Fe-BEA Zeolite Catalysts for NH3-SCR of NOx

Iron-containing zeolites are known to be promising catalysts for the NH₃-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied.     

Elimination Reactions over Polar Catalysts: Mechanistic Considerations

In order to form a double bond in an organic molecule, two fragments (atoms or groups) are abstracted from adjacent carbon atoms.

Such a reaction is called a β-elimination [12, 221. In many cases one of the fragments is hydrogen.     

Elimination Reactions over Polar Catalysts: Mechanistic Considerations

In order to form a double bond in an organic molecule, two fragments (atoms or groups) are abstracted from adjacent carbon atoms.

Such a reaction is called a β-elimination [12, 221. In many cases one of the fragments is hydrogen.     

Morphology-Sensitive Sulfation Effect on Ceria Catalysts for NH3-SCR

Topics in Catalysis - In this work, sulfation effect on NH3-SCR performance over CeO2 with different morphology (nanocubes and nanorods) was carefully studied. A morphology-sensitive sulfation...     

金属基分子筛型NH3选择性催化还原氮氧化物催化剂的研究进展

氨气选择性催化还原(NH3-SCR)消除氮氧化物(NOx)以其高效、低成本的优势成为目前最具潜力和最广泛应用的固定源脱硝技术.传统的NH3-SCR以V2O5/WOx-TiO2为催化剂,但该类催化剂水热稳定性差,易中毒且其本身就具有毒性,因此开发金属基分子筛催化剂是当前的研究热点之一.本文介绍了分子筛型NH3-SCR催化剂的研究进展,总结了不同金属负载分子筛对选择性催化还原的影响及其反应机理,探讨了催化剂失活的影响因素.     

Low-Temperature SCR of NO with NH3 over USY-Supported Manganese Oxide-Based Catalysts

A series of catalysts of manganese oxide, manganese–cerium and iron–manganese oxide supported on USY (ultra-stable Y zeolite) were studied for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. It was found that MnO_x/USY have high activity and high selectivity to N₂ in the temperature range 80-180 °C. The addition of iron and cerium oxide increased NO conversion significantly although the single-component Fe/USY and Ce/USY catalysts had low activities. Among the catalysts studied in this work, the 14% Ce-6% Mn/USY showed the highest activity. The results showed that this catalyst yielded nearly 100% NO conversion at 180 °C at a space velocity of 30 000 cm³ g^-1 h^-1. The only product is N₂ (with no N₂O) below 150 °C. The effects of the concentration of oxygen, NO and NH₃ were studied and the steady-state kinetics were also investigated. The reaction order is 1 with respect to NO and zero with respect to NH₃ on the 14% Ce-6% Mn/USY catalyst at 150 °C.     

A Modeling Study of NH3 Slip Catalysts: Analysis of the SCR/PGM Interactions

We present a simulation study which comparatively analyzes the performances of four configurations of NH₃ slip catalysts (ASC) for automotive NH₃–SCR based Diesel aftertreatment systems. The comparison in terms of NH₃ conversion and N₂ selectivity over a wide range of operating conditions highlights the positive interaction of NH₃–SCR and PGM oxidation chemistries, which is best exploited by a dual-layer configuration with the SCR catalyst on top. This study also emphasizes the key role of modeling and simulation tools in the development of complex exhaust aftertreatment systems as well as the importance of a clear understanding of the catalytic chemistry involved in automotive deNOx converters.     

Mechanistic Modelling of the Catalytic Pyrolysis of Methylcyclohexane

A detailed chemical kinetic mechanism describing the thermal and catalytic cracking of methylcyclohexane over a 12CaO.7Al₂O₃ catalyst is presented. The model is based on balanced equations for both molecular and radical species describing an experimental fixed‐bed reactor system. The mechanistic model is based on overall first‐order decomposition kinetics, which satisfactorily describes experimental data. The simulated product distributions show a reasonably good agreement with the experimental results and confirm the hypothesis that the catalyst does not affect the pyrolysis mechanism and only increases the rate of the initiation steps.     

Mechanistic Insight in the Ethane Dehydrogenation Reaction over Cr/Al2O3 Catalysts

A Cr/Al₂O₃ alkane dehydrogenation catalyst exhibits a maximum in ethylene yield during an ethane dehydrogenation cycle. Isotopic labelling experiments with monolabelled ¹³C-ethane and deuterium were used to elucidate whether the initial activity increase could be due to formation of an active, larger hydrocarbon intermediate on the surface. The results strongly indicate that this is not the case, and instead point to a traditional reaction cycle involving adsorption of ethane to form an ethyl species, followed by desorption of ethene and hydrogen. Transient kinetic data suggest that ethane adsorption is the rate-determining step of reaction.     

Alkali Resistant Fe-Zeolite Catalysts for SCR of NO with NH3 in Flue Gases

Fe-zeolite catalysts were prepared by ion-exchange and characterized by nitrogen physisorption, electron paramagnetic resonance (EPR) spectroscopy, NH₃-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR) and Energy dispersive X-ray spectroscopy (EDX) methods. The effect of potassium doping on the acidic and redox properties of the Fe-zeolite catalysts were studied. The prepared catalysts showed high surface area and surface acidity. This is essential for increased alkali resistivity in comparison with conventional metal oxide supports like, e.g. TiO₂ and ZrO₂, towards e.g. potassium salts in flue gases from biomass fired power plants. These properties allowed both undoped and potassium doped Fe-zeolite catalysts to posses high activity during the selective catalytic reduction (SCR) of NO with NH₃. The extent of deactivation of the Fe-zeolite catalysts was further compared with commercial V₂O₅–WO₃–TiO₂ catalyst (VWT) with various levels of potassium poisoning. While VWT catalysts severely deactivated at relative low potassium concentration levels the Fe-zeolite catalysts also showed superior alkali resistivity even at high potassium loadings.     

Study of Cu/Mn Catalysts for Coreactions of NH3-SCR and CO Oxidation

Catalysis Letters - To explore the possibility of coreaction of selective catalytic reduction with NH3 (NH3-SCR) and CO oxidation (CO-O), bimetallic doping catalysts of Mn and Cu were synthesized...     

溶胶凝胶自蔓延法制备过渡金属离子掺杂NH3-SCR催化剂性能研究

采用溶胶凝胶自蔓延方法制备出不同过渡金属掺杂的R-MnOx(R=Ce、Co、Cr、Cu) NH3-SCR催化剂.采用TG-DSC、BET、XRD等进行催化剂结构与性能的表征,并采用NH3-SCR模拟测试装置对R-MnOx进行催化效果测试.结合第一性原理对催化剂的吸附性能进行模拟,进一步解释不同掺杂元素对催化剂的影响.结果 表明,Ce、Co掺杂能够有效降低MnOx吸附能势垒,增加NO与NH3气体分子与催化剂活性位点的接触机会,从而提高催化剂的低温催化活性.Ce-MnOx具有较低的结晶度和更大的比表面积,也增大了气体分子与催化剂活性位点的接触机会.因此,Ce-MnOx具有最好的NH3-SCR催化效果,在120 ～240℃范围内NO的转化率能达到88％以上.     

Combination of Low- and Medium-Temperature Catalysts for the Selective Catalytic Reduction of NOx with NH3

Topics in Catalysis - In this study, we developed a novel combination model for different types of catalysts, which could generate synergistic effects for the catalysts with different functions. A...     

Role of B5-Type Sites in Ru Catalysts used for the NH3 Decomposition Reaction

A series of activated carbon supported Ru catalysts have been reduced at different temperatures under hydrogen flow, and in some cases under ammonia flow, in order to modify the morphology and the particle size of the metallic active sites. CO chemisorption and transmission electron microscopy have been applied to follow the variations of these particles. The samples have been tested in the ammonia decomposition reaction, where systematic differences in catalytic activities as consequence of the support modification as well as due to the changes in the Ru particle sizes have been detected. Furthermore when potassium is added as catalyst promoter the sintering of Ru particles is significantly diminished and thus the changes in catalytic activities are inhibited. The electronic states of the Ru particles have been evaluated by determination of the chemisorption heats of the CO probe molecule. A part of other promoter or support effects it seems to exit a critical mean size for Ru particles on where maximum of catalytic activity is achieved. This behavior can be rationalized by the presence of surface highly active B5 sites, which consist of an arrangement of three Ru atoms in one layer and two further Ru atoms in an internal layer. These especial surface sites are expected to be in a higher proportion over Ru crystallites of those critical sizes, namely for Ru diameter sizes in the rage of 3–5 nm.     

Improved Automotive NO x Aftertreatment System: Metal Ammine Complexes as NH3 Source for SCR Using Fe-Containing Zeolite Catalysts

Ammonia storage is a challenge in the selective catalytic reduction of NO _x in vehicles. We propose a new system, based on metal ammines as the ammonia source. In combination with iron containing zeolites as the SCR catalyst it should be possible to obtain a low temperature system for NO _x removal.     

碳基催化剂上低温NH_3选择性催化还原NO的研究进展

综述了碳基载体(活性炭、碳纳米管、活性炭纤维、蜂窝状活性炭)担载不同金属氧化物(V2O5、Mn Ox、Ce O2、Cu O、Fe2O3)所制催化剂在低温下的NH3选择性催化还原(SCR)NOx性能,并总结了SO2和/或H2O对脱硝性能的影响机理,为进一步低温SCR催化剂的应用和开发提供参考。     

Selective Catalytic Reduction of NO with NH3 over Fe-ZSM-5 Catalysts Prepared by Sublimation of FeCl3 at Different Temperatures

Fe-ZSM-5 catalysts were prepared by subliming FeCl₃ into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl₃ exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl₃ into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl₃ at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl₃ at 700 °C were found to be more active for NO reduction with NH₃ in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl₃ at 320 °C. To determine the active sites, the catalysts were characterized by H₂-TPR, in situ DRIFTS of NO adsorption, NH₃-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH₃ could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when positions in Fe-ZSM-5, corresponding to Fe²⁺(NO) band at 1877 cm^-1 in DRIFTS, were preferentially occupied.