performed in a broad range of operation conditions, e.g., residence time, temperature, and oxygen concentration, are used for the postulation of a reaction network, providing the basis for mathematical modeling of the individual five reaction rates with a reduced mechanistic approach. A simulation study based on the derived reaction kinetics and parameters revealed the high potential of a distributed oxygen dosing at high residence times, outperforming the conventional fixed-bed reactor by up to 6% in the yield of DMM and up to 19% in the yield of MF. The formation of DMM is favored at low temperatures, whereas the formation of MF is supported by high temperatures.

Structure - Catalytic Activity Correlation in Aluminium Hydroxide Supported Vanadia Catalysts

Aluminium hydroxide samples containing vanadium in the range 5 - 25 wt % have been prepared by incipient wetness impregnation method. The catalysts have been characterized through % composition of vanadium, BET surface area, FTIR, PXRD, SEM and solid state V-NMR. Liquid phase conversion of benzyl alcohol over the above materials into various products has been used as a chemical probe to investigate the activity of these catalysts. Benzyl alcohol has been converted into benzaldehyde, toluene and 1, 2-diphenyl ethane (dibenzyl). Formation of various products at different loadings of vanadium is found to be related to structural features of vanadium oxo-species. Oxidation- reduction products and 1, 2-diphenyl ethane have been formed selectively, at lower loadings of vanadium, which was in the tetrahedral environment of oxygen and at higher loading when vanadium was in square pyramidal environment catalytic activity increased but with low selectivity. When aluminum hydroxide was used as a support monolayer coverage was completed only at higher loading indicating better dispersion of metal - oxo species over this support.

Vanadium-doped graphitic carbon nitride for high performance lithium-sulfur batteries.

To promote polysulfide conversion in lithium sulfur batteries (LSB) and alleviate the shuttle effect, we designed and fabricated a novel catalyst of vanadium-doped graphite phase carbon nitride with nitrogen defects (V@gC3N4-ND) and high vanadium loading (3.46 at%) by defect engineering and two-step pyrolysis. Employing a V@gC3N4-ND modified separator, the LSB yielded capacities of 934 mA h g-1 at 1C and 404 mA h g-1 at 4C; the former was retained by 61% and 45% after 500 and 1000 cycles, respectively. In particular, the initial capacity of the battery reached 969 mA h g-1 at a sulfur loading of 10.0 mg cm-2. This work provides a facile route to the preparation of high-loading vanadium active site catalysts with nitrogen defects in the support, which are promising for high performance LSB applications.

Low-temperature propane oxidative dehydrogenation over UiO-66 supported vanadia catalysts: Role of support confinement effects

Overoxidation is the principal barrier against commercializing propane oxidative dehydrogenation (PODH) catalysts for propylene production. The current approach to reducing overoxidation, i.e., coating the non-selective support surface with a monolayer of active phase, can itself increase the probability of overoxidation of the produced propylene due to polymerization of active phase species. Incorporating the “confinement agents” onto the metal oxide support might be considered as an alternative solution to prevent hydrocarbons from reaching the support and overoxidizing. Herein, the UiO-66 metal–organic framework, which contains numerous organic ligands connected to the zirconia nodes, was used as support for the vanadia active phase to highlight the role of support's confinement effects on the overall catalytic performance toward the PODH. The UiO-66 supported vanadia catalysts with various vanadium loadings were fabricated via an ultrasonic-assisted wet impregnation procedure. The catalytic function is related to the underlying chemical processes at catalyst surfaces using physicochemical characterization techniques, PODH performance measurements, and machine learning tools. The results showed that the catalyst with a relatively low vanadia density of 2.7 nm−2, equivalent to less than half of the entire support surface coverage, could achieve propylene productivity of 4.43 gC3H6gcat-1h-1, propane conversion of 17.1%, and propylene selectivity of 49.7% at 350 °C.

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.