稀土在机动车尾气催化净化中的应用与研究进展

随着我国机动车尾气排放法规日趋严格,对机动车尾气净化催化剂性能提出了更高的要求.稀土元素由于独特的4f电子层结构和储放氧性能等特性,在机动车尾气催化剂中得到广泛应用.本文综述了稀土元素在机动车尾气催化剂中的应用及相关机理研究现状,并依据京V排放法规要求探讨了最新排放限值对尾气净化催化剂性能的要求,分析了稀土在开发高性能催化剂中的作用,并对稀土在机动车尾气净化催化剂中的应用前景进行了展望.     

稀土在汽车尾气净化催化剂中的作用

通过对稀土在汽车尾气净化催化剂中的作用综述,阐明随着贵金属资源的日趋耗竭和越来越严格的排放法规在全世界范围的推行,稀土在高性价比汽车尾气净化催化剂中必将扮演越来越重要的角色,发挥其它元素甚至贵金属元素都无法取代的作用.     

稀土在汽油车尾气净化中的应用

截至2021年底,中国的汽车保有量超过3亿辆,其中汽油车占比90%以上,是中国最重要的汽车类型。为了应对汽油车尾气中的氮氧化物(NO_x)、碳氢化合物(HC)和一氧化碳(CO)等典型污染物,“三效催化剂”这一具有里程碑意义的汽油车尾气后处理技术被开发、应用并不断完善。新近流行的汽油缸内直喷(GDI)技术会导致显著的颗粒污染物(PM)排放,由此又催生了汽油车颗粒物过滤器(GPF)技术。上述技术的实施或多或少都需要依赖中国战略资源——稀土的参与。本文首先对各类汽油车尾气净化技术的发展进行了回顾,之后重点分析了(以CeO₂为主的)稀土材料在三效催化剂储氧材料、催化剂载体/贵金属稳定剂和汽油车颗粒物过滤器中的具体应用方式和效果。可以看出,随着新型稀土材料的开发和技术迭代,现代汽油车尾气净化技术正在变得越来越高效、越来越便宜。最后,本文对汽油车尾气净化用稀土材料的发展趋势进行了展望,分析了相关产业未来升级的重点和难点所在。     

稀土氧化渣净化铸造铁水的实验研究与热力学分析

用30 kg中频炉和自制的硅钼棒炉,对不同硫、磷含量的铸造铁水用稀土氧化渣进行了净化处理研究,对处理过程中的脱硫和脱磷行为进行了热力学分析。研究表明,与传统的钙系渣处理相比成本可降低50％以上,脱硫率可提高30～40％;且兼有提高铸件性能及脱磷、脱氧的作用。     

汽车尾气净化用稀土钙钛石型复合氧化物催化剂

稀土钙钛石型复合氧化物催化剂是一种性能良好的汽车尾气净化催化剂 ,是贵金属三效催化剂未来的替代品。本文对此催化剂的研究进展及其负载技术作一简述     

过滤净化用多孔金属材料的开发应用与进展

综述了过滤净化用多孔金属材料的最新开发应用进展与市场状况, 对我国目前过滤净化用多孔金属材料的研发应用及市场等各方面存在的现象进行了初步分析, 并对这一领域的发展前景进行了展望.     

含新型稀土储氧材料的高性能天然气汽车尾气净化Pd催化剂

制备了以La-Al2O3和La-Al2O3+CeO2-ZrO2-MnOx为载体的天然气汽车尾气净化Pd催化剂. 结果表明, 与Pd/La-Al2O3相比, Pd/Al2O3+CeO2-ZrO2-MnOx催化剂能极大地降低CH4的起燃温度并显著改善催化剂的反应性能. 经1000 ℃水热老化后, CH4的起燃温度仅上升了40 ℃, 表现出优异的抗老化性能.     

稀土催化材料研究与应用

稀土具有特殊的物理和化学性质,在化学反应过程中表现出良好的催化效果,在多种领域得到了广泛应用.目前,稀土催化材料在石油化工催化、机动车尾气催化、燃料电池催化、催化燃烧、制氢催化及其他环保催化的相关材料方面发挥着重要的作用.尽管稀土催化应用广泛,但是稀土对于各个催化过程的作用鲜见系统总结,因此,本文主要对近年来上述领域关...     

氧渗透膜反应器的烷烃氧化脱氢

研究了乙烷和丙烷在催化膜反应器中的氧化脱氢反应．所用的膜材料为La2Ni0.9V0.1O4＋δ和Ba0.5Sr0.5Co0.8Fe0.2O3-δ．为了平衡氧气通量和额外的均匀气相反应,实验选择在中温段进行（550或者650℃）．实验结果表明膜的氧渗透通量和膜表面上主要激活烷烃的活性位在获得高的烷烃转化率过程中起决定性作用．乙烷和丙烷的氧化脱氢实验数据均符合Mars-van Krevelen机理,其中烷烃和膜表面的晶格氧反应产生相应的烯烃．同时证明了气相和膜表面的氧浓度是决定烯烃选择性的关键．     

富有“磁力”的稀土元素——钕、钐、钆、镝、铒等元素的磁性质在生产、生活和研究中的应用

简要介绍了稀土元素的电子结构特点，并以稀土永磁体、稀土单离子磁体、稀土磁共振造影剂和稀土分子量子比特等主题为例，介绍了部分稀土元素在和磁性质相关的生产和研究中的应用。     

Hydrofluoride Synthesis of Fluorides of Some Rare-Earth Elements

Thermal gravimetric, X-ray phase, IR spectroscopic, and chemical analyses were applied to study the reaction of yttrium and neodymium oxides with NH₄HF₂.     

稀土氧化物超微粉的催化酯化行为

制备了5种稀土氧化物超微粉并考察了它们的催化酯化的活性,发现超微粉的催化活性均高于普通稀土氧化物,Y_2O_3超微粉催化酯化产物的酸值接近0.1,有应用前景。     

Content of Rare-Earth Elements in Soils of Technogeochemical Anomalies

Russian Journal of General Chemistry - This review presents geochemical and medical-ecological information on the content, distribution, and accumulation of rare-earth elements in soils of...     

稀土元素测定方法的研究进展

综述了稀土元素测定方法(包括电感耦合等离子体质谱法、电感耦合等离子体原子发射光谱法、原子吸收光谱法、荧光光度法、紫外-可见分光光度法、高效液相色谱法、电化学方法、常规化学分析法和在线联用技术等)的研究进展(引用文献37篇)。     

稀土A-Ce-O催化剂的合成及性能研究

采用改进的溶胶-凝胶法合成出了几种含铈稀土复合氧化物催化剂,运用XRD,IR等不同测试手段对复合氧化物催化剂进行了表征,测试了甲烷催化燃烧活性.XRD分析结果表明:经1200 ℃焙烧3 h后4种催化剂中Ba-Ce-O,Sr-Ce-O主要以单一相钙钛矿结构BaCeO3和SrCeO3的形式存在,La-Ce-O体系催化剂呈现面心立方晶体结构特征衍射峰,与立方结构CeO2的衍射峰相似,只是峰的位置偏向低角度;Mg-Ce-O主要以简单氧化物CeO2的相存在,在甲烷催化燃烧反应中La-Ce-O显示出了良好的催化活性,T10为510 ℃,T90为670 ℃;主相为SrCeO3的Sr-Ce-O体系催化剂的甲烷催化活性最差,T10为570 ℃,T90为743 ℃.     

Extraction of Rare-Earth Elements in Hydrofluoride Decomposition of Loparite Concentrate

Distribution and existence forms of rare-earth elements in decomposition of the loparite concentrate with ammonium hydrofluoride were studied. It was found that, in the course of the aqueous leaching of the fluorinated concentrate, rare-earth elements fully remain in the insoluble residue as complex salts of general formula NaLnF₄. The process of pyrohydrolysis of the insoluble residue was examined. It was shown that varying the process conditions always results in that a NaLnF4-containing product is obtained. It was found that rare-earth elements can be extracted from the insoluble residue and separated from calcium and thorium, and the conditions for this extraction were determined.     

Optical and Chromaticity Characteristics of Arsenazo III Complexes of Rare-Earth Elements

Optimal conditions for the complexation of La, Nd, Sm, Tb, Dy, Gd, Ho, Er, and Yb ions with Arsenazo III were found, and molar absorptivities of the complexes were calculated. Chromaticity characteristics of the complexes were determined. The coefficients of calibration plot equations and molar coefficients of chromaticity functions were calculated for the concentration range 10–50 g of rare-earth element per 25 mL of solution. It was demonstrated that the use of the most sensitive chromaticity functions increases the sensitivity of the reaction by 1.5–2 orders of magnitude compared to the photometric method.     

Rare-Earth Elements in Molecular Conductors: Crystal and Electronic Structures

The new molecular conductors with some rare-earth metal-complex anions (ET)₅[M(NCS)₆NO₃]·C₂H₅OH (M=Dy (1), Y (2), Ho (3)) and (TMTSF)₃[Y(NO₃)₅]·2C₆H₅Cl (4) as well as a new low-temperature modification of tetra-n-buthylammonium dysprosium(III) complex, (Bu₄N)₃[Dy(NCS)₄(NO₃)₂] (5) used for the preparation of salt 1 were synthesized and studied by X-ray crystallography at 295 and 110 K. Salts 1-3 have a layered crystal structure with a new packing type of the radical cation layers, called an ω-type. Electronic structure calculations for the compounds 1-3 showed that the paired ET molecules have a positive charge +1 and the single ET molecules are neutral. The directions of the TMTSF stacks in the neighboring organic layers of 4 are practically perpendicular so that salt 4 can be regarded as a precursor of 2D conductors formed by mutually perpendicular directions of conductivity.     

Isolation of Rare-Earth Elements from Mixtures of Calcium and Lanthanide Oxalates

The temperature regions for separate crystallization of rare-earth element (REE) oxides of the cerium group in the presence of CaCO₃ have been determined using X-ray diffraction, differential thermogravimetric analysis, inductively coupled plasma mass spectroscopy, and X-ray fluorescence. The possibility to separate REE oxides from CaCO₃ in H₂SO₄ solutions after heat treatment (450–600°C) has been studied. The solid phase of the precipitate is represented by slightly soluble calcium sulfate, whereas the REE oxides pass into the liquid phase in the form of highly soluble sulfates. After heat treatment of the test mixture of REE oxalates and calcium oxalate at a temperature higher than 750°C, calcium compounds pass into 1–2% HNO₃ liquid phase in the form of nitrates, whereas lanthanide oxides remain in the insoluble phase of REE oxide solid solution having CeO₂ structure.