V2O5/TiO2 oxidation catalysts. II. Texture properties

The texture properties (specific surface area and porosity) of V₂O₅/TiO₂ catalysts obtained from VO(acetylacetonate)₂ have been studied. The presence of sodium leads to a marked decrease in the S_BET values, probably as a consequence of the formation of Na-V bronzes, which lead to a rutilization of the support.

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( ) V₂O₅/TiO₂, - VO()₂. S_BET, , Na-V, .

     

V2O5/TiO2 oxidation catalysts, III. Oxidation of CO on pure and sodium-doped systems

The activity of vanadia/titania catalysts in CO oxidation has been tested and found to be of the same order as that observed for unsupported vanadia; the simultaneous presence of vanadium-sodium compounds cancels the activity, probably because of the elimination of labile V=0 species at surface defects.

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V₂O₅/TiO₂ CO, V₂O₅; - , , V=0 .

     

Lithium-promoted V2O5?TiO2 catalysts for o-xylene oxidation to phthalic anhydride

A V₂O₅–Li₂O–TiO₂ (a) based catalyst for o-xylene oxidation to phthalic anhydride has been synthesized. The activity and selectivity of the specimen obtained are comparable with those of industrial catalysts.     

Vapor phase oxidation of 2-methylpyridine on V2O5/TiO2 (anatase) catalysts

The influence of catalyst composition and reaction parameters on the yield of pyridine-2-carboxaldehyde has been studied for the title process. It has been established that monolayer vanadia on TiO₂ (anatase) is a highly selective catalyst for the partial oxidaton of 2-methylpyridine to pyridine-2-carboxaldehyde.

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-2-. , TiO₂ () 2- -2-.

     

V2O5/TiO2 oxidation catalysts. I. Preparation and characterization by XRD and IR spectroscopy

V₂O₅/TiO₂ systems have been prepared by reacting VO-(acetylacetonate)₂ with differently hydroxylated TiO₂ supports. When the OH population is increased, a larger vanadia content, but well dispersed, is achieved. The presence of sodium ions leads to the formation of Na–V bronze crystallites, decreasing the dispersity of the supported phase.

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V₂O₅/TiO₂ VO()₂ TiO₂, . OH V₂O₅, , , . Na–V, .

     

V2O5/TiO2 oxidation catalysts: Effect of sodium impurities and of the precursor salt on their texture

A series of V₂O₅/TiO₂ systems was prepared from TiO₂ (Degussa, P-25) using two precursor vanadium salts, NH₄VO₃ and VO(acac)₂ (acac, acetylacetonate). For some of the samples, the surface OH population of the starting support was increased by equilibrating a dehydroxylated support with an alkaline solution (pH 8.5) containing NaCl. In some cases the presence of Na in the final materials was observed. The structure and surface properties of the solids obtained were studied with the aid of X-ray diffraction, spectrophotometry (IR and UV-Vis), and nitrogen adsorption. The results indicate that highly dispersed, amorphous V₂O₅ is formed when NH₄VO₃ is used as precursor, and from VO(acac)₂ if the starting support is Na-free. When sodium is present, formation of the Na-V compounds is observed if VO(acac)₂ is used as precursor. In the latter case, a sharp decrease in the specific surface area, probably as a consequence of an increase in the content of rutile in the support, is observed. Both samples obtained from VO(acac)₂ exhibit a microporous structure, more developed in the sample where such Na-V compounds are formed.     

纳米负载型V2O5-WO3/TiO2催化剂碱中毒及再生研究

实验制备了陶瓷颗粒为骨架的纳米级V₂O₅-WO₃/TiO₂(C)催化剂。采用浸渍法模拟碱金属中毒,研究了中毒及再生对催化剂脱硝活性的影响,运用XRD、FT-IR、H₂-TPR、XPS技术表征分析了碱金属对催化剂的失活作用。实验表明,碱金属能使催化剂活性降低,钾的毒性大于钠。FT-IR结果显示,催化剂以Lewis酸作为活性酸位。H₂-TPR、XPS结果表明,钾的加入降低了催化剂的氧化能力,主要影响了催化剂表面的吸附氧。采用单纯的水洗方法并不能提高催化剂活性,而酸洗再生后催化剂在较高反应温度下活性得到较好的恢复。     

Studies on the V2O5?TiO2 system, V. Equilibrium pressures

The oxygen equilibrium pressures from pure V₂O₅ and co-precipitated V₂O₅–TiO₂ system were measured in the range of 200–450 °C. The behavior of the equilibrium pressure with changes of temperature of the samples with and without TiO₂ is attributed to Ti⁴⁺ interaction with the V₂O₅ lattice.

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V₂O₅ - V₂O₅–TiO₂ 200–450°C. TiO₂ Ti⁺⁴ V₂O₅.

     

Role of the V=O double bond in the selective oxidation of benzene on V2O5 and V2O5?MoO3 catalysts

Infrared spectra of both fresh and reductively activated V₂O₅ and V₂O₅–MoO₃ catalysts were recorded and compared with the results of catalytic measurements. The results indicate that the presence of V=O double bonds in the catalytically active mass is not essential for the selective oxidation of benzene to maleic anhydride.

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, V₂O₅ V₂O₅–MoO₃. . , V=O .

     

Catalytic combustion of chlorobenzene over V2O5/TiO2 catalysts prepared by the precipitation-deposition method

Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO₂ was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VO_x/TiO₂catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However, in the VO_x/TiO₂catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared to the impregnation method. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relationship between sulfur dioxide oxidation and selective catalytic NO reduction by ammonia on V2O5?TiO2 catalysts doped with WO3 and Nb2O5

The performance of V₂O₅–TiO₂ catalysts doped by WO₃ and Nb₂O₅ in sulfur dioxide oxidation, and in selective catalytic reduction (SCR) of NO by ammonia has been studied. Addition of tungsten and niobium oxides was found to suppresses sulfur dioxide oxidation thus increasing the catalysts resistance to SO₂ poisoning and their activity in SCR.     

Selective oxidation of methanol on a system of V2O5 O2 catalysts. Influence of operating variables

The partial oxidation of methanol on a system of van-dium-titanium catalysts has been studied. Results demonstrated that the conversio degree of reactant and the selectivity tointermediate oxidation products depend markedly on temperature and residence time.     

Coherent interfaces: Efficient boundary conditions in solid state reactivity. Study in V2O5AlNbO4, V2O5GaNbO4, and V2O5TiNb2O7 systems

The thermodynamically unexpected reduction of V₂O₅ in the presence of the mixed oxides AlNbO₄, GaNbO₄, and TiNb₂O₇ under nitrogen at 630°C is reported and gives a supplementary example of the kind of interfacial reaction observed in the V₂O₅TiO₂ system. It is shown that this phenomenon comes from the establishment of coherent interfaces between the cleavage planes of two crystals belonging to the same crystallo-chemical family. The reduction enables the system to diminish the elastic stress created by the slight interfacial misfit. A thermodynamic and kinetic explanation, based on structural factors, is given.     

浆态反应器中铁／活性炭催化剂上还原研究

众所周知，费托合成（Fischer-Tropsch synthesis,FTS)反应是一个有理论与应用价值的研究课题。数十年来，学者们已发现了铁系，钴系和钌系等具有优良FTS反应性能的催化剂体系，铁／活性炭（Fe/Activated Carbon,AC)催化剂是中国科学院大连化学物理研究所八十年代末开发的一类费托合成催化剂，由于活性炭载体发达的孔结构使得该催化剂上FTS反应产物中汽油，柴油选择性高（烃类碳数小于20）和油收率大（C5^ ,112g/m^3 sysgaa)^[1,2]，具有工业放大前景。本文采用1L浆态床反应器，应用不同的还原方法（原位高压还原和反应器外还原）和XRD物相表征手段，了铁／活性炭催化剂在浆态床中的还原与反应问题，得到了一些有用的信息。     

Effect of the extent of reduction of V2O5 on the adsorption of propylene and the oxidative dehydrogenation of propane to give propylene on V2O5 and V2O5/TiO2-SiO2

An increase in the propylene output in the oxidative dehydration of propane on V₂O₅/TiO₂-SiO₂ was observed after prior reduction of V₂O₅ in the reaction mixture to V₂O₄, which reduces the destructive chemisorption of propylene. A low titanium dioxide content in TiO₂-SiO₂ hinders the deep reduction of V₂O₅ to V₂O₃, which reduces the conversion of propane. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 373–378, November–December, 2007.     

Acidic properties of V2O5-WO3/ZrO2 catalysts

The adsorption of pyridine on V₂O₅−WO₃/ZrO₂ has been studied by FTIR. In V₂O₅/ZrO₂ (2 wt.%), the number of both Br?nsted and Lewis acidic sites increased with the addition of WO₃, while in V₂O₅/ZrO₂ (5 wt.%), Br?nsted sites increased and Lewis sites did not change.     

Determination of the exposed surface area of V2O5 on a V2O5/Al2O3 catalyst

NH₃, NO and CO₂ were tested as adsorbates for selective determination of exposed surface area of V₂O₅ on a V₂O₅/Al₂O₃ catalyst. The most promising appears to be CO₂ which interacts with the support Al₂O₃ only.

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NH₃, NO CO₂ V₂O₅ V₂O₅/Al₂O₃. CO₂, Al₂O₃.

     

添加Cl离子对V_2O_5-WO_3/TiO_2催化剂低温NO转化率的影响

考察添加不同含量Cl离子对浸渍法制备的Cl-V_2O_5-WO_3/TiO_2催化剂低温NO转化率的影响。随着Cl离子质量添加量从0增加到2.5%,Cl-V_2O_5-WO_3/TiO_2催化剂NO转化率先升高后降低,结合在含有SO_2和H2O的SCR实验结果,确定1.5%Cl-V_2O_5-WO_3/TiO_2为性能最优催化剂。在反应温度为149-362℃,NO转化率大于95%;在145-385℃,NO转化率大于90%。采用XRF、BET、XRD、TG、FT-IR和H2-TPR等方法表征了催化剂的物理化学性能和结构。结果表明,在反应气氛中加入SO_2和H2O后,催化剂比表面积和孔容均减小,副反应产物含有NH+4和SO_2-4。适量Cl离子可以抑制硫物种沉积,减少副反应产物生成,增强催化剂抗中毒能力。     

平板式V_2O_5-MoO_3/TiO_2型SCR催化剂的中低温脱硝和抗中毒性能研究

针对中低温锅炉烟气脱硝技术需求的特点,采用等体积浸渍法,以V_2O_5为活性组分、MoO_3为助剂,制备了高钒高钼含量的V_2O_5-MoO_3/TiO_2型粉末和平板式SCR脱硝催化剂,考察了活性组分和助剂含量对催化剂活性以及抗SO_2和H_2O中毒性能的影响,对反应前后的催化剂进行了微观表征,并针对最优催化剂研究了其在不同烟气工况下催化剂的脱硝性能。结果表明,提升V_2O_5负载量可以有效提高催化剂的脱硝活性;MoO_3助剂的添加也可以提高催化剂的脱硝活性。XPS、XRF、FTIR等表征结果表明,MoO_3的含量会影响催化剂中V~(4+)/V~(5+)的比值,其相对含量的增加有利于催化剂中非化学计量钒物种的形成以及化学吸附氧比例的增加,钼与钒物种间的交互作用是抑制SO_2和H_2O对催化剂的毒化作用的关键。3V_2O_5-10MoO_3/TiO_2平板式催化剂在温度为200℃、空速为3 500 h~(-1)含SO_2和H_2O烟气条件下,经30 d连续反应,脱硝效率稳定维持在82%左右,该催化剂在中低温下具有优异的抗SO_2和H_2O中毒性能以及稳定性。     

V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。