CeO2基氧化物储氧材料研究(Ⅱ)添加贵金属改进储氧能力

在高温老化的复合氧化物CZO和CZYO体系中,添加微量贵金属(Pt,Pd,Rh)明显提高还原速度并增加OSC.含贵金属的CZO或CZYO的OSC与其组成和贵金属的种类有关.较长时间(10 h)老化后含Pd的CZO3样品的OSC明显下降,CZYO2样品的OSC略有下降.含Pt/Rh,10 h老化后CZO3和CZY02样品的OSC均高于相应同条件老化的含Pd样品的OSC.     

CeO2基氧化物储氧材料研究(Ⅱ)添加贵金属改进储氧能力

在高温老化的复合氧化物CZO和CZYO体系中,添加微量贵金属(Pt,Pd,Rh)明显提高还原速度并增加OSC.含贵金属的CZO或CZYO的OSC与其组成和贵金属的种类有关.较长时间(10 h)老化后含Pd的CZO3样品的OSC明显下降,CZYO2样品的OSC略有下降.含Pt/Rh,10 h老化后CZO3和CZY02样品的OSC均高于相应同条件老化的含Pd样品的OSC.     

不同沉淀剂对Ce0.65Zr0.35O2复合氧化物性能的影响

本文选用不同沉淀剂,用共沉淀法制备了稀土储氧材料Ce0.65Zr0.35O2复合氧化物,对用不同沉淀剂制备出的氧化物样品进行了XRD,BET,OSC和H2-TPR的测试和分析。结果表明,用不同沉淀剂制备出的氧化物,均为立方相的铈锆固溶体,经1000℃5小时老化后也无相的分离;以(NH4)2CO3和NH3.H2O的混合物为沉淀剂制备出的氧化物有最大的比表面积,经600℃焙烧后高达120m2/g以上;并且样品具有良好的储氧性能及低温还原能力。     

添加剂对铈锆复合氧化物性能的影响

制备了铈锆及含有氧化钇、氧化镧和氧化镨的铈锆复合氧化物,并用XRD和BET手段对新鲜及高温老化后的样品进行了表征.结果表明,制备的样品具有单一的立方晶相,并能耐较高的温度;同时,添加剂能增大铈锆复合氧化物的孔径,提高其耐热性能.     

铈锆铝复合氧化物的制备及其性能研究

以硝酸铈和硝酸锆为原料,氨水为沉淀剂,双氧水为氧化剂,采用共沉淀法将铈锆固溶体负载在固态铝源(拟薄水铝石、活性氧化铝和改性氧化铝)表面,制备了铈锆铝复合氧化物。通过XRD,TEM,BET,TPR等手段对铈锆铝复合氧化物进行了结构表征和性能分析。研究结果表明:铈锆固溶体负载在氧化铝上,颗粒明显变小,老化性能得到显著改善;不同形态固态铝源制备的铈锆铝复合氧化物性能各异,以拟薄水铝石为铝源制备的样品比表面积最大,以改性氧化铝为铝源制备的样品表现出最佳的储氧性能。     

不同制备方法对铈锆复合氧化物结构及性能的影响

采用共沉淀法、均相沉淀法以及反相微乳法制备了铈锆复合氧化物.通过XRD,TEM,BET等表征手段来分析所得铈锆氧化物粉体的性质,将制得的粉体涂覆在堇青石蜂窝陶瓷载体上作为涂层,担载一定量的贵金属Pt作为活性组分制得整体催化剂,并在低温水汽变换反应上考察它们的催化性能.分析结果表明3种方法都得到了单相的铈锆固溶体;微乳法制得的纳米级铈锆固溶体粒径分布均匀、平均粒径尺寸为6 nm;所得纳米级铈锆复合氧化物的比表面积大小为微乳法＞均相沉淀法＞共沉淀法.实验结果表明用微乳法制得的铈锆复合氧化物的催化性能要优于其他两种方法.     

掺杂元素对铈锆固溶体性能的影响

用共沉淀法制备了CeZr,CeYZr,LBCeZr,LaCePrZr,LaCePrYZr和LaCePr固溶体,并对样品进行了XRD,BET,OSC以及催化性能测试和分析,表明所制备的固溶体全部为立方相结构,少量掺杂Y可以提高固溶体的比表面积和热稳定性;少量掺杂La也可以提高固溶体的热稳定性,但掺杂量过大时固溶体的比表面积和热稳定性均下降;用包头稀土矿提Nd后的LaCePr富集物制备的LaCePrZr和LaCePrYZr固溶体也具有较大比表面积和较好热稳定性.同时也采用浸渍法用Al2O3和SiO2对CeZr固溶体进行了包覆,CeZr固溶体包覆Al2O3和SiO2后比表面积和老化后的比表面积都有很大的提高.     

共沉淀法合成铈锆复合氧化物及表征

以共沉淀法制备了Ce0.8Zr0.2O2复合氧化物. 样品经BET法比表面积测定, XRD, SEM和粒度分布等表征, 结果显示500 ℃时(Ce-Zr)O2即形成单一立方相固溶体, SBET可达到135 m2*g-1, D50为7.17 μm, 经900 ℃老化6 h后, 仍保持相结构不变, SBET还大于40 m2*g-1, 显示了较高的热稳定性.     

不同铝源与铈锆复合的性能及机制

制备了CZ及CZ/AL,CZ/AS与CZ/AM(铈锆固溶体与氧化铝的复合氧化物),通过X射线衍射(XRD)、比表面(BET)、储放氧(OSC)和透射电镜(TEM)等手段对样品的晶相结构、比表面、储氧性能及微观结构等进行表征。结果表明:CZ/AL及CZ/AS都可形成单一稳定的立方晶型结构,氧化铝的掺杂可提高铈锆固溶体的比表面及耐高温稳定性,其中CZ/AS的比表面最高,CZ/AL储氧性能最大。此外,其复合机理表明,Al2O3与铈锆固溶体在纳米级别上的化学复合与纯粹的机械混合相比,前者具有更加稳定的晶型结构、更大的比表面和更好的储氧性能。     

还原热处理对铈锆铝复合氧化物性能的影响

采用共沉淀法制备铈锆铝复合氧化物(CeO2-ZrO2-Al2O3,CZA)和铈锆复合氧化物(CeO2-ZrO2,CZ),将样品分别在空气和10%H2/Ar气氛下进行热处理,利用X射线粉末衍射(XRD)、O2脉冲吸附、H2程序升温还原(H2-TPR)等手段研究了复合氧化物的结构及性能.结果表明:CZA样品经950℃还原热处理后出现CeAlO3晶相,热处理温度越高,越有利于CeAlO3物相生成.CZA储氧量(OSC)随着还原热处理温度升高逐渐增大,至900℃达到1270.3μmo·lg-1;温度继续升高,OSC减小,1100℃还原热处理后CZA的OSC仅为23.2μmo·lg-1.研究发现还原热处理中形成CeAlO3,其显著影响CZA样品的储氧性能和还原性能.     

Metal–Organic Frameworks for Oxygen Storage

We present a systematic study of metal–organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10 000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST‐1 (Cu‐BTC) and NU‐125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST‐1 and NU‐125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU‐125 has an increased excess capacity for oxygen of 237 % and 98 %, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.     

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage

Titanium dioxide (TiO₂) is a promising anode material for sodium-ion batteries (SIBs) due to its low cost, natural abundance, nontoxicity, and excellent electrochemical stability. Oxygen vacancies, the most common point defects in TiO₂, can dramatically influence the physical and chemical properties of TiO₂, including band structure, crystal structure and adsorption properties. Recent studies have demonstrated that oxygen-deficient TiO₂ can significantly enhance sodium storage performance. Considering the importance of oxygen vacancies in modifying the properties of TiO₂, the structural properties, common synthesis strategies, characterization techniques, as well as the contribution of oxygen-deficient TiO₂ on initial Coulombic efficiency, cyclic stability, rate performance for sodium storage are comprehensively described in this review. Finally, some perspectives on the challenge and future opportunities for the development of oxygen-deficient TiO₂ are proposed.     

储氧材料制备过程中的结构及织构变化

Ce_0.65Zr_0.35O₂ solid solution was prepared by co-precipitation method and characterized by X-ray diffraction (XRD), Raman spectra, BET, oxygen storage capacity (OSC) and temperature-programmed reduction measurements (H₂-TPR) after calcination at 100 ℃, 300 ℃, 600 ℃, and 1 000 ℃. The results showed that the precipitation was a crystalline of fluorite structure, and in the process of the precipitation transformation into Ce_0.65Zr_0.35O₂ solid solution, the fluorite structure of the precipitation kept unchanged. The samples had different BET surface areas and OSC at different temperatures, but they held the performance of stable structure. After 1 000 ℃, there didn′t appear the other crystalline phase. So the samples prepared by co-precipitation method had excellent texture and higher thermal stability.     

表面活性剂对CeZrYO储氧材料性能的影响

采用表面活性剂聚乙二醇改性共沉淀法制备了铈锆钇储氧材料,并详细考察了表面活性剂的添加方式和添加量对储氧材料性能的影响.采用X射线衍射、氧脉冲吸附、H2程序升温还原和N2吸附技术对储氧材料的晶体结构、储氧性能、还原性能和织构性能进行了表征.结果表明,表面活性剂的添加方式和添加量对储氧材料的性能有重要影响.随着表面活性剂添加量的增加,储氧材料的储氧量先增加后减少,在添加量为50%时达最大值.在表面活性剂添加量相同的情况下,与一次性添加制得的样品相比,分两次添加制得的样品的比表面积和孔体积有所增大,抗老化性能有所提高.一次性添加表面活性剂制得的样品经高温老化后,小于10nm的孔基本消失;而分两次添加表面活性剂制得的样品经高温老化后,仍保持有这些小孔.     

Oxygen Storage Materials for Automotive Catalysts: Ceria-Zirconia Solid Solutions

This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan.Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La⁴⁺ or Zr⁴⁺. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term partial OSC was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the total OSC. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the diffusion barrier concept, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air.Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper.For ceriazirconia solid solutions composed of equimolar CeO₂ and ZrO₂(Ce/Zr=1), the total or partial OSC of the -phase CeZrO₄, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value.For a ceriazirconia solid solution composed of non-equimolar CeO₂ and ZrO₂(Ce/Zr 1), the partial OSC of a ceria--phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a -phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O₂/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%.The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis.     

Nitrogen/Oxygen Co-Doped Hierarchically Porous Carbon for High-Performance Potassium Storage

Although the insertion of potassium ions into graphite has been proven to be realistic, the electrochemical performance of potassium-ion batteries (PIBs) is not yet satisfactory. Therefore, more effort is required to improve the specific capabilities and achieve a long cycling life. The mild carbonization process in molten salt (NaCl-KCl) is used to synthesize nitrogen/oxygen co-doped hierarchically porous carbon (NOPC) for PIBs by using cyanobacteria as the carbon source. This exhibits highly reversible capacities and ultra-long cycling stability, retaining a capacity of 266 mA h g⁻¹ at 50 mA g⁻¹ (100 cycles) and presents a capacity of 104.3 mA h g⁻¹ at 1000 mA g⁻¹ (1000 cycles). Kinetics analysis reveals that the potassium ion (K⁺) storage of NOPC is controlled by a capacitive process, which plays a crucial role in the excellent rate performance and superior reversible ability. The high proportion of capacitive behavior can be ascribed to the hierarchically porous structure and improved conductivity resulting from nitrogen and oxygen doping. Furthermore, density functional theory (DFT) calculations theoretically validate the enhanced potassium storage effect of the as-obtained NOPC. More importantly, the route to NOPC from cyanobacteria in molten salt provides a green approach to the synthesis of porous carbon materials.     

Hydrothermal Preparation and Oxygen Storage Capacity of Nano CeO2-based Materials

"catalysts were synthesized by hydrothermal method. The X-ray diffraction result showed that the averageparticle size was in the range of 11-12 nm, which was correspondence to the high-resolution transmission electron microscopy result that the average particle size was about 12 nm. The specific surface area of the NiO-CeO2 binary compounds was in the range of 54-75 m2/g. Also the average particle size of the Bi2O3-CeO2 binary compounds was in the range of 8-11 nm. The oxygen storage capacity of the NiO-CeO2 and Bi2O3-CeO2 binary compounds was investigated under reduction and oxidation conditions. When the Ni and Bi concentration in CeO2 was up to 30%, the OSC values reached 2465 and 2560 1molO/g separately, which indicated that NiO and Bi2O3 compounded CeO2 materials have fine catalysis activity than other cations doped CeO2-based materials and appear to be very promising for practical applications such as OSC materials"