Vanadium Loading Research Articles

Titanium dioxide doped with vanadium as effective catalyst for selective oxidation of diphenyl sulfide to diphenyl sulfonate

Diphenyl sulfide was oxidized to sulfoxide and sulfone over V-doped TiO2 using a 30% solution of H2O2. The TiO2 samples with different intended content of vanadium (0.02, 0.05, 0.1 and 0.18 mass%) were prepared by incipient wetness impregnation. Physicochemical properties of the V-doped TiO2 were characterized by chemical analysis (ICP-OES), X-ray diffraction (XRD/in situ HT-XRD), UV–Vis diffuse reflectance spectrometry (UV–Vis DRS), N2-sorption measurements, electron paramagnetic resonance and cyclic voltammetry. Both vanadium oxide loading and calcination temperature influenced the structure of the V-TiO2 samples. Vanadium species deposited on TiO2 decreased temperatures required for anatase to rutile phase transformation. The V-TiO2 samples were found to be efficient catalysts for oxidation of sulfides to sulfones. The sample with the lowest vanadium content (0.02VTiO2) presented among the studied catalysts the best catalytic properties with respect to high conversion of diphenyl sulfide to diphenyl sulfonate. An increase in vanadium loading resulted in decrease in catalytic activity of the samples. Also non-modified TiO2 presented significantly lower catalytic activity in comparison with 0.02VTiO2. This interesting effect was related to the formation of highly dispersed vanadium species catalytically active in Ph2S oxidation in the case of the samples with lower V-content. An increase in vanadium loading results in the formation of more aggregated V-species inactive, or less active, in the process of diphenyl sulfide oxidation.

Characterization and reactivity of vanadium oxide supported on TiO2-SiO2 mixed oxide support

A TiO2-SiO2 support, 90Ti-Si, containing 90 wt.% TiO2 was synthesized by the sol-gel method. Several supported vanadium oxide (vanadia) catalysts, xV90Ti-Si (x = 2–12.5 wt.%) were synthesized by incipient wetness impregnation method using this support. The catalysts and support were characterized and probed with the propane oxidative dehydrogenation (ODH) reaction. The support possesses no rutile phase and retains 30–40% of its initial surface area even after calcination at 1073 K. The surface area loss is accelerated in the presence of vanadia and the rutile phase appears below 1073 K. Surface vanadia species are present for the supported vanadia catalysts calcined at 673 K and the propane ODH activity and propene yield increases with vanadia loading. The ODH activity of the 2V90Ti-Si sample at 673 K is retained even after the catalyst is pre-calcined at 1023 K. Interestingly, the activity of the 4V90Ti-Si sample at 673 K reaches a maximum at an intermediate pre-calcination temperature. The higher vanadia loading samples deactivate with an increase in calcination temperature. The ODH reactivity reveals that the propene yield at iso-conversion increases with loading. Analysis of kinetic parameters also reveals that the rate constant ratio increases with vanadia loading.

Catalytic Activity Studies of Vanadia/Silica–Titania Catalysts in SVOC Partial Oxidation to Formaldehyde: Focus on the Catalyst Composition

In this work, silica–titania supported catalysts were prepared by a sol–gel method with various compositions. Vanadia was impregnated on SiO2-TiO2 with different loadings, and materials were investigated in the partial oxidation of methanol and methyl mercaptan to formaldehyde. The materials were characterized by using N2 physisorption, X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS), Scanning transmission electron microscope (STEM), NH3-TPD, and Raman techniques. The activity results show the high importance of an optimized SiO2-TiO2 ratio to reach a high reactant conversion and formaldehyde yield. The characteristics of mixed oxides ensure a better dispersion of the active phase on the support and in this way increase the activity of the catalysts. The addition of vanadium pentoxide on the support lowered the optimal temperature of the reaction significantly. Increasing the vanadia loading from 1.5% to 2.5% did not result in higher formaldehyde concentration. Over the 1.5%V2O5/SiO2 + 30%TiO2 catalyst, the optimal selectivity was reached at 415 °C when the maximum formaldehyde concentration was ~1000 ppm.

Separation characteristics of vanadium from leach liquor of red mud by ion exchange with different resins

Resin D201, D314 and 717 were compared for their efficiency to extract vanadium from hydrochloric acid leaching solution of red mud. The adsorption parameters were investigated in details by using the three resins. The separation characteristics and mechanism of vanadium were analyzed with infrared spectroscopy and adsorption kinetics. More than 99% of vanadium was selectively adsorbed by using resin D201 at pH value of 2.0, flow speed of 6m3/h·m3 resin, resin D314 at pH value of 3.0, flow speed of 4.8m3/h·m3 resin, and resin 717 at pH value of 5.0, flow speed of 7.92m3/h·m3 resin, respectively. The maximum loading of vanadium by using resin D201 was more than resin 717 and D314. The vibration peak of functional group on the resins increased after adsorption of vanadium from the leaching solution. The adsorption process of vanadium was according with the pseudo-second adsorption kinetic model.

Oxidative dehydrogenation of propane over vanadium catalyst supported on nano-HZSM-5

Vanadium catalyst supported on nano-HZSM-5 was utilized in oxidative dehydrogenation of propane to propylene. The physicochemical properties of the elaborated catalysts were investigated by means of XRD, SEM, FTIR spectra, UV-vis, Raman, NH3-TPD and H2-TPR techniques. The effect of vanadium loading (2–10 wt %), temperature (500–600°C) and oxygen to propane ratio (0.5–1.5) on conversion, propylene and ethylene selectivity was studied using full factorial design of experiments. The obtained data were statistically analyzed using the Analysis of Variance (ANOVA) and a p < 0.05 was considered statistically significant. The mathematical relationship of conversion, propylene and ethylene selectivity on three independent variables approximated by a second-order quadratic model. Two-dimensional contour plots were drawn to investigate the effect of independent variables and their interaction on the chosen responses. The function of temperature, oxygen to propane ratio and vanadium content such as acidity and reducibility on the performance of supported vanadium catalysts were discussed.

Studies on dispersion and reactivity of vanadium oxides deposited on lamellar ferrierite zeolites for condensation of glycerol into bulky products

The acetalization of acetone with glycerol was investigated using vanadium-impregnated catalysts. The siliceous supports FER, a purely microporous material, and ITQ-6, a micro/mesoporous material, were obtained from a ferrierite lamellar precursor, PreFER. Both supports were impregnated with 1, 5 or 10wt.% of vanadium. The structural properties were characterized by X-ray diffraction and N2 adsorption/desorption, the dispersion and speciation of surface vanadium were analyzed by diffuse reflectance UV–vis spectroscopy and X-ray absorption spectroscopy (XANES and EXAFS), and the total acidities of the catalysts were evaluated by temperature-programmed NH3 desorption. The [5V]Si-ITQ-6 and [10V]Si-ITQ-6 catalysts provided the best catalytic results, with conversions of 100 and 90%, respectively, and selectivity towards solketal of approximately 99%. The higher surface area generated by mesoporosity in the Si-ITQ-6 support, compared to the microporous Si-FER support, provided good access for the diffusion of reactants and products, and good dispersion of vanadium, even at high vanadium loadings (10wt.%), with preferential formation of VO4 monomers and VOx oligomers on the surface. The greater contributions of these species to the total acidities of the catalysts resulted in higher catalytic activities, compared to the effect of V2O5 agglomerates.

Effect of Preparation Method and Vanadium Loading Amount on the Catalytic Activity of V/TiO2 Nanoparticles

Effect of Preparation Method and Vanadium Loading Amount on the Catalytic Activity of V/TiO₂ Nanoparticles

Effect of the preparation method and of the vanadium content on the physicochemical and surface properties of vanadium–magnesium-based catalysts for the selective oxidation of n-butane

Two series of V–Mg–O catalysts with vanadium contents of 30 and 60 wt % were synthesized using sol–gel (SG) and wet impregnation (IMP). The elaborated catalysts were characterized by X-ray diffraction, Fourier transform infrared, X-ray fluorescence, Brunauer–Emmett–Teller, NH3–temperature-programmed desorption, transmission electron microscopy and energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The preparation method and the vanadium content strongly influenced the textural, structural, and surface properties, as well as the reactivity of catalysts. The increase in the vanadium content leads to the formation of V–Mg mixed phases, which decreased the specific surface area. The lowest crystallite size and the highest surface area were obtained with the SG solids. The morphology of our catalysts is immensely affected by the preparation procedure; so the SG method leads to a smooth surface compared to the impregnation method. The NH3–temperature-programmed desorption analysis showed a weak acid character of the catalytic surface, the weakest of which was found in SG series. The X-ray photoelectron spectroscopy analysis revealed an enrichment of the catalytic surface with magnesium and the presence of three types of oxygen surface species (O2−, O2−, and O−). For both methods, the catalytic performances evaluated in the selective oxidation of n-butane are enhanced by the increase in the vanadium loading. The higher activity and selectivity to butenes were obtained with the SG solids.

Supported Vanadium Oxide Clusters in Partial Oxidation Processes: Catalytic Consequences of Size and Electronic Structure

AbstractThe catalytic activity for ethanol partial oxidation of vanadium oxide (VOx) anchored on titanium oxide was correlated to their electronic structure. In situ Raman spectroscopy and temperature‐programmed desorption (TPD) experiments indicate that the presence of catalytically active VOx moieties is very sensitive to vanadia loading: highly dispersed VOx predominantly exists at low VOx contents whereas larger vanadia clusters coexist at higher VOx loadings. In situ UV/Vis spectroscopy revealed that a significant fraction of these larger clusters remain reduced during catalysis, and thus do not fully participate in catalytic turnovers. The electronic structures of model VOx nanoclusters of different sizes (monomer, dimer, trimer, and one‐dimensional polymers) were investigated by using periodic density functional theoretical calculations. Results indicate that their electronic structures are significantly affected by their size. Our analysis also revealed that the formation of reduced VOx species (V4+) during catalysis is concomitant to the reduction of adjacent Ti cations (Ti3+). Theoretically calculated optical absorption spectra matched the experimental spectroscopic results obtained under in situ reaction conditions. Furthermore, the determination of defect formation enthalpies reported previously as the main descriptor for catalytic activity of vanadia nanoclusters, predicted that isolated monomeric VOx clusters predominantly take part in catalytic turnovers.

Propane Oxidative Dehydrogenation Using Consecutive Feed Injections and Fluidizable VOx/γAl2O3 and VOx/ZrO2–γAl2O3 Catalysts

Propane oxidative dehydrogenation (PODH) was studied using VOx/γAl2O3 and VOx/ZrO2–γAl2O3 catalysts and consecutive propane injections. These catalysts were synthesized with 2.5, 5, and 7.5 wt % vanadium (V) loadings. Temperature-programmed reduction by hydrogen displayed one reduction peak for VOx/γAl2O3 and two for VOx/ZrO2–γAl2O3 (5 and 7.5 wt % vanadium). Temperature-programmed desorption of ammonia (NH3-TPD) and pyridine Fourier transform infrared spectroscopy showed that zirconia on γAl2O3 reduces the catalyst acidity. NH3-TPD kinetics gave for VOx/ZrO2–γAl2O3 higher desorption activation energies than those for VOx/γAl2O3. PODH runs in the Chemical Reactor Engineering Center Riser Simulator were developed under an oxygen-free atmosphere at 550 °C, close to 1 atm, 20 s, and a 42.0 catalyst/propane weight ratio (g/g). PODH runs for the 7.5% V/ZrO2–γAl2O3 showed (a) 93% propylene selectivity and 25% propane conversion (based on propane converted into gaseous carbon-containing products), (b) 85% propyl...

Dispersed Vanadium in Three-Dimensional Dendritic Mesoporous Silica Nanospheres: Active and Stable Catalysts for the Oxidative Dehydrogenation of Propane in the Presence of CO2.

The uniform monodispersed vanadium-doped three-dimensional dendritic mesoporous silica nanospheres (nV-MSNSs) were successfully synthesized in a heterogeneous oil-water biphase stratification reaction system and characterized by several state-of-the-art methods. The synthesized nV-MSNSs were applied to the oxidative dehydrogenation of the propane (ODHP) reaction with the presence of CO2 and exhibited excellent catalytic performances. The results show that the vanadium loading (1.3-8.0 wt %) evidently influences the textural properties, oxidation state, and polymerization degree of vanadium species of nV-MSNSs. The specific surface area (SBET), pore diameter (Dp), and pore volume (Vp) of nV-MSNSs decrease with the loading of vanadium species. The excessively high vanadium loading leads to the slight connection of nanospheres, but does not affect the assembly and growth of the three-dimensional (3D) dendritic channels. The percentage of highly dispersed vanadium VV species gradually increases and attains the maximum value for 5.2V-MSNSs with the loading of vanadium and then decreases with further vanadium addition. The higher-polymerized VOx species gradually generates above 5.2 wt % vanadium content for nV-MSNSs. The lower-polymerized VOx species appear to be more active than the higher-polymerized VOx species. Markedly, the 5.2V-MSNSs exhibit the highest catalytic activity with the initial propane conversion of 58% for the ODHP. The excellent catalytic performance can be maintained after eight reaction-regeneration cycles. The silica mesoporous frameworks can be well preserved in the reaction-regeneration cycles; meanwhile, the highly dispersed vanadium oxide also can be fully recovered after in situ regeneration. Hence, nV-MSNS catalysts exhibit outstanding activity and stability, and it would have a promising application in the DH of alkanes.

A novel methodology for in situ redox active site titration of TiO2-supported vanadia during ethanol partial oxidation catalysis

An advanced titration method during ethanol partial oxidation with tert-butanol is proposed to quantify the number of active redox sites in supported vanadia-titania catalytic systems (VOx/TiO2). In agreement with previous reports, our results indicate that not all vanadia atoms equally participate in the catalytic redox cycle. Therefore, the use of total vanadium loadings to calculate turnover frequencies results in an underestimation of actual turnover frequency values. The kinetically-relevant rate constants for ethanol partial oxidation obtained on the basis on the number of active sites calculated by our method indicate that these rate constants are independent of vanadia loading. This in turn suggests that the main species active for ethanol partial oxidation are well dispersed small sized vanadia clusters with a small number of VOV bridging bonds, predominant at low vanadia coverages.

Vanadium oxide supported on mesoporous SBA-15 modified with Al and Ga as a highly active catalyst in the ODS of DBT

Vanadium oxides supported on mesoporous SBA-15 catalysts with different vanadium loadings were studied in the oxidative desulfurization (ODS) of dibenzothiophene as a model sulfur compound. The catalytic activity was improved when SBA-15 framework was modified by adding Al and Ga. Structural and textural characterization of the catalysts were performed by means of XRD, N2 adsorption, UV–Vis–DRS, XPS, NMR, TEM, Raman, TPR and Py-FTIR. UV–Vis–DRS and Raman demonstrated that highly dispersed vanadium VO4−3 species are responsible for the high activity in the sulfur removal. The Ga modified support with an intermediate V/Si ratio of 1/30 was the most active catalyst for ODS of DBT, using hydrogen peroxide as oxidant and acetonitrile as solvent. 100% of DBT elimination was attained at a short time in mild conditions. Gallium and aluminum incorporation into the support modified successfully the nature of the SBA-15 surface by generating Bronsted and Lewis acidity. The interaction between the acid sites with the active vanadium sites improved the activity of the catalysts. The high dispersion depended on the vanadium loading and on the nature of the support. The more acidic support allowed better dispersion of the vanadium species due to stronger interaction metal-support. The reusability of the catalysts indicates that vanadium oxide supported on mesoporous SBA-15 modified with Ga and Al are potential catalysts for the ODS of dibenzothiophene.

Propane oxidative dehydrogenation over VOx/SBA-15 catalysts

VOx/SBA-15 catalysts with five different vanadium loadings were prepared by a modified wet impregnation method, characterized using N2 adsorption, XRD, EDX, SEM, Raman and UV–vis spectroscopies and H2-TPR techniques, and tested in the oxidative dehydrogenation of propane in the temperature range 450–600°C. For all the catalysts the propane conversion increases with both reaction temperature and vanadium loading, while the selectivity for propene decreases mainly to the benefit of carbon oxides. Several types of VOx species coexist on the catalyst surface, with monomeric and low-polymerized ones leading mainly to propene, while V2O5 crystallites at high vanadium loadings producing more carbon oxides. Propene was determined to be the only primary product irrespective of the vanadium content.

Structure and activity of Pd/V2O5/TiO2 catalysts in Wacker oxidation of ethylene

The present study concerns preparation of Pd/V2O5/TiO2 catalysts and activity of the catalysts in selective gas phase oxidation of ethylene by O2 in presence of water at atmospheric pressure and in the temperature range of 100–200°C. The influence of palladium and vanadia loading and the partial pressures of the reactants on the yield of oxidation products (acetaldehyde and acetic acid) were examined. The surface-bound vanadia forms were identified by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and FT-Raman spectroscopy. The best activities were achieved with catalysts having near to nominal monolayer vanadia coverage of the support. Time-on-stream catalytic tests and chemical analysis of the fresh and used catalysts proved the structural and catalytic stability of the Pd/V2O5/TiO2 preparations. It was shown that under the conditions of Wacker-oxidation primary product acetaldehyde could be further oxidized to CO2, whereas no consecutive oxidation of product acetic acid proceeded.

Dioxidovanadium(V) complexes containing thiazol-hydrazone NNN-donor ligands and their catalytic activity in the oxidation of olefins

The reaction between tridentate NNN donor ligands, (E)-2-(2-(pyridin-2-ylmethylene)hydrazinyl)benzo[d]thiazole (HL1) and (E)-2-(2-(phenyl(pyridin-2-yl)methylene)hydrazinyl)benzo[d]thiazole (HL2), with VO(acac)2 in ethanol gave [VO2(L1)] (1) and [VO2(L2)] (2) complexes. Complex [VO2(L2)]·0.2(H2O) (3) was produced from the reaction of HL2 and V2O5 in ethanol. Molecular structures of complexes were determined by single-crystal X-ray diffraction. All of the investigated compounds were further characterized by elemental analysis, FT-IR, UV–vis and NMR spectroscopy. The dioxidovanadium(V) species were used as catalysts for olefin oxidation in the presence of hydrogen peroxide (H2O2) as an oxidant. Under similar experimental conditions with equal vanadium loading, the presence of the [VO2(L1)] (1) resulted in higher conversion than in the case of using [VO2(L2)] (2) and [VO2(L2)]·0.2(H2O) (3) as catalytic agents.

The oxidative aromatization of n-hexane over VMgO catalysts

Vanadium magnesium oxide (VMgO) catalysts with different vanadium loadings were synthesized and tested for catalytic activity in the oxidative dehydrogenation of n-hexane. High surface area catalysts were obtained by the wet impregnation technique. Magnesium oxide (MgO) and magnesium orthovanadate [Mg3(VO4)2] were the only phases observed in each catalyst. All the catalysts were tested at 0.6–7.8 % of n-hexane in air within a temperature range of 350–550 °C, varying the gas hourly space velocities. Catalytic testing conducted below the lower flammability limit (0.6 % n-hexane in air) showed only benzene and carbon oxides in the product stream, whereas for experiments done above the upper flammability limit (7.8 % n-hexane in air), hexenes, in addition to benzene and carbon oxides were observed. Decreasing the feed composition from 7.8 to 5.5 % resulted in higher yields towards benzene and total dehydrogenated products. The effect of variations in the gas hourly space velocity investigated using the 19 wt% vanadium catalyst and a feed concentration of 7.8 % showed that the selectivity to benzene increased slightly with an increase in the gas hourly space velocity.

Phy-chemical Attributes of Nano-scale V2O5/TiO2 Catalyst and Its’ Effect on Soot Oxidation

The V2O5 catalysts which supported on nano-scale TiO2 with variation of vanadium contents (5%, 10%, 20% and 40%) were prepared by an incipient-wetness impregnation method. The phase structures of nano-scale V2O5/TiO2 catalysts with different loading rates were characterized by Scanning electron microscope (SEM), X-Ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra. The oxidation activities of catalysts over diesel soot were performed in a themogravimetric analysis (TGA) system. The kinetics of the catalytic oxidation process were analyzed based on Flynn-Wall-Ozawa method. The characterization results showed that the phase structure of V2O5 supported on TiO2 depends heavily on the vanadium contents, which will put great effects on the catalytic performances for soot oxidation. At a low vanadium loading rates (V5-V20), active species exist as monomers and polymeric states. At a high loading rate (V40), the crystalline bulk V2O5 covers the surface of TiO2. The formed crystal structure occupied the active sites and led a decreasing in the catalytic effect. By comparing the characteristics temperatures of soot oxidation over V2O5 catalysts, the catalytic activities of catalysts with different loading rates for soot oxidation can be ranked as: V5 &lt; V10 &lt; V40 &lt; V20. Via pyrolysis kinetics analysis, it is revealed that the activation energy of soot oxidation is minimum when the vanadium loading rates is 20%, which is fit well with the TG experimental results. The consistency of pyrolysis kinetics and TG experimental results confirm that the best activity catalyst is V20 in discussed catalysts of this paper, which is nearest to the monolayer dispersion saturated state of V2O5/TiO2 catalyst. Moreover, it convincingly demonstrate the obvious threshold effect in V2O5 catalysts.

Oligomerization of Supported Vanadia: Structural Insight Using Surface-Science Models with Chemical Complexity

In light of the ongoing debate on the structure of supported vanadia, we report on a spectral marker enabling the direct identification of oligomeric surface structures. A series of VOx/SiO2/Si(100) planar samples with chemical complexity was synthesized by spin-coating and investigated in detail by UV resonance Raman spectroscopy at 256.7 nm excitation as well as by X-ray photoelectron spectroscopy. The enhanced Raman sensitivity allows vibrational spectra to be recorded as a function of vanadium loading (0 ≤ LV ≤ 20.2 V nm–2) despite the small surface area of the planar model samples. At low loadings (LV < 7.3 V nm–2) the spectra are dominated by dispersed vanadia species, whereas at higher loadings the presence of crystalline V2O5 is also observed. We identify new spectral features at 492, 562, and 676 cm–1, which are attributed to V–O–V-related modes of oligomeric vanadia surface species. The vanadia surface species show a linear increase with vanadium loading, saturating at a loading of LV = 7.3 V nm...

Vanadium and titanium oxide supported on mesoporous CMK-3 as new catalysts for oxidative desulfurization

Vanadium supported-CMK-3 catalysts with vanadium loading of 1–7wt.% were studied in the oxidative desulfurization (ODS) of dibenzothiophene as a model sulfur compound. The activity was compared with titanium supported-CMK-3. Structural and textural characterization of the catalysts was performed by means of N2 adsorption, XRD, UV–vis–DRS, Raman spectroscopy, XPS, TEM and TPR. The dispersion and the nature of the vanadium species depend on the V loading, so does the catalyst activity. Vanadium supported-CMK-3 with 7wt.% of vanadium loading was the most active catalyst for ODS of DBT using hydrogen peroxide (H2O2) as oxidant and acetonitrile as solvent. 100% of DBT elimination was attained at short time in mild conditions. Carbon ordered mesoporous CMK-3 with high surface area and high pore volume promotes a very good anchorage of metallic oxides in the carbons framework reaching high active sites distribution and more stable nanoclusters. The reusability of the catalyst indicates that V-CMK-3 is a potential catalyst for the ODS of dibenzothiophene.