富氢气中CO氧化脱除研究

富氢气中少量的CO会导致燃料电池电极中毒,质子交换膜燃料电池 (PEMFC) 的发展急需解决该问题。目前以催化氧化脱除富氢气中少量CO是较理想的方式。本文概述了富氢气中CO选择性氧化脱除的研究进展,并展望了今后研究的方向及应用前景。     

Au/Fe2O3催化剂的制备及其对富氢气体中一氧化碳选择性氧化的催化性能

 采用共沉淀法制备了1.5%Au/Fe2O3催化剂,考察了加料方式对Au/Fe2O3催化剂化学组成及其催化富氢气体中CO选择性氧化性能的影响. 结果表明,正加法制备的Au/Fe2O3催化剂的性能明显好于反加法制备的催化剂,80 ℃时前者对富氢气体中CO选择性氧化反应的转化率为94%,CO2选择性为65%,连续反应10 h,催化剂活性没有变化. XRD,XPS和TEM等的测试结果表明,正加法制备的Au/Fe2O3催化剂中金粒子的平均粒径为2～4 nm,金粒子高度分散在载体上,并与载体之间发生了较强的相互作用,从而表现出较高的催化性能.     

氧化铈气凝胶担载氧化铜催化剂上的一氧化碳氧化

 以一氧化碳氧化为探针反应,考察了氧化铈气凝胶担载氧化铜催化剂的催化活性,研究了催化剂中氧化铜的含量、载体及催化剂的焙烧温度对催化剂活性的影响．结果表明,氧化铈气凝胶担载的氧化铜催化剂对一氧化碳氧化反应呈现出高催化活性,适当温度下焙烧载体及催化剂有利于提高催化剂的催化活性;随着催化剂中氧化铜含量的增加,一氧化碳完全转化的温度降低,但当w（CuO）＞12％时,过量的氧化铜以体相形式而不是以高分散形式存在,对催化剂活性的影响很小．     

银负载量及反应气预处理对银催化剂上氢气中CO选择氧化反应的影响

 考察了银负载量及反应气预处理对银催化剂上CO选择氧化反应的影响．结果表明，O2转化率、CO的转化率及选择性都随着银负载量的增加而升高，CO氧化的选择性随着温度的降低而升高，低温下的选择性可达70％～80％．CO－TPR谱显示，产物CO2脱附量及脱附温度的次序与CO选择氧化活性有一致的对应关系．当反应气处理温度为300℃时，催化剂上CO氧化活性最高；随着反应气处理温度的继续升高，CO氧化活性及选择性反而降低．金属银的粒子尺寸随着银负载量的增加而增大；高温下反应气处理后，金属银粒子的尺寸明显减小．催化剂上CO氧化活性及选择性与银粒子的大小及催化剂的表面结构有关．     

Selective Oxidation of CO in Excess H2 over Ru/Al2O3 Catalysts Modified with Metal Oxide

The Ru/Al_2O_3 catalysts modified with metal oxide(K_2O and La_2O_3)were prepared via incipient wetness impregnation method from RuCl_3·nH_2O mixed with nitrate loading on Al_2O3 support. The activity of catalysts was evaluated under simulative conditions for the preferential oxidation of CO (CO-PROX)from the hydrogen-rich gas streams produced by reforming gas,and the performances of catalysts were investigated by XRD and TPR.The results showed that the activity temperature of the modified catalysts Ru-K_2O/Al_2O3 and Ru-La_2O_3/Al_2O_3 were lowered approximately 30℃compared with pure Ru/Al_2O_3,and the activity temperature range was widened.The conversion of CO on Ru-K_2O/Al_2O_3 and Ru-La_2O_3/Al_2O_3 was above 99% at 140-160℃,suitable to remove CO in a hydrogen-rich gas and the selectivity of Ru-La_2O_3/Al_2O_3 was higher than that of Ru-K_2O/Al_2O_3 in the active temperature range. Slight methanation reaction was detected at 220℃and above.     

富氢气体中CO优选氧化反应: Au与载体相互作用的影响

以Fe2O3,Co3O4,ZrO2和ZrO2-CeO2为载体,研究了负载型Au催化剂在CO优选氧化反应中的性能,并用高分辨透射电子显微镜、X射线衍射和X射线光电子能谱等技术对催化剂进行了表征,考察了Au与载体之间的相互作用对Au电子性质的影响.结果表明,在60℃以下,Au/Fe2O3上CO能被完全氧化,且CO氧化反应选择性约为50%,而在Au/Co3O4,Au/ZrO2和Au/ZrO2-CeO2催化剂上,CO在更低的温度下才能被完全氧化.这是由于具有拉电子效应的载体(如Fe2O3和Co3O4)能使Au带有部分正电荷,从而对CO优选氧化反应具有较高的催化活性.因此,选择合适的载体或对载体进行掺杂改性,调节Au的正电荷数目,有可能进一步提高Au催化剂的催化活性.     

CuxCe1-xO2-x/SiO2催化剂上Co催化氧化及反应活化能

以SiO2为载体,利用共浸渍法制备了不同Cu、ce摩尔比和含量的CuxCe1-xO2-x/SiO2(x-0～1)催化剂,在消除内、外扩散的条件下,评价了催化剂的CO催化氧化活性,求取了反应的活化能,并对催化剂的结构进行了表征.结果表明,CuxCe1-xO2-x/SiO2催化剂的活性和反应活化能与Cu、Ce摩尔比和CuxCe1-xO2-x含量都有关系,其中Cu、ce摩尔比为1:1的25%Cu0.5,Ce0.5,O1.5/SiO2催化剂具有最好的催化活性和最低的反应活化能,CO能够在169℃时完全转化,反应的活化能为56.1 kJ/mol.对于Cu0.5Ce0.5O1.5系列催化剂,活性组分含量较低时,催化剂的物相主要是CuO-CeO2固溶体,含量大于35%时开始有CuO物相生成.对于不同Cu、Ce摩尔比的催化剂,Cu摩尔含量较高时主要是CuO物相,Cu摩尔含量较低时主要是CuO-CeO2固溶体和CeO2物相.活性组分Ce和Cu之间、活性组分和载体之间存在着一定的相互作用,其对催化剂的活性和反应活化能有一定的影响.     

Au/MOx/Al2O3催化剂催化CO低温氧化

 采用沉积沉淀法，将金负载在复合氧化物载体MOx/Al2O3上，制备得到了Au/MOx/Al2O3催化剂的活性要高于Au/Al2O3催化剂。Au/FeOx/Al2O3催化剂能够在低于223K的温度下实现CO完全催化氧化。TEM图象分析表明，纳米级高分散的金颗粒是金催化剂高活性的前提，但载体的选择，以及复合氧化物载体中过渡金属氧化物的选择，也会对金催化剂的活性产生明显的影响。     

不同CuO/CeO2催化剂上CO低温氧化反应

 分别用热解硝酸铈法和浸渍法制备了不同物性的CeO2粉体和相应的CuO/CeO2催化剂,并用XRD, HRTEM和TPR等对样品进行了表征,利用微反-色谱装置考察了其催化CO低温氧化的活性. 结果表明,热解温度影响CeO2的物性(形貌、粒度大小及分布等). 相同条件下,不同物性的CeO2载体上CuO的负载情况不同, 500 ℃热解获得的CeO2载体上非晶态CuO负载量最高,相应的CuO/CeO2催化剂活性也较高. 非晶态CuO一部分进入CeO2晶格,另一部分高度分散于CeO2表面上. 焙烧温度较低时(≤ 600 ℃), 催化剂活性受焙烧温度的影响较小,而高温(800 ℃)焙烧后,催化剂则因载体粒度增大和CuO烧结团聚等因素导致催化活性明显降低.     

组合催化剂上丙烷选择氧化制丙烯酸

考察了在C3H8氧化脱氢的NiZrO催化剂和C3H6选择氧化的Mo基催化剂组成的组合催化剂上C3H8选择氧化制取丙烯酸的反应性能.结果表明,两个催化剂比例适当时,反应的丙烯酸收率可达最大.优化温度、烷氧比、空速以及N2含量等反应条件的结果发现,反应体系中O2的匮乏会严重影响反应性能.在有氧分布器的反应装置中对所选组合催化剂在优化的反应条件下进行了30h稳定性测试,结果表明,在340oC,反应性能基本稳定,C3H8转化率和丙烯酸选择性可分别维持在～20%和～74%.     

Effect of Addition of Base on Ceria and Reactivity of CuO/CeO2 Catalysts for Low-Temperature CO Oxidation

In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.     

负载型La-Sr-Cu系复合氧化物催化剂用于CO氧化

 采用柠檬酸盐法经650 ℃焙烧制备了莫来石负载的具有K2NiF4型结构的A2BO4型复合氧化物La2-xSrxCuO4 (0.4≤x≤1.0), 用XRD和SEM考察了该系列氧化物的晶体结构和形貌特征. 在固定床微型反应器中于含氧的CO气氛中测试了催化剂对CO氧化的催化活性; 结果表明反应的起燃温度低,当x=0.8～1.0时催化剂具有良好的CO氧化活性,在300 ℃时CO的转化率可达100%. 在流化床反应器中以此催化剂作为CO助燃剂对积炭的催化裂化待生剂CRC-1进行的再生实验结果表明,当x=0.8时催化剂的助燃活性最高,CO2/CO比值R可达488, CO的相对转化率 可达99.5%.     

富氢条件下Au／γ－Al2O3催化剂上CO的选择氧化反应

 用脉冲反应考察了富氢条件下Au／γ－Al2O3催化剂上CO的选择氧化反应．结果表明，CO和O2在Au／γ－Al2O3催化剂表面同时发生吸附，其吸附活性中心都在催化剂的活性组分表面，CO的吸附强度大于O2的吸附强度，吸附态的CO和吸附态的O2之间反应生成CO2．提高反应温度和增加原料中氧的含量都能提高CO的转化率．在所考察的实验条件下，O2的反应选择性基本上为100％．     

Temperature Hysteresis in Oxidation of CO on Complex Oxide Catalysts

We have used thermal desorption (TD) with mass spectrometric detection of the desorbed species to study the state of the surface of oxide catalysts for oxidation of CO. Detection of weakly bound forms of water and the species H₃O⁺ and HO ₂ ^⋅ in the thermal desorption spectra correlates with the existence of temperature hysteresis in these samples. The data obtained are explained by the reaction occurring in a highly active state via a heterogeneous-homogeneous mechanism, and also by the effect of local superheating. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 323–327, September–October, 2005.     

Selective Oxidation of Isobutane over NH4CsFePVMoAs Heteropolycompound Catalysts

A series of NH4Cs1.5Fe0.08HxPVMo11AsαOy heteropolycompound catalysts for the selective oxidation of isobutane, having Keggin structure, were synthesized by using co-precipitation method. The catalysts were characterized by FT-IR, H2-TPR, TG-DTA, SEM and XRD. Effects of the As content,reaction time, reaction temperature and molar ratio of isobutane to oxygen in feedstock on the activity and selectivity of the catalyst were investigated. The activation energy of the catalysts was measured by kinetics researches. Results showed the introduction of Cs^ into the catalysts shortened the stable period of them and enhanced their catalytic activity for the selective oxidation of isobutane. The highest conversion of isobutane and the total selectivity to liquid products were 18.6% and 81.2%, respectively,which were obtained at 380 *(3 with a space velocity of 975h^-1 over the NH4Cs1.5Fe0.08HxPVMo11 As0.3Oy heteropolycompound catalyst. It is confirmed that completely oxidized products were controlled well.     

碘酸改性溶胶凝胶法制备CuO/CeO2催化剂及富氢条件下催化CO氧化

采用一种碘酸改性的柠檬酸溶胶-凝胶法制备了CuO/CeO₂催化剂, 研究其在富氢气氛中CO优先氧化反应(CO-PROX)的催化活性. 与传统柠檬酸溶胶-凝胶法制备的催化剂相比, 碘酸改性溶胶-凝胶法制备的催化剂活性更好. 程序升温还原、 X射线衍射、 透射电子显微镜和X射线光电子能谱等表征证明该催化剂粒径较小, 表面含有更多的Ce³⁺及还原性氧化铜物种, 有利于提高催化剂的催化活性.     

Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO2 catalyst

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h-1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction （XRD） and temperature programmed reduction （TPR） measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.     

负载型金催化剂催化乙醇选择氧化反应

选择不同氧化物(Al2O3,SiO2,TiO2,MgO)和H-ZSM-5分子筛作为载体,以尿素为沉淀剂,采用沉积-沉淀法制备了一系列负载型金催化剂.采用X射线衍射、电感耦合等离子体发射光谱、程序升温还原、NH3程序升温脱附和透射电镜等技术对催化剂样品进行了表征,并测定了催化剂对乙醇选择氧化反应的催化性能.选择Au/Al2O3催化剂,考察了金负载量、反应条件(温度、压力、时间)和添加剂对乙醇选择氧化反应的影响.结果表明,所制备的Au/Al2O3催化剂的金负载率较高,金粒子较小(3～4 nm)且分布均匀.载体对金催化剂催化乙醇氧化反应有显著影响,主要产物为乙醛、乙酸乙酯和缩醛.以TiO2为载体时,乙醇转化率较高.以Al2O3为载体时,乙酸乙酯选择性较高;少量碱性添加剂可抑制缩醛的生成,并可提高乙醇转化率和乙酸乙酯选择性.在优化的条件下,乙醇转化率可达4.7%,乙酸乙酯选择性可达93.5%.     

CuO／CeO2和CuO／Al2O3催化剂的催化性能

本文以ＣＯ氧化为模式反应考察了ＣｅＯ２和Ａｌ２Ｏ３负载氧化铜催化剂的氧化活性，运用ＸＲＤ和ＴＰＲ技术研究了催化剂的还原性能和物相结构，结果表明：载体性质对负载ＣｕＯ催化剂的ＣＯ氧化活性有很大影响，ＣｕＯ／ＣｅＯ２催化剂活性明显高于ＣｕＯ／Ａｌ２Ｏ３催化剂．催化剂的还原特性随载体不同而不同．同时发现，热处理对催化剂铜物种的存在形式，晶粒大小、还原特性及其催化活性有明显影响，ＣｕＯ／Ａｌ２Ｏ３催化剂活性下降的主要因素是生成了活性较低的ＣｕＡｌ２Ｏ４相，而ＣｕＯ／ＣｅＯ２催化剂活性下降是由于ＣｕＯ和ＣｅＯ２发生烧结，晶粒变大     

丙烷选择氧化催化剂Mo-V-Zr-O的研究

研究了Zr添加量对Mo-V-O基催化剂丙烷选择氧化制丙烯醛催化性能的影响.对催化剂的BET、X射线衍射、H2-程序升温还原、NH3-程序升温脱附和异丙醇分解表征结果表明,Zr的添加改变了催化剂的物相结构、氧化还原性和酸碱性质,从而影响催化剂的催化性能,其中Mo2VZr0.5Ox催化剂表现出较好的催化活性和丙烯醛选择性.