Improving the denitration performance and K-poisoning resistance of the V2O5-WO3/TiO2 catalyst by Ce4+ and Zr4+ co-doping

A series of V₂O₅-WO₃/TiO₂-ZrO₂, V₂O₅-WO₃/TiO₂-CeO₂, and V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalysts were synthesized to improve the selective catalytic reduction (SCR) performance and the K-poisoning resistance of a V₂O₅-WO₃/TiO₂ catalyst. The physicochemical properties were investigated by using XRD, BET, NH₃-TPD, H₂-TPR, and XPS, and the catalytic performance and K-poisoning resistance were evaluated via a NH₃-SCR model reaction. Ce⁴⁺ and Zr⁴⁺ co-doping were found to enhance the conversion of NO_x, and exhibit the best K-poisoning resistance owing to the largest BET-specific surface area, pore volume, and total acid site concentration, as well as the minimal effects on the surface acidity and redox ability from K poisoning. The V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalyst also presents outstanding H₂O + SO₂ tolerance. Finally, the in situ DRIFTS reveals that the NH₃-SCR reaction over the V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalyst follows an L-H mechanism, and that K poisoning does not change the reaction mechanism.     

Selective oxidation of hydrogen sulfide to ammonium thiosulfate and sulfur over vanadium-bismuth oxide catalysts

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over vanadium-bismuth mixed oxide catalysts. The investigation was focused on understanding the complex reaction steps and the roles of each metal oxide. Therefore, supported V₂O₅/TiO₂, V-Bi-O/TiO₂ catalysts and a mechanical mixture of V₂O₅ + Bi₂O₃ were tested in the reaction. Ammonia reacted either with H₂S or SO₂, produced from the oxidation of H₂S. Water vapor promoted the reaction of ammonia and SO₂. Strong synergistic phenomena in catalytic activity were observed for the mechanically mixed catalyst of V₂O₅ and Bi₂O₃. V-Bi-O/TiO₂ catalyst showed very high H₂S conversion without any considerable emission of SO₂. Temperature-programmed studies (TPR and TPO), XRD and Raman analyses revealed that the high catalytic performance of V-BiO/TiO₂ catalyst originated from the high redox capacity of the bismuth vanadate phase.     

ACo_2O_4/HZSM-5催化剂上N_2O的直接分解

分别采用柠檬酸络合燃烧法和低温络合浸渍法制备尖晶石型复合金属氧化物催化剂ACo2O4(A=Mg,Ni,Zn)和分子筛负载尖晶石型复合金属氧化物催化剂ACo2O4/HZSM-5(A=Mg,Fe,Ni,Cu,Zn,Zr,La).采用X射线衍射(XRD)、氨程序升温脱附(NH3-TPD)、扫描电子显微镜(SEM)和X射线能谱(EDS)等手段对催化剂进行表征,并在固定床微型反应器中评价其催化分解N2O活性.实验结果表明,A位离子种类影响ACo2O4/HZSM-5催化剂活性,以Ni、Fe、Zr或La为A位离子时,催化剂的活性较好,N2O分解温度低.ACo2O4/HZSM-5催化剂的活性高于ACo2O4尖晶石型复合氧化物,一方面是ACo2O4在分子筛HZSM-5载体上高度分散,使其以超细颗粒形态存在,另一方面ACo2O4/HZSM-5催化剂具有适宜的酸性,可提高催化剂的活性.     

焙烧温度对MnOx-CeO2-WO3-ZrO2催化剂上NH3选择性还原NO的影响

采用共沉淀法制备了MnO_x-CeO₂-WO₃-ZrO₂催化剂,考察了催化剂焙烧温度对O₂和H₂O存在下NH₃选择性催化还原（NH₃-SCR） NO的影响,并利用低温N₂吸附、X射线衍射（XRD）、透射电镜（TEM）、X射线光电子能谱（XPS）、NH₃程序升温脱附（NH₃-TPD）和CO脉冲反应对催化剂进行了表征. 结果表明在NH₃-SCR反应中,催化剂的低温活性随焙烧温度的提高而降低,这是由于催化剂表面化学吸附氧和酸性位减少引起的;催化剂的高温活性随焙烧温度的提高先增加后减小,这与催化剂表面最易释放氧数量的变化趋势相反. 700 ℃焙烧的催化剂具有良好的低温活性和最宽的反应温度窗口,在空速为90000 h^-1的条件下,该催化剂的起燃温度（50% NO转化率）为189 ℃,且反应温度在218-431 ℃范围内,NO转化率可达到80%-100%.     

NH3选择性还原NOx技术在重型柴油车尾气净化中的应用

基于实验室对柴油车用V₂O₅-WO₃/TiO₂催化剂配方以及涂覆成型技术的大量研究,设计了一条产量为6000只/月的NH₃选择性催化还原NO_x （NH₃-SCR）催化剂中试生产线,并对生产的催化剂产品进行了发动机台架测试. 结果表明,实验室制备的V₂O₅-WO₃/TiO₂粉体催化剂和生产线产品,在空速为50000 h^-1和200-450 ℃条件下NO_x转化率均可达80%以上;采用大尺寸堇青石载体涂覆后制备的V₂O₅-WO₃/TiO₂整体催化剂经实验室小样测试,在空速为10000-30000 h^-1和250-450 ℃条件下NO_x转化率也为80%以上. 发动机台架测试结果表明,该催化剂产品可使重型柴油机NO_x排放达到国IV标准中欧洲稳态循环（ESC）和欧洲瞬态循环（ETC）排放限值的要求. 该生产线经适当调整后也可用于生产非钒基NH₃-SCR整体催化剂,以满足未来钒基NH₃-SCR催化剂更新换代的需求.     

Vapour phase oxidation of 4-methylanisole to anisaldehyde over V2O5 /MgO-Al2O3 catalysts

The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over different V₂O₅ /MgO-Al₂O₃ catalysts at 673 K and normal atmospheric pressure. Among various catalysts investigated the 16 wt% V₂O₅ /MgO-Al₂O₃ catalyst provided good conversion and product selectivity. The MgO-Al₂O₃ mixed oxide was obtained by a co-precipitation method and V₂O₅ was impregnated from ammonium metavanadate. The MgO-Al₂O₃ support and various V₂O₅ /MgO-Al₂O₃ catalysts were characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, ammonia and carbon dioxide chemisorption methods. The characterization results suggest that vanadia does not form layer structures on the support surface, instead interacts very strongly with the support, in particular with MgO, and forms amorphous compounds. The NH₃ and CO₂ uptake results provide an interesting information on the acid-base characteristics of these catalysts and correlate with their catalytic properties.     

Catalytic Activity for Ammonia Synthesis of Iron Supported Catalysts Prepared from an Acid-modified λ-Al2O3 Method

Iron supported catalysts were prepared by impregnation of several acid-modified λ-Al₂O₃ samples with a K₄[Fe(CN)₆] aqueous solution. A concentration range between 0–20 mmole H⁺ added · g^?1λ-Al₂O₃ was used. The quantitative determination of the acid site and iron contents of the modified λ-Al₂O₃ samples was followed by UV spectrometry and F.A.A.S., respectively. An increasing final iron content of the catalysts with increasing acid site content of the support is observed. The catalytic activity for ammonia synthesis was followed at atmospheric pressure and 593 K (N₂/H₂ = 1/3). An increasing ammonia production per gram of catalyst with increasing protonation of the support was observed in the range 0–8 mmole H⁺ added · g^?1λ-Al₂O₃. The catalytic activity of iron supported catalysts prepared by this method was higher (up to twofold) that of a catalyst prepared by the incipient wetness method.     

Kinetic Peculiarities in the Low-Temperature Oxidation of H2S on Vanadium Catalysts

H₂S oxidation by oxygen on catalysts V₂O₅/Al₂O₃, V₂O₅/TiO₂, V₂O₅/Al₂O₃/TiO₂ was studied at temperatures below the sulfur dew point. High activity and the oscillation character of the oxidation were demonstrated by catalysts with low contents of V₂O₅ (3–5 wt.%). The increase in the V₂O₅ concentration to 10–20 wt.% results in the reduction of the catalytic activity and oscillation ability. On a pure V₂O₅ catalyst, the oscillations were not detected. The difference between the catalysts with the high and low concentrations of V₂O₅ is explained in terms of the structures of the V⁵⁺ species formed in the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

High catalytic activity of V2O5-ZrO2 modified with H2SO4 for propene partial oxidation

For V₂O₅–ZrO₂ catalysts, up to 10 mol% the crystalline structure of V₂O₅ was not observed, indicating a good dispersity the surface of ZrO₂. V₂O₅–ZrO₂ catalyst modified with H₂SO₄ exhibited much on higher catalytic activity for propene partial oxidation than unmodified catalysts due to the increased acidity and acid strength of modified catalyst.     

NO-NH3-O2 reaction catalyzed by V2O5/AC at low temperatures

The effects of SO₂, V₂O₅ loading and reaction temperature on the activity of activated carbon supported vanadium oxide catalyst have been studied for the reduction of NO with NH₃ at low temperatures (150—250°C). It is found that SO₂ significantly promotes the catalyst activity. Both V₂O₅ loading and reaction temperature are vital to the promoting effect of SO₂. The catalysts with V₂O₅ loadings of 1—5 weight percent have a positive effect on the promotion of SO₂, while the catalysts with V₂O₅ loadings of above 7 weight percent have not such an effect or show a negative effect. At lower temperatures (<180°C) SO₂ poisons the catalyst but at higher temperatures promotes it. The reason of the SO₂ promotion was also discussed; it may results from the formation of SO₄ ^2? on the catalyst surface, which increases the surface acidity and hence the catalytic activity.     

宽工作温度烟气脱硝催化剂制备及反应机理研究

以溶胶-凝胶法制备介孔TiO₂载体,采用分步浸渍法制备了V₂O₅-WO₃/TiO₂催化剂,借助BET、NH₃-TPD、H₂-TPR、SEM、活性评价、In-situ FT-IR等手段,考察了催化剂的结构、酸性、还原性、脱硝活性及反应机理等。介孔TiO₂载体比表面积为158.6 m²/g,制成催化剂后比表面积略有降低,约为136.7 m²/g。针对模拟烟气在φ_NH3/φ_NO=0.8的条件下测试催化剂的脱硝活性温度窗口为250~400 ℃,脱硝转化率达到80%。NH₃-TPD和H₂-TPR表征结果表明,催化剂在活性温度范围内具有典型的表面酸性位,载体TiO₂与V₂O₅之间存在的相互作用使得V₂O₅还原温度降低。利用In-situ FT-IR研究NH₃和NO在V₂O₅-WO₃/TiO₂催化剂表面吸附和氧化的反应过程发现,NH₃可同时吸附在L酸位和B酸位,NH₃在活性位上氧化脱氢形成NH₂物种是SCR脱硝反应的控制步骤。研究NO+O₂+NH₃反应时发现,吸附NH₃的催化剂引入NO和O₂后,共价吸附的NH₃首先消失。选择性催化还原反应发生在吸附态NH₃和气态或弱吸附态的NO之间,该反应遵从Eley-Rideal反应机理。     

不同RuO2含量对RuO2-Fe2O3催化剂氨选择性催化氧化性能的影响

采用溶胶-凝胶法（sol-gel）制备了一系列具有不同RuO₂含量的RuO₂-Fe₂O₃催化剂,并将其应用于氨选择性催化氧化（NH₃-SCO）研究中。结果表明,所有RuO₂-Fe₂O₃催化剂都表现出较好的低温活性,且RuO₂含量对催化剂的NH₃催化氧化活性影响显著。此外,利用BET、XRD、H₂-TPR和DRIFTS等表征手段研究了催化剂的物理化学性质和催化活性之间的关系。结果表明,RuO₂的加入增大了催化剂的比表面积。RuO₂与Fe₂O₃之间存在的协同效应提高了催化剂的氧化还原能力,从而提高了催化剂的氨氧化活性。同时,RuO₂含量对催化剂表面酸性影响很大,且催化剂表面主要存在Lewis酸性位点。     

三核钨簇合物-V2O5催化剂对苯乙烯氧化反应的催化

本文研究了三核钨簇合物［W₃O₂(CH₃CO₂)₆(H₂O)₃］Br₃·2H₂O与一些物质组成的二元催化剂对苯乙烯氧化反应的催化作用,结果表明：钨簇合物-V₂O₅催化剂对苯乙烯氧化反应的催化效果特别显著,而且在反应前后其重量、结构及催化活性基本不变,可以多次回收重复使用。对影响钨簇合物-V₂O₅催化剂催化性能的几个因素进行了讨论,测定了催化剂及其吸附氧气的红外光谱,说明钨簇合物及V₂O₅可以与O₂形成分子氧配合物及超氧(O^-₂)配合物。     

Investigations on the selectivity of catalytic no reduction by ammonia

The activity and selectivity of V₂O₅/γ-Al₂O₃ catalyst were studied in the catalytic reduction of nitrogen oxide by ammonia. The activity of the catalyst monotonically increases as a function of temperature, however, its selectivity decreases. The DeNOx reaction of nitrogen oxides with ammonia can be described well by a mathematical model, which considers selectivity-decreasing side reactions as well in a wide temperature range (220–420°C).     

The Effect of MoO3 Addition to V2O5/Al2O3 Catalysts for the Selective Catalytic Reduction of NO by NH3

The effect of MoO₃ addition to alumina supported vanadia catalysts on the catalytic activity for the selective catlaytic reduction of NO is investigated. Upon the addition of MoO₃, catalytic activity is enhanced and the particle size of V₂O₅ which is shown by the results of XRD and Raman spectroscopy is decreased. The MoO₃-V₂O₅/Al₂O₃ catalyst also exhibits more resistance to SO₂ deactivation than V₂O₅/Al₂O₃ does.     

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.     

NO-NH3-O2 reaction catalyzed by V2O5/AC at low temperatures —Effects of SO2, V2O5 loading and reaction temperature

The effects of SO₂, V₂O₅ loading and reaction temperature on the activity of activated carbon supported vanadium oxide catalyst have been studied for the reduction of NO with NH₃ at low temperatures (150—250°C). It is found that SO₂ significantly promotes the catalyst activity. Both V₂O₅ loading and reaction temperature are vital to the promoting effect of SO₂. The catalysts with V₂O₅ loadings of 1—5 weight percent have a positive effect on the promotion of SO₂, while the catalysts with V₂O₅ loadings of above 7 weight percent have not such an effect or show a negative effect. At lower temperatures (<180°C) SO₂ poisons the catalyst but at higher temperatures promotes it. The reason of the SO₂ promotion was also discussed; it may results from the formation of SO₄ ²⁻ on the catalyst surface, which increases the surface acidity and hence the catalytic activity.     

The Role of Lewis and Brønsted Acid Sites in NO Reduction with NH<Subscript>3</Subscript> on Sulfur Modified TiO<Subscript>2</Subscript>-Supported V<Subscript>2</Subscript>O<Subscript>5</Subscript> Catalyst

V₂O₅/S-doped TiO₂ was prepared by the sol-gel and impregnation methods. The adsorption of NO, NH₃, and O₂ over the catalyst was studied by in situ DRIFTS spectroscopy to elucidate the reaction mechanism of the low-temperature selective catalytic reduction of NO with NH₃. Exposing the catalyst to O₂ and NO, three types of nitrates species appeared on the surface. The introduction of S to TiO₂ could generate large amounts of acid sites for ammonia adsorption on the catalyst, which was believed to be an important role in the SCR reaction and hereby improved the catalytic activity. The results indicated two possible SCR reaction pathways for catalyst. One was that NO was absorbed to form nitrite species, which could react with NH₃ on Lewis acid sites, producing N₂ and H₂O. Another way was that NH₃ was adsorbed, then reacted with gas phase NO (E–R) and nitrite intermediates on the surface (L–H).     

V2O5/C catalyst for liquid phase oxidation of glyoxal to glyoxylic acid

A study of the catalytic activity of V₂O₅/C catalyst for the oxygen oxidation of glyoxal has been made, showing that glyoxylic acid can be formed without control of pH value and there is little oxalic acid from the excessive oxidation of glyoxylic acid. The studies of XRD and TEM have shown that V₂O₅ diffraction peaks gradually strengthen with the increase of the content of V₂O₅. With the content of 3% V₂O₅ and the calcination temperature of 573 K, V₂O₅/C catalyst displayed the best activity and selectivity. The conversion of glyoxal and the selectivity of glyoxylic acid reached 18.76% and 77.70% after 5 h, respectively. Moreover, V₂O₅/C catalyst showed small deactivation after recycling three times, which indicates that V₂O₅/C has a higher stability than noble metal catalysts in the reaction medium. Supported by the Technology Research and Development Project for University of Shanxi Province of China (Grant No. 20051272)     

钒氧化物催化CO2氧化异丁烷脱氢的研究

采用溶胶-凝胶法制备了一系列钒氧化物催化剂,并用于CO₂氧化异丁烷脱氢反应. 采用X射线衍射、低温N₂吸附-脱附、O₂程序升温氧化、程序升温表面反应和原位傅里叶变换红外光谱等方法研究了催化剂的性质. 反应结果表明,尽管所有钒氧化物催化剂的丁烯选择性都大于85%,但随着催化剂组成和制备方法的改变,催化活性和稳定性差异显著. 其中,12 wt% V₂O₅/Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的催化活性最高,而6 wt% V₂O₅-Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的稳定性最佳. 关联分析催化反应结果与催化剂表征表明,钒氧化物的催化活性取决于VO_x物种的结晶度和分散度,而催化剂表面所积重质焦炭的特性是决定催化剂稳定性的关键. 非稳态反应和原位光谱结果确认,CO₂氧化异丁烷脱氢遵循Mars-van Krevelen氧化还原机理.