Vanadia Titania Research Articles

Hydroxylation of Arylboronic Acids to Phenols on a Vanadia–Titania Catalyst

Hydroxylation of Arylboronic Acids to Phenols on a Vanadia–Titania Catalyst

Empirical Study on Reduction Behavior and Metallurgical Properties of Vanadia–Titania Magnetite in Blast Furnace

The loss of permeability affects the reduction of the ferrous burden in the cohesive zone of a blast furnace (BF). Vanadia–titania magnetite (VTM) burden of various chemical compositions have different metallurgical properties. The reduction and softening-melting-dripping properties of different kinds of VTM were investigated. The results showed that the core of sinter or pellet is indirectly reduced to wustite and (Fe,Ti)Ox, and the periphery contains interlinked metallic iron and CaSiO3 in the cohesive zone. Wustite and (Fe,Ti)Ox are directly reduced in the melting-dripping zone. The aggregate (Fe, V, Cr) present in the non-dripping causes a loss of valuable components. With the increase in TiO2 content, the substrate phase of molten slag changes from melilite to titanaugite, and the mass of dripping decreases gradually. In addition, the permeability index S increased and the melting zone widened, which indicates that the increase in TiO2 content negatively affected the melting-dripping performance. The mass of the dripping is directly proportional to the pellet ratio. Considering the adverse effect of TiO2 on softening-melting-dripping properties, it is recommended that high TiO2 VTM is smelted while mixed with ordinary ores or with an increased pellet ratio in the burden structure.

Effect of Incremental Utilization of Unground Sea Sand Ore on the Consolidation and Reduction Behavior of Vanadia–Titania Magnetite Pellets

In the iron and steel industry, improving the usage amount of New Zealand sea sand ore as a raw material for ironmaking can reduce the production costs of iron and steel enterprises to a certain extent. In this paper, New Zealand sea sand ore without any grinding pretreatment was used as a raw material, oxidized pellets were prepared by using a disc pelletizer, and the effect of sea sand ore on the performance of green pellets and the metallurgical properties of oxidized pellets was investigated. The effects of sea sand ore on the compressive strength, falling strength, compressive strength of oxidized pellets, and reduction performance were mainly investigated. X-Ray Diffraction (XRD) patterns and Scanning Electron Microscope (SEM) analysis methods were used to discuss the influence of sea sand ore on the microstructure of the pellets’ oxidation and reduction process. As the amount of sea sand ore used increased, the compressive strength of green pellets was gradually decreased, and the falling strength of green pellets and the compressive strength of oxidized pellets were gradually increased. When the amount of sea sand ore used was 40%, the reduction swelling index of pellets was 16.31%. The increase of sea sand ore used made the reduction of pellets suppressed and the reduction rate decreased. When the amount of sea sand ore used increased to 40%, the reduction degree of sea sand ore pellets was only 60.06%. The experimental results in this paper provide specific experimental data for the large-scale application of New Zealand sea sand ore in the blast furnace ironmaking process.

Effects of High Proportion Unground Sea Sand Ore on the Preparation Process and Reduction Performance of Oxidized Pellets

The New Zealand sea sand ore is a kind of vanadia–titania magnetite formed by erosion in the coastal zone. Because of its coarse particle size, smooth spherical particles, complex chemical composition, it has been added to sinter as an auxiliary material. Based on the principle of optimizing ore blending to strengthen advantages and weaken disadvantages, this paper used New Zealand sea sand raw ore that has not undergone any pretreatment as the main material and prepared it into oxidized pellets using a disc pelletizer and explored the influence of high-proportion unground sea sand ore on the preparation process and reduction performance of oxidized pellets. The influence of unground sea sand ore on the falling strength, compressive strength, reduction swelling index, and reduction degree of pellets was analyzed by the ICPAES, XRF, XRD, SEM-EDS, and other detection methods, and the change laws and influencing factors of oxidized pellets were analyzed. With the increase of the amount of unground sea sand ore used, the falling strength and compressive strength of the green pellets first decreased and then gradually increased, while the compressive strength of the oxidized pellets first increased and then decreased. At the same time, as the amount of sea sand ore used increased, the reduction process of pellets was restricted. The reduction swelling index and the reduction degree index generally show a downward trend. However, the compressive strength of the pellets gradually increased after reduction. Through the research on the pellet-forming performance and reduction properties of unground sea sand ore, it is shown that when the amount of unground sea sand ore used was 40%, it can still be used as raw material for blast furnace ironmaking. Thus, this research provided specific data support for iron and steel enterprises to improve the ratio of unground sea sand ore and reduce production cost.

Preparation and Characterization of V2O5/a-TiO2(101) Model Catalysts

We prepared vanadia–titania model catalysts with V(+5) oxidation state by sublimating V2O5 powder onto clean anatase TiO2(101) [a-TiO2(101)]. The V2O5/a-TiO2(101) model catalysts with V2O5 in the s...

The Effect of Abandoned Basic Oxygen Furnace Gas Blowing on the Softening–Melting–Dripping Performance of Full High Cr‐Bearing Vanadia–Titania Magnetite Pellets

It is inevitable to encounter increase in slag thickness, foaming slag, and high iron loss due to excessive formation of titanium carbonitride in blast furnace smelting of full high Cr‐bearing vanadia–titania magnetite (HCVTM). The effects of softening–smelting–dripping properties, the content variation of titanium carbonitride, and mineral element migration process of full HCVTM pellets with abandoned BOF gas (ABOFG) blowing are studied using X‐ray diffraction (XRD), X‐ray fluorescent (XRF), inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES), X‐ray photoelectron spectroscopy (XPS), electron probe microanalysis‐wavelength‐dispersive spectrometer (EPMA‐WDS), and scanning electron microscope‐energy dispersive spectroscopy (SEM‐EDS). ABOFG is a type of neglected byproduct gas resource produced in the steelmaking process with high physical and chemical thermal energies and contains 20–40% CO, 20–30% CO2, 2–5% O2, and 30–50% N2. As the concentration of CO2 in ABOFG increases, the position and height of the cohesive zone decline, and the concentration of titanium carbonitride decreases from 1.424% to 1.035%, which are beneficial to the BF smelting process. In addition, the migration processes of Ti, V, and Cr are also affected, especially Ti tends to enrich in the dripped slag, whereas V and Cr tend to concentrate at the dripped iron.

Extraction method for valuable elements of low-grade vanadia–titania magnetite

The reduction performance and mechanism of low-grade vanadia–titania magnetite (LGVTM) were investigated using stoichiometric Al powder as a reductant. Subsequently, experiments were conducted to study the effect of Al ratio on the composition and microstructure evolution of ferroalloys and recoveries of Fe, V, Ti, and Cr. It was found that the oxides of valuable elements were reduced to metals simultaneously in a thermal explosion at 940 °C, forming a multicomponent ferroalloy. Ti, V, and Cr contents had common regularities in the ferroalloy, which first increased and then decreased, while Fe decreased with an increase in Al ratio. The main oxide inclusion transformed from Fe2SiO4 to Al2O3 in the ferroalloy with an increasing Al ratio. The recovery of Fe increased at first and then basically was constant. The recoveries of V, Ti, and Cr first increased and then decreased with Al ratio. The optimum Al ratios are different for each element, being 1.1, 1.15, 1.0, and 0.9 for Fe, Ti, V, and Cr, respectively. The combination of Al2O3 and TiO and the formation of (Al0.948Cr0.052)2O3 negatively affected the recovery of Ti and Cr, respectively.

A Mechanistic Study of Dehydrogenation of Propane over Vanadia–Titania Catalysts

The oxidative and non-oxidative dehydrogenation of propane over a monolayer V2O5/TiO2 catalyst was examined using in situ Fourier transform infrared spectroscopy and pseudo in situ X-ray photoelect...

Synergistic catalytic action of vanadia-titania composites towards the microwave-assisted benzoin oxidation.

Intensification of chemical processes according to the motto "faster, simpler, greener" is among the main concerns nowadays. One of the ways of intensification is the application of synergistic catalytic effects when the overall efficiency of a composite catalyst is much higher than the sum of the component activities. Here, we report on the preparation of synergistic catalytic materials by a simple and straightforward ball milling procedure. Oxidation of benzoin was selected as a model reaction to demonstrate the viability of the concept. For the V2O5-TiO2 (95 : 5) composite material, the synergistic effect is triggered by low power microwave irradiation with more than a tenfold jump in the catalytic activity in comparison to the activities of the individual components.

Highly Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate Catalyzed by Mesoporous Vanadia–Titania

The direct oxidative dehydrogenation of lactates with molecular oxygen is a “greener” alternative for producing pyruvates. Here we report a one-pot synthesis of mesoporous vanadia–titania (VTN), acting as highly efficient and recyclable catalysts for the conversion of ethyl lactate to ethyl pyruvate. These VTN materials feature high surface areas, large pore volumes, and high densities of isolated vanadium species, which can expose the active sites and facilitate the mass transport. In comparison to homogeneous vanadium complexes and VOx/TiO2 prepared by impregnation, the meso-VTN catalysts showed superior activity, selectivity, and stability in the aerobic oxidation of ethyl lactate to ethyl pyruvate. We also studied the effect of various vanadium precursors, which revealed that the vanadium-induced phase transition of meso-VTN from anatase to rutile depends strongly on the vanadium precursor. NH4VO3 was found to be the optimal vanadium precursor, forming more monomeric vanadium species. V4+ as the major valence state was incorporated into the lattice of the NH4VO3-derived VTN material, yielding more V4+–O–Ti bonds in the anatase-dominant structure. In situ DRIFT spectroscopy and density functional theory calculations show that V4+–O–Ti bonds are responsible for the dissociation of ethyl lactate over VTN catalysts and for further activation of the deprotonation of β-hydrogen. Molecular oxygen can replenish the surface oxygen to regenerate the V4+–O–Ti bonds.

Fundamental chemistry of V-SCR catalysts at elevated temperatures

Understanding the structural properties of vanadium at high temperatures for vanadia-based SCR at nearly monolayer coverage is an important topic, which has influence on e.g. automotive applications. Nowadays, improved, stabilized Anatase combined with profound technical insights makes high and low temperature behavior of V-SCR significantly better. However, the equilibrium between surface anchored Vv=O and interstitial V4+ species intercalated into the TiO2 matrix is changed during a thermal runaway of the catalytic system in question, and vanadium catalyzes Rutilation of the Anatase. Hydrothermal aging of the V-SCR catalyst is not related to vanadium evaporation, but to changes of the surface chemistry. Our observations were achieved by using in-situ Raman spectroscopy at relevant temperatures and gas conditions, showing that the vanadia-tungsta catalyst is stable under hydrothermal conditions at 550°C and that a VXTi1-XO2 phase is formed during thermal runaway of the catalyst, exemplified by exposure of an excess monolayer vanadia titania model catalyst to 750°C. These observations, combined with new achievements at low temperature for corrugated monolithic catalysts at 200°C reveal that vanadium based catalysts remain a robust, cost efficient and sulfur tolerant solution for automotive exhaust gas cleaning meeting future demands.

A complete reaction mechanism for standard and fast selective catalytic reduction of nitrogen oxides on low coverage VOx/TiO2(0 0 1) catalysts

We present a complete catalytic mechanism describing both the Standard and the Fast selective catalytic reduction (SCR) reactions in their correct stoichiometric form on a vanadia titania (anatase 001 facet) based catalyst model. It consists of two cycles, a NO-activation cycle and a Fast SCR cycle that share the same reduction part but use NO+O2 and NO2 respectively for the reoxidation. The stoichiometry of the Standard SCR reaction is obtained by coupling the two cycles and the stoichiometry of the Fast SCR reaction is represented by the Fast SCR cycle. We establish structures and energetics for each elementary reaction allowing us to calculate the rate for the two reactions by microkinetic modeling. We find at low temperatures the rate for the Standard SCR reaction is determined by H2O formation and desorption as neither NO nor O2 reacts exothermically with the reduced site prior to H2O desorption. On the contrary NO2 reacts directly with the reduced site resulting in higher rate for the Fast SCR reaction at low temperatures. The rate for the two reactions is the same at higher temperatures as the rate determining step is in the reduction part which is common to both reactions.

Catalytic Mechanisms of Methanol Oxidation to Methyl Formate on Vanadia–Titania and Vanadia–Titania–Sulfate Catalysts

Density functional theory calculations were carried out using both cluster and slab models to investigate the catalytic reaction network and the effect of sulfate promoter on methanol selective oxidation using the V2O5/TiO2 catalyst. The hemiacetal mechanism was reaffirmed to be the most favorable reaction pathway for the formation of methyl formate (MF) by the prediction of another reaction pathway involving formic acid. Molecular oxygen was found to assist the desorption of the reaction products from the reduced catalyst active site, both formaldehyde and methyl formate (MF). The mechanism of catalyst regeneration was elucidated based solely on first-principles calculations, which involve the conversion of another methanol molecule to formaldehyde over a peroxo species. This leads to our formulation of a complete catalytic reaction network for methanol selective oxidation to formaldehyde and MF on the V2O5/TiO2 catalyst. In addition, the detailed mechanism for the formation of formaldehyde and MF was al...

Highly Efficient and Stable Vanadia–Titania–Sulfate Catalysts for Methanol Oxidation to Methyl Formate: Synthesis and Mechanistic Study

Vanadia–titania–sulfate nanocatalysts for methanol oxidation to methyl formate (MF) were prepared by coprecipitation. When calcinated at 400 °C, both methanol conversion and MF selectivity reached ∼98.5% at reaction temperatures of 140–145 °C. Characterizations with several experimental techniques revealed the catalysts as highly dispersed vanadia supported by anatase titania with acidic sites of significant strength and density. The catalysts also showed very high stability with lifetime exceeding 4500 h. Extensive density functional theory calculations using both cluster and surface models revealed MF to form via the hemiacetal mechanism, involving the condensation of methanol and formaldehyde at acidic sites and methanol and hemiacetal oxidations at redox sites. The alternative formyl mechanism was predicted kinetically much less favorable, showing these catalysts to work in a distinct mechanism from the rutile titania photocatalyst. Interestingly, methanol chemisorption at redox sites leads to the formation of acidic sites capable of catalyzing the condensation reaction.

Preparation of vanadia-containing aerogels by rapid supercritical extraction for applications in catalysis

We have developed a variety of vanadia-containing aerogels using a rapid supercritical extraction method that employs a contained mold held within a hydraulic hot press. Sol–gels were prepared with silica, silica–titania, titania and alumina backbones using a variety of precursor chemicals: tetramethyl orthosilicate, tetraethyl orthosilicate, vanadyl acetylacetonate, titanium (IV) butoxide and titanium (IV) isopropoxide. Total fabrication time (including processing) was ca. 9 h for sol–gels prepared without solvent exchange. When sol–gel aging and solvent exchange steps are employed, the overall fabrication time was on the order of several days. The aerogels were characterized by physical appearance (color), bulk density, Brunauer–Emmett–Teller surface area, Barrett–Joyner–Halenda pore distribution, scanning electron microscopy and Fourier transform infrared spectroscopy. All of the resulting aerogels have average bulk densities below 0.12 g/cm3 and surface areas ranging from 500 to 770 m2/g, with the exception of the vanadia–titania materials, which have surface areas of 140 m2/g. Variation in speciation and complexation of vanadia in the resulting aerogels is evidenced by significant differences in color observed for various precursor recipes and processing conditions. Preliminary catalytic testing under conditions that mimic automotive exhaust gas indicates that the aerogels are catalytically active for the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides.

The one-step oxidation of methanol to dimethoxymethane over sulfated vanadia–titania catalysts: influence of calcination temperature

The highest methanol conversion was obtained on catalysts calcined at 723 and 773 K.

Mercury removal over the vanadia–titania catalyst in CO2-enriched conditions

The removal of gas-phase elemental mercury was investigated in CO2-enriched flue gas (oxy-fuel combustion) using selective catalytic reduction (SCR) catalysts (V2O5–WO3/TiO2). Experiments were carried out using various concentrations of CO2, O2, NH3, NO and temperatures. The removal of NO and Hg0 in the CO2-enriched flue gas condition increased with the temperature and decreased again, the maximum Hg0 and NO removal was observed at approximately 65% and 85%, respectively at 250–350°C, which indicated that Hg0 and NO could be simultaneously removed over V2O5–WO3/TiO2. The presence of enriched CO2 (80vol.%) assisted the Hg0 removal and inhibited the NO removal, whereas the effect of NO on the Hg0 removal varied according to the NO concentrations. The presence of Hg0 promoted NO removal in CO2-enriched flue gas at low temperature 200–300°C whereas inhibited NO removal greatly at high temperature (>300°C). In the SCR system, the presence of NH3 inhibited the Hg0 removal greatly. The mercury species analysis and catalyst characterization results showed that the removal of Hg0 over V2O5–WO3/TiO2 at 250–350°C was mainly attributed to the oxidation of Hg0. Mechanisms of the oxidation of Hg0 at 250–350°C in the CO2-enriched flue gas condition over the V2O5–WO3/TiO2 catalysts were: (1) the reaction between vanadia oxide and Hg0 to form adsorbed mercuric oxide (HgO(ad)–V2O4); (2) the oxidation of Hg0 by chemisorbed oxygen on the surface of catalyst; (3) the oxidation of Hg0 by function group of CO to form HgO and COC.

Apparent Absorption Spectra of Silica Supported Vanadium–Titanium Oxide Catalysts: Experimental Study and Modeling

The structures of different titania, vanadia, and vanadia–titania clusters located on the surface of mesoporous silica SBA-15 are optimized using density functional theory (DFT). The apparent absor...

Modeling, design and operation of pilot plant for two-stage oxidation of methanol into formic acid

The new technology of formic acid production from methanol is developed. Methanol oxidation into formaldehyde in a tubular reactor with iron-molybdenum catalyst is carried out at the first stage similarly to existing technology of formalin production, Formaldehyde is oxidized into formic acid in a tubular reactor with an appropriate vanadia–titania catalyst at the second stage. Mathematical modeling of the process second stage is performed on basis of the detailed kinetic model. Design parameters and performance of large-scale multitubular reactors were determined and reproduced in the constructed pilot plant with a capacity of 2–3kg of formic acid per hour. Process feasibility was confirmed by operation of the pilot plant. Formic acid yield at the second stage was shown to be 87–88%. The technology is ready for further scaling up to industrial level.

Effect of support on V2O5 catalytic activity in chlorobenzene oxidation

The present paper investigates the influence of the direct incorporation of ceria in TiO2 aerogels support (sulfated and unsulfated) prepared by a sol–gel route on the catalytic properties of vanadia based materials in the total oxidation of chlorobenzene. ICP-AES, N2 physisorption, XRD, DRIFTS, Raman spectroscopy, XPS, H2-TPR and NH3-TPD were employed for catalyst characterization. This study demonstrated that cerium oxide is present as CeO2 form at the catalyst surface, which can improve the catalyst redox properties and so enhance the catalytic activity at high temperature (400°C). Besides, sulfate containing vanadia–titania samples (doped or not with ceria) had their catalytic performances considerably improved (due to sulfates) at lower temperatures (range 200–300°C). This is due to an increased global acidity and higher reactivity of redox sites thanks to the superficial interaction between (i) vanadia and sulfate, and (ii) when ceria is present, between ceria and sulfate leading to higher efficiency of catalysts in the chlorobenzene oxidation.