Selective oxidation of methanol to dimethoxymethane over acid-modified V2O5/TiO2 catalysts

Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V₂O₅/TiO₂ catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V₂O₅ (W(V₂O₅) = 15%) components loaded in the acid-modified V₂O₅/TiO₂ catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H₂SO₄-modified V₂O₅/TiO₂ catalyst gives a much higher DMM yield at 150 °C than the unmodified one.     

Effect of ceria on the structure and catalytic activity of V2O5/TiO2–ZrO2 for oxidehydrogenation of ethylbenzene to styrene utilizing CO2 as soft oxidant

The present study was undertaken to investigate the influence of ceria on the physicochemical and catalytic properties of V₂O₅/TiO₂–ZrO₂ for oxidative dehydrogenation of ethylbenzene to styrene utilizing CO₂ as a soft oxidant. Monolayer equivalents of ceria, vanadia and ceria–vanadia combination over TiO₂–ZrO₂ (TZ) support were impregnated by a coprecipitation and wet impregnation methods. Synthesized catalysts were characterized by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature programmed reduction, transmission electron microscopy and BET surface area methods. The XRD profiles of 550 °C calcined samples revealed amorphous nature of the materials. Upon increasing calcination temperature to 750 °C, in addition to ZrTiO₄ peaks, few other lines due to ZrV₂O₇ and CeVO₄ were observed. The XPS V 2p results revealed the existence of V⁴⁺ and V⁵⁺ species at 550 and 750 °C calcinations temperatures, respectively. TEM analysis suggested the presence of nanosized (<7 nm) particles with narrow range distribution. Raman measurements confirmed the formation ZrTiO₄ under high temperature treatments. TPR measurements suggested a facile reduction of CeO₂–V₂O₅/TZ sample. Among various samples evaluated, the CeO₂–V₂O₅/TZ sample exhibited highest conversion and nearly 100% product selectivity. In particular, the addition of ceria to V₂O₅/TZ suppressed the coke deposition and allowed a stable and high catalytic activity.     

Electrochemical performance of Li3V2(PO4)3/C cathode material using a novel carbon source

Polyethylene glycol (PEG, mean molecular weight of 10,000) has been used to prepare a Li₃V₂(PO₄)₃/C cathode material by a simple solid-state reaction. The Raman spectra shows that the coating carbon has a good structure with a low I_D/I_G ratio. The images of SEM and TEM show that the carbon is dispersed between the Li₃V₂(PO₄)₃ particles, which improves the electrical contact between the corresponding particles. The electronic conductivity of Li₃V₂(PO₄)₃/C composite is 7.0 × 10⁻¹ S/cm, increased by seven orders of magnitude compared with the pristine Li₃V₂(PO₄)₃ (2.3 × 10⁻⁸ S/cm). At a low discharge rate of 0.28C, the sample presents a high discharge capacity of 131.2 mAh/g, almost achieving the theoretical capacity (132 mAh/g) for the reversible cycling of two lithium. After 500 cycles, the discharge capacity is 123.9 mAh/g with only 5.6% fading of the initial specific capacity. The Li₃V₂(PO₄)₃/C material also exhibits an excellent rate capability with high discharge capacities of 115.2 mAh/g at 1C and 106.4 mAh/g at 5C.     

Characterization and activity of vanadia-promoted Pt/ZrO2 catalysts for the water–gas shift reaction

Pt/ZrO₂ catalysts for the water–gas shift (WGS) were promoted with various amounts of vanadia. Analyses by XRD, N₂ adsorption, Raman, and UV–vis DRS showed that vanadia is present below monolayer coverage as monovanadate and polyvanadate, with the former dominating at lower loadings, and that following monolayer formation, VO₅ species appear, with the eventual generation of V₂O₅ and ZrV₂O₇ for a vanadia weight loading of 13%. Though in all cases vanadia induced an enhancement in WGS activity, the best catalyst, that contained 3 wt.% of vanadia, gave a rate that was nearly double that of the unpromoted Pt/ZrO₂. That superior global activity probably results from the monovanadate that is the main species at low loadings. It is believed that monovanadate promotes the WGS by rendering the support's surface more oxidizing through its VOZr bonds.     

Dielectric properties and microstructures of CaSiO3 ceramics with B2O3 addition

The effects of B₂O₃ additives on the sintering behavior, microstructure and dielectric properties of CaSiO₃ ceramics have been investigated. The B₂O₃ addition resulted in the emergence of CaO–B₂O₃–SiO₂ glass phase, which was advantageous to lower the synthesis temperature of CaSiO₃ crystal phase, and could effectively lower the densification temperature of CaSiO₃ ceramic to as low as 1100 °C. The 6 wt% B₂O₃-doped CaSiO₃ ceramic sintered at 1100 °C possessed good dielectric properties: _r = 6.84 and tan δ = 6.9 × 10⁻⁴ (1 MHz).     

Low-temperature firing and microwave dielectric properties of 16CaO–9Li2O–12Sm2O3–63TiO2 ceramics with V2O5 addition

The sintering behaviors and microwave dielectric properties of the 16CaO–9Li₂O–12Sm₂O₃–63TiO₂ (abbreviated CLST) ceramics with different amounts of V₂O₅ addition had been investigated in this paper. The sintering temperature of the CLST ceramic had been efficiently decreased by nearly 100 °C. No secondary phase was observed in the CLST ceramics and complete solid solution of the complex perovskite phase was confirmed. The CLST ceramics with small amounts of V₂O₅ addition could be well sintered at 1200 °C for 3 h without much degradation in the microwave dielectric properties. Especially, the 0.75 wt.% V₂O₅-doped ceramics sintered at 1200 °C for 3 h have optimum microwave dielectric properties of Kr = 100.4, Q × f = 5600 GHz, and TCF = 7 ppm/°C. Obviously, V₂O₅ could be a suitable sintering aid that improves densification and microwave dielectric properties of the CLST ceramics.     

Adsorption and oxidation of NH3 over V2O5/AC surface

V₂O₅/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH₃ at around 200 °C and resistant to SO₂ deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH₃ over V₂O₅/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH₃ take place mainly at VO bond of V₂O₅. A higher V₂O₅ loading results in more NH₃ adsorption on the catalyst. V₂O₅ contains both Brnsted and Lewis acid sites; NH₄⁺ on Brnsted acid sites is less stable and easier to be oxidized than NH₃ on Lewis acid sites. Gaseous O₂ promotes interaction of NH₃ with AC and oxidation of NH₃ over V₂O₅/AC. NH₃ is oxidized into NH₂ and acylamide structures and then to isocyanate species, which is an intermediate for N₂ formation.     

Influence of low concentration of SO2 for selective reduction of NO by C3H8 in lean-exhaust conditions on the activity of Ag/Al2O3 catalyst

The effect of SO₂ for the selective reduction of NO by C₃H₈ on Ag/Al₂O₃ was investigated in the presence of excess oxygen and water vapor. The NO_x conversion decreased permanently even in the presence of a low concentration of SO₂ (0.5–10 ppm) at <773 K. The increase in SO₂ concentration resulted in a large decrease in NO_x conversion at 773 K. However, when the reaction temperature was more than 823 K, the activity of Ag/Al₂O₃ remained constant even in the presence of 10 ppm of SO₂. The sulfate species formed on the used Ag/Al₂O₃ were characterized by a temperature programmed desorption method. The sulfated species formed on silver should mainly decrease the deNO_x activity on the Ag/Al₂O₃. The sulfated Ag/Al₂O₃ was appreciably regenerated by thermal treatment in the deNO_x feed at 873 K. The moderate activity remains at 773 K in the presence of 1 ppm SO₂ for long time by the heat treatment at every 20 h intervals.     

Catalytic NO–H2–CO–O2 reactions over Pt-supported mesoporous yttrium oxide

Catalytic light-off of a stream of NO, H₂, CO in an excess O₂ has been studied over various metal oxides loading 1 wt% Pt. Because a low-surface area Y₂O₃ (<5 m² g⁻¹) was found to exhibit the highest de-NO_x activity, a mesoporous Y₂O₃ was then synthesized from an yttrium-based surfactant mesophase templated by dodecyl sulfate , which was anion-exchanged by acetate (AcO = CH₃COO⁻). The product showed a 3-D mesoporosity with a large surface area (396 m² g⁻¹) and the Pt-supported catalyst achieved much improved light-off characteristics suitable for the low-temperature de-NO_x in the presence of CO and excess O₂.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Role of vanadium sites in NO and O2 adsorption processes over VOx/CeO2-ZrO2 catalysts – EPR and IR studies

The interaction of NO and O₂ with 5 mol.% of vanadia deposited on Ce_0.10Zr_0.90O₂ and Ce_0.69Zr_0.31O₂ supports by wet impregnation was studied by means of EPR and IR. The supports were structurally characterized by XRD and Raman spectroscopy. Influence of the phase composition of the support on vanadium speciation as well as on surface architecture of the oxovanadium entities was discussed. The NO forms adsorbed on vanadium-containing systems were compared to those observed on bare CeO₂-ZrO₂ supports. The main products appearing on the catalysts surface during the consecutive reaction with NO and O₂ were identified and their thermal evolution was observed. Changes in vanadium speciation accompanying redox processes related to NO and O₂ activation were also observed and discussed.     

In situ Raman microspectrometry investigation of electrochemical lithium intercalation into sputtered crystalline V2O5 thin films

We report here the first in situ Raman microspectrometry study of the electrochemical lithium insertion and de-insertion reaction into crystalline sputtered Li_xV₂O₅ thin films (0 ≤ x ≤ 0.94) in liquid electrolyte. We show that the orthorhombic Pmmn symmetry of the pristine material is kept upon lithium intercalation in the Li_xV₂O₅ film (0 ≤ x ≤  0.94). In fact, a subsequent and unexpected solid solution behaviour is evidenced, leading to the typical Raman fingerprint of the -LiV₂O₅ phase for the Li₀.₉₄V₂O₅ composition. After the charge, a complete recovery of the local structure is found, in good accord with the excellent electrochemical reversibility exhibited by these thin films. Such limited structural changes differ from that usually observed for the bulk material, which emphasizes the key role of the microstructure and morphology on the nature and magnitude of the structural rearrangements induced by the lithium insertion process.     

NOx adsorption and diesel soot combustion over La2O3 supported catalysts containing K, Rh and Pt

In this work we report results of NOx adsorption and diesel soot combustion on a noble metal promoted K/La₂O₃ catalyst. The fresh-unpromoted solid is a complex mixture of hydroxide and carbonate compounds, but the addition of Rh favors the preferential formation of lanthanum oxycarbonate during the calcination step. K/La₂O₃ adsorbs NOx through the formation of La and K nitrate species when the solid is treated in NO + O₂ between 70 and 490 °C. Nitrates are stable in the same temperature range under helium flow. However, they become unstable at ca. 360 °C when either Rh and/or Pt are present, the effect of Rh being more pronounced. Nitrates decompose under different atmospheres: NO + O₂, He and H₂. The effect of Rh might be to form a thermally unstable complex (Rh–NO⁺) which takes part both in the formation of the nitrates when the catalyst is exposed to NOx and in the nitrates decomposition at higher temperatures. Regarding soot combustion, nitrates react with soot with a temperature of maximun reaction rate of ca. 370 °C, under tight contact conditions. This temperature is not affected by the presence of Rh, which indicates that the stability of nitrates has little effect on their reaction with soot.     

A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

Electrochemical lean-deNOx catalyst using H-conducting solid polymer electrolyte

The reduction of NO to N₂/N₂O in the presence of excess O₂ has been successfully achieved at 70 °C using an electrochemical cell of the type, 0.1% NO, 0–10% O₂, Pt | NAFION | Pt, H₂O. An H⁺-conducting solid polymer electrolyte (SPE) plays a key role in evolving hydrogen on the Pt cathode, where the catalytic NO–H₂ takes place. It was revealed that the competitive H₂–O₂ reaction is suppressed because the Pt surface was covered with stable nitrate (NO₃) species, which blocks oxygen adsorption hereon. The inhibition of H₂–O₂ reaction becomes most efficient at 100 °C in agreement with the optimal operation temperature range of SPE. The reduction efficiency of NO in an excess O₂ could be improved by packing 1 wt% Pt/ZSM-5 catalyst in the cathode room. The combination between the SPE cell and Pt catalysts can broadly be applied to novel low-temperature deNO_x processes in a strongly oxidizing atmosphere.     

Lithium insertion in ultra-thin nanobelts of Ag2V4O11/Ag

In this study, ultra-thin nanobelts of Ag₂V₄O₁₁/Ag were successfully synthesized. The synthesized ultra-thin nanobelts of Ag₂V₄O₁₁/Ag are highly crystalline and the thickness is found to be about 5 nm. A lithium battery using ultra-thin nanobelts of Ag₂V₄O₁₁/Ag as the active materials of the positive electrode exhibits a high initial discharge capacity of 276 mAh g⁻¹, corresponding to the formation of Li_xAg₂V₄O₁₁ (x = 6). With increased cycling, the electrode made of ultra-thin nanobelts of Ag₂V₄O₁₁/Ag tends to loose electrochemical activity due to Ag⁺ ions in the ultra-thin nanobelts of Ag₂V₄O₁₁ were reduced and new phase was formed.     

Vanadium loaded carbon-based monoliths for the on-board No reduction: Influence of vanadia and tungsten loadings

Carbon-coated catalysts doped with tungsten and vanadia oxides with different V and W loadings have been prepared by the ionic exchange method and characterized. The surface, structure and composition have been investigated by XPS, Raman, N₂ sorption at 77 K, TPD-NH₃ and reactivity tests for the SCR of NO with NH₃ at low temperatures. Under reaction conditions, NO conversions were found to go through a maximum with vanadia surface coverage at approximately half a monolayer. The observed decrease in the SCR activity at higher vanadia loadings can be attributed to either a loss of dispersion or loss of textural properties. Maximum NO conversion is ascribed to the higher Brönsted proton acidity (V⁴⁺) of the centres that decreases with increasing vanadia loadings up to 3 wt% loading due to the increase of V⁴⁺/V⁵⁺ ratio.Large amounts of tungsten (5%, w/w) upon or before addition of vanadia do not provide an enhancement of activity. The results indicate that W addition increases surface acidity leading to stronger Brönsted or even Lewis acid centre creation.     

Catalytic Wet Oxidation of H<Subscript>2</Subscript>S to Sulfur on V/MgO Catalyst

The V/MgO catalysts with different V₂O₅ loadings were prepared by impregnating MgO with aqueous vanadyl sulfate solution. All of the catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). It was observed that the H₂S removal capacity with respect to vanadia content increased up to 6 wt%, and then decreased with further increase in vanadia loading. The prepared catalysts had BET surface areas of 11.3 ~ 95.9 m²/g and surface coverages of V₂O₅ of 0.1 ~ 2.97. The surface coverage calculation of V₂O₅ suggested that a vanadia addition up to a monomolecular layer on MgO support increased the H₂S removal capacity of V/MgO, but the further increase of VO _x surface coverage rather decreased that. Raman spectroscopy showed that the small domains of Mg₃(VO₄)₂ could be present on V/MgO with less than 6 wt% vanadia loading. The crystallites of bulk Mg₃(VO₄)₂ and Mg₂(V₂O₇) became evident on V/MgO catalysts with vanadia loading above 15 wt%, which were confirmed by a XRD. The TPR experiments showed that V/MgO catalysts with the loading below 6 wt% V₂O₅ were more reducible than those above 15 wt% V₂O₅. It indicated that tetrahedrally coordinated V⁵⁺ in well-dispersed Mg₃(VO₄)₂ domains could be the active species in the H₂S wet oxidation. The XPS studies indicated that the H₂S oxidation with V/MgO could proceed from the redox mechanism (V⁵⁺ V⁴⁺) and that V³⁺ formation, deep reduction, was responsible for the deactivation of V/MgO.     

Self Assembly and Properties of C:WO3 Nano-Platelets and C:VO2/V2O5 Triangular Capsules Produced by Laser Solution Photolysis

Laser photolysis of WCl₆ in ethanol and a specific mixture of V₂O₅ and VCl₃ in ethanol lead to carbon modified vanadium and tungsten oxides with interesting properties. The presence of graphene’s aromatic rings (from the vibrational frequency of 1,600 cm⁻¹) together with C–C bonding of carbon (from the Raman shift of 1,124 cm⁻¹) present unique optical, vibrational, electronic and structural properties of the intended tungsten trioxide and vanadium dioxide materials. The morphology of these samples shows nano-platelets in WO _x samples and, in VO _x samples, encapsulated spherical quantum dots in conjunction with fullerenes of VO _x . Conductivity studies revealed that the VO₂/V₂O₅ nanostructures are more sensitive to Cl than to the presence of ethanol, whereas the C:WO₃ nano-platelets are more sensitive to ethanol than atomic C.