Amounts Of Vanadia Research Articles

Design, synthesis and characterization of vanadia-doped iron-oxide pillared montmorillonite clay for the selective catalyticoxidation of H2S

A series of vanadia-doped iron-oxide-pillared clays (V/Fe-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H(2)S was investigated. V/Fe-PILCs were characterized using X-ray diffraction (XRD), surface area- and pore volume measurements, chemical analysis, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H(2) (H(2)-TPR). V/Fe-PILCs showed better catalytic performance than Fe-PILC without any significant SO(2) emissions. The H(2)S conversion over V/Fe-PILCs increased with increasing vanadia content up to 7 wt.%. However, it decreased at higher vanadia loading due to the decrease in surface area and the formation of the crystalline V(2)O(5) phase. The presence of water vapor in the reactant mixture resulted in a decrease of H(2)S conversion.

The dehydrogenation of ethylbenzene with CO 2 over V 2O 5/Ce xZr 1− xO 2 prepared with different methods

The high-surface-area Ce x Zr 1− x O 2 composite oxides with various compositions were prepared with modified hydrothermal and sol–gel methods, respectively. Different amounts of vanadia were loaded via an incipient wetness technique for the preparation of the V 2O 5/Ce x Zr 1− x O 2. The prepared samples were subjected to the dehydrogenation of ethylbenzene (EB) in the presence of CO 2 in a fixed-bed reactor under the conditions of T = 823 K, P = 1 atm, and CO 2/BE molar ratio = 20. The hydrothermal Ce x Zr 1− x O 2 loaded with 6 wt.% V 2O 5 showed obviously higher EB conversion than the 6 wt.% V 2O 5/Ce x Zr 1− x O 2(sol–gel) although similar styrene selectivity was obtained. Moreover, the V 2O 5 loadings and the Ce/Zr ratios had clear influence on both the activity and the stability of the catalyst. Irrespective of the preparation methods and Ce/Zr ratios, XRD results indicate that nanocrystalline Ce x Zr 1− x O 2 solid solution was exclusively formed. Independent of the Ce/Zr ratios, the Ce x Zr 1− x O 2 prepared with hydrothermal method was composed of pure cubic phase while mixed phases were observed for the sol–gel samples as revealed from Raman results. With increasing vanadia loadings from 3 to 15 wt.%, different forms of vanadium species, such as vanadates and crystalline V 2O 5, were observed from Raman spectra. Irrespective of the V 2O 5 loadings, a single-step reduction of the supported V 2O 5 was revealed from the TPR patterns. Based on these and the TGA/DSC analysis of the used catalysts, the experimental results were extensively discussed and tentatively explained.

Selective catalytic oxidation of H2S to elemental sulfur over V2O5/Zr-pillared montmorillonite clay

The performance of vanadia-doped zirconia-pillared clay (V/Zr-PILC) for the selective catalytic oxidation of H2S was investigated in this study. A series of vanadia-doped zirconia pillared clays (V/Zr-PILCs) with various amounts of vanadia were prepared and characterized using X-ray diffraction (XRD), surface area-pore volume measurements, chemical analysis, infrared (FTIR) spectroscopy, UV–vis-diffuse reflectance spectroscopy (UV–vis-DRS), X-ray photoelectron spectroscopy (XPS), and thermogravimetric (TG) analysis. V/Zr-PILCs showed better catalytic performance than Zr-PILC at temperatures ranging from 220–300 °C without any considerable SO2 emission. The H2S conversion over V/Zr-PILCs increased with increasing vanadia content up to 6 wt%. However, it decreased at higher vanadia loadings due to the decrease of surface area and to the formation of the crystalline V2O5 phase. The results of a regeneration experiment using 6 wt% V/Zr-PILC catalyst showed good reproducibility in its catalytic activity, even through five successive sulfidation-regeneration cycles at 280 °C.

Synthesis, characterization and catalytic performance of vanadia-doped delaminated zirconia-pillared montmorillonite clay for the selective catalytic oxidation of hydrogen sulfide

A series of vanadia-doped zirconia-pillared clays (V/Zr-PILCs) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H 2S was investigated in this study. V/Zr-PILCs were characterized using X-ray diffraction (XRD), surface area-pore volume measurements, chemical analysis, X-ray photoelectron spectroscopy (XPS), 51V spin-echo NMR, temperature-programmed reduction by H 2 (H 2-TPR) and temperature-programmed desorption of ammonia (NH 3-TPD). V/Zr-PILCs showed better catalytic performance than as such Zr-PILC at temperatures ranging from 220 to 300 °C without any considerable SO 2 emission. The H 2S conversion over V/Zr-PILCs increased with increasing vanadia content up to 6 wt.%. This superior catalytic performance might be related to the uniform dispersion of vanadia in the form of monomeric and polymeric species. However, it decreased at higher vanadia loadings due to the decrease of surface area and to the formation of crystalline V 2O 5 phase. The presence of water vapor in the reactant mixture resulted in the decrease of the H 2S conversion.

Catalytic performance of vanadia-doped titania-pillared clay for the selective catalytic oxidation of H 2S

A series of vanadia-doped titania pillared clay (V/Ti-PILC) with various amounts of vanadia were prepared and their performance for the selective catalytic oxidation of H 2S was investigated in this study. V/Ti-PILCs were characterized using X-ray diffraction (XRD), BET apparatus, and X-ray photoelectron spectroscopy (XPS). V/Ti-PILCs showed better catalytic performance than as such Ti-PILC at temperatures ranging from 220 to 300 °C without any considerable SO 2 emission. The H 2S conversion over V/Ti-PILC increased with increasing vanadia content up to 5 wt.%. This superior catalytic performance might be related to the uniform dispersion of vanadia in the form of monomeric and polymeric species. However, it decreased at 10 wt.% vanadia loading due to the decrease of surface area and to the formation of crystalline V 2O 5 phase. The presence of water vapor in the reactant mixture resulted in the decrease of the H 2S conversion.

Characterization and activity of vanadia-promoted Pt/ZrO 2 catalysts for the water–gas shift reaction

Pt/ZrO 2 catalysts for the water–gas shift (WGS) were promoted with various amounts of vanadia. Analyses by XRD, N 2 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, VO 5 species appear, with the eventual generation of V 2O 5 and ZrV 2O 7 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/ZrO 2. 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 V O Zr bonds.

Vanadia-doped titania-pillared montmorillonite clay for the selective catalytic oxidation of H2S

Abstract The performance of vanadia-doped titania-pillared clay (V/Ti-PILC) in the selective catalytic oxidation of H 2 S was investigated in this study. A series of V/Ti-PILC with various amounts of vanadia were prepared and characterized. XRD analysis revealed the presence of titania anatase peak without any evidence of crystalline vanadia. V/Ti-PILC showed a very good catalytic performance towards H 2 S oxidation at temperatures ranging from 220–300 °C without the considerable emission of SO 2 . At 300 °C, all the catalysts showed high H 2 S conversion of about 85%. The H 2 S conversions over V/Ti-PILC increased with increasing vanadia content and temperature.

Selective catalytic reduction of NO with ammonia over V2O5 supported sulfated titanium-pillared clay catalysts: influence of V2O5 content

A series of V2O5 supported sulfated titanium-pillared clay catalysts with various amounts of vanadia were prepared and characterized by BET, DRX, XPS and NH3-TPD then studied for selective catalytic reduction (SCR) of NO by NH3 in the presence of oxygen. It was found that vanadia supported on sulfated Ti-pillared clay is more active at any temperature than sulfated Ti-pillared clay for the SCR of NO by NH3. The NO conversions over V2O5 supported sulfated Ti-pillared clay catalysts were found to increase with vanadia content, but the selectivity into nitrogen decreases upon sulfation, suggesting that there is an optimum of activity as a function of the number of acid sites.

Characterization of La 2O 3-TiO 2 and V 2O 5/La 2O 3-TiO 2 catalysts and their activity for synthesis of 2,6-dimethylphenol

The La 2O 3-TiO 2 (1:5 molar ratio) mixed oxide was prepared by a co-precipitation method with in situ generated ammonia and was impregnated with various amounts of vanadia (4–12 wt.%). The La 2O 3-TiO 2 and the V 2O 5/La 2O 3-TiO 2 catalysts were subjected to thermal treatments from 773 to 1073 K and were investigated by X-ray diffraction, FT-infrared, BET surface area, and O 2 chemisorption methods to establish the effects of vanadia loading and thermal treatments on the surface structure of the dispersed vanadium oxide species and the temperature stability of these catalysts. Conversion of cyclohexanol to cyclohexanone/cyclohexene was investigated as a model reaction to assess the acid–base properties of these materials. The catalytic property was evaluated for a single step synthesis of 2,6-dimethylphenol from cyclohexanone and methanol in the vapor phase at normal atmospheric pressure. Characterization results suggest that the co-precipitated La 2O 3-TiO 2 when calcined at 773 K is in X-ray amorphous state and exhibits reasonably high specific surface area. The amorphous La 2O 3-TiO 2 is converted into crystalline compounds La 2Ti 2O 7 and La 4Ti 9O 24 at 873 and 1073 K, respectively. The La 2O 3-TiO 2 also accommodates a monolayer equivalent of V 2O 5 (12 wt.%) in a highly dispersed state on its surface. The V 2O 5/La 2O 3-TiO 2 catalyst is thermally quite stable up to 873 K calcination temperature. When subjected to thermal treatments beyond 873 K, the dispersed vanadium oxide selectively interacts with La 2O 3 portion of the mixed oxide and forms a LaVO 4 compound. The remaining TiO 2 appears in the form of anatase phase. The La 2O 3-TiO 2 and the V 2O 5/La 2O 3-TiO 2 differ in terms of acid–base properties and the 12% V 2O 5/La 2O 3-TiO 2 catalyst provided a maximum yield of 2,6-dimethylphenol among various catalysts investigated.

Selective catalytic reduction of NO with ammonia over V2O5 doped TiO2 pillared clay catalysts

A series of vanadia doped TiO2-pillared clay (TiO2-PILC) catalysts with various amount of vanadia were studied for selective catalytic reduction (SCR) of NO by ammonia in the presence of excess oxygen. It was found that the V2O5/TiO2-PILC catalysts were highly active for the SCR reaction. The catalysts showed a broad temperature window, and the maximum NO conversion was higher than that on V2O5/TiO2 catalyst and was the same as the commercial V2O5+WO3/TiO2 catalyst. The V2O5/TiO2-PILC catalysts also had higher N2/N2O product selectivities as compared to V2O5 doped TiO2 catalysts. In addition, H2O+SO2 slightly increased the activities at high temperatures (>350°C) for the V2O5/TiO2-PILC catalysts. Addition of WO3 to V2O5 further increased the activities of the PILC catalysts. These results indicate that TiO2-PILC is a good support for vanadia catalysts for the SCR reaction. In situ FT–IR experiment indicated that both Brønsted acid sites and Lewis acid sites exist on the catalyst surface, but with a large proportion being Brønsted acid sites at low temperatures (e.g., 100°C). The reaction path for NO reduction by NH3 on the V2O5/TiO2-PILC is similar to that on V2O5/TiO2 catalyst, i.e., N2 originates from the reaction between gaseous NO and NH3 adspecies.

Phases in vanadium pentoxide–tungsten trioxide catalysts

The X-ray diffraction (XRD) patterns of the V2O5–WO3 catalysts containing 0–100 mol% WO3, obtained from a solution of ammonium metavanadate and ammonium polytungstate in oxalic acid, are discussed. It has been found that (i) the V–O catalyst consists of V2O5 and traces of V2O4 phases, (ii) the W–O catalyst contains a monoclinic WO3 phase structurally related to the orthorhombic one (MrO) and (iii) mixed V2O5–WO3 catalysts are composed of V2O5 and of a monoclinic WO3 phase structurally related to the tetragonal (MrT) one. The MrT polymorph of tungsten trioxide is shown to be formed as a result of introducing vanadium ions into the WO3 lattice. The amount of vanadia dissolved in tungsten (VI) oxide under the conditions of catalyst preparation has been estimated to be not lower than 10 mol%. The significant decrease in the grain size of V2O5 and small decrease in the grain size of WO3 due to WO3–V2O5 and V2O5–WO3 solid solution formation, are discussed. The creation of mixed crystals due to epitaxial growth of (i) vanadia on MrT tungsten trioxide crystals in tungsten-rich catalysts and (ii) MrT WO3 on vanadia crystals in vanadium-rich catalysts is postulated.

Surface reactivity and morphology of vanadia-titania catalysts

Abstract Vanadia/titania samples have been prepared from two different titania supports (P-25 from Degussa and anatase from Tioxide) by impregnation with aqueous solutions of NH4VO3 and calcination at 723 K. A decrease in the specific surface area is observed on increasing the amount of vanadia; titania from Degussa being non-porous, only development of wide pores is observed upon supporting vanadia. However, while the unloaded Tioxide support shows pores with average diameters of 8 and 5 nm, these latter disappear upon incorporation of vanadia. The reactivity of the V2O5/TiO2 sample prepared using the P-25 support in olefin oxidation has been studied by FTIR spectroscopy in the temperature range 150–673 K. Ethylene and propene are adsorbed as such at low temperatures, become hydrated to alkoxy species at medium temperatures and later undergo oxidation to carbonyl compounds (acetaldehyde and acetone). Allylic oxidation of propene and oxidative breaking of the CC bonds is also observed.

Structure and selectivity changes in vanadia—titania catalysts used to promote the reduction of nitric oxide with ammonia

Heat treatment of vanadia—titania (anatase) catalysts at temperatures lower than those required for the anatase—rutile transformation has been found to cause changes in the structure of the catalyst and the selectivity for the reaction between ammonia and nitric oxide. As the temperature increases from 350 to 440°C, and as the time of heat treatment increases, the surface area decreases, the amount of vanadia (V) species weakly interacting with titania increases and needle-like crystals are formed. At the same time, the reduction of nitric oxide to nitrogen decreases while the formation of nitrous oxide is promoted. Washing the catalyst with ammonia solution removes the crystal deposits and avoids the production of nitrous oxide.

Structure and selectivity changes in vanadia-titania catalysts used to promote the reduction of nitric oxide with ammonia

Heat treatment of vanadia-titania (anatase) catalysts at temperatures lower than those required for the anatase-rutile transformation has been found to cause changes in the structure of the catalyst and the selectivity for the reaction between ammonia and nitric oxide. As the temperature increases from 350 to 440°C, and as the time of heat treatment increases, the surface area decreases, the amount of vanadia (V) species weakly interacting with titania increases and needle-like crystals are formed. At the same time, the reduction of nitric oxide to nitrogen decreases while the formation of nitrous oxide is promoted. Washing the catalyst with ammonia solution removes the crystal deposits and avoids the production of nitrous oxide.

Ammoxidation of alkylaromatics over V 2O 5/TiO 2 catalysts

V 2O 5/TiO 2 (anatase) catalysts prepared by the coprecipitation technique were tested in the reaction of alkylaromatics ammoxidation to the corresponding nitriles. The main factors influencing the selectivity were the ammonia partial pressure and the amount of vanadia in the catalyst. NH 3 was found to inhibit the overall reactant conversion relative to its oxidation. Moreover, ammonia stabilizes the intermediate of alkylaromatic activation, avoiding its combustion. At high hydrocarbon conversion, high degrees of ammonia combustion led to a decrease of the selectivity. The best catalytic performance was obtained with amounts of vanadia corresponding to the formation of a monolayer coverage of the anatase surface. For higher V 2O 5 content a strong increase of NH 3 combustion led to decrease of the nitrile yield. The catalysts were found to be active and selective in the ammoxidation of toluene, p- and m-xylene and o-chlorotoluene.