Selective catalytic reduction of NO with NH3 over Nb2O5-promoted V2O5/TiO2 catalysts

In contrast to previous claims, the addition of niobia to catalysts containing vanadia supported on titania resulted in much enhanced activity for low-temperature SCR of NO with NH₃ only at low vanadia loadings. Niobia promoted catalysts could also be demonstrated to show higher selectivities to N2, especially at high temperatures and low vanadia loading. This enhancement of the activity cannot be explained only on the basis of the observation that niobia stabilized the surface area of the catalyst: calculations of the activation energy suggest that a different mechanism of the reaction may be at work at low vanadia loadings.     

氨法选择性催化还原脱硝催化剂的研究

采用浸渍法,以TiO₂为载体,负载P₂ O₅、V₂O₅和MoO₃或WO₃制备选择性催化还原(SCR)催化剂,研究了不同磷含量以及水蒸汽对催化剂性能的影响。结果表明,随着催化剂中磷含量增加,P₂O₅-V₂O₅-MoO₃/TiO₂催化剂的SCR活性呈先上升后下降的趋势,其中,含质量分数0.5%P₂ O₅催化剂的活性较好。反应体系中水蒸汽的存在对催化剂的低温活性有明显的抑制作用。     

V_2O_5/TiO_2催化剂上NH_3选择性催化还原NO反应动力学研究

采用浸渍法制备了V2O5/TiO2催化剂,研究了V2O5/TiO2催化剂上NH3选择性催化还原NO的反应动力学,运用Eley-Rideal机理模型确定了相关的动力学参数,推导出本征动力学方程,得到反应的活化能为41.9 kJ/mol。     

V2O5-MoO3/TiO2 催化剂的NOx选择性催化还原及SO2氧化活性

采用浸渍法以TiO₂为载体制备V₂O₅-MoO₃/TiO₂ 选择性催化还原催化剂,研究V₂O₅和MoO₃负载量对于催化剂选择性催化还原反应及SO₂氧化活性的影响,并考察氧含量、氨氮物质的量比和反应空速对3%V₂O₅-6%MoO₃/TiO₂催化剂选择性催化还原脱硝活性的影响。结果表明,随着催化剂中V₂O₅负载质量分数增加,V₂O₅-MoO₃/TiO₂ 催化剂的选择性催化还原活性和SO₂氧化活性均呈上升趋势。MoO₃的负载对催化剂的SO₂氧化活性有明显抑制作用。MoO₃负载质量分数超过9%,制备的催化剂既保持较高的低温选择性催化还原活性,又使选择性催化还原反应中的SO₂转化率小于1%。     

丙烯选择还原一氧化氮反应铜基交联黏土催化剂的研究

采用聚合羟基阳离子合成交联蒙脱土(PILC),经SO2-4改性,制备了应用于C3H6选择还原NO的铜基交联黏土催化剂。考察了交联剂种类、Cu担载量及水蒸气存在对催化剂性能的影响,并采用DTA、XRD对PILC进行表征。研究发现,Al-PILC较Zr-PILC具有较好的热稳定性;350℃时Cu/Al-PILC(Cu质量分数为3%)上NO转化率达52.0%;由于金属氧化物交联柱表面的疏水特性,Cu/Al-PILC较Cu/ZSM-5具有较强的抗水蒸气能力,10%水蒸气存在仅使NO最大转化率下降了13.7%,NO和C3H6转化曲线较不含水蒸气时向高温方向移动。     

Selective catalytic reduction of NO with ammonia over porous clay heterostructures modified with copper and iron species

Porous clay heterostructures (PCH), obtained on the basis of synthetic saponite, were modified with copper and iron ions by an ion-exchange method and tested as catalysts for the selective reduction of NO with ammonia (NH₃-SCR). Transition metal ions were introduced into H⁺ and NH₄⁺ forms of PCH. The catalysts were characterized with respect to their texture (BET), composition (EPMA), coordination of transition metals (UV–vis-DRS) and surface acidity (FT-IR, NH₃-TPD). The PCH-based catalysts have been found to be active, selective and stable in the NH₃-SCR process. The Cu-containing catalysts effectively operated at temperatures significantly lower than the Fe-modified samples. The catalyst obtained by exchanging copper ions in the ammonium form of PCH was considerably more active compared to the sample obtained from H⁺-PCH.     

TiO2 nanotube-supported V2O5 catalysts for selective NO reduction by NH3

TiO₂ nanotubes (TNT) were prepared by hydrothermal method at 140 °C for 23 h. The V₂O₅/TNT (VTNT) catalysts were obtained by impregnation in NH₄VO₃ solution. The VTNTs exhibited much higher denitration efficiency than those supported on the raw TiO₂, and satisfactory resistance to water and sulfur. Results from BET, TEM, XRD, NH₃-TPD and EPR verified that V₂O₅ was dispersed well on TNT, thus favoring NH3 adsorption, promoting the transformation from V⁵⁺ to V⁴⁺, conducing to the formation of oxygen vacancies and superoxide radicals in the presence of NH₃ and O₂, and then resulting in the high catalytic activity of VTNTs.     

Phase structure of V2O5/TiO2 catalyst and catalytic behavior with removal of NO by ammonia

V₂O₅/TiO₂ catalyst with 3% (w/w) V loading has been prepared by sol–gel method. The characterization results of the catalyst structure and catalytic activity show that VO _X state is strongly dependent on the calcination temperature. Little effect is found for phase structure of TiO₂ support on catalytic activity. High catalytic activity in wide temperature range (240–420 °C) is observed for the catalysts calcinated at different temperatures at a space velocity of 50,000 h^?1. Space velocity and alkali metal oxides strongly influence the catalytic activity of the catalyst which was calcinated at 450 °C, furthermore, the one has high tolerance to SO₂ in our test conditions.     

制备方法对V_2O_5-WO_3/TiO_2选择性催化还原催化剂性能的影响

采用共沉淀法、溶胶-凝胶法和浸渍法制备了V2O5质量分数4%和WO3质量分数6%的V2O5-WO3/TiO2选择性催化还原催化剂,对比了3种方法制备的催化剂选择性催化还原NO性能。采用X射线衍射、热重、N2吸附-脱附和程序升温还原等对制备的V2O5-WO3/Ti O2催化剂的结构和性质进行表征,结果表明,共沉淀法制备的V2O5-WO3/TiO2催化剂具有更好的选择性催化还原NO活性和更大的比表面积,影响共沉淀法选择性催化还原NO活性的主要因素是催化剂的热稳定性、表面羟基数量、比表面积、粒径分布以及V、W与Ti之间的内在作用。     

Selective reduction of NO by NH3 over Fe-zeolite-promoted V2O5-WO3/TiO2-based catalysts: Great suppression of N2O formation and origin of NO removal activity loss

Great depression of the formation N₂O in the selective catalytic reduction of NO by NH₃ (NH₃-SCR) has been studied by combining a V₂O₅-WO₃/TiO₂ (VWT) catalyst with a Fe-exchanged ZSM-5 zeolite (FeZ). At temperatures > 400 °C, N₂O formation was significant over VWT but < 5 ppm over FeZ/VWT catalysts with the FeZ ≥ 8%. Unfortunately, all these FeZ-promoted catalysts disclosed a decrease in deNO_xing performances, due to an enhanced NH₃ oxidation into NO. At temperatures > 350 °C, the chemically-combined VWT-based FeZ systems could facilitate both N₂O reduction with NH₃ and N₂O decomposition, thereby suppressing N₂O emissions in NH₃-SCR reaction.     

Boosting low-temperature selective catalytic reduction of NO with NH3 of V2O5/TiO2 catalyst via B-doping

A series of B-doped V₂O₅/TiO₂ catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NO_x with NH₃. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H₂ and temperature-programmed desorption of NH₃ technology were used to study the effect of the B-doping on the structure and NH₃-SCR activity of V₂O₅/TiO₂ catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB_2.0 with 2.0% doping amount of B and the NO_x conversion rate is up to 94.3% at 210 ℃. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH₃-SCR performance. These results suggest that the V₂O₅/TiO₂ catalysts with an appropriate B content afford good candidates for SCR in the low temperature window.     

V2O5/TiO2基SCR脱硝催化剂的制备及其催化性能

采用纳米TiO₂为催化剂载体原料,V₂O₅为催化剂,通过混合、球磨、干燥和焙烧等工艺制备选择性催化还原脱硝法催化剂,研究了催化剂的制备工艺和催化性能。通过差热分析研究催化剂的相变和烧结温度,通过模拟烟气分析装置表征催化剂的催化性能。结果表明,加入V₂O₅可以提高催化性能,以6%V₂O₅-94%TiO₂为配方的催化剂对NO的脱除率达97.5%,温度窗口为（300～420） ℃。     

Low temperature selective catalytic reduction of NO by NH3 over V2O5 supported on TiO2–SiO2–MoO3

The V₂O₅ catalysts supported on TiO₂–SiO₂–MoO₃ (TSM) prepared by the coprecipitation method were investigated for the selective catalytic reduction (SCR) of NO by NH₃ at low temperatures. The V₂O₅/TSM catalyst with 7–13 wt% SiO₂ was found to exhibit a superior SCR activity and a good sulfur tolerance at low temperatures (<250 °C). The presence of highly active polymeric vanadates formed by the incorporation of MoO₃ to TiO₂–SiO₂ and superior redox properties seems to enhance SCR activity, and furthermore the very lower SO₂ oxidation activity due to the higher acidity leads to the remarkable improvement of sulfur tolerance.     

Selective catalytic reduction of NO by ammonia with fly ash catalyst

This paper investigates the selective catalytic reduction (SCR) of NO with NH₃ using fly ash catalyst. The catalytically active elements investigated here included Fe, Cu, Ni and V. The results indicated that fly ash, after pre-treatment, can be reasonably used as the SCR catalyst support to remove NO from flue gas. Cu gave the highest catalytic activity and NO conversion, compared with Fe, Ni and V. In the pre-treatment process, the nitric acid treatment and drying temperatures for the fly ash particles had little effect on the NO conversion. However, the calcination temperature had an important effect on the catalyst preparation process.     

Selective catalytic reduction of NO by NH3 on titanium pillared montmorillonite

The acidity of a titanium pillared montmorillonite (Ti-PILC) has been modified by two methods of sulfation. The acidic properties of these pillared clays have been studied by temperature-programmed ammonia desorption and FTIR analysis of pyridine adsorption. The catalytic activity of these titanium pillared clays in the selective catalytic reduction (SCR) of NO by NH₃ with or without SO₂ has been investigated. For the three titanium pillared clays, a high resistance to SO₂ presence has been observed.     

铜系催化剂选择性催化还原脱除NOx研究

以硅胶改性堇青石蜂窝陶瓷为载体,分别制备了以Cu-O、Cu-Ce-O和Cu-Ce-Mn-O为活性组分的催化剂。以CO(NH₂)₂为还原剂,在固定床反应器中进行选择性催化还原NO的研究。采用XRD、SEM和BET等测试方法对催化剂进行表征。结果表明,在温度(300～500) ℃,催化剂Cu-Ce-Mn-O/SiO₂/堇青石的活性优于催化剂Cu-O/SiO₂/堇青石和Cu-Ce-O/SiO₂/堇青石,反应温度为450 ℃、空速为8 000 h^-1时,Cu-Ce-Mn-O/SiO₂/堇青石催化剂催化还原NO的转化率可达到88%。     

Selective catalytic reduction of NO with propane over CoZSM-5 containing alkaline earth cations

Selective catalytic reduction (SCR) of nitric oxide (NO) with propane is studied over CoZSM-5 catalysts with a series of exchanged cobalt concentrations (0.9-7.5 wt.-%). The overall activity for SCR of NO is found to increase linearly with the cobalt content in the range below the maximum exchange capacity (CoAl= 0.5). However, when the cobalt loading exceeds the exchange capacity of the zeolite, viz.CoAl 0.5, the combustion of propane is favored significantly, resulting in a decrease of the NO conversion. The presence of excess Co²⁺ in zeolite appears to bring about the marked falls in adsorption of NO. In this case cobalt oxide particles are presumed to form, which promote the oxidation of propane. Nevertheless, the addition of alkaline-earth metal cations (Ba, Ca) resulted in the suppression of propane oxidation over CoZSM-5, and improved the NO conversion dramatically.     

Mn-Cu-Ce-Fe/REY系列催化剂上NH3选择性催化还原NO性能

采用正交实验设计和浸渍法制备Mn-Cu-Fe-Ce/REY催化剂。采用固定床微型反应器评价SO₂存在下催化剂在NH₃选择性催化还原NO反应中的活性,考察Mn、Cu、Fe和Ce各活性组分对催化剂活性的影响,并采用XRD、H₂-TPR和SEM等手段对催化剂进行表征。结果表明,Mn、Cu、Fe和Ce各活性组分对催化剂活性影响顺序为：Cu＞Fe＞Ce＞Mn,催化剂的氧化还原性能影响催化剂活性。     

Selective catalytic reduction of nitric oxide with ammonia on Fe-ZSM-5 catalysts prepared by different methods

Fe-ZSM-5 catalysts, prepared by different methods, have been characterized by TPR and XRD and tested in the NO-SCR by NH_3. The sublimation method leads to the most active catalysts. Nevertheless the preparation starting from Fe(acac)₃, which is a preparation easy to implement from an industrial point of view, seems to be a very attractive alternative way.On the most active catalyst, Fe(0.83)_subZSM-5, prepared starting from FeCl₃, a study of the mechanism was undertaken. In the initial step of the SCR reaction, the oxidation of NO in NO₂, the re-oxidation of Fe^II species in the active iron oxo species is the slow phase.     

Selective catalytic reduction of NOx, by propene over copper-exchanged pillared clays

Copper-exchanged pillared clays were examined as an SCR catalyst for NO_x, removal by propene. Both micropores and mesopores were simultaneously developed by pillaring a bentonite with TiO₂. Therefore, TiO₂-pillared clay has about 8 to 9 times higher surface area and 3 times higher pore volume than the parent unpillared bentonite. The presence of water in the feed gas stream caused a small and reversible inhibition effect on NO removal activity of Cu/Ti-PILC. The water tolerance of Cu/Ti-PILC was higher than copper-exchanged zeolites such as CuHM and Cu/ZSM-5 due to its high hydrophobicity as confirmed by H₂O-TPD experiment. Copper-exchanged PILC was confirmed to be an active catalyst for NO_x, removal by propene. The addition of copper to TiO₂-pillared clay greatly enhanced the catalytic activity for NO removal. Cupric ions on Ti-PILC were active reaction sites for the present reaction system. The state of copper species on the surface of Ti-PILC varied with the content of copper and TiO₂. The catalyst having more easily reducible cupric ions showed maximum NO conversion at relatively lower reaction temperatures. It indicates that the redox behavior of cupric ions is directly related to NO removal mechanism. The redox property of cupric ions depended on the copper content and dehydration temperature of PILC.