Reduced‐order modeling for the control of selective noncatalytic reduction of nitrogen monoxide

The design of a reduced‐order model is discussed to help in the control of selective noncatalytic reduction (SNCR) of nitrogen monoxide. Instead of relying on a look‐up table of nominal operating points, it is proposed to solve for the time evolution of a set of stochastic particles interacting through a model for turbulent mixing and a reduced chemistry. Each particle is representative of a fraction of the mass flowing in the system in gaseous or liquid form. To calibrate and validate the reduced‐order model, which runs in a few minutes on a desktop computer, reference three‐dimensional and unsteady large‐eddy simulation is performed in the complex geometry of a real incinerator. This is done solving the full set of conservation equations of mass, momentum, and energy over a 162 million cells mesh. The results confirm the possibility of real‐time SNCR optimization from the solving of partial differential equations. © 2015 American Institute of Chemical Engineers AIChE J, 62: 928–938, 2016     

过渡金属/分子筛催化剂上选择性催化还原氮氧化物的研究进展

综述了近十年来过渡金属/分子筛催化剂上氨和碳氢化合物选择性催化还原NOx方面的研究进展。在NH3-SCR体系,着重介绍了铜基和铁基分子筛催化剂的研究状况,探讨了分子筛催化剂在该体系中的失活原因;在HC-SCR体系,总结了不同过渡金属、分子筛类型、还原剂、H2O和SO2等对催化剂活性的影响,探讨了目前比较公认的碳氢化合物选择性催化还原NOx的反应机理。最后展望了分子筛催化剂在选择性催化还原NOx领域今后的研究方向。     

载体对铁基整体式催化剂上丙烯催化还原NO的影响

以Al₂O₃、SiO₂和TiO₂为载体,采用凝胶-溶胶法和浸渍法制备铁基堇青石整体式催化剂,并对其丙烯选择性催化还原NO性能进行了研究。通过N₂物理吸附/脱附、XRD、SEM、H₂-TPR、Py-FTIR和原位DRIFTS技术对催化剂进行了表征。不同载体对催化剂的表面酸性、氧化还原性能、比表面积和表面形貌有显著影响,从而导致丙烯还原NO的催化活性明显差异。C₃H₆-SCR的催化活性按Fe/Al₂O₃/CM > Fe/SiO₂/CM > Fe/TiO₂/CM依次降低。在450℃的有氧条件下,在Fe/Al₂O₃/CM上催化C₃H₆还原NO效率可达到100%,这主要是因为较好的氧化还原性能和丰富的Lewis酸性位。基于原位的DRIFTS研究表明,Lewis酸性位的增加有助于促进形成NO₂/NO₃^-物种,从而提高了催化性能。     

Iron ion-exchanged zeolite: the most active catalyst at 473 K for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere

Among various metal ion-exchanged zeolites, metal loading alumina, and oxides, iron ion-exchanged mordenite was the most active for the selective reduction of nitrogen monoxide to nitrogen by ethene in the presence of oxygen at the temperature as low as 473 K. The catalytic activities of iron ion-exchanged zeolites depended on the zeolite structure and the iron ion exchange level. The effects of the zeolite structure are in the order of MOR > FER > MFI > Y > LTL at 473 K. The activity of iron ion-exchanged mordenite increased with the increment in the exchange level and levelled off above about 60%.     

Enhancement of catalytic activity of alumina by copper addition for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere

The catalytic activity of alumina for the title reaction has been found to be greatly improved by the loading of copper. The addition of copper resulted in lowering the active temperature region, the higher maximum activity, and the enhancement of the reaction rate. The maximum effect was observed at 0.3 wt% of the loading amount of copper. A similar enhancement was also confirmed on SiO₂-Al₂O₃.     

Partial oxidation of propene over metal oxide catalysts pretreated with NO2

Titania pretreated with NO₂ has been found to catalyze the partial oxidation of propene into oxygenates such as acetone and acrolein at around 623 K, while fresh TiO₂ produces only carbon oxides. Temperature‐programmed desorption (TPD) revealed that nitrogen oxides adsorbed on TiO₂ are stable at temperatures below 673 K. Even after the propene oxidation at 573 K for 2 h, nitrogen oxides were confirmed still to exist on the TiO₂ surface. At temperatures higher than 673 K, however, the desorption and/or the reduction of the adsorbed nitrogen oxides took place, and concomitantly the catalytic ability giving oxygenates disappeared. This revised version was published online in July 2006 with corrections to the Cover Date.     

Marked difference in activity of alumina catalysts for selective catalytic reduction of nitrogen monoxide by ethene in excess oxygen

Alumina is well-known as an effective catalyst for the title reaction. The present study revealed that the activity of an alumina catalyst for the reaction largely depended on its type. A critical factor affecting the activity of an alumina was neither the surface area nor pore structure, but the purity; the higher the purity, the higher the activity. Active alumina catalysts showed high activity for both the oxidation of NO to NO₂ and the reduction of NO₂ by ethene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dependence of selective reduction of NO with C3H6 on acid properties of ion-exchanged zeolites

The effect of amount and strength of acid sites on the activity and selectivity for the selective reduction of NO with C₃H₆ in the presence of excess oxygen over H-form and ion-exchanged zeolites has been investigated. The activity was found to be proportional to the acid amount determined by NH₃-temperature programmed desorption, but independent of the acid strength of the zeolites. The selectivity, i.e., the ratio of the reduction of NO with C₃H₆ to the oxidation of C₃H₆ by O₂, was independent of the amount and strength of acid sites.     

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。     

Preparation and characterization of three pure magnesium vanadate phases as catalysts for selective oxidation of propane to propene

Three magnesium vanadate phases, i.e., MgV₂O₆ (metavanadate), -Mg₂V₂O₇ (pyrovana-date) and Mg_s V₂O₈ (orthovanadate), have been successfully prepared with high purity by the citrate method at a relatively low temperature (550°C). FT-IR, LRS, XRD and SEM techniques have been used to characterize these vanadate phases. The effect of calcination temperature has also been investigated. It was found that the particle size and morphology of the MgV₂O₆ phase, which is a function of calcination temperature, appear to have a strong effect on the infrared spectra. Furthermore, the catalytic properties of the three phases were examined in the oxidative dehydrogenation of propane. The propene selectivity follows the order: -Mg₂V₂O₇ > Mg₃ Vg₂O₈ > MgV₂O₆, which is consistent with their redox properties. This fact suggests that there is some correlation between the catalytic and redox properties of these magnesium vanadate phases.     

新型金属有机骨架材料催化剂选择性催化还原氮氧化物研究进展

综述新型有机金属骨架材料和复合金属骨架材料催化剂在选择性催化还原氮氧化物方面的研究进展,讨论金属有机骨架材料催化剂的低温脱硝活性和抗硫抗水性能,介绍脱硝反应过程中氮氧化物的反应机理。针对金属有机骨架材料表现出的良好低温脱硝活性,认为其有可能替代传统脱硝催化剂。     

The role of acid sites in cobalt zeolite catalysts for selective catalytic reduction of NOx

The role of the acidic support in ion-exchanged cobalt-zeolite, lean NO_x catalysts has been determined by studying the individual steps in the selective reduction pathway. At a GHSV of 10,000 and reaction temperatures below 400°C, NO oxidation is not sufficiently rapid to obtain equilibrium over, for example, 1–4 wt% Co-mordenite catalysts. The NO oxidation rate increases in the order H⁺Co²⁺ Co oxide, and neither the number, nor the strength of the acid sites affects the specific rate of the Co²⁺ ions. For reduction of NO₂ by propylene at 300°C and methane at 400°C, the formation of N₂ is suggested to occur at support protons sites. In addition, the rate of N₂ formation increases linearly with an increase in the number of acid sites, and the specific activity increases with an increase in acid strength. Cobalt (2+) ions do not contribute significantly to the formation of N₂, but do non-selectively reduce NO₂ to NO. It is proposed that the formation of N₂ occurs by protonation of the reducing agent followed by attack of the carbocation by gas phase NO₂. Thus, the selective reduction of NO requires two catalytic functions, metal and acid sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

凹凸棒石低温SCR脱硝催化剂的研究进展

选择性催化还原（SCR）脱硝技术是目前主流的氮氧化物脱除技术,其核心是催化剂。凹凸棒石成本低廉,性能优越,适合用作SCR催化剂的载体,而且以凹凸棒石为载体的催化剂显示出良好的低温选择性和稳定性,具有很好的应用前景。本文总结了凹凸棒石低温SCR脱硝催化剂的研究进展,阐述了活性组分、制备方法、前体物种、活性组分负载量、煅烧温度、元素掺杂等因素对催化剂脱硝活性的影响,同时简要介绍了导致此类催化剂失活的原因以及失活催化剂的再生方法,并指出在凹凸棒石负载型低温脱硝催化剂上进行的SCR脱硝反应遵循E-R机理,最后指出此类催化剂的未来研究方向主要是进一步提高现有催化剂的低温催化活性和抗中毒能力,实现工业化应用。     

Role of supported metals in the selective reduction of nitrogen monoxide with hydrocarbons over metal/alumina catalysts

The promoting effect of supported metals on alumina catalyst was investigated for the reduction of nitrogen monoxide in oxygen-rich atmospheres. For NO reduction with propene over impregnated CoO/A1₂O₃, the first reaction step was found to be the oxidation of NO to NO₂ probably catalyzed by dispersed cobalt species. The next reaction step, which is the reaction of NO₂ with propene to form N₂, was considered to take place on the alumina surface. Although the activity of impregnated FeO/A1₂O₃ was low because of the presence of large iron oxide particles catalyzing propene oxidation with dioxygen, FeO/A1₂O₃ prepared with sol-gel method showed excellent deNO_x activity.     

电催化还原二氧化碳制一氧化碳催化剂研究进展

电催化还原CO₂作为缓解能源危机和全球变暖的有效途径已成为催化领域的研究热点。然而,不同反应途径的氧化还原电位较为接近,使产物的选择性成为电催化还原CO₂所需解决的主要问题。迄今为止,在水性电解质中可实现CO₂选择性地转化为一氧化碳（CO）和甲酸（HCOOH）。本文简述了电催化还原CO₂制CO的机理,包括CO₂吸附过程、二电子转移过程和CO脱附过程。从贵金属的晶面设计、形貌调控和表面功能化对反应活性和产物选择性的影响,铁卟啉、钴酞菁和镍三嗪在还原CO₂为CO反应中的电子转移途径,非金属碳基材料中杂原子和碳基质间的耦合效应等方面,重点介绍了近年来贵金属催化剂、过渡金属络合物催化剂和非金属碳基材料催化剂的研究进展,总结了各类催化剂的优缺点。指出在三类电催化还原CO₂制CO的催化剂中,非金属碳材料具有较高的CO法拉第效率,尤其是非金属碳材料成本较低、制备简单、结构易调控,在电催化还原中具有潜在的应用优势,是有望实现商业化应用的新型催化剂的候选材料之一。     

Ir基催化剂用于CO选择性催化还原NO的研究进展

针对具有烟温低、氧含量高和CO浓度大等特征的固定源烟气（钢铁烧结/球团烟气和焦化烟气等）脱硝领域,CO选择性催化还原NO _x （CO-SCR）技术具有良好的发展前景。Ir基贵金属催化剂因其在CO-SCR反应体系中表现出了良好的抗氧能力和较高的催化活性成为催化脱硝领域研究的热点之一。本文重点总结了单一载体、复合载体与复合活性组分三类Ir基催化剂在CO-SCR脱除NO _x 中的催化性能,同时从制备条件和反应条件两大方面归纳了其对Ir基催化剂的CO-SCR脱硝性能的影响,简要阐述了Ir基催化剂表面反应机理,并对未来研究工作进行了展望,指出采用多种手段对催化剂进行改性,并通过降低Ir负载量、反应温度窗口以及提升其催化活性等方式来降低成本,为实现Ir基催化剂CO-SCR工业化应用提供借鉴。     

Selective conversion of propane to propene by the catalytic oxidative dehydrogenation over cobalt and magnesium molybdates

Catalytic performances of various metal molybdates were tested in the oxidative dehydrogenation of propane to propene with molecular oxygen under an atmospheric pressure. Most of the molybdates tested promoted the selective oxidative conversion of propane to propene and among them cobalt and magnesium molybdates were found highest in the activity and selectivity. It was also found that their catalytic activities were highly sensitive to the catalyst composition, and it turned out that Co_0.95MoO _x and Mg_0.95MoO _x catalysts which have slightly excess molybdenum showed the highest activity in the oxidative dehydrogenation of propane. Under the optimized reaction conditions, higher reaction temperatures and lower partial pressures of oxygen, these catalysts gave 60% selectivity to propene at 20% conversion of propane. Since the molybdates having the surface enriched with molybdenum oxide tended to show high activity for the propane oxidation, surface molybdenum oxide clusters supported on metal molybdate matrix seem to be the active sites for the selective oxidative dehydrogenation of propane.     

Effect of sodium on the catalytic properties of iridium black in the selective reduction of NOx by propene under lean-burn conditions

The effect of sodium promotion on the performance of an iridium black catalyst for the selective catalytic reduction of NO by propene has been investigated. Sodium loadings above 1 at% were found to increase the nitrogen selectivity close to 100% in the whole temperature range investigated (150–450°C). However, the presence of Na shifted the on-set of all reactions to higher temperatures (ca. 20–50°C for the highest promoter loadings, i.e., 10 at% Na), leading to a narrowing of the operation temperature window. Consequently, moderate sodium loadings in the range of 1–3 at% represent the best compromise for a beneficial application of iridium in DeNO_x catalysis. Combined thermogravimetry–mass spectrometry investigations revealed that not only NO dissociation, but also, e.g., the decomposition of propene and the adsorption of oxygen as well as the oxidation of iridium are influenced by the presence of sodium. Mechanistically, our observations are consistent with a model, where the removal of adsorbed oxygen could represent the rate-limiting step under the applied conditions.     

Reduction of nitrogen monoxide to nitrogen at gas diffusion electrodes with noble metal catalysts

The electrochemical reduction of NO in alkaline solutions was investigated at gas diffusion electrodes with various metal (Ru, Rh, lr, Pd and Pt) catalysts at various NO flow rates. Reduction currents are observed at potentials more negative than 0.95 V, which increase with the decrease in potential and also with increasing gas flow rate. The faradaic efficiencies of N2O formation decrease with decreasing NO flow rate and with decrease in potential. The faradaic efficiencies of N2 formation increase with decreasing flow rate and with decrease in potential. The reduction of NO to N2 at a flow rate of 5mlmin–1 occurs selectively at potentials more negative than 0.1V; the faradaic efficiency of N2 formation is approximately 95 at Pd catalysts.Electricity production and NO decomposition can be carried out simultaneously using an H2NO fuel cell reactor. The faradaic efficiency of N2 formation at a flow rate of 5mlmin–1 is approximately 80 at a cell voltage of 0.25 V.     

添加剂有机胺对丙烯选择性氧化制丙烯醛催化剂活性的影响

采用共沉淀法制备丙烯选择性氧化制丙烯醛催化剂,考察有机胺的加入对丙烯选择性氧化制丙烯醛催化性能的影响。结果表明,添加有机胺后,催化剂活性在维持不变的情况下,选择性显著提高。采用扫描电镜、X射线衍射、吡啶吸附红外光谱和N₂物理吸附表征等对不同催化剂的物化性能进行表征。结果发现,添加有机胺后,催化剂比表面积略有下降,但催化剂表面的L酸性中心强度明显增加,对催化剂活性影响不大;另一方面,MoO₃结晶度的下降与(Co_0.7Fe_0.3)(MoO₄)结晶度的上升对催化剂选择性均是积极因素。同时孔容的减小以及大孔比例增加更有利于主反应产物的脱附,能抑制深度氧化物的生成。