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1.
Min Kang Jinsoon Choi Yong Tae Kim Eun Duck Park Chee Burm Shin Dong Jin Suh Jae Eui Yie 《Korean Journal of Chemical Engineering》2009,26(3):884-889
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. 相似文献
2.
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. 相似文献
3.
Tungsten oxide-titania catalysts were prepared by drying powdered Ti(OH)4 with ammonium metatungstate aqueous solution, followed
by calcining in air at high temperature. Characterization of prepared catalysts was performed by using FTIR, Raman, XPS, XRD,
and DSC and by measuring surface area. Upon the addition of tungsten oxide to titania up to 20 wt%, the specific surface area
and acidity of catalysts increased in proportion to the tungsten oxide content due to the interaction between tungsten oxide
and titania. Since the TiO2 stabilizes the tungsten oxide species, for the samples equal to or less than 20 wt%, tungsten oxide was well dispersed on
the surface of titania, but for the samples containing 25 wt% or above 25 wt%, the triclinic phase of WO3 was observed at calcination temperature above 400 °C. The catalytic activities for 2-propanol dehydration and cumene dealkylation
were correlated with the acidity of catalysts measured by ammonia chemisorption method.
This paper was presented at the 8th APCChE (Asia Pacific Confederation of Chemical Engineering) Congress held at Seoul between
August 16 and 19, 1999. 相似文献
4.
Burkardt A. Weisweiler W. van den Tillaart J.A.A. Schäfer-Sindlinger A. Lox E.S. 《Topics in Catalysis》2001,16(1-4):369-375
In this paper the effect of the vanadium oxide loading on the surface vanadia structure and the activity as well as selectivity in the catalytic reduction of NO with NH3 was studied for a V2O5/TiO2 model system. A series of TiO2 (WO
x
stabilized anatase) supported vanadia catalysts with varying loadings were characterized by laser Raman spectroscopy, 51V MAS-NMR, V K XANES. To determine the acidic properties, DRIFTS measurements were done with pyridine adsorbed on the samples. The measurements indicate that with increasing active phase loading square pyramidal coordinated surface vanadia species are replaced by an amorphous highly dispersed vanadium oxide phase with a coordination like V2O5. In addition, the ratio of Brønsted to Lewis acid sites is shifted from a comparatively low to an equal level at high loadings. This structural change is accompanied by a clearly improved catalytic activity and selectivity. 相似文献
5.
CO2 reforming of CH4 was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature
combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%)
was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al2O3, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al2O3 model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the
most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts.
BET surface area, XRD, EA, TGA and TPO were performed for surface characterization.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
6.
M.D. Soriano J. Jimnez-Jimnez P. Concepcin A. Jimnez-Lpez E. Rodríguez-Castelln J.M. Lpez Nieto 《Applied catalysis. B, Environmental》2009,92(3-4):271-279
Vanadium oxide supported on mesoporous zirconium phosphate catalysts has been synthesized, characterized and tested in the selective oxidation of H2S to sulfur. The nature of the vanadium species depends on the V-loading of catalyst. Catalysts with a V-content lower than 4wt% present both isolated vanadium species and V2O5 crystallites. However, V2O5 crystallites have been mainly observed in catalysts with higher V-content, although the presence of isolated V-species on the surface of the metal oxide support cannot be completely ruled out. The catalytic behaviour also depends on V-loading of catalysts. Thus, while the catalytic activity of catalysts can be related to the number of V-sites, the catalyst decay is clearly observed in samples with low V-loading. The characterization of catalysts after the catalytic tests indicates the presence of sulfur on the catalyst, which is favoured on catalysts with low V-loading. However, a clear transformation of V2O5 to V4O9 can be proposed according to XRD and Raman results of used catalysts with high V-loading. The importance of V5+–O–V4+ pairs in activity and selectivity is also discussed. 相似文献
7.
Parisa Taghavinezhad Mohammad Haghighi Reza Alizadeh 《Korean Journal of Chemical Engineering》2017,34(5):1346-1357
The ZrO2 was treated by various molarities of H2SO4 solution (0, 0.5, 1 and 2) then mixed by MgO and impregnated with 5 wt% of V2O5. The synthesized catalysts were characterized by XRD, FESEM, PSD, EDX, BET and FTIR techniques. According to the results obtained by characterization studies, the modification of MgO-ZrO2 support by various molarities of H2SO4 solution had a great impact on the crystallinity, morphology and functional groups of prepared nanocatalysts. On the other hand, the catalytic activity of synthesized nanocatalysts in the oxidative dehydrogenation of ethane to ethylene is affected by the sulfur content on the support. The crystalline structures of MgO and ZrO2 were confirmed by XRD analysis. The crystallinity of tetragonal ZrO2 was decreased by increasing H2SO4 molarity used in ZrO2 (Sx) synthesising. The highest catalytic performance and ethylene productivity (C2H4 yield of 48% and ethane conversion of 79% at 700 °C) were obtained on the V2O5/MgO-ZrO2 (S1) nanocatalyst. This could be related to the superior acid-base property, smaller particles, better dispersion of active phase and uniform morphology of V2O5/MgO-ZrO2 (S1). 相似文献
8.
Jiangyin Lu Zhen Zhao Chunming Xu Aijun Duan Xiaoning Wang Pu Zhang 《Journal of Porous Materials》2008,15(2):213-220
Several systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with different ratios of SiO2/Al2O3 (25,38,50,80, and 150) were prepared and they were characterized by means of X-ray diffraction (XRD), UV–Vis, NH3-TPD and BET techniques. The results indicated that, compared with uncalcined HZSM-5 zeolites, the total acid amounts, acidic
site density and acidic strength of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts obviously decreased, while those of weak
acid amounts obviously enhanced with the decrease of SiO2/Al2O3 molar ratio. When the ratio of SiO2/Al2O3 is less than 50, the three systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with same ratio of SiO2/Al2O3 gave similar and high isobutane conversions. However, when the ratio of SiO2/Al2O3 was equal to or greater than 80, these three systems of catalysts possessed different altering tendencies of isobutane conversions,
thus their isobutene conversions were different. High yields of light olefins were obtained over the FeHZSM-5 and CrHZSM-5
zeolite catalysts with high ratio of SiO2/Al2O3 (≥80). The ratio of SiO2/Al2O3 has large effects on the surface area, and acidic characteristics of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolites catalysts, and
thus further affect their catalytic performances for isobutane cracking. That is the nature of SiO2/Al2O3 ratio effect on the catalytic performances. 相似文献
9.
A lithium insertion material having the composition LiNi0.3Co0.3Mn0.3Fe0.1O2 was synthesized by simple sol-gel method. The structural and electrochemical properties of the sample were investigated using X-ray diffraction spectroscopy (XRD) and the galvanostatic charge-discharge method. Rietvelt analysis of the XRD patterns shows that this compound can be classified as α-NaFeO2 structure type (R3m; a=2.8689(5) Å and 14.296(5) Å in hexagonal setting). Rietvelt fitting shows that a relatively large amount of Fe and Ni ion occupy the Li layer (3a site) and a relatively large amount of Li occupies the transition metal layer (3b site). LiNi0.3Co0.3Mn0.3Fe0.1O2 when cycled in the voltage range 4.3–2.8 V gives an initial discharge capacity of 120 mAh/g, and stable cycling performance. LiNi0.3Co0.3Mn0.3Fe0.1O2 in the voltage range 2.8–4.5 V has a discharge capacity of 140 mAh/g, and exhibits a significant loss in capacity during cycling. Ex-situ XRD measurements were performed to study the structure changes of the samples after cycling between 2.8–4.3 V and 2.8–4.5 V for 20 cycles. The XRD and electrochemical results suggested that cation mixing in this layered structure oxide could be causing degradation of the cell capacity. 相似文献
10.
Jong Min Won Min Su Kim Sung Chang Hong 《Korean Journal of Chemical Engineering》2018,35(12):2365-2378
We investigated the correlation between vanadium surface density and VOx structure species in the selective catalytic reduction of NOx by NH3. The properties of the VOx/TiO2 catalysts were investigated using physicochemical measurements, including BET, XRD, Raman spectroscopy, FE-TEM, UV-visible DRS, NH3-TPD, H2-TPR, O2-On/Off. Catalysts were prepared using the wet impregnation method by supporting 1.0-3.0 wt% vanadium on TiO2 thermally treated at various calcination temperatures. Through the above analysis, we found that VOx surface density was 3.4 VOx/nm2, and the optimal V loading amounts were 2.0-2.5 wt% and the specific surface area was 65-80m2/g. In addition, it was confirmed that the optimal VOx surface density and formation of vanadium structure species correlated with the reaction activity depending on the V loading amounts and the specific surface area size. 相似文献
11.
The catalytic decomposition of CFC-12 (CCl2F2) in the presence of water vapor was investigated over a series of solid acids WO3/ZrO2. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO3/ZrO2 catalysts. CFC-12 decomposition activities of WO3/ZrO2 catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO3/ZrO2 catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction. 相似文献
12.
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. 相似文献
13.
J.D.A. Bellido 《Fuel》2009,88(9):1673-1034
ZrO2, γ-Al2O3 and ZrO2/γ-Al2O3-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H2, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO2/γ-Al2O3 matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO2. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO2. 相似文献
14.
Various vanadium oxide nanostructures are currently drawn interest for the potential applications of Li batteries, super capacitors,
and electrochromic display devices. In this article, the synthesis of V2O5 nanotubes by hydrothermal method using 1-hexadecylamine (HDA) and PEO as a template and surface reactant were reported, respectively.
The structural properties and electrochemical performances of these nanostructures were investigated for the application of
Li batteries. Structure and morphology of the samples were investigated by XRD, FTIR, SEM, and TEM analysis. The battery with
V2O5 nanotubes electrode showed initial specific capacity of 185 mAhg−1, whereas the PEO surfactant V2O5 nanotubes exhibited 142 mAhg−1. It was found that PEO surfactant V2O5 nanotubes material showed less specific capacity at initial stages but better stability was exhibited at higher cycle numbers
when compared to that of V2O5 nanotubes. The cyclic performance of the PEO surfactant material seems to be improved with the role of polymeric component
due to its surface reaction with V2O5 nanotubes during the hydrothermal process. 相似文献
15.
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. 相似文献
16.
A series of WO3-promoted Cr2O3-based catalysts were prepared and tested for the simultaneous dehydrogenation and isomerization of n-butane to isobutene. It is found that a Cr2O3/WO3–ZrO2 system is an effective catalyst for this reaction; however, the catalytic behavior is dependent on Cr2O3 and WO3 contents, space velocity and temperature. 10 wt% Cr2O3/20 wt% WO3–ZrO2 can give high initial conversion and isobutene selectivity, but it deactivates rapidly due to the variation of surface properties
and pore structure caused by carbon deposition.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Dal-Rae Cho Sang-Yun Kim Dae-Won Park Pierre Hubert Mutin 《Korean Journal of Chemical Engineering》2009,26(2):377-381
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. 相似文献
18.
How oxide carriers affect the reactivity of V2O5 catalysts in the oxidative dehydrogenation of propane 总被引:1,自引:0,他引:1
The catalytic pattern of several oxide carriers (MgO, Al2O3, ZrO2, TiO2, SiO2, HY zeolite) and supported V2O5 (4.7–5.3 wt%) catalysts in the oxidative dehydrogenation of propane to propylene (PODH) has been comparatively investigated.
The fundamental role of the oxide support on both reducibility and reactivity of vanadia catalysts has been assessed. A direct
relationship between the specific surface activity of oxide carriers and that of vanadia catalysts is discussed. The inverse
relationship between the specific activity and the onset temperature of reduction marks the prevailing redox behaviour of
V2O5 catalysts in the PODH reaction.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
《Catalysis communications》2002,3(1):7-13
The influence of molybdenum oxide on the dispersion of vanadium oxide supported on niobia was investigated. A series of MoO3–V2O5/Nb2O5 catalysts with varying MoO3 content ranging from 1% to 5% (w/w) with fixed V2O5 content were prepared by impregnation of previously prepared 5 wt% V2O5/Nb2O5 with requisite amounts of ammonium molybdate solution. X-ray diffraction patterns indicate the presence of β-(Nb,V)2O5 phase with the addition of MoO3 up to a loading of 3 wt%. Temperature-programmed reduction (TPR) results suggest that the reducibility is decreasing with MoO3 loading. The results of temperature programmed desorption (TPD) of ammonia suggest that the acidity of the catalysts increased with the addition of MoO3. The catalytic properties of the catalysts in the ammoxidation of 3-picoline were correlated with the characterization data. 相似文献
20.
Takashi Ohno Eiji Tanaka Fumikazu Hatayama Yoshio Toda Hisashi Miyata 《Catalysis Letters》2001,77(4):183-187
The effect of Pt addition to a V2O5/ZrO2 catalyst on the reduction of NO by C3H6 has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C3H6 reaction through a reduction–oxidation cycle between its oxide and cluster form. 相似文献