• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.576-580
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• 2017

In the present paper, the thermal deactivation characteristics of plate-type commercial $V_2O_5-WO_3/TiO_2$ SCR catalyst were investigated. For this purpose, the plate-type catalyst was calcined at different temperatures ranging from $500^{\circ}C$ to $800^{\circ}C$ for 3 hours. Structural and morphological changes were characterized byXRD, specific surface area, porosity, SEM-EDS and also NOx conversion with ammonia according to the calcine temperature. The NOx conversion decreased with increasing calcine temperature, especially when the catalysts were calcined at temperatures above $700^{\circ}C$. This is because the crystal phase of $TiO_2$ changed from anatase to rutile, and the $TiO_2$ grain growth and $CaWO_4$ crystal phase were formed, which reduced the specific surface area and pore volume. In addition, $V_2O_5$, which is a catalytically active material, was sublimated or vaporized over $700^{\circ}C$, and a metal mesh used as a support of the catalyst occurred intergranular corrosion and oxidation due to the formation of Cr carbide.

• Clean Technology
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• v.17 no.4
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• pp.370-378
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• 2011

Catalytic activity of $V_2O_5-WO_3/TiO_2$-based SCR catalyst was examined for the oxidation of gas-phase elemental mercury to oxidized mercury. Mercury species was not detected on the commercial SCR catalyst after the oxidation reaction of elemental mercury, regadless of the presence of HCl acting as oxidant and the reaction conditions. This suggests that elemental mercury oxidation by HCl could occur via a Eley-Rideal mechanism with gas phase or weakly-bound mercury on the surface of $V_2O_5-WO_3/TiO_2$ SCR catalyst. The activity for mercury oxidation was significantly increased with the increase of $V_2O_5$ loading, which indicates that $V_2O_5$ is the active site. However, turnover frequency for mercury oxidation was decreased with the increase of $V_2O_5$ loading, indicating the activity for mercury oxidation was strongly dependent on the surface structure of vanadia species. The activity for oxidation of elemental mercury under SCR condition was much less than that under oxidation condition at the same HCl concentration and reaction temperature.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.6
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• pp.791-797
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• 1999

The activity of domestic pigment titania$(TiO_2)$ impregnated with vanadia$(V_2O_5)$ was investigated in the laboratory microreactor. The meta-titanic acid$(TiO(OH)_2)$ which was produced at Hankook Titanium was selected as the precursor for support. The domestic pigment $TiO_2$ showed higher activity in the reduction of NO with $NH_3$ than the foreign commercial $TiO_2$. $WO_3$ were added to domestic $V_2O_5/TiO_2$ catalytic system to improve the catalytic activity at higher reaction temperature between 400~50$0^{\circ}C$ Also, the deactivation of domestic $V_2O_5/TiO_2$ and $WO_3-V_2O_5/TiO_2$ catalyst by $SO_2$ and $H_2O$ was investigated.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.83-88
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• 2011

Nano-technology is a super microscopic technology to deal with structures of 100 nm or smaller. This technology also involves the developing of $TiO_2$ materials or $TiO_2$ devices within that size. The aim of the present paper is to synthesize $WO_x$ doped nano-$TiO_2$ by the Sonochemistry method and to evaluate the effect of different percentages (0.5-5 wt%) of tungsten oxide load on $TiO_2$ in methylene blue (MB) elimination. The samples were characterized using such different techniques as X-ray diffraction (XRD), TEM, SEM, and UV-VIS absorption spectra. The photo-catalytic activity of tungsten oxide doped $TiO_2$ was evaluated through the elimination of methylene blue using UV-irradiation (315-400nm). The best result was found with 5 wt% $WO_x$ doped $TiO_2$. It has been confirmed that $WO_x-TiO_2$ could be excited by visible light (E<3.2 eV) and that the recombination rate of electrons/holes in $WO_x-TiO_2$ declined due to the existence of $WO_x$ doped in $TiO_2$.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.357-364
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• 2023

Selective catalytic reduction (SCR) is the most effective method for reducing nitrogen oxide emissions, but the operating temperature range of V₂O₅-WO₃/TiO₂ catalysts is narrow (300~400℃). In this study, a new catalyst with an operating temperature range of 200~450℃ was developed. The catalyst poison, ammonium bisulfate, generated during the SCR process can be removed by heating above 350℃. To increase the number of active sites and promote the dispersion of active materials, titanium isopropoxide (TTIP) treatment was performed on the TiO₂ support with various TTIP/TiO₂ mass ratios. Among them, the 5 wt% TTIP loaded catalyst showed improved performance due to higher thermal stability caused by high W dispersion and the formation of V⁵⁺. In addition, the 5 wt% TTIP-loaded catalyst prepared by a one-step co-precipitation method showed greater V-OH and W-OH dispersion and enhanced interactions in contrast to conventional methods, resulting in higher catalytic activity at lower temperatures. This review article aims to provide an accessible explanation for researchers investigating how to improve the surface properties of TiO2 catalysts using TTIP.

• Korean Journal of Materials Research
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• v.32 no.11
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• pp.496-507
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• 2022

For the selective catalytic reduction of NOx with ammonia (NH₃-SCR), a V₂O₅WO₃/TiO₂ (VW/nTi) catalyst was prepared using V₂O₅ and WO₃ on a nanodispersed TiO₂ (nTi) support by simple impregnation process. The nTi support was dispersed for 0~3 hrs under controlled bead-milling in ethanol. The average particle size (D₅₀) of nTi was reduced from 582 nm to 93 nm depending on the milling time. The NOx activity of these catalysts with maximum temperature shift was influenced by the dispersion of the TiO₂. For the V_0.5W₂/nTi-0h catalyst, prepared with 582 nm nTi-0h before milling, the decomposition temperature with over 94 % NOx conversion had a narrow temperature window, within the range of 365-391 ℃. Similarly, the V_0.5W₂/nTi-2h catalyst, prepared with 107 nm nTi-2h bead-milled for 2hrs, showed a broad temperature window in the range of 358~450 ℃. However, the V_0.5W₂/Ti catalyst (D₅₀ = 2.4 ㎛, aqueous, without milling) was observed at 325-385 ℃. Our results could pave the way for the production of effective NOx decomposition catalysts with a higher temperature range. This approach is also better at facilitating the dispersion on the support material. NH₃-TPD, H₂-TPR, FT-IR, and XPS were used to investigate the role of nTi in the DeNOx catalyst.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.4
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• pp.609-617
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• 2000

This study is aimed at investigating an effect of HCl gas on selective reduction of NOx over a CuHM and $V_2O_5-WO_3/TiO_2$ catalyst. SCR process is the most effective method to remove NOx, but catalyst can be deactivated by the acidic gas such as HCl gas which is also included in flue gas from the incinerator. In dry condition of flue gas, the CuHM catalyst treated by HCl gas has shown higher NO removal activity than the fresh catalyst. The activity of the catalyst can be restored by treating at $500^{\circ}C$. On the contrary. $V_2O_5-WO_3/TiO_2$ catalyst is obviously deactivated by HCl and the deactivation increases in proportion to the concentration of HCl gas. The deactivated catalyst is not restored to it's original activity by heat treatment for regeneration. In wet flue gas stream, the CuHM catalyst has shown lower activity than fresh catalyst and $V_2O_5-WO_3/TiO_2$ catalyst was severely deactivated by HCl treatment. The activity loss of catalysts are mainly due to the decrease of Br$\ddot{o}$nsted acid site on the catalyst surface by $NH_3$ TPD. The change of BET surface area of CuHM catalyst after the reaction isn't observed but $V_2O_5-WO_3/TiO_2$ catalyst is observed. The amount of $Cu^{{+}{+}}$ and $V_2O_5$ is decreased after the reaction. From these results, it is expected that CuHM catalyst should be better than $V_2O_5-WO_3/TiO_2$ catalyst for its application to the incineration of flue gas.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.6-12
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• 2014

In the present work, $WO_3$ and $WO_3-TiO_2$ were prepared by the chemical deposition method. Structural variations, surface state and elemental compositions were investigated for preparation of $WO_3-TiO_2$ sonocatalyst. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM) were employed for characterization of these new photocatalysts. A rhodamine B (Rh.B) solution under ultrasonic irradiation was used to determine the catalytic activity. Excellent catalytic degradation of an Rh.B solution was observed using the $WO_3-TiO_2$ composites under ultrasonic irradiation. Sonocatalytic degradation is a novel technology of treating wastewater. During the ultrasonic treatment of aqueous solutions sonoluminescence, cavitaties and "hot spot" occurred, leading to the dissociation of water molecules. In case of a $WO_3$ coupled system, a semiconductor coupled with two components has a beneficial role in improving charge separation and enhancing $TiO_2$ response to ultrasonic radiations. In case of the addition of $WO_3$ as new matter, the excited electrons from the $WO_3$ particles are quickly transferred to $TiO_2$ particle, as the conduction band of $WO_3$ is 0.74 eV which is -0.5 eV more than that of $TiO_2$. This transfer of charge should enhance the oxidation of the adsorbed organic substrate. The result shows that the photocatalytic performance of $TiO_2$ nanoparticles was improved by loading $WO_3$.

• Applied Chemistry for Engineering
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• v.5 no.3
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• pp.478-500
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• 1994

The preparation of potassium hexatitanate whisker by flux method was investigated. In this study, 8 types synthesis of flux such as $V_2O_5$, $Bi_2O_3$, $B_2O_3$, $Pb_3O_4$, KCl, $K_4P_2O_7$, $K_2WO_4$ and $K_2MoO_4$ were tested to find a suitable flux for the synthesis of potassium hexatitanate whisker. Effects of various reaction variables such as reaction temperature, time, $TiO_2$ mole ratio to $K_2CO_3$, flux mole ratio to the mixture of $K_2CO_3$ and $TiO_2$, and slow-cooling treatment on the crystallization of potassium hexatitanate whisker were investigated. $K_2MoO_4$ and $K_2WO_4$ were better flux than others tested for the synthesis of potassium hexatitanate. In the presence of $K_2MoO_4$ or $K_2WO_4$ flux, the optimum condition for the synthesis of potassium hexatitanate whisker was that reaction temperature of $1000{\sim}1100^{\circ}C$, reaction time of 5 hours, $TiO_2$ mole ratio to $K_2CO_3$ of 6.0, and flux mole ratio to mixture ($K_2O+nTiO_2$) of 4.0. Slow-cooling treatment showed good effect on the growth of long fibrous potassium hexatitanate.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.9
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• pp.970-977
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• 2005

The commercial $V_2O_5-WO_3/TiO_2$ catalysts which had been exposed to the off gas from incinerator for a long time were remanufactured by washing with distilled water and arid solution and reimpregnation with catalytic active components($V_2O_5-WO_3$). The catalytic properties and NOx conversion reactivity of those catalysts were examined by analysis equipment and NOx conversion experiment. Under the experimental condition used in this study, the remanufactured catalysts activated by distilled water ultra sonic cleaning, the catalytic activity was recovered in the range of $66{\sim}93%$ of that of the fresh and the maximum activity was showed when the ultra sonic cleaning time was more than 3 minutes. The remanufactured catalysts by acid solution ultra sonic cleaning, the catalytic activity was recovered in the range of $81{\sim}97%$ of that of the fresh catalyst and the maximum catalytic activity was shooed when the pH of the acid solution was 5. The remanufactured catalysts by reimpregnation with $V_2O_5$ and $WO_3$, the catalytic activity was recovered in the range of $87{\sim}100%$ of that of the fresh catalyst. Maximum catalytic activity was showed when the $V_2O_5$ was reimpregnated more than 1.0 wt %. In this case, the catalytic activity was recovered 97% of that of the fresh catalyst especially at the $150^{\circ}C$ of the experimental temperature.