Two-stage catalytic system of Sn/Al2O3 and Pt/Al2O3for NO reduction by propene in lean conditions

The Pt/Al₂O₃, Sn/Al₂O₃catalysts were prepared by the single sol-gel method. The two-stage Sn/Al₂O₃and Pt/Al₂O₃catalyst in series for NO reduction with propene were investigated. The coexistance of water vapor enhanced the activity at medium temperature of 300-400^oC, and the NO conversion was above 50% at 225 to 500^oC even in the presence of water vapor and SO₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Catalytic reduction of nitrogen monoxide with propene over Nb/TiO2 mixed mechanically with Mn2O3

Selective catalytic reduction of nitrogen monoxide (NO) over a catalyst of mechanically mixed Nb/TiO₂ and Mn₂O₃ (Mn₂O₃+Nb/TiO₂) in an oxidizing atmosphere with propene (C₃H₆) was studied. The Mn₂O₃+Nb/TiO₂ catalyst showed high activity for the reduction of NO to N₂. The maximum conversion of NO to N₂ was observed at 200∼300°C, with about 80% reduction of NO to N₂. Mn₂O₃ enhanced the formation of NO₂ from NO and the activation of propene to react with NO₂ for reduction to N₂.     

The direct decomposition of NO over the La2CuO4 nanofiber catalyst

The NO catalytic direct decomposition was studied over La₂CuO₄ nanofibers, which were synthesized by using single walled carbon nanotubes (CNTs) as templates under hydrothermal condition. The composition and BET specific surface area of the La₂CuO₄ nanofiber were La₂Cu_0.88²⁺Cu_0.12⁺O_3.94 and 105.0 m²/g, respectively. 100% NO conversion (turnover frequency-(TOF): 0.17 g_NO/g_catalyst s) was obtained over such nanofiber catalyst at temperatures above 300 °C with the products being only N₂ and O₂. In 60 h on stream testing, either at 300 °C or at 800 °C, the nanofiber catalyst still showed high NO conversion efficiency (at 300 °C, 98%, TOF: 0.17 g_NO/g_catalyst s; at 800 °C, 96%, TOF: 0.16 g_NO/g_catalyst s). The O₂ and NO temperature programmed desorption (TPD) results indicated that the desorption of oxygen over the nanofibers occurred at 80-190 and 720-900 °C; while NO desorption happened at temperatures of 210-330 °C. NO and O₂ did not competitively adsorb on the nanofiber catalyst. For outstanding the advantage of the nanostate catalyst, the usual La₂CuO₄ bulk powder was also prepared and studied for comparison.     

Cu/La2O3-ZrO2-Al2O3催化剂的制备及其对NO选择性还原的催化性能

采用将Al(NO3)3、La(NO3)3和ZrOCl2的混合液滴入沉淀剂(NH4)2CO3中的共沉淀法制备La2O3-ZrO2-Al2O3复合载体,然后负载上Cu2+,制成Cu/La2O3-ZrO2-Al2O3催化剂。考察了该催化剂在富氧条件下对C3H6选择还原NO的催化性能,并借助扫描电子显微镜（SEM）、X射线衍射（XRD）、比表面积测定（BET）、吡啶吸附红外光谱（Py-IR）、程序升温还原（TPR）和热重分析（TG）等方法研究催化剂制备方法与结构、性能的关系。实验结果表明,采用将Al(NO3)3滴入(NH4)2CO3制得的γ-Al2O3能有效地增大催化剂的比表面积,加入La2O3能提高催化剂的热稳定性,加入ZrO2能大幅度增加催化剂表面L酸和B酸的酸量。因此,采用共沉淀法制备的La2O3-ZrO2-Al2O3复合载体能够使Cu/La2O3-ZrO2-Al2O3催化剂具有良好的催化性能,最佳催化活性温度为300℃,NO最大转化率高达88.9%,在有10%水蒸气存在的情况下,仍可达81.9%。     

The influence of La2O3 and TiO2 on NiO/MgO/α-Al2O3

Summary The effect of La₂O₃ and TiO₂ on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al₂O₃ catalyst were studied in a simultaneous steam and CO₂ reforming of methane to syngas. La₂O₃ and TiO₂ were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively.     

Selective Catalytic Reduction of NO with Propene over Au/Fe2O3/Al2O3 Catalysts

A series of Au/Fe₂O₃/Al₂O₃ catalysts were prepared by the homogeneous deposition-precipitation method. The catalytic activity of the catalyst samples for selective catalytic reduction of NO by propene under oxygen-rich atmosphere was evaluated. The results showed that 2%Au/10%Fe₂O₃/Al₂O₃ exhibited good low-temperature activity. The maximum of NO conversion reached 43% at 300 °C, while it was only 21% over the 2%Au/Al₂O₃ catalyst at the same temperature. The addition of 2% steam to the feed gas had little effect on the catalytic activity. X-ray diffraction results indicated that both Au and Fe₂O₃ particles were highly dispersed over Al₂O₃. H₂-temperature-programmed reduction results indicated that there was strong interaction between Au and Fe₂O₃, which made the reduction of Fe₂O₃ easy. The synergistic effect between Au and Fe₂O₃ was probably responsible for the good catalytic performance of the Au/Fe₂O₃/Al₂O₃ catalyst at low temperature.     

Preparation of ZrO2-TiO2-CeO2 and Its Application in the Selective Catalytic Reduction of NO with NH3

TiO₂,ZrO₂-TiO₂,andZrO₂-TiO₂-CeO₂ were prepared by co-precipitation method and characterized by X-ray diffraction (XRD), specific surface area measurements (BET), temperature programmed desorption (NH₃-TPD), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results showed that ZrO₂-TiO₂-CeO₂ exhibited large number of surface strong acid, possessed some oxygen storage capacity, and strong redox property. The three materials were used as supports and the monolith catalysts were prepared with 1% (w) V₂O₅ and 9% (w)WO₃ for selective catalytic reduction (SCR) of NO with ammonia in the presence of excessive O₂, and the results of catalytic activity showed that the catalyst used ZrO₂-TiO₂-CeO₂ as support yielded nearly 100% NO conversion at 275 °C at a gas hourly space velocity (GHSV) of 10000 h⁻¹, and it had the best catalytic activity and showed great potential for practical application.     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

Fe2O3/ATP载氧体制备及煤化学链燃烧性能研究

以天然凹凸棒(ATP)为载体,分别利用机械混合法、浸渍法和溶胶-凝胶法制备了3种铁基复合载氧体。利用X射线衍射(XRD)、能谱(EDS)、N₂-吸附脱附等温线等对其进行物化表征,并在900 ℃流化床中考察其煤化学链燃烧反应性能。结果表明,ATP能显著增加载氧体比表面积和抗磨损能力,并对煤转化过程有催化作用,其与Fe₂O₃的协同作用使初始碳转化速率显著提高。溶胶-凝胶法制备的U-Fe4ATP6表面Ca元素含量为4.3%,比表面积为4.920 7 m²/g,均高于其他两种载氧体,表现出更高的催化性能和反应活性:初始碳转化速率为0.168 min^-1,平均CO₂浓度为98.6%,燃烧效率为98.7%。20次反应后,U-Fe4ATP6催化性能略有降低,对应的初始碳转化速率降至0.108 min^-1,停留时间t₉₅延长到18 min;且能维持较高的反应活性,对应的CO₂捕集效率和燃烧效率分别稳定在98.6%和96.7%。     

TiO2晶相对MnOx/TiO2催化剂催化NO氧化性能的影响

以浸渍在不同晶相TiO₂ （金红石型（R）、锐钛矿型（A）和P25型（P））上的锰基催化剂为对象,研究了TiO₂晶相对MnO_x/TiO₂催化剂催化NO氧化活性的影响。 结果表明,MnO_x/TiO₂（P）催化剂活性最高,NO转化率在300℃及GHSV = 20000 h^-1条件下可达83%。 各催化剂活性顺序为MnO_x/TiO₂（P）>MnO_x/TiO₂（A）>MnO_x/TiO₂（R）。采用X射线粉末衍射、场发射扫描电子显微镜、X射线光电子能谱、H₂程序升温还原和O₂程序升温脱附等手段研究了TiO₂晶相影响MnO_x/TiO₂催化剂催化活性的作用机理。结果表明,相比于A和R型TiO₂,P型TiO₂能够增加MnO_x在其表面的分散度并抑制催化剂颗粒的团聚和粘连,且更有利于Mn₂O₃的生成,而后者催化NO氧化活性比其它MnO_x更高;此外,P型TiO₂可以增加MnO_x尤其是Mn₂O₃的还原性,并可促进O₂^-从M³⁺-O键的脱附。     

Effect of sol-gel derived Al2O3-ZrO2 and Al2O3-TiO2 oxides on the selectivity of NO reduction by CO under oxidizing conditions

The role of Al₂O₃-ZrO₂ and Al₂O₃-TiO₂ sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. ²⁷Al MAS-NMR spectra have shown the formation of pentacoordinate Al^V in alumina-zirconia support. ZrO₂ or TiO₂ crystalline phases cannot be identified by XRD diffraction, suggesting the formation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO₂ were observed on Pt/Al₂O₃-ZrO₂catalyst, while the formation of N₂O is more prononced on Pt/Al₂O₃-TiO₂ catalyst. The effect of water during NO reduction is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Catalytic Dehydrogenation of c2h6 to c2h4 under non-Oxidative Conditions over the 6cr/g-al2o3Catalyst

In the present paper, the catalytic dehydrogenation of C₂H₆ to C₂H₄ under non-oxidative conditions was investigated in a fixed-bed micro-reactor under ambient pressure at 823 - 923 K. The 6Cr/g-Al₂O₃ catalyst was found to be the best catalyst among the g-Al₂O₃, SiO₂, MCM41, MgO and Si-2 supported chromium oxide catalysts. The features of the 6Cr/g-Al₂O₃ catalyst for the reaction could be listed as follows: (1) At 823 - 923 K, the C₂H₄ selectivity of 92.5-78.6% at a C₂H₆ conversion of 9.5-29.8% could be obtained. (2) The catalyst had the good regeneration performance, i.e., could be regenerated by air repeatedly. (3) The main products were C₂H₄, CH₄, H₂ and coke. No carbon oxides were identified.     

(La0.8A0.2)MnO3 (A = Sr,K) perovskite catalysts for NO and C10H22 oxidation and selective reduction of NO by C10H22

In this work, we studied the catalytic activity of LaMnO₃ and (La_0.8A_0.2)MnO₃ (A = Sr, K) perovskite catalysts for oxidation of NO and C₁₀H₂₂ and selective reduction of NO by C₁₀H₂₂. The catalytic performances of these perovskites were compared with that of a 2 wt% Pt/SiO₂ catalyst. The La site substitution increased the catalytic properties for NO or C₁₀H₂₂ oxidation compared with the non-substituted LaMnO₃ sample. For the most efficient perovskite catalyst, (La_0.8Sr_0.2)MnO₃, the results showed the presence of two temperature domains for NO adsorption: (1) a domain corresponding to weakly adsorbed NO, desorbing at temperatures lower than 270 ℃ and (2) a second domain corresponding to NO adsorbed on the surface as nitrate species, desorbing at temperatures higher than 330 ℃. For the Sr-substituted perovskite, the maximum NO₂ yield of 80% was observed in the intermediate temperature domain (around 285 ℃). In the reactant mixture of NO/C₁₀H₂₂/O₂/H₂O/He, (La_0.8Sr_0.2)MnO₃ perovskite showed better performance than the 2 wt% Pt/SiO₂ catalyst： NO₂ yields reaching 50% and 36% at 290 and 370 ℃, respectively. This activity improvement was found to be because of atomic scale interactions between the A and B active sites, Sr²⁺ cation and Mn⁴⁺/Mn³⁺ redox couple. Thus, (La_0.8Sr_0.2)MnO₃ perovskite could be an alternative free noble metal catalyst for exhaust gas after treatment.     

组合型Pt3Sn/Al2O3催化剂用于芳香硝基化合物一锅法合成N-烷基芳胺

采用吸附法制备了组合型Pt₃Sn/Al₂O₃双金属催化剂, 将该催化剂用于芳香硝基化合物原位液相加氢一锅法合成N-烷基芳胺. 研究表明, 在503 K, 空速为7.5 h^-1, 水体积分数为5%时, 1%(质量分数)Pt₃Sn/Al₂O₃催化剂具有较高的催化性能, 硝基苯的转化率为100%, N-乙基苯胺和N,N-二乙基苯胺的总选择性为98.2%. 同时,该催化剂对原位液相加氢烷基化反应具有一定普适性, 本文研究的14 种芳香硝基化合物与低级脂肪醇反应,均具有较高的N-烷基化产率.     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

The mechanism of SO2 oxidation by CH3O2 radicals. Rate coefficients for the reactions of CH3O2 with SO2 and NO

The reactions of CH₃O₂ with SO₂ and NO have been studied by steady state photolysis of azomethane in the presence of O₂SO₂→NO mixtures at 296 K and 1 atm total pressure. The quantum yield of NO oxidation by CH₃O₂ radicals is increased substantially when SO₂ is added to the system indicating an SO₂ induced chain oxidation of NO. The rate law gives k₁/k₂ = (2.5 ± 0.5) × 10^?3 for CH₃O₂ + SO₂ → CH₃O₂SO₂ (1), CH₃O₂ + NO → CH₃O + NO₂ (2). Combining this ratio with the absolute value of k₁ = 8.2 × 10^?15 cm³ s^?1 gives k₂ = 10^{?11.5 ± 02} cm³ s^?1.     

REDUCTION OF NO BY CO OVER NiWO4, NiO, AND WO3 CATALYSTS

We present a comparative study of NiWO₄, NiO, and WO₃ catalysts for simultaneous conversion of NO and CO. Samples were synthesized by reacting ammonium metatungstate and/or nickel nitrate at high temperature (773 K to 903 K) under an oxygen stream. Catalysts were characterized by X-ray diffraction, surface area measurements, energy dispersive spectroscopy and scanning electron microscopy. The catalytic reduction of NO by CO took place in the temperature range (523 to 973) K under highly reductive conditions (NO:CO= 1:5) over NiWO₄NiO, and WO₃, respectively. The 100 % NO conversion at GHSV of 11460 h^-1 was achieved at 773 K over NiWO₄ and at 848 K over NiO. The WO₃ was deactivated at 898 K. However, in the range (523 to 723) K NiO was more active than NiWO₄ and WO₃ catalysts.     

Selective catalytic reduction of NO over metal oxide or noble metal-doped In2O3/Al2O3 catalysts by propene in the presence of oxygen

The activities of metal oxide CuO, SnO₂, CoO, Ag₂O, ZnO or noble metal Pt, Pd, Rh-doped In₂O₃/Al₂O₃ catalysts for selective catalytic reduction of NO by propene were investigated. The temperature windows for NO reduction over noble metal-doped In₂O₃/Al₂O₃ catalysts were shifted and broaden slightly compared with single component catalyst alone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cu/NiO-V2O5/SiO2催化剂光催化CO2和甲醇合成碳酸二甲酯的研究

采用表面改性法和等体积浸渍法制备了NiO-V₂O₅/SiO₂和Cu/NiO-V₂O₅/SiO₂光催化剂. 用TPR, XRD, UV-Vis DRS, IR和TPD-MS技术对催化剂的结构、吸光性能和化学吸附性能进行了表征, 研究了催化剂上CO₂和甲醇光促表面催化反应的反应性能. 结果表明, 半导体NiO和V₂O₅复合后部分形成了Ni^2＋—O—V^5＋键联, 而且NiO和V₂O₅在催化剂表面有相互修饰作用, NiO的加入有助于提高V₂O₅在载体SiO₂表面的分散程度, 抑制V₂O₅的聚集, 而且金属Cu和NiO的引入扩展了催化剂的光响应范围. 在催化剂表面存在多种活性吸附位, 催化剂对CO₂和甲醇的有效吸附使得其在较低温度下就能促进碳酸二甲酯的紫外光化学合成. 用Cu/NiO-V₂O₅/SiO₂催化剂, 在常压、空速300 h^－1、140 ℃和125 W紫外灯辐照的情况下, CH₃OH的转化率为14.2%, 碳酸二甲酯的选择性可达89.9 %.