烟气NOx低温选择性催化还原催化剂研究进展

催化剂是选择性催化还原(SCR)脱硝技术的核心,其催化性能直接关系到脱硝效果的好坏。近年来,由于低温选择性催化还原法具有良好的经济性,引起各国环保研究工作者的关注,成为近年SCR研究的热点。本文概述了贵金属、金属氧化物、分子筛和碳基材料催化剂的低温(低于250℃)选择性催化还原法脱除NOx研究进展。其中,以碳基材料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。     

NOx低温选择性催化还原催化剂研究进展

催化剂是选择性催化还原脱硝技术的核心,其催化性能直接关系到脱硝效果的好坏。本文介绍了该领域新开发的贵金属、金属氧化物、分子筛、碳基催化剂等低温脱硝体系及其最新研究进展。对碳纳米材料催化剂和新型杂多酸催化剂等新成果作了介绍,并且对今后的研究方向作了展望。     

低温等离子体诱导低碳烃选择性催化还原NOx研究进展

综述了近年来低温等离子体诱导低碳烃选择性催化还原NOx的研究进展,详细介绍了难活化的甲烷及较易活化的非甲烷低碳烃气体如乙烯、丙烯及丙烷等的研究现状,探讨了低温等离子体诱导低碳烃选择性催化还原NOx的反应机理,并展望了低温等离子体诱导低碳烃选择性催化还原NOx今后研究方向。     

锰基NH_3-SCR低温脱硝催化剂研究进展

锰基催化剂在低温氨选择性催化还原(NH3-SCR)脱硝反应中表现出良好的催化活性。讨论H_2O和SO_2对锰基催化剂活性的影响,综述通过制备方法改性、添加助剂和优化载体改善锰基催化剂抗H_2O和抗SO_2性能的研究进展,并对锰基低温SCR催化剂的研究方向进行展望。     

低温NH3-SCR锰基催化剂的研究进展

低温NH₃-SCR消除NO_x是一种很有潜力的电厂烟气脱硝技术。该技术的核心为低温NH₃-SCR催化荆,当今研究开发低于200℃的低温NH₃-SCR催化剂仍是一大挑战,其中锰基催化剂由于良好的低温脱硝活性成为研究重点,本文就近年来国内外低温NH₃-SCR锰基催化剂的研究进展进行了综述。     

选择性催化还原(SCR)法脱除NOx的研究进展

本文介绍了用作NOx选择催化还原的碳氢化物、氨气、尿素等几种还原剂和活性炭、分子筛、金属氧化物、堇青石蜂窝陶瓷、复合载体等几类载体催化剂的研究进展情况，并阐述了各自的优缺点，综述．了尿素作为还原剂，复合载体的催化剂将是脱除氮氧化物的研究热点。     

MnOx/WO3/TiO2低温选择性催化还原NOx机理的原位红外研究

浸渍法制备15% MnO_x/5% WO₃/TiO₂低温脱硝催化剂,利用原位傅里叶变换红外（in situ FT-IR）设计包括多种吸附反应以及不同预处理方式的微观暂态试验与微观稳态试验,研究其NH₃-SCR脱硝反应机理,并推测反应路径。结果表明,催化剂的NH₃-SCR反应主要以Eley-Rideal机理方式进行,仅在一定温度条件下可以看到Langmuir-Hinshclwood反应路径。催化剂表面Lewis酸位的NH₃吸附是还原剂的主要来源,Brønsted酸位吸附的NH₄⁺随温度上升参与反应的比例略有提高。NH₃的吸附活化是整个反应的控制步骤,吸附态NH₃更易与NO₂发生反应,NO与催化剂表面的相互作用明显弱于NO₂。NO会在催化剂表面氧化活性中心形成大量双齿配位型硝酸盐,阻碍NH₃的吸附和活化,O₂存在条件下促进NH₃-SCR反应进行,阻止NO在催化剂表面形成双齿硝酸盐。NO与NH₃在催化剂表面存在吸附竞争,NO的吸附作用强于NH₃,温度达到100℃后吸附的NH₃方可大量活化并与NO_x发生进一步反应。     

柴油车NH3选择性催化还原NOx催化剂研究进展

柴油车是机动车NO_x排放的主要来源,NH_3选择性催化还原(NH_3-SCR)技术能有效控制NO_x排放,SCR催化剂作为该技术的核心而备受关注。本文总结了柴油车SCR催化剂的主要类型,概述了不同催化剂表面的催化反应机理,分析了催化剂中毒失活的机制及催化反应动力学,并对柴油车SCR催化剂的发展前景进行了展望,指出开发多功能、新型、高效的耦合催化单元是今后的研发方向。     

焦化行业烟气低温SCR脱硝中试研究

目前,国内焦化行业还没有烟气低温SCR脱硝的工程应用,有关研究也主要集中在实验室小试范围,模拟烟气实验很难反映出催化剂在实际烟气中的运行状况。本文选用乌海某焦化厂烟气进行现场脱硝中试,考察了所选催化剂在工况条件下的脱硝情况。结果表明,脱硝效率稳定在80%左右,催化剂活性没有明显降低,说明此催化剂及低温脱硝工艺适用于焦化行业烟气脱硝,对工程化应用有重要参考价值。     

V2O5/AC催化剂吸附NH3及其选择性还原脱硝活性

在不同活性焦(Activated Coke, AC)载体上以等体积浸渍法负载V2O5,制备出一系列V2O5/AC催化剂. 通过NH3暂态响应实验和NH3穿透时间实验考察了在200℃下V2O5/AC的表面积、灰分、表面官能团和V2O5对NH3的吸附量及NO的选择性催化还原活性的影响. 结果表明,对于载体未经硝酸处理的催化剂,NH3的吸附位主要是V2O5(参与脱硝反应的NH3的吸附量与催化剂上V2O5负载量的比值为1:5),活性焦及其中的灰分对NH3的吸附量很小;硝酸处理在活性焦表面引入的含氧和含氮酸性官能团对参与脱硝反应的NH3的吸附量是V2O5上吸附量的1.3倍,这些官能团不影响V2O5对NH3的吸附;活性焦上吸附的NH3的脱硝活性很低,但可迁移至V2O5上参与脱硝.     

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。     

选择性催化还原NOx催化剂的研究进展

综述了选择性催化还原法脱除NOx的各类催化剂,包括贵金属、分子筛、金属氧化物等。传统催化剂由于不能同时兼备优良的催化活性、热稳定性、抗中毒能力,因此难以真正实现商业化。由不同类型催化剂优化组合而成的复合型催化剂和NOx的存储一还原型催化剂克服了传统催化剂的上述缺点,在脱除NOx领域具有广阔的应用前景。     

Comparison of Design and Operation Strategies for Temperature Control during Selective Catalytic Reduction of NOx

The problem of controlling temperature profile along a monolithic reactor in which an exothermic reaction (selective catalytic reduction of NO_x by hydrocarbons) takes place is considered. Several solutions are proposed and compared. It is shown that a near‐optimum temperature profile can be achieved by two rather different approaches – one based on periodic switching of a hot reactant and a cold inert stream between two thermally coupled monoliths, and one based on pre‐mixing the reactant and coolant streams. An adaptive control scheme based on model‐predictive control is proposed and shown to be efficient for the case of time‐variable properties of the reactant stream.     

Hydrogen Lean-DeNOx as an Alternative to the Ammonia and Hydrocarbon Selective Catalytic Reduction (SCR)

The present article consists a critical up-to-date review of the research conducted so far on the selective catalytic reduction of NO_x with hydrogen under lean-burn conditions as an alternative technology to the existing NH₃- and HC-SCR. Noble Metal based catalysts are described in detail with emphasis on the analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the support chemical composition and the preparation method and structure of the catalysts on the reaction mechanism is also discussed. Finally, the effects of various reaction parameters on the catalysts activity, selectivity and stability with reaction time are discussed in detail.     

Ce改性Fe2O3/AC催化剂低温SCR脱硝性能

以活性焦(AC)为载体、Fe和Ce为活性组分,采用等体积浸渍法制备了Fe2O3/AC和Ce?Fe2O3/AC催化剂,研究了Fe含量及Ce掺杂对Fe2O3/AC催化剂低温脱硝性能的影响,并对催化剂进行了表征. 结果表明,当Fe负载量为6wt%时,Fe2O3/AC催化剂的NOx转化率最高,240℃下达93.9%. 掺杂Ce后Ce?Fe2O3/AC催化剂的催化效率明显提高,当质量比Ce:Fe=0.5:6时,NOx转化率较高,120~200℃下NOx转化率比负载6wt% Fe的催化剂提高了5%?20%,且抗硫性能较好,240℃下通入100?10?6(vol) SO2,NOx转化率稳定在94.1%. 掺杂少量Ce可使γ-Fe2O3均匀分散在催化剂表面,且表面吸附氧Oα比例增大,催化剂的还原性增强,促进了选择性催化还原反应进行.     

火电厂选择性催化还原脱硝技术的可行性研究

选择性催化还原（SCR）技术是目前研究较多的治理氮氧化物的方法。本文综述了选择性催化还原法降低氮氧化物排放的机理,介绍了SCR技术反应器的设计,催化剂的使用情况和研究现状,同时展望了这一技术领域的重点研究方向。     

Liquid-Phase Catalytic Decomposition of Novel Ammonia Precursor Solutions for the Selective Catalytic Reduction of NOx

Aqueous solutions of NH₃-precursor compounds (i.e. urea and methanamide) were catalytically hydrolyzed in the liquid phase by applying a pressure of 50 bar during contact with the catalyst in a heated tube. Methanamide could be hydrolyzed on an Au/TiO₂ catalyst to yield not only NH₃, but also H₂. Decomposition of urea under high pressure in the liquid phase could even be achieved without the addition of a catalyst. Due to the large excess of water present during decomposition, side products could be avoided. As the reactor tube is electrically heated, the presented method provides a possibility to reliably transform NH₃-precursor compounds into gaseous NH₃ independent of the engine exhaust gas temperature. The NH₃-flow can be added to the main exhaust duct to enable the selective catalytic reduction of NO_x at the light-off of the SCR catalyst.     

Diesel Soot Catalyzes the Selective Catalytic Reduction of NOx with NH3

The catalytic activity of soot samples for the selective catalytic reduction (SCR) of NO_x with NH₃ was investigated in dependence of the NO₂, NO and NH₃ concentration in the temperature range between 200 and 350 °C. The highest NO_x reduction of up to 25 % was measured in the presence of both NO₂ and NO at a GHSV of 35,000 h^?1. Decreasing space velocities resulted in an increase of the SCR activity. In the absence of NO₂, NO_x reduction was not observed. Carbon oxidation and SCR reaction occurred in parallel due to the presence of NO₂ and O₂, but hardly influenced each other, which suggested that in the NO_x reduction on soot most probably physisorbed species were involved. The observed stoichiometries indicated the action of the fast SCR reaction in the presence of NO and the NO ₂ SCR reaction in the absence of NO, while the observed gas phase and surface species pointed at reaction steps similar to those on classical SCR catalysts.