Removing nitric oxide from flue gases by catalytic reduction

A Ti-W-V catalyst has been proposed for removing NO by means of ammonia reduction from flue gases from power stations and boiler systems operating with natural gas; it contains 10% W0₃ and 5% V₂O₅ deposited on anatase. The optimum NH₃/NO ration is 0.8. oxygen at levels of 0.1–7.8 vol. % does not affect the reduction of the NO. Industrial tests in flue gas from a power station show that the reduction of the NO is 96% at 240–270°C. The basic technological parameters have been determined.State Research and Development Institute for the Nitrogen Industry and Organic Synthesis Products, Moscow. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 27, No. 5, pp. 595–598, September–October, 1991. Original article submitted July 5, 1991.     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al = 2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al=2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH₃-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.     

Selective catalytic reduction of nitric oxide with ammonia: A theoretical ab initio study

Ab initio quantum chemical studies at the HF/Lanl2dz level were carried out to investigate the interaction of ammonia, NO, and a mixture of the two with vanadia/titania. It was found that the replacement of Ti_6c by V_6c is the only feasible way to form highly dispersed vanadia over the titania. The V?O species thus formed will be in octahedral symmetry with the axial distortions, and no tetrahedrally coordinated V species can be formed. Ammonia fully covers the catalyst surface either through the associative interaction with the Lewis acid site of Ti_5c or the dissociative adsorption channels. The dissociation of ammonia on the O site bridging the Ti_6c and V_6c octahedra and on the V?O group can proceed with the highest gain in energy. The formation of an adsorbed ammonium ion was found to be an energetically highly unfavorable process. The V?O group is no longer expected to play a major role in the stabilization of the surface ammonium ion. NO can be activated on the Ti_5c site of the catalyst containing predissociated ammonia on the bridging O site and V?O group. It can be expected that the SCR reaction products are formed through the reactions of both adsorbed NO and NH₂ or the desorbed NH₂ group with NO in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Gas chromatographic analysis of the products of catalytic reduction of nitric oxide by ammonia

The behavior of small amounts of nitric oxide in the presence of ammonia and excess oxygen on adsorbents of different textures was studied by gas chromatography. A scheme for the gas chromatographic analyses of the products of catalytic reduction of nitric oxide by ammonia and the catalytic oxidation of ammonia by oxygen was suggested. The scheme makes it possible to prevent chemical reactions between components of the gas mixture analyzed during the accumulation of the products and their analysis, to exclude the partial or complete adsorption of NO on microporous adsorbents, and to monitor the content of components at a level of 500 ppm and lower.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2508–2513, October, 1996.     

双金属Cr-In/H-SSZ-13催化剂上CH4选择催化还原NO

天然气 (主要成分为甲烷) 储量丰富,价格低,随着国内电厂煤改气的进行,甲烷作为还原剂选择催化还原氮氧化物成为电厂烟气脱硝的理想选择,受到广泛关注.In 改性分子筛催化剂在甲烷选择催化还原一氧化氮反应 (CH4-SCR) 中表现出一定催化性能,而 In 基双金属被认为是最有前景的 CH4-SCR 催化剂.本文通过湿浸渍法制备了分子筛双金属催化剂,并成功应用于CH4-SCR.我们首先研究了不同分子筛载体、助剂及含量、氧气浓度、甲烷浓度和空速对反应的影响,发现0.5%Cr-2%In/H-SSZ-13 在 CH4-SCR中表现出最佳的催化性能:NO 转化率 ＞ 90%,N2选择性 ＞ 99% (反应条件:550 ℃,6% H2O,空速 75000 /h).从透射电镜照片可以看出,0.5%Cr-2%In/H-SSZ-13催化剂上均匀分布纳米尺寸颗粒,扫描透射-高角环形暗场像元素分布分析表明 Cr 与 In 出现在同一个位置,即 Cr 与 In 紧密接触.X射线光电子能谱结果表明,与单金属催化剂相比,双金属催化剂中 In 的能谱发生了明显偏移,Cr 与 In 存在电子相互作用.CH4-SCR 反应活性实验发现,双金属催化剂活性远远超过单金属催化剂活性及其机械混合物,表明 Cr 的添加可以明显促进 In 的活性.换言之,双金属催化剂中,Cr 与 In 存在协同催化作用.Cr-In/H-SSZ-13在严苛反应条件下的活性长期保持不变,具有良好稳定性,这与沸石分子筛载体 H-SSZ-13 的高热稳定性分不开.结合稳态反应与程序升温表面反应结果,可以推测有氧条件下 CH4和 NO 分别在 In和 Cr 位点上活化.     

catalytic activity of comgal, coal and mgal of mixed oxides derived from hydrotalcites in the selective catalytic reduction of no with ammonia

Summary Calcined CoMgAl LDHs and a Co-impregnated LDH were characterized by XRD, N₂ physisorption, TPR and ICP elemental analysis, then tested in the selective catalytic reduction (SCR) of NO with ammonia. Cobalt deposited by impregnation on LDH leads to the more active and selective catalyst. On this type of catalyst nearly 80% of conversion and selectivity to N₂ were reached at 578 K with a volume space velocity of 2200 h^-1.     

Effect of SO2 on the selective catalytic reduction of NO by ammonia

An experimental study has shown that the addition of SO₂ may either hinder or accelerate the selective catalytic reduction of NO by ammonia on oxide catalysts. The nature of the effect of SO₂ depending on its concentration and temperature has been elucidated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 165–168, March–April, 1993.     

Cu-ETS-10催化NH3选择性还原NOx性能

采用离子交换法制备了Cu-ETS-10钛硅分子筛催化剂,该催化剂对于NH₃选择性催化还原（SCR）NO_x反应具有较高的催化活性、N₂选择性和抗SO₂性能.结果表明,Cu-ETS-10钛硅分子筛具有丰富的微孔结构和较高的比表面积（288-380m²/g）;原子发射光谱、程序升温还原技术和原位红外漫反射等表征结果表明,Cu在Cu-ETS-10钛硅分子筛中具有多种存在形态,其中Cu²⁺物种为Cu-ETS-10的活性中心,其含量随Cu含量的增加而先增后降,与催化活性的变化趋势一致.     

催化剂低温NH3选择催化还原NO的研究

研究了碳纳米管担载的五氧化二钒（V₂O₅/CNTs）催化剂上NO低温选择催化还原反应（SCR）。与活性炭载体的催化剂作了对比,结果显示,在负载低含量V₂O₅时碳纳米管较活性炭显示了更好的催化能力,而且在SO₂存在下,催化性能有更大幅度的提高。暂态反应实验显示,V₂O₅/CNTs 催化剂上NO选择催化还原反应遵循Eley Rideal机理,即反应发生于吸附态的NH₃和气相或弱吸附的NO之间。     

Potentials of gas chromatography in the determination of reaction products in the catalytic oxidation of ammonia to nitrogen(II) oxide

Peculiarities of the determination of nitrogen oxides and ammonia in the reaction products of ammonia oxidation are studied by gas chromatography. Particular attention was paid to the sampling problem. It is shown that in the course of the transportation of samples containing nitrogen(II) oxide and oxygen, the oxidation of nitrogen(II) oxide to nitrogen(IV) oxide takes place in the vapor phase. The conditions were found for suppressing or even eliminating the gas-phase reaction of NO oxidation to NO₂. A procedure for the gas-chromatographic analysis of the reaction products in the catalytic oxidation of ammonia is proposed using several samples and packed columns, including the determination of NO with respect to NO₂ formed in the gas-phase oxidation of NO.     

Ag(x)/ZSM-5催化剂的CH4-SCR脱硝性能

采用浸渍法制备Ag(x)/ZSM-5(x=3、6、9)催化剂。采用XRD、SEM、NH_3-TPD、Py-FTIR、XPS和NO-TPD等手段对催化剂的理化性质进行表征,在常压固定床微型反应器中评价催化剂甲烷选择性催化还原(CH_4-SCR) NO催化性能,考察Ag负载量对Ag(x)/ZSM-5催化剂CH_4-SCR脱硝性能的影响。结果表明,ZSM-5分子筛负载Ag,催化剂的酸性和酸量发生变化,改善了催化剂对NO的吸附脱附性能。随着Ag负载量增加,形成较大的Ag晶粒,有利于甲烷活化,Ag(x)/ZSM-5催化剂CH_4-SCR脱硝活性提高。Ag(9)/ZSM-5催化剂CH_4-SCR脱硝性能较好,在350℃时NO转化率为41.87%。     

富氧条件下Fe-Mn/Beta选择性催化丙烯还原氮氧化物

以Beta分子筛为载体，采用等体积浸渍法制备Fe-Mn/Beta催化剂，并对其在富氧条件下丙烯选择性催化还原NO性能进行了研究。通过N₂吸附-脱附、X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、程序升温还原（H₂-TPR）和原位漫反射傅里叶变换红外光谱（in-situ DRIFTS）等研究手段对催化剂进行表征，考察Mn组分对催化剂的物理化学性质、C₃H₆-SCR反应活性和反应中间产物的影响。结果表明，引入Mn物种可以显著提高Fe-Mn/Beta催化剂的低温催化活性，1.5Fe1.0Mn/Beta催化剂NO还原效率350℃最高可达99.4%，在250-400℃反应温度下显示出很高的反应活性和N₂选择性。原位红外光谱研究表明，分子筛离子交换位上孤立的铁离子是丙烯选择性氧化的主要活性位，分散良好的MnO₂物种不能提高催化剂对丙烯的活化能力，但有助于促进形成NO₂吸附物种，从而提升了Fe-Mn/Beta催化剂的低温C₃H₆-SCR性能。经高温水热老化处理后，Fe-Mn/Beta催化剂脱硝活性明显下降，这与孤立的Fe³⁺离子迁移形成Fe_xO_y团聚物种有关。     

双金属Ce-Mn/ZSM-5催化剂的制备及NH3-SCR脱硝性能研究

采用浸渍法制备了铈锰复合氧化物分子筛催化剂(Ce-Mn/ZSM-5),在固定床反应器上考察不同Ce/Mn质量比对分子筛催化剂选择催化还原NO的影响,利用XRD、TEM、NH_3-TPD、H_2-TPR、in-situ DRIFTS等手段对催化剂进行了表征分析。结果表明,双金属改性的Ce-Mn/ZSM-5催化剂在NH_3-SCR反应中表现出较为优异的催化活性,具有较宽的活性温度窗口。当Ce/Mn质量比为0.4时,催化剂具有最佳的脱硝效率,在265-465℃脱硝率均可达到80%以上,在370℃时,NO的转化率最高可达97.28%。锰和铈物种高度分散于催化剂表面,未改变ZSM-5的晶体结构,且构成协同作用。0.4Ce-Mn/ZSM-5具备丰富的酸性位、良好的氧化还原性能,该配比有助于催化剂的催化活性和稳定性的提高,在NH_3-SCR反应过程同时遵循E-R机理和L-H机理。     

Novel ultrasonic-modified MnOx/TiO2 for low-temperature selective catalytic reduction (SCR) of NO with ammonia

A novel ultrasonic-modified MnO(x)/TiO(2) catalyst was prepared and compared with two different kinds of MnO(x)/TiO(2) catalysts in the process of low-temperature selective catalytic reduction of NO with NH(3). The physicochemical properties of the catalysts were studied by using various characterization techniques, such as Brunauer-Emmett-Teller (BET) surface measurement, X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and in situ Fourier transform infrared spectroscopy (in situ FT-IR). The ultrasonic-modified process introduced ultrasound in the solution impregnation step of traditional impregnation method for MnO(x)/TiO(2) catalyst preparation. In this study, ultrasonic process significantly improved the dispersion behavior and surface acid property of manganese oxide on TiO(2) as well as the catalytic activity, especially at temperature below 120°C. The NO conversion could reach 90% at 100°C. For the novel ultrasonic-modified catalyst, the combination analysis of XRD and HRTEM confirmed that manganese oxide was in a highly dispersed state and Ti and Mn had strong interaction. Furthermore, in situ FT-IR studies revealed that there were significant amounts of Lewis acidity and high Mn atom concentration on the surface of the novel catalysts.     

Metal oxide promoted TiO2 catalysts for photo-assisted selective catalytic reduction of NO with NH3

The photo-assisted selective catalytic reduction (SCR) of NO with NH₃ (Photo-SCR) was performed over TiO₂ modified by supporting 1 wt% of various transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ta or W) oxides aiming at the improvement of the photo-SCR activity. The addition of Nb, Mo or W oxide to TiO₂ was found to enhance the photo-SCR activity. We have reported that the amount of acid sites on TiO₂ is one of the key factors to the photo-SCR activity. The increase in the activity depends on the enhancement of acidity of catalyst by the addition of Nb, Mo or W oxide. In contrast, the addition of V, Cr, Mn, Fe, Co, Ni or Cu oxide to TiO₂ lowered the photo-SCR activity, although addition of metal cations also changed the acidity of TiO₂. We guess that the reduction of the activity was caused by two reasons; the first is that the sites newly formed on these transition metal oxides is not photoactive and the second is that TiO₂ supporting V, Cr, Mn, Fe, Co, Ni or Cu oxides had low stabilities under the reaction conditions, i.e., the chemical state of the cations changed during the reaction. Therefore, we concluded that the increase in the acid sites that are active sites for photo-SCR and the stability of the catalysts are important for the photo-SCR.     

铁铈复合氧化物催化剂SCR脱硝的改性研究

利用共沉淀法制备了铁铈催化剂,考察添加钛、锆、钨和钼对其SCR脱硝的改性规律。结果表明,钨和钼的添加提高了铁铈催化剂高温脱硝性能,却使其低温活性有所降低;钛的添加对铁铈催化剂脱硝性能具有促进作用,尤其提高了其低温活性,并拓宽了其完全转化温度窗口,为最佳改性物。当钛的物质的量比逐渐由0.10增至0.40,铁铈钛催化剂低温脱硝效率先增大后减小,但其高温脱硝效率逐渐增大至100%,钛的最佳物质的量比为0.15。XRD和N₂吸附分析结果表明,钛能优化铁铈催化剂的孔隙结构,增大其比表面积和比孔容,细化其孔径,并与催化剂中铁、铈氧化物形成良好的固溶体,从而提高了铁铈催化剂的SCR脱硝性能。Fe_0.8Ce_0.05Ti_0.15O_z催化剂在150～400℃取得了高于90%的NO_x转化率。