Supported Vanadium Oxide Research Articles

Maximization of Micractinium sp., biomass and use of Dual-Purpose reduced graphene supported vanadium oxide nanoparticles for harvesting and subsequent biodiesel production

A sustainable media composition comprising of nanourea (NU), groundnut de-oiled cake (GDOC), and seaweed Extract (SE) was formulated using a mixture design for the cultivation of Micractinium sp. Maximum biomass yield and productivity of 5.52 ± 0.09 g/L and 0.72 ± 0.03 g/L d−1 were observed at 1.67 mM NU, 0.134 g/L GDOC and 0.250 mL L−1 SE, respectively. The highest lipid yield of 2.73 ± 0.24 g/L was also observed, respectively. The reduced graphene-supported vanadium oxide nanoparticles (RGO-VNPs) with a net surface charge of + 34.10 mV were developed, which acted as a % as well as a catalyst for transesterification. A maximum flocculation efficiency of 98 % was observed with 200 ppm of RGO-VNPs. The Fatty Acid Methyl Ester (FAME) yield of 96.81 ± 1.61 % was observed. Thus, the present study could provide a plausible solution for one-pot harvesting and synthesis of biodiesel utilizing microalgal lipids.

O2 and CO2 assisted oxidative dehydrogenation of propane using ZrO2 supported vanadium and chromium oxide catalysts

Zirconia supported vanadium oxide (vanadia) and chromium oxide (chromia) catalysts of 1–3 wt% of V or Cr were prepared, characterized, and tested for the oxidative dehydrogenation (ODH) of propane (C3H8) with O2 and CO2. Characterization results reveal that 2.5% metal loading is in slight excess of monolayer loadings for this ZrO2, which has a surface area of 48 m2.g−1. The reaction results reveal that supported vanadia catalysts are better for O2-ODH and supported chromia catalyst are better for CO2-ODH at a reaction temperature of 550 °C. Furthermore, the C3H8 conversion and propene (C3H6) yield increases with loading and the highest conversion and yield are also achieved at 2.5% metal loading. With higher loadings the conversion and yield decreases, clearly indicating that the surface metal oxide species are more active than their crystalline counterparts. As the contact time increases, for inlet stoichiometric ratios of the reactants for the two reactions, C3H8/CO2 = 1 and C3H8/O2 = 2, C3H8 conversion and C3H6 yield both monotonically increase and appear to approach a constant value; however, the difference between C3H8 conversion and C3H6 yield also increases. The C3H6 selectivity during O2-ODH (∼30%) is much lower than C3H6 selectivity during CO2-ODH (86–94%). Furthermore, during CO2-ODH of propane the conversions of C3H8 and CO2 are similar, and it appears that under the operating conditions used, the dry reforming of propane does not occur. Overall, the CO2-ODH of propane reaction at 550 °C using stoichiometric ratios of C3H8/CO2 over ZrO2 supported chromia catalyst provides a better C3H6 yield and selectivity, with an additional advantage of converting CO2.

Bridging the structural gap of supported vanadium oxides for oxidative dehydrogenation of propane with carbon dioxide

Bridging the structural gap of supported vanadium oxides for oxidative dehydrogenation of propane with carbon dioxide

Facilitating CO2 dissociation via Fe doping on supported vanadium oxides for intensified oxidative dehydrogenation of propane

Selective oxidative dehydrogenation of propane with CO2 (CO2-ODP) represents a promising pathway of propylene production and CO2 utilization. Presently, vanadium (V) based catalysts are commonly used due to the excellent redox ability originated from the multivalent V. However, the CO2-ODP reaction mechanism remains elusive, limiting the rational design of highly efficient catalytic systems. Herein, we introduced Fe into impregnated V-Al2O3 to build a dual-sites catalyst including Fe and V, achieving a C3H8 conversion at ∼43 % and C3H6 selectivity exceed 80 %. Via regulating the Fe/V molar ratio, we clearly describe that the formation of unique Fe-O-V facilitated the CO2 dissociation. Intrinsically, V is the main active site contributing for C3H8 dehydrogenation while Fe site is responsible for the CO2 dissociation, replenishing lattice oxygen to enhance oxidative dehydrogenation of C3H8. The design of dual-sites catalyst and extraction of molecular understanding provide guidance for the rational development of highly active CO2-ODP catalysts.

A DFT study of the catalytic ODH of n-hexane over a cluster model of vanadium oxide

Supported vanadium oxides are one of the most widely reported catalysts for the selective oxidative dehydrogenation (ODH) of alkanes to alkenes. These vanadium oxide catalysts contain at least three distinct O species classified by their coordination to the vanadium cations. The involvement in ODH of the different oxygen species is thought to follow the coordination environment with singly coordinated vanadyl V(V)=O being the most reactive. A quantitative understanding of the relative activity of the different oxygen species in vanadium oxides could inform catalyst design to further enhance productivity and selectivity in the ODH reaction. Here we use computational models based on hybrid density functional theory to study the mechanistic pathway for n-hexane to 1- and 2-hexene. We compare the potential energy surfaces calculated for these reactions initiated by β-H abstraction with H transfer to the vanadyl oxygen, V(V)=O, with that involving H transfer to a two-coordinate bridging O atom. An isolated H4V2O7 cluster is used to represent the supported vanadium oxide catalyst so that the reactivity of oxygen species can be understood in the absence of support effects. Gibbs energy calculations were carried out at temperatures of 573, 673 and 773 K to mirror laboratory experimental conditions. We find that the rate-determining step (RDS) in the conversion of n-hexane to either alkene is associated with n-hexane interaction with H4V2O7 through a secondary CH bond. This leads to β-H abstraction with the calculated reaction barrier for abstraction by a V(V)=O (ΔE‡ = +32.7 kcal mol−1) significantly lower than that for the two-coordinate bridging O (ΔE‡ = +43.9 kcal mol−1). H-abstraction leads to reduction of one of the vanadium cations. Removal of the second H atom to form an alkene can follow several pathways. We have considered the second step leading to 2-hexene (γ-H abstraction) using either an adjacent V(V)=O on the reduced V(IV)-O-V(V) unit, a different active V(V)=O site on a fully oxidised cluster, or gas-phase molecular O2. Our results show that the ODH process is likely to proceed via a Mars-van Krevelen redox mechanism. In a practical catalyst the results imply that catalyst activity will depend on the surface coverage of V(V)=O active sites and the n-hexane to gas-phase molecular oxygen ratio. In addition to the pathways leading to alkene products we have noted the formation of CO bonds by the radical intermediate formed from the initial β-H abstraction. From this observation, we suggest that the low yields of 1- and 2-hexene (< 20%) obtained in our laboratory experiments with V2O5/MgO catalysts may be a result of the chemisorption properties of the radical intermediate (∙C6H13) on bridging or terminal O sites in the V(V)-O-V(V) units, leading to undesired products including oxygenates.

Mesoporous sol-gel silica supported vanadium oxide as effective catalysts in oxidative dehydrogenation of propane to propylene.

Vanadium oxide incorporated mesoporous silica (V-m-SiO2) were designed and synthesized using a surfactant-modified sol-gel method. Detailed characterization shows that monomeric [VO4] sites containing one terminal V[double bond, length as m-dash]O bond and three V-O-support bonds are dominated until atomic ratio of vanadium to silicon approaches to 5%. It is also confirmed that such V-m-SiO2 catalyst contains high proportion of vanadium oxide species interacting strongly with silica. Compared to vanadium oxide supported mesoporous silica (V/m-SiO2) prepared using a traditional impregnation method, present V-m-SiO2 catalyst exhibits more superior ability to catalyze oxidative dehydrogenation of propane to propylene. By correlation with structural data, superior catalytic performance of present V-m-SiO2 catalyst can be reasonably attributed, in part, to its favorable geometric and electronic properties rendered by the unique preparation method.

Oxidative Dehydrogenation of Ethane on Oxide-Supported Vanadium Phosphorus Oxide Catalysts

Comparative results of studying the oxidative dehydrogenation of ethane (ODE) on catalytic vanadium-phosphorus oxide systems deposited by the molecular layering method on the surface of oxide supports (Al2O3, SiO2) have been presented. It has been found that the highest activity in ODE and selectivity for ethylene are exhibited by vanadium-phosphorus-containing catalysts. The influence of the acidity of catalytic systems on the activity and selectivity of the process has been revealed. The selectivity of the ODE process for ethylene reaches 90%. An increase in the oxygen concentration in the initial mixture from 3.5 to 20% leads mainly to a decrease in the selectivity of the ODE process with respect to the ethylene yield.

Oxidative Dehydrogenation of Ethane on Oxide-Supported Vanadium Phosphorus Oxide Catalysts

Oxidative Dehydrogenation of Ethane on Oxide-Supported Vanadium Phosphorus Oxide Catalysts

Roles of V−O sites for non-oxidative propane dehydrogenation over supported vanadium oxides

Supported vanadium oxides (VOx) are alternative candidates for non-oxidative propane dehydrogenation (PDH) owing to their competitive performance. This paper describes the roles of V−O sites on PDH over monomeric VOx species supported on ZrO2, Al2O3 and SiO2. With the control of pre-reduction, stable structures of V−O sites are obtained for PDH, including V−O-support (V−O−S), V−OH and V=O sites. By tuning the V densities over individual support, the propylene formation rate shows a linear correlation with the number of the V−O−S site, which indicates the V−O−S site plays a decisive role in PDH rather than V−OH and V=O sites. Moreover, the specific activity per V−O−S site over ZrO2 (8.2 × 10−3 s−1) is higher than those over Al2O3 (6.7 × 10−3 s−1) and SiO2 (2.8 × 10−3 s−1), due to the discrepant Lewis acidity of various V−O−S sites. This research provides a fundamental insight into the intrinsic nature of V−O sites for non-oxidative propane dehydrogenation.

Supported vanadium oxide catalyst over HY-zeolite-alumina composite fabricated by extrusion for oxidative desulfurization of dibenzothiophene

Despite the advantages of zeolite catalysts/carriers, the small pore size of HY zeolite causes diffusion limitations especially for bulky refractory sulfur compounds in oxidative desulfurization (ODS) of fuels. To overcome this restriction, extruded HY-zeolite/Alumina composites containing both micro and meso‑pores were successfully synthesized and used as an attractive carrier for the vanadium dispersion. Insights about the interactions between zeolite and alumina and their effects on the vanadium impregnation were given implementing different analysis approaches; BET, SEM-EDX, TEM, NH3-TPD, and UV-vis. Alumina particle piling created meso‑pores in the composites providing a positive impact on the ODS of bulky dibenzothiophene (DBT). Comparing to physical mixing of the alumina and zeolite, the extrusion approach notably enhanced the weak acid sites due to the removal/distorting tetrahedrally coordinated Al from the zeolite framework. A less increase in the strong acid sites was also resulted from the reaction of Al-OH in the alumina with the free Si-OH over the zeolite. The proposed catalyst (V/HYZ-Al(alumina/zeolite ratio=50%) exhibited an excellent DBT removal so that 1000 ppmw of DBT was eliminated completely under the optimal investigated conditions (T = 50 °C, O/(S+N)=12 mol/mol, time=90 min, Mcatalyst/Vfuel=10 g/L). The catalyst recyclability was proved to be acceptable during four examined successive ODS cycles.

Effect of promoters on o-xylene oxidation pathways reveals nature of selective sites on TiO2 supported vanadia

The o-xylene oxidation pathways on TiO2 supported vanadium oxide catalysts are affected by Cs+ and Sb4+ promoters. Reaction kinetics change remarkably at 360 °C: while at lower temperatures the rate determining step is the C-H bond cleavage in xylene methyl groups, the catalyst reoxidation becomes kinetically limiting at higher temperatures. Promotion by Sb4+ is related to an increase in the availability of oxygen at high temperatures for the reoxidation of V sites. The presence of Cs+ enhances the reoxidation of V sites and increases the ratio of nucleophilic to electrophilic oxygen on the surface. Catalytic tests of benzene oxidation confirm the lack of electrophilic sites on Cs-promoted VOx/TiO2 catalyst. Combined evidence points to a key role of the bridging lattice oxygen in V-O-V species as active site for the activation of o-xylene and its selective transformation to phthalic anhydride.

Supported Vanadium Oxide as a Photocatalyst in the Liquid Phase: Dissolution Studies and Selective Laser Excitation

AbstractSupported vanadium oxide species are tested for their capability to perform photocatalytic methyl orange degradation in the aqueous phase. Excitation is performed with a frequency‐tripled (λ=270 nm) or frequency‐doubled (λ=405 nm) Ti:sapphire laser in a newly designed 15 ml photoreactor. Photocatalytic activity in dye degradation is only observed at 270 nm excitation, indicating that larger vanadium oxide structures (V2O5 nanoparticles, decavanadates) are either not present in sufficient quantities, or not active in the reaction. Reference experiments exclude pure photodegradation of the dye. It is found that a major part of the supported vanadium oxide species becomes detached from the silica support, and a very small fraction detaches from alumina. Considerations of the aqueous phase chemistry of dissolved vanadate ions allow to identify the formed dissolved species to be predominantly H2VO4− ions. These doubly protonated monovanadates are the main active species in the photocatalytic reaction, together with small anchored species on alumina.

Effects of alumina phases on the structure and performance of VOx/Al2O3 catalysts in non-oxidative propane dehydrogenation

Abstract Supported vanadium oxides are promising in propane non-oxidative dehydrogenation and the activity of which shows clear support effects. The present study reports the effects of alumina polymorphs on the structure and performances of VOx-based catalysts. VOx/Al2O3 catalysts with the same V surface density were prepared over four different alumina supports (γ-Al2O3, δ-Al2O3, θ-Al2O3, θ,α-Al2O3) obtained by varying the calcination temperature of boehmite. The alumina calcination temperature was shown to affect the surface acid properties and VOx-support interactions and make it possible to tune the activity and coking behavior of catalysts. Weakening the VOx-support interactions due to the change in alumina surface properties was found critical to improve the intrinsic activity of catalysts. The coking behavior of catalysts was shown to depend on both total acid sites and VOx polymerization degree. This study may provide basic principles to tune the performance of VOx-based catalysts for non-oxidative dehydrogenation.

Mechanistic Studies of Reduction and Initiation over the Vanadium-Oxide Polyethylene Catalyst

Supported vanadium oxides are one of the most promising candidates for ultrahigh molecular weight polyethylene, and cocatalysts play a key role in this system. In this work, a fundamental insight i...

Initial Steps in the Selective Catalytic Reduction of NO with NH3 by TiO2-Supported Vanadium Oxides

Electronic structure calculations at the density functional theory/B3LYP level (selectively benchmarked by CCSD(T)) were performed on neutral and protonated monomer and dimer clusters of vanadium o...

Dehydrogenation of 1-butene with CO2 over VOx supported catalysts

Butadiene (BD) is an important intermediate in chemical industry and is obtained predominantly from fossil sources. In the future new and sustainable BD sources and synthesis routes might be required to meet the rising demands for this compound. Here, the synthesis of BD from 1-butene in the presence of CO2 was studied using supported vanadium oxide as active compound. Among the tested supports SBA-15 was shown to be the most effective one and a maximum BD yield of 39 % could be achieved. The VOx/SBA-15 catalysts were characterized by complementary methods to obtain insight about the effect of catalyst synthesis and vanadium loadings on the formation of VOx surface structures as well as the catalytic performance. CO2 has a positive impact on the reaction. Coking was considered to be the main reason for the catalyst deactivation and the decreasing BD yield with increasing time on stream.

Non-oxidative dehydrogenation of isobutane over supported vanadium oxide: nature of the active sites and coke formation

We combine Raman spectroscopy, EPR, XPS, temperature programmed reduction, XRD, 51V MAS ssNMR, TEM and N2-physisorption to unravel structure–activity relationships during the non-oxidative dehydrogenation of isobutane over a V based catalyst.

Al2O3-Supported W–V–O bronze catalysts for oxidative dehydrogenation of ethane

Vanadium-containing hexagonal tungsten bronze (HTB) structures supported on Al2O3are more selective to ethylene during ethane ODH than supported vanadium oxides.

Cover Feature: Understanding the Synthesis of Supported Vanadium Oxide Catalysts Using Chemical Grafting (Chem. Eur. J. 5/2020)

Cover Feature: Understanding the Synthesis of Supported Vanadium Oxide Catalysts Using Chemical Grafting (Chem. Eur. J. 5/2020)

Understanding the Synthesis of Supported Vanadium Oxide Catalysts Using Chemical Grafting.

The complexity of variables during incipient wetness impregnation synthesis of supported metal oxides precludes an in-depth understanding of the chemical reactions governing the formation of the dispersed oxide sites. This contribution describes the use of vapor phase deposition chemistry (also known as grafting) as a tool to systematically investigate the influence of isopropanol solvent on VO(Oi Pr)3 anchoring during synthesis of vanadium oxide on silica. The availability of anchoring sites on silica was found to depend not only on the pretreatment of the silica but also on the solvent present. H-bond donors can reduce the reactivity of isolated silanols whereas disruption of silanol nests by H-bond acceptors can turn unreactive H-bonded silanols into reactive anchoring sites. The model suggested here can inform improved syntheses with increased dispersion of metal oxides on silica.