N2O直接分解催化剂的研究进展

概述了用于催化分解温室气体N2O的贵金属、金属氧化物、分子筛等催化剂的研究进展,讨论了N2O催化分解的反应机理,分析了不同类型催化剂的特点及存在的问题。通过比较发现金属离子改性的分子筛催化剂活性较优,并展望了N2O催化分解研究的发展趋势。     

M_(0.5)Co_(2.5)O_4(M=La,Ce,Pr,Nd)尖晶石型复合氧化物催化剂催化分解N_2O性能

采用共沉淀法制备了M_(0.5)Co_(2.5)O_4(M=La,Ce,Pr,Nd)钴基尖晶石型复合氧化物催化剂,运用XRD、SEM、H_2-TPR和O_2-TPD-TG等对催化剂物化性能进行表征,并在固定床微型反应器中评价催化剂催化分解N_2O性能。结果表明,稀土金属掺杂改性的钴基尖晶石型复合氧化物催化剂粒径明显减小,比表面积增加,氧化还原性能得到改善,催化分解N_2O活性提高,其中,M_(0.5)Co_(2.5)O_4催化剂催化分解N2O温度低,T10和T95分别为342℃和499℃。     

水分对N_2O减排装置影响因素探讨

辽阳石化公司N2O减排装置采用的是德国BASF公司的催化分解技术,实际生产中发现水分对N2O的催化分解效果有一定影响,本文对水分影响催化分解效果的情况进行研究分析,揭示其内在原理。     

负载型NiO和CoO催化剂上N2O分解研究

本研究在对多种金属氧化物催化剂进行初步筛选的基础上，研制出以莫来石为载体的负载型NiO、CoO催化剂，考察了分解温度、催化剂组成和负载量对N2O分解率的影响，并对其分解反应动力学进行了研究。结果表明莫来石负载NiO、CoO催化剂对N2O分解有良好的催化性能；其反应速度对N2O均为一级反应；同样负载量下NiO有更好的催化分解活性；这一研究为开发阻力低、催化性能好的工业用蜂窝型规整填料奠定了基础。     

铁改性分子筛直接催化分解一氧化二氮

采用以离子交换法制备的Fe-ZSM-5、Fe-MCM-22和Fe-Beta分子筛催化剂,系统地考察了分子筛构型、酸性和酸中心分布对N2O直接催化分解的影响.采用N2吸附、红外光谱仪(FT-IR)、NH3程序升温脱附实验(NH3-TPD)、H2程序升温还原实验(H2-TPR)和原位漫反射红外光谱(in situ DRIFTS)等方法考察了铁离子负载量、Si与Al摩尔比和分子筛构型对N2O催化分解的影响.结果表明,价键补偿Fe3 离子是N2O分解的主要活性组分;分子筛活性随Si和Al摩尔比的减少和铁离子负载量的增加而增加;Fe-Beta分子筛的催化活性明显高于Fe-ZSM-5和Fe-MCM-22分子筛;分子筛酸性和酸中心分布影响铁离子的分布,从而导致不同构型分子筛催化分解N2O的活性具有明显差异.     

N2O催化分解技术在处理己二酸尾气中的应用

介绍了分解己二酸生产过程中产生的N2O的常用方法,重点介绍了催化分解N2O技术以及工艺特点,对此项技术在试车及生产中可能出现的问题做出详细的分析,并提出相应的预防和改进措施。     

N2O分解催化剂的研究进展

介绍了催化分解N2O最主要的几类催化剂的研究进展,包括贵金属催化剂、金属氧化物催化剂以及分子筛催化剂等,并分析了不同类型催化剂的优缺点以及存在的主要问题。最后,展望了N2O分解催化剂的未来发展趋势。     

煤制乙二醇含N_2O废气处理工艺设计

比较了催化还原、高温分解和De O23种常用含N2O废气处理工艺,针对煤制乙二醇工艺废气的特性,选择了高温分解工艺。研究了分解温度和废气组成对该工艺的影响。通过采用辅助气源CO的燃烧,同时应用先进的焚烧炉技术,使炉内温度快速升到1 100℃以上,确保N2O的分解率达95%以上,再依据废气组成情况,选配选择性非催化还原反应器。该工艺还设置了不同形式的换热器以回收能量,降低能耗。     

类水滑石复合产物催化消除氮氧化物的研究进展

综述了国外多种类水滑石热分解复合产物M(Ⅱ)M(Ⅲ)HT[M(Ⅱ)=Mg，Co，Ni，Cu，Zn，Pd；M(Ⅲ)=Al，Fe，Cr，La，Rh]用于消除不同排放气氛中N2O的催化分解活性及类水滑石中含不同二价离子和价离子时对催化分解N2O性能的影响。通过与其他类型催化剂如离子交换分子筛、金属氧化物比较，发现类滑石热分解复合产物在低温下即有很高的反应活性。在实验模拟的多种排放气氛中考察时，发现它具有不易其他组分如H2O、O2、SO2等影响的稳定性能，其中CoAl-HT热分解复合产物催化剂在模拟含O2和H2O的龙66生产排放气氛中稳定性可达175h。通过对国内外多种类水滑石复合产物上催化消除NOx的介绍，表明水滑石热分解复合产物同样具有以上催化分解N2O时所表现的各种优良催化性能，特别是具有很好的抗SO2中毒能力。     

Fe/beta分子筛催化N2O分解

通过液相离子交换法对H-beta分子筛进行改性得到Fe/beta分子筛,并应用于催化N2O直接分解反应,考察加入HNO3后的体系pH值对Fe/beta催化性能的影响。采用N2物理吸附-脱附、XRD、IR、DR UV-Vis、NH3-TPD和ICP-OES等对Fe/beta分子筛进行分析表征。结果表明,溶液pH值降低过程中催化剂的结晶度、比表面积、孔容及Fe3+含量呈现先增加后减少。溶液pH为2.0时所制备的Fe/beta分子筛催化N2O完全分解温度明显低于pH为2.6和1.0时制备的Fe/beta催化剂,显示了较好的催化活性。     

单分散Co3O4@SiO2核壳催化剂的制备及N2O催化分解性能

N₂O是一种重要的温室气体,且对臭氧层有很大的破坏作用,而直接催化分解法是除去N₂O最经济有效的方法之一。针对目前报道较多的钴氧化物催化剂活性较差的问题,将包覆型Co₃O₄核壳材料引入N₂O直接催化分解反应,利用核壳结构的限域特性与壳层的多孔孔道使Co₃O₄分散性增加,粒径减小,金属载体相互作用与接触反应界面增强,从而提高了催化剂在N₂O直接催化分解反应中的低温活性。此外,还制备了一系列不同金属含量的Co₃O₄@SiO₂球形核壳催化剂来研究包覆结构对催化剂性能的影响,通过X射线荧光光谱（XRF）、透射电镜（TEM）、X射线衍射（XRD）、N₂物理吸附、H₂-程序升温还原（H₂-TPR）等表征,证实在保证稳定单分散核壳结构的前提下,活性Co₃O₄位点越多,催化剂反应活性越好。     

Catalytic decomposition of N2O and catalytic reduction of N2O and N2O + NO by NH3 in the presence of O2 over Fe-zeolite

The decomposition of N₂O, and the catalytic reduction by NH₃ of N₂O and N₂O + NO, have been studied on Fe-BEA, -ZSM-5 and -FER catalysts. These catalysts were prepared by classical ion exchange and characterized by TPR after various activation treatments. Fe-FER is the most active material in the catalytic decomposition because “oxo-species” reducible at low temperature, appearing upon interaction of Fe^II-zeolite with N₂O (-oxygen), are formed in largest amounts with this material. The decomposition of N₂O is promoted by addition of NH₃, and even more with NH₃ + NO in the case of Fe-FER and -BEA. It is proposed that the NO-promoted reduction of N₂O originated from the fast surface reaction between -oxygen O^* and NO^* to yield NO₂^*, which in turn reacts immediately with NH₃.     

The peculiarities of N2O activation over oxides of alkali-earth metals in the oxidative coupling of methane

The catalytic properties of Na/CaO with a low amount of alkali promoter and SrO were studied under comparable conditions, using CH₄-O₂ and CH₄-N₂O reaction mixtures. CH₄ conversion was similar for both oxidants ( <5%). Nitrous oxide was shown to be more active and selective oxidant than oxygen. It was noted that molecular oxygen influenced the rate of N₂O decomposition over SrO, while for Na/CaO catalysts such effect was not observed. Two different schemes for N₂O decomposition over catalysts studied were found. Carbon dioxide decreases the production of ethane over SrO when N₂O is used as an oxidant.     

Selective reduction of nitrogen oxides with various organic substances on precious metal catalysts under a high GHSV condition

Performances of Pt and Rh catalysts for the selective reduction of NO were investigated using various reducing agents under high gas hourly space velocity (GHSV). Higher activities were attained when olefins were used for both Pt and Rh catalysts, and when oxygen containing substances such as methyl tert.-butyl ether (MTBE) were used in the case of Rh catalysts. Selectivity toward N₂ for the NO converted was from 7% to 38% for Pt catalysts and from 45% to 67% for Rh catalysts. A comparison of N₂O decomposition rates on these catalysts has shown that gaseous N₂O is not a principal intermediate in the pathway for N₂ formation. The high selectivity toward N₂ for Rh/Al₂O₃ at low GHSV conditions is attributed to an additional catalytic effect of A1₂O₃, which can reduce NO₂ with propylene at temperatures as low as 350°C.     

Transfer and Reaction Performances of Selective Catalytic Reduction of N2O with CO over Monolith Catalysts

This work tries to identify the relationship between geometric configuration of monolith catalysts, and transfer and reaction performances for selective catalytic reduction of N2O with CO. Monolith cat...     

Catalytic decomposition of N2O over supported Rh catalysts: effects of supports and Rh dispersion

The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al₂O₃, ZrO₂, FSM-16, CeO₂, La₂O₃) showed that the activities of Rh/Al₂O₃ and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N₂O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N₂O experiment over a Rh/USY catalyst suggested that the catalytic N₂O decomposition occurs on oxygen-covered surface and that O₂ may be freed on collision of N₂O molecules with the adsorbed oxygen atoms.     

The role of carbon surface chemistry in N2O conversion to N2 over Ni catalyst supported on activated carbon

The effect of acidic treatments on N₂O reduction over Ni catalysts supported on activated carbon was systematically studied. The catalysts were characterized by N₂ adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It is found that surface chemistry plays an important role in N₂O-carbon reaction catalyzed by Ni catalyst. HNO₃ treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a more uniform catalyst dispersion and higher catalytic activity. However, HCl treatment decreases active acidic groups and increases the inactive groups, playing an opposite role in the catalyst dispersion and catalytic activity. A thorough discussion of the mechanism of the N₂O catalytic reduction is made based upon results from isothermal reactions, temperature-programmed reactions (TPR) and characterization of catalysts. The effect of acidic treatment on pore structure is also discussed.     

己二酸尾气中N_2O处理技术进展

介绍了己二酸尾气中N_2O处理技术进展,对比焚烧技术、催化分解技术和氧化苯制苯酚技术处理N_2O的优劣,分析各技术的性质特点及应用历程,指出N_2O直接分解技术因不产生NOx,对环境无污染,是工业应用最优技术。开发自主知识产权的N_2O处理技术,制备性能优异的N_2O分解催化剂,有效减少N_2O的排放,将对环境、社会和经济效益带来巨大影响。     

汽车尾气净化三效催化剂中N2O和NH3的生成及控制研究进展

N₂O和NH₃的排放主要来自于机动车尾气排放。本文总结了近十几年来轻型汽油车N₂O和NH₃排放的研究进展,阐述了两种气态污染副产物在三效催化剂中的形成机理,通过对影响N₂O和NH₃生成的贵金属种类和含量、载体材料、不同气体组成和浓度、老化条件、不同车辆及测试工况、反应温度等主要影响因素的综述,总结了各要素对N₂O和NH₃形成的影响,得出N₂O和NH₃主要在富燃条件下冷启动阶段生成,NO的解离在N₂O和NH₃的生成中起关键作用;影响N₂O和NH₃生成的各因素之间相互关联,相互影响;催化剂的老化增加N₂O和NH₃的排放;贵金属Rh比Pd和Pt更有利于N₂O和NH₃的分解等结论。发动机、后处理策略系统的升级、更合适测试循环的开发以及催化剂的优化可以进一步降低N₂O和NH₃的排放。     

Catalytic decomposition of nitrous oxide over Ru-exchanged zeolites

We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N₂O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N₂O per Ru³⁺ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N₂O: 5.132 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-HNaUSY at 200°C versus 5.609 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-NaZSM-5 at 300°C). The kinetics of decomposition of N₂O over a Ru-NaZSM-5 (Ru: 0.99 wt.-%), a Ru-HNaUSY (Ru: 1.45 wt.-%) and a Ru-free, Na-ZSM-5 catalyst were studied over the temperature range from 40 to 700°C using a temperature-programmed micro-reactor system. With partial pressures of N₂O and O₂ up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN₂O/dt=itk(P_N2O) (P_O2)^−0.5 for Ru-HNaUSY, −dN₂O/dt=k(P_N2O) (P_O2)^−0.1 for Ru-NaZSM-5, and −dN₂O/dt=k(P_N2O)^−0.2 (P_O2)^−0.1 for Na-ZSM-5. Oxygen had a stronger inhibition effect on the Ru-HNaUSY catalyst than on Ru-NaZSM-5. The oxygen inhibition effect was more pronounced at low temperature than at high temperature. We propose that the negative effect of oxygen on the rate of N₂O decomposition over Ru-HNaUSY is stronger than Ru-NaZSM-5 because at the lower temperatures (<200°C) the desorption of oxygen is a rate-limiting step over the faujasite-based catalyst. The apparent activation energy for N₂O decomposition in the absence of oxygen is much lower on Ru-HNaUSY (E_a: 46 kJ mol⁻¹) than on Ru-NaZSM-5 (E_a: 220 kJ mol⁻¹).