Phase cooperation of V<Subscript>2</Subscript>O<Subscript>5</Subscript> and Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> in the selective oxidation of H<Subscript>2</Subscript>S containing ammonia and water

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over vanadium oxide-based catalysts. The investigation was focused on the role of V₂O₅, and phase cooperation between V₂O₅ and Bi₂O₃ in this reaction. The conversion of H₂S continued to decrease since V₂O₅ was gradually reduced by treatment with H₂S. The activity of V₂O₅ was recovered by contact with oxygen. A strong synergistic phenomenon in catalytic activity was observed for the mechanically mixed catalysts of V₂O₅ and Bi₂O₃. Temperature-programmed reduction (TPR) and oxidation (TPO) and two bed reaction tests were performed to explain this synergistic effect by the reoxidation ability of Bi₂O₃. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Oxidation of ASD-4 Powder Modified by V<Subscript>2</Subscript>O<Subscript>5</Subscript>

The sequence of phase formation in the oxidation of ASD-4 aluminum powder modified by vanadium pentoxide during heating in air in the temperature range 873–1073 K has been studied by synchrotron radiation x-ray diffraction. It has been shown that the sharp acceleration of the oxidation of the modified powder is related to the loss of the protective properties of the oxide shell on the particle surface due to the polyvalence of vanadium, which provides structural and phase changes on the surface and in the depth of the oxidized metal.     

The role of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on the Structural and Optical Properties of MgO-ZnO-CdO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses and the Impact of Gamma Irradiation

The quaternary glasses of mixed divalent oxides including ZnO, MgO, CdO within a phosphate network former were prepared. Vanadium pentoxide was introduced as a dopant in the range from 0.5 to 3%. Optical and infrared absorption studies for all glass samples were carried out. The optical spectra reveal the presence of both V³⁺ and V⁴⁺ ions in the studied host mixed divalent oxides phosphate glass. Fourier transform infrared absorption spectral analysis indicates the appearance of distinct vibrational bands due to the presence of characteristic phosphate groups depending on the glass composition and the ratio of V₂O₅ content. The optical band gap and Urbach energy were calculated and discussed in relation to the effect of V₂O₅ content. Finally, the glasses were optically and structurally examined affter gamma irradiation with a dose of 80 KGy.     

Synthesis,characterization and electrical properties of polypyrrole/V<Subscript>2</Subscript>O<Subscript>5</Subscript> composites

Polypyrrole (PPy) and its composites with vanadium pentoxide (V₂O₅) were synthesized in aqueous medium by chemical oxidation polymerization using FeCl₃·6H₂O as an oxidant. The materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD), thermogravimetry analyzer (TGA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV/visible spectroscopic techniques and LCR-meter. The FT-IR results confirmed the successful synthesis of PPy and PPy/V₂O₅ composites. The XRD study showed the amorphous and crystalline nature of PPy and PPy/V₂O₅ composites, respectively. The TGA analysis showed slight increase in the thermal stability of the composites. The SEM data verified the porous nature of PPy and the composites. The UV/visible spectrometry confirmed the doping of PPy in composites. The electrical properties of the materials displayed their semiconducting nature. The resistance of the samples was found to be dependent on temperature and the contents of V₂O₅ in the composites.     

Catalytic performance of CuCl<Subscript>2</Subscript>-modified V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> catalyst for Hg<Superscript>0</Superscript> oxidation in simulated flue gas

CuCl₂-SCR catalysts prepared by an improved impregnation method were studied to evaluate the catalytic performance for gaseous elemental mercury (Hg⁰) oxidation in simulated flue gas. Hg⁰ oxidation activity of commercial SCR catalyst was significantly improved by the introduction of CuCl₂. Nitrogen adsorption, XRD, XRF and XPS were used to characterize the catalysts. The results indicated that CuCl₂ was well loaded and highly dispersed on the catalyst surface, and that CuCl₂ played an important role for Hg⁰ catalytic oxidation. The effects of individual flue gas components on Hg⁰ oxidation were also investigated over CuCl₂-SCR catalyst at 350 oC. The co-presence of NO and NH₃ remarkably inhibited Hg⁰ oxidation, while this inhibiting effect was gradually scavenged with the decrease of GHSV. Further study revealed the possibility of simultaneous removal of Hg⁰ and NO over CuCl₂-SCR catalyst in simulated flue gas. The mechanism of Hg⁰ oxidation was also investigated.     

Thermal oxidation of A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductors with V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanolayers on the surface

The specific features of the interaction of vanadium(V) oxide nanofilms with the surface of gallium arsenide and indium phosphide semiconductors under thermal oxidation conditions have been considered. The kinetics and mechanism of thermal oxidation of GaAs and InP with deposited V₂O₅ layers 15 and 25 nm in thickness have been studied. It has been revealed that vanadium(V) oxide exerts a specific effect on the oxidation of gallium arsenide and indium phosphide as compared to other d-metal oxides. It has been established that the oxidation occurs with the formation of a phase predominantly consisting of indium phosphates or gallium arsenates and intermediate products based on vanadium compounds in different oxidation states. Schemes have been proposed for the development of the oxidation processes with due regard for the chemical nature of vanadium(V) oxide.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Effect of Potassium on the Physiochemical and Catalytic Characteristics of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> Catalysts in <Emphasis Type="Italic">o</Emphasis>-Xylene Partial Oxidation to Phthalic Anhydride

Abstract

Vanadia species formed on the surface depend on the K/V atomic ratio. At small K/V ratios, Raman spectra show the formation of the K-doped and K-perturbed monomeric species. At K/V?=?1, kristalline KVO₃ is mainly present on the surface. In situ high temperature XRD-results exhibit a promoting effect on the anatase to rutile phase transformation in the presence of 0.03 and 0.21 wt% potassium. Large amount of K (3 wt%) provides thermal stability of V/Ti/O catalyst and no transformation is found up to 600?°C. Reduction of vanadia K-doped vanadia catalysts is moved to higher temperatures than for the catalyst without potassium. The catalyst having 0.21 wt% K possesses the highest activity in o-xylene oxidation. Furthermore, the K-doped monomeric vanadia species in this catalyst leads to a promoted adsorption or a prevented desorption of phthalide, resulting in a decreased selectivity towards phthalide and CO_x and a increased PA selecticity.

Graphical Abstract

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Reduced graphene oxide supported V<Subscript>2</Subscript>O<Subscript>5</Subscript>-WO<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> catalysts for selective catalytic reduction of NOx

We present a reduced-graphene-oxide (rGO)-supported V2O₅-WO₃-TiO₂ (VWTi) catalysts for the efficient selective catalytic reduction of NOx. The rGO support provides well-dispersed functional sites for the nucleation of nanoparticles, allowing the formation of VWTi catalysts with high specific surface areas. The dispersion of the nanoparticles, as observed by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), confirmed the uniform dispersion of the particles on the rGO surface. Detailed Fourier-transform infrared (FT-IR) and NH₃ temperature-programmed desorption (NH₃-TPD) analyses indicated that the high density of acidic sites provided by the rGO is key to the observed enhancement of NOx removal efficiency, and the rGO-supported catalysts exhibit improved NOx removal efficiencies with smaller amounts of V₂O₅ and WO₃ compared with the commercially available V₂O₅-WO₃-TiO₂ catalysts.     

Effects of preparation methods for V<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript> aerogel catalysts on the selective catalytic reduction of NO with NH<Subscript>3</Subscript>

A series of V₂O₅-TiO₂ aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO₂. The main variables in the sol-gel method were the amounts of V₂O₅ and when the vanadium precursor was introduced. V₂O₅-TiO₂ xerogel and V₂O₅/TiO₂ (P-25) were also prepared for comparison. The V₂O₅-TiO₂ aerogel catalysts showed much higher surface areas and total pore volumes than V₂O₅-TiO₂ xerogel and impregnated V₂O₅/TiO₂ (P-25) catalysts. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H₂ (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O₂ was studied over these catalysts. Among various V₂O₅-TiO₂ catalysts, V₂O₅ supported on aerogel TiO₂ showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility and monomeric and polymeric vanadia surface species. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Combustion of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al thermit mixtures in steel tubes

Explored was the combustion of Fe₂O₃/TiO₂/Al thermit mixtures in steel tubes upon variation in green composition and with special emphasis on the dependence of combustion temperature T _c and burning velocity U on reaction heat Q. Special attention was given to incompleteness of combustion for compositions with low Q.     

Effect of TiO<Subscript>2</Subscript> loading on the activity of V/TiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the catalytic oxidehydrogenation of ethylbenzene with carbon dioxide

TiO₂-Al₂O₃ mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO₂ were prepared by sol-gel method and impregnated with different amounts of VO _x . Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H₂-TPR), and ammonia temperature programmed desorption (NH₃-TPD). TiO₂ content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO₂ content was 50 wt-%.     

Biosynthesized Au/TiO<Subscript>2</Subscript>@SBA-15 catalysts for selective oxidation of cyclohexane with O<Subscript>2</Subscript>

A variety of TiO₂@SBA-15 supporters with various TiO₂ loadings were synthesized using a facile sol-gel method. Gold (Au)-based catalysts were prepared with an environmentally benign and economical bioreduction method via Cacumen Platycladi (CP) leaf extract and immobilized on various TiO₂@SBA-15 supporters with different TiO₂ loadings. The as-prepared biosynthesized Au catalysts were applied in the liquid-phase cyclohexane oxidation. The results showed that the Au nanoparticles were well-dispersed on TiO₂@SBA-15, and the Au existed as Au⁰. These biosynthesized Au catalysts are promising for cyclohexane oxidation, achieving a turnover frequency up to 3,426 h^?1 with a 14.1% cyclohexane conversion rate.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.