The study on the selective oxidation of H<Subscript>2</Subscript>S over the mixture zeolite NaX-WO<Subscript>3</Subscript> catalysts

At temperatures lower than 250 °C the deactivation of zeolite NaX catalyst occurred in the presence of water vapor. The gradual accumulation of water vapor on the surface of catalyst could cause deactivation of catalyst. The zeolite NaX-WO₃ catalysts were prepared to study a method preventing deactivation of catalysts from the adsorption of water vapor. The zeolite NaX-WO₃ (9 : 1) with a low content of WO₃ showed the highest conversion of H₂S. It is believed that the addition of WO₃ caused either a decrease of the strong adsorption of water vapor on the zeolite NaX or an increase of the reducibility of WO₃ by some interactions between zeolite NaX and WO₃. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Selective catalytic oxidation of H<Subscript>2</Subscript>S using nonhydrolytic vanadia-titania xerogels

A series of vanadia-titania (V-Ti) xerogel catalysts were prepared by nonhydrolytic sol-gel method. These catalysts showed much higher surface area and total pore volumes than the conventional V₂O₅-TiO₂ xerogel. Two species of surface vanadium in the xerogel catalysts were identified by Raman measurements: monomeric vanadyl and polymeric vanadates. The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studied over these catalysts. Xerogel catalysts from the nonhydrolytic method showed very high conversion of H₂S without harmful emission of SO₂. The conversion of H₂S increased with increasing vanadia loading up to 10V-Ti; however, it decreased at higher vanadia loading (12V-Ti and 18V-Ti) probably due to the formation of crystalline V₂O₅.     

Methanol selective oxidation to dimethoxymethane on H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>/SBA-15 supported catalysts

A series of SBA-15 supported H₃PMo₁₂O₄₀ catalysts were prepared for the one-step oxidation of methanol to dimethoxymethane (DMM). The evaluation and characterization revealed that higher DMM selectivity obtained on the incipient wetness impregnation (IM) catalyst was related to the instability of H₃PMo₁₂O₄₀ on it. Raman spectra showed that 12-molybdophosphoric acid was more stable on the direct synthesis (DS) catalyst than on the IM catalyst and the existence of SBA-15 support enhanced the stability of H₃PMo₁₂O₄₀. Moreover, higher H₃PMo₁₂O₄₀ loading resulted in more acid sites and low DMM selectivity, furthermore the thermal pretreatment on H₃PMo₁₂O₄₀ influenced its structure and thus affected DMM selectivity. This paper was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.     

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.     

Selective oxidation of h2s in the presence of ammonia and water using co3o4/sio2 catalyst

The catalytic performance of some metal oxides in the selective oxidation of H₂S in the stream containing water vapor and ammonia was investigated in this study. Among the catalysts tested, Co₃O₄SiO₂ was the most promising catalyst for practical application. It showed very small amount of SO₂ emission even in the presence of excess water and ammonia. The solid product formed in the reaction was a mixture of elemental sulfur, ammonium thiosulfate and ammonium sulfate.     

Simultaneous biofiltration of H<Subscript>2</Subscript>S,NH<Subscript>3</Subscript> and toluene using cork as a packing material

Simultaneous removal of ternary gases of NH₃, H₂S and toluene in a contaminated air stream was investigated over 185 days in a biofilter packed with cork as microbial support. Multi-microorganisms including Nitrosomonas and Nitrobactor for nitrogen removal, Thiobacillus thioparus (ATCC 23645) for H2S removal and Pseudomonas aeruginosa (ATCC 15692), Pseudomonas putida (ATCC 17484) and Pseudomonas putida (ATCC 23973) for toluene removal were used simultaneously. The empty bed residence time (EBRT) was 40–120 seconds and the inlet feed concentration was 50-180 ppmv for NH₃, 30–160 ppmv for H₂S and 40–130 ppmv for toluene, respectively. The observed removal efficiency was 45–100% for NH₃, 96–100% for H₂S, and 10–99% for toluene, respectively. Maximum elimination capacity was 5.5 g/m³/hr for NH₃, >20.4 g/m³/hr for H₂S and 4.5 g/m³/hr for toluene, respectively. During long-term operation, the removal efficiency of toluene gradually decreased, mainly due to depositions of elemental sulfur and ammonium sulfate on the cork surface. The results of microbial analysis showed that nearly the same population density was observed on the surfaces of cork chips collected at each sampling point. Kinetic model analyses showed that there were no particular evidences of interactions or inhibitions among the microorganisms.     

Selective oxidation of H<Subscript>2</Subscript>S to ammonium thiosulfate and elemental sulfur using mixtures of V-Bi-O and Sb<Subscript>2</Subscript>O<Subscript>4</Subscript>

The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was investigated by using vanadium-bismuth based mixed oxide catalysts. Synergistic effect on catalytic activity was observed for the mechanical mixtures of V-Bi-O and Sb₂O₄. Temperature programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS), and two separated bed reactivity test results supported the role of Sb₂O₄ for reoxidizing the reduced V-Bi-O during the reaction. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Synthesis of nanometer sized Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>s by a hydrothermal method and their conductivities

Nanometer-sized bismuth tungsten oxides, Bi₂WO₆s, were successfully synthesized by hydrothermal treatment at 200 °C for 24 hr, and their morphologies and crystallite sizes were influenced by adjusting the conditions to pH 4, 7, and 9. TEM images revealed that the particles were sheet-shaped and the crystallite sizes ranged from 7–120 nm. The samples absorbed in the visible range at about 380–400 nm. The lowest conductivity, 1.0×10⁶ ohm/square, was observed for Bi₂WO₆ prepared at pH 4 with a 150 nm film thickness. As the annealing temperature for Bi₂WO₆ prepared at pH 7 was increased, the conductivity decreased due of formation of larger particles by coagulation and sintering at high temperatures. Conductivity appears to improve with increasing film thickness up to 1,500 nm.     

Preparation of CuO-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst with mesopore structure for water gas shift reaction

The water gas shift (WGS) reaction has been investigated widely in fuel cell technologies due to the potential for high fuel efficiency and lower emissions during the production of pure hydrogen. Industrially, the WGS reaction occurs in one of the following two ways: (a) high-temperature in the range of 310–450°C with Fe-Cr catalyst, (b) low-temperature in the range of 210–250°C with Cu-ZnO-Al₂O₃. In this study, a mesoporous catalyst was prepared, with a large surface area and uniformity in both pore size and distribution, by using a one-pot synthesis method. The prepared CuO-CeO₂-Al₂O₃ brought high CO conversion (82%), and was suitable for WGS reaction at low temperature (250 °C). This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.     

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.     

CeO<Subscript>2</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZSM-5 sorbents for high-temperature H<Subscript>2</Subscript>S removal

Performance of CeO₂-La₂O₃/ZSM-5 sorbents for sulfur removal was examined at temperature ranging from 500 oC to 700 oC. The sulfur capacity of 5Ce5La/ZSM-5 was much bigger than that of CeO₂/ZSM-5. H₂ had a negative impact on the sulfidation; however, CO had little influence on sulfur removal. The characterization results showed that CeO₂ and La₂O₃ were well dispersed on ZSM-5 because of the intimate admixing of La₂O₃ and CeO₂, the major sulfidation products were Ce₂O₂S and La₂O₂S, the XRD and SEM results revealed that ZSM-5 structure could remain intact during preparation and sulfidation process, the H₂-TPR showed that the reducibility of CeO₂ can be remarkably enhanced by addition of La.     

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 evolution during mechanochemical coreduction of V<Subscript>2</Subscript>O<Subscript>5</Subscript> and TiO<Subscript>2</Subscript> with A

The direct preparation of V-Ti solid solution alloy by coreduction of V₂O₅ and TiO₂ with Al in an attritor mill was investigated. The reduction of V₂O₅ with Al is highly exothermic, whereas reduction of TiO₂ with Al is not sufficiently exothermic for a self-sustaining reaction. A range of compositions of a mixture of V₂O₅ and TiO₂ can be so chosen as to make the overall reduction of V₂O₅ and TiO₂ with Al sufficiently exothermic for a self-sustaining reaction. Initial studies were done to identify the reaction products obtained by reducing V₂O₅ with Al. The reaction yielded the intermetallic phase (Al₃V), V, and Al₂O₃. SEM images indicated melting and solidification of the phases, leading to agglomeration. Further experiments involved mixing appropriate amounts of TiO₂ with V₂O₅ and reducing the mixture with Al. XRD data for products showed the presence of V, V₅Al₈, and Al₂O₃. X-Ray Florescence (XRF) analysis and energy dispersive analyzer (EDAX) of SEM sample images indicated the formation of V-Ti solid solution. Microstructure of the milled charges taken out prior to reaction initiation indicated morphology change in Al powder and agglomeration/segregation of reactants. As a result, the reaction of V₂O₅ with the excess Al at certain regions also promoted the formation of vanadium aluminide.     

Effect of H<Subscript>2</Subscript>O<Subscript>2</Subscript> modification of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>@carbon for m-xylene oxidation to isophthalic acid

The production of isophthalic acid (IPA) from the oxidation of m-xylene (MX) by air is catalyzed by H₃PW₁₂O₄₀ (HPW) loaded on carbon and cobalt. We used H₂O₂ solution to oxidize the carbon to improve the catalytic activity of HPW@C catalyst. Experiments reveal that the best carbon sample is obtained by calcining the carbon at 700 °C for 4 h after being impregnated in the 3.75% H₂O₂ solution at 40 °C for 7 h. The surface characterization displays that the H₂O₂ modification leads to an increase in the acidic groups and a reduction in the basic groups on the carbon surface. The catalytic capability of the HPW@C catalyst depends on its surface chemical characteristics and physical property. The acidic groups play a more important part than the physical property. The MX conversion after 180 min reaction acquired by the HPW@C catalysts prepared from the activated carbon modified in the best condition is 3.81% over that obtained by the HPW@C catalysts prepared from the original carbon. The IPA produced by the former is 46.2% over that produced by the latter.     

Effect of reaction conditions on the catalytic performance of Co<Subscript>9</Subscript>Fe<Subscript>3</Subscript>Bi<Subscript>1</Subscript>Mo<Subscript>12</Subscript>O<Subscript>51</Subscript> in the oxidative dehydrogenation of n-butene to 1,3-butadiene

Oxidative dehydrogenation of n-butene to 1,3-butadiene over Co₉Fe₃Bi₁Mo₁₂O₅₁ catalyst was conducted in a continuous flow fixed-bed reactor. The effect of reaction conditions (steam/n-butene ratio, reaction temperature, and space velocity) on the catalytic performance of Co₉Fe₃Bi₁Mo₁₂O₅₁ was investigated. Steam played an important role in decreasing contact time, suppressing total oxidation of n-butene, and removing coke during the reaction. Yield for 1,3-butadiene showed a volcano-shaped curve with respect to steam/n-butene ratio. The compensation between thermodynamic effect and kinetic effect led to a volcano-shaped curve of 1,3-butadiene yield with respect to reaction temperature. The Co₉Fe₃Bi₁Mo₁₂O₅₁ catalyst showed the best catalytic performance at a certain value of space velocity. The optimum steam/n-butene ratio, reaction temperature, and gas hourly space velocity were found to be 15, 420 °C, and 675 h⁻¹, respectively.     

Selective oxidation of hydrogen sulfide over LaCoO<Subscript>3</Subscript> and LaSrCoO<Subscript>4</Subscript> mixed oxides

Perovskite LaCoO₃ and perovskite-like LaSrCoO₄ mixed oxides were prepared by polyglycol gel method, and their catalytic performance was compared for the selective oxidation of hydrogen sulfide in a stream containing excess amount of ammonia and water for the first time. These samples were investigated by using XRD, BET, O₂-TPD and XPS. The catalytic activity and the selectivity to solid products (ammonium thiosulfate and elemental sulfur) of LaCoO₃ were better than those of LaSrCoO₄, and this is explained in terms surface contents of oxygen and cobalt, oxidation state of cobalt, and BET surface area.     

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.     

Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Immobilization of H<Subscript>3</Subscript>PMo<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst on the nitrogen-containing mesoporous carbon and its application to the vapor-phase 2-propanol conversion reaction

Nitrogen-containing mesoporous carbon (N-MC) with high surface area (=1,115 m²/g) and large pore volume (=1.18 cm³/g) was synthesized by a templating method. The surface of N-MC was then modified to form a positive charge, and thus, to provide sites for the immobilization of [PMo₁₂O₄₀]³⁻. By taking advantage of the overall negative charge of [PMo₁₂O₄₀]³⁻, H3PMo₁₂O₄₀ (PMo₁₂) was chemically immobilized on the N-MC support as a charge matching component. It was found that the PMo₁₂/N-MC still retained relatively high surface area (=687 m²/g) and large pore volume (=0.67 cm³/g) even after the immobilization of PMo₁₂. It was also revealed that PMo₁₂ species were finely and molecularly dispersed on the N-MC support via chemical immobilization. In the vapor-phase 2-propanol conversion reaction, the PMo₁₂/N-MC showed a higher conversion than the unsupported PMo₁₂. Furthermore, the PMo₁₂/N-MC showed an enhanced oxidation catalytic activity and a suppressed acid catalytic activity compared to the unsupported PMo₁₂. This catalytic behavior of PMo₁₂/N-MC was due to the molecular dispersion of PMo₁₂ on the N-MC support formed via chemical immobilization by sacrificing the proton.     

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.