整体式Fe-β分子筛成型方法及其催化N_2O分解反应性能

为了降低催化剂床层压降,提高Fe-β分子筛催化剂用于N_2O催化分解的能力,通过研究整体式分子筛催化剂制备方法,优化出最优原料配比为ω(拟薄水铝石)=40%,ω(硝酸)=8%,水粉比为0.6 m L·g~(-1)。研究了成型过程对分子筛催化剂结构及性能的影响,并在不同孔密度分子筛催化剂、N_2O浓度和空速条件下考察N_2O分解反应性能。结果表明,在相同温度、空速和N_2O浓度下,分子筛催化剂的孔密度越高,催化活性呈增强趋势;对于相同孔密度的分子筛催化剂,随着空速的增加,相同温度下的N_2O转化率逐渐下降;对于相同孔密度的分子筛催化剂,在相同反应空速和温度下,随着N_2O浓度的增大,N_2O转化率呈上升趋势。     

Cu-Mn氧化物催化N_2O直接分解性能

分别以Cu(NO_3)_2·3H_2O和50%Mn(NO_3)_2水溶液为铜源和锰源,K_2CO_3为沉淀剂,采用沉淀法和共沉淀法制备单一Cu、Mn氧化物催化剂和Cu-Mn-O复合氧化物催化剂,用于催化N_2O直接分解反应,并利用N_2物理吸附-脱附、XRD、FT-IR和TPR等进行表征。结果表明,单一Cu和Mn氧化物分别以体相CuO和Mn2O_3物相形式存在,Cu-Mn-O复合氧化物中除形成CuMn_2O_4尖晶石物相外,还有一定量小晶粒CuO,较单一氧化物具有更加优异的还原性能,表现出较高的催化N_2O直接分解活性。在空速10 000 h~(-1)和N_2O体积分数0.1%条件下,Cu-Mn-O复合氧化物催化剂可在440℃催化N_2O完全分解,分别较单一Cu和Mn氧化物催化剂降低了40℃和60℃。     

Co-Cu-Ce-Fe/γ-Al_2O_3催化剂催化分解N_2O的性能

以等体积浸渍法制备γ-Al_2O_3负载的Co、Cu、Ce和Fe氧化物催化剂,利用正交试验设计实验条件,采用XRD、BET和H_2-TPR等对催化剂进行表征,并考察活性组分对催化剂催化分解N_2O活性的影响。结果表明,催化剂具有尖晶石结构,其BET比表面积随着金属氧化物负载量增加而降低。催化剂中铜的氧化物可以降低还原峰温度,进而明显提高催化活性,Co和Fe的加入对活性有一定的提高,Ce对催化活性没有明显影响。     

负载型钴锰复合金属氧化物催化剂催化分解N_2O

以ZrO_2为载体,采用浸渍法制备负载型钴锰复合金属氧化物催化剂,研究催化剂活性组分负载量、Co与Mn物质的量比、焙烧条件及含H_2O气氛对N_2O转化率的影响。结果表明,催化剂最佳制备条件为:活性组分Co负载质量分数3%,Co与Mn物质的量比为1∶1,焙烧升温速率2℃·min-1,焙烧温度900℃。该条件制备的负载型钴锰复合金属氧化物催化剂在反应温度850℃时,N_2O转化率达98.7%。当反应气氛中H_2O体积分数小于20%条件下,850℃时N_2O转化率高于90%,表明催化剂具有较强的抗水性能。     

分子筛催化剂上N2O催化分解的研究进展

氧化亚氮(N2O)会造成温室效应和臭氧层破坏,N2O的控制日益引起关注。催化分解技术是控制N2O的有效手段,分别对Fe基、Cu基和Co基分子筛催化剂催化分解N2O的研究现状进行总结和评述,并展望未来发展方向。     

动物骨源羟磷灰石负载Co3O4用于N2O催化分解

通过焙烧猪骨和鸡骨获得羟磷灰石(nHAP)载体,并采用浸渍法制备Co3O4/nHAP催化剂。采用XRD、N2物理吸附-脱附、FT-IR和H2-TPR等对催化剂进行表征,在连续流动微反装置上考察催化剂催化分解N2O的性能。结果表明,相比于鸡骨源Co3O4/nHAP催化剂,以猪骨源HAP为载体的催化剂因其较大的比表面积以及较小的Co3O4粒径尺寸,提供了更多的活性位点。特别是猪骨源Co3O4/nHAP催化剂中适量的K、Na等元素促进了Co^3+到Co^2+的还原,削弱了Co-O键,使催化剂的催化活性显著提高。     

成型条件对Co/ZSM-5催化剂催化分解N2O性能影响

采用挤条成型法制备Co/ZSM-5催化剂，通过X射线衍射、BET比表面积、氢气程序升温还原（H₂-TPR）、氨气程序升温脱附法（NH₃-TPD）和颗粒径向抗压碎（侧压）强度测试对催化剂进行表征，在固定床微型反应器中评价催化剂催化分解N₂O活性，对Co/ZSM-5(N-50)催化剂进行稳定性测试。结果表明，钴物种以Co₃O₄尖晶石氧化物形式存在于Co/ZSM-5催化剂中，胶溶剂种类显著影响催化剂抗压碎强度；黏合剂用量影响催化剂抗压碎强度、酸量、氧化还原性和催化剂催化分解N₂O活性；以硝酸为胶溶剂，黏合剂（SB粉）用量为30%和50%制备的催化剂，抗压碎强度大，分别为208N/cm和230N/cm，催化分解N₂O温度T ₉₅分别为485℃和500℃。在固定床微型反应器中，模拟工业尾气组成（ {\phi }_{{\mathrm{N}}_2\mathrm{O}} =11%、 {\phi }_{{\mathrm{O}}_2} =16%、N₂为平衡气），反应温度446℃、空速6000h^-1条件下，Co/ZSM-5(N-50)催化剂在1000h稳定性测试中表现出良好的催化活性和稳定性，N₂O转化率高于98%。     

Fe/beta分子筛催化N2O分解

通过液相离子交换法对H-beta分子筛进行改性得到Fe/beta分子筛,并应用于催化N2O直接分解反应,考察加入HNO3后的体系pH值对Fe/beta催化性能的影响。采用N2物理吸附-脱附、XRD、IR、DR UV-Vis、NH3-TPD和ICP-OES等对Fe/beta分子筛进行分析表征。结果表明,溶液pH值降低过程中催化剂的结晶度、比表面积、孔容及Fe3+含量呈现先增加后减少。溶液pH为2.0时所制备的Fe/beta分子筛催化N2O完全分解温度明显低于pH为2.6和1.0时制备的Fe/beta催化剂,显示了较好的催化活性。     

以活性炭纤维为载体的金属氧化物上分解N2O研究

制备了载有K、Fe、Cu、Sr、Mg金属氧化物的活性炭纤维(M/ACF)催化剂,用于N2O分解反应.实验结果表明它们对该反应的活性顺序为K/ACF>Fe/ACF>Cu/ACF>Mg/ACF>Sr/ACF>ACF, 其中K/ACF可在350℃时将N2O完全分解.基于K/ACF特殊的高活性,对该催化剂及空白炭纤维进行了TPD、TG实验,并进一步进行了活性实验.结果表明,N2O在K/ACF上,反应产物中CO2含量明显低于文献中已报导的其它C(NXO脱除反应产物中的CO2含量,其原因在于,对于K/ACF,在K2O活性中心作用下N2O的分解温度明显低于C(O)活性中心作用下炭纤维的氧化温度,在较低的温度范围内(280～330℃),K2O活性中心起主要的活性作用,使得N2O在K/ACF上大量分解, 而C(O)活性中心却没有明显的参与反应,所以CO2的生成量较小.反应前后K/ACF的SEM图样对比也表明经过反应,活性炭纤维表面没有明显的损伤,C(O)活性中心作用并不明显.     

N2O催化分解技术在处理己二酸尾气中的应用

介绍了分解己二酸生产过程中产生的N2O的常用方法,重点介绍了催化分解N2O技术以及工艺特点,对此项技术在试车及生产中可能出现的问题做出详细的分析,并提出相应的预防和改进措施。     

N2O catalytic decomposition over various spinel-type oxides

Various spinel-type catalysts AB₂O₄ (where A = Mg, Ca, Mn, Co, Ni, Cu, Cr, Fe, Zn and B = Cr, Fe, Co) were prepared and characterized by XRD, BET, TEM and FESEM-EDS. The performance of these catalysts towards the decomposition of N₂O to N₂ and O₂ was evaluated in a temperature programmed reaction (TPR) apparatus in the absence and the presence of oxygen. Spinel-type oxides containing Co at the B site were found to provide the best activity. The half conversion temperature of nitrous oxide over the MgCo₂O₄ catalyst was 440 °C and 470 °C in the absence and presence of oxygen, respectively (GHSV = 80,000 h⁻¹).

On the grounds of temperature programmed oxygen desorption (TPD) analyses as well as of reactive runs, the prevalent activity of the MgCo₂O₄ catalyst could be explained by its higher concentration of suprafacial, weakly chemisorbed oxygen species, whose related vacancies contribute actively to nitrous oxide catalytic decomposition. This indicates the way for the development of new, more active catalysts, possibly capable of delivering at low temperatures amounts of these oxygen species even higher than those characteristic of MgCo₂O₄.     

Mechanism of N2O decomposition over a Rh black catalyst studied by a tracer method: The reaction of N2O with O(a)

N₂O decomposition on an unsupported Rh catalyst has been studied using tracer technique in order to reveal the reaction mechanism. N₂¹⁶O was pulsed onto ¹⁸O/oxidized Rh catalyst at 220°C and desorbed O₂ molecules (m/e=32,34,36) were monitored by means of mass spectrometer. The ¹⁸O fraction in the desorbed dioxygen was the same value as that on the surface oxygen. The result shows that the O₂ molecules desorb via Langmuir–Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, TPD measurements in He showed that desorption of oxygen from the Rh black catalyst occurred at the higher temperatures. Therefore, reaction-assisted desorption of oxygen during N₂O decomposition reaction at the low temperature was proposed.     

Potassium-doped Co3O4 catalyst for direct decomposition of N2O

Direct decomposition of nitrous oxide (N₂O) on K-doped Co₃O₄ catalysts was examined. The K-doped Co₃O₄ catalyst showed a high activity even in the presence of water. In the durability test of the K-doped Co₃O₄ catalyst, the activity was maintained at least for 12 h. It was found that the activity of the K-doped Co₃O₄ catalyst strongly depended on the amount of K in the catalyst. In order to reveal the role of the K component on the catalytic activity, the catalyst was characterized by XRD, XPS, TPR and TPD. The results suggested that regeneration of the Co²⁺ species from the Co³⁺ species formed by oxidation of Co²⁺ with the oxygen atoms formed by N₂O decomposition was promoted by the addition of K to the Co₃O₄ catalyst.     

Development of a new Rh/TiO2–sepiolite monolithic catalyst for N2O decomposition

Monolithic catalysts based on Rh/TiO₂–sepiolite were developed and tested in the decomposition of N₂O traces. Several effects such as the presence of NO, O₂ and NO + O₂ in the gas mixture, the catalysts pre-treatment and the metal loading were evaluated. The system was extremely sensitive to the amount of rhodium, passing through a maximum in the catalytic activity at a Rh content of 0.2 wt.%. It has been demonstrated that both NO and O₂ compete for the same adsorption sites as N₂O; however, this effect was not as severe as for other previously reported Rh systems. For NO + O₂ gas mixtures the inhibition effect was stronger than when only NO or O₂ was present. Analysis of the pre-reduced sample by XPS showed Rh mainly in the metal state, even after treatment with N₂O + O₂ mixtures, suggesting that the oxygen consumption observed in the Temperature Programmed Reaction experiments was related to the oxygen uptake by vacancies in the support. The presence of sepiolite in the support preparation and its role as a matrix over which TiO₂ particles were distributed, seems to play an important effect in the migration process of oxygen species through the support vacancies. The Rh/TiO₂ monolithic system is an attractive alternative for the elimination of N₂O traces from stationary sources due to the combination of high catalytic activity with a low pressure drop and optimum textural/mechanical properties.     

Superior performance of Ir-substituted hexaaluminate catalysts for N2O decomposition

Novel Ir-substituted hexaaluminate catalysts were developed for the first time and used for catalytic decomposition of high concentration of N₂O. The catalysts were prepared by one-pot precipitation and characterized by X-ray diffraction (XRD), N₂-adsorption, scanning electronic microscopy (SEM) and temperature-programmed reduction (H₂-TPR). The XRD results showed that only a limited amount of iridium was incorporated into the hexaaluminate lattice by substituting Al³⁺ to form BaIr_xFe_1−xAl₁₁O₁₉ after being calcined at 1200 °C, while the other part of iridium existed as IrO₂ phase. The activity tests for high concentration (30%, v/v) of N₂O decomposition demonstrated that the BaIr_xFe_1−xAl₁₁O₁₉ hexaaluminates exhibited much higher activities and stabilities than the Ir/Al₂O₃-1200, and the pre-reduction with H₂ was essential for activating the catalysts. By comparing BaIr_xFe_1−xAl₁₁O₁₉ with BaIr_xAl_12−xO₁₉ (x = 0–0.8), it was found that iridium was the active component in the N₂O decomposition and the framework iridium was more active than the large IrO₂ particles. On the other hand, Fe facilitated the formation of hexaaluminate as well as the incorporation of iridium into the framework.