高热稳定性、 高比表面积低铈型铈锆钇储氧材料的制备及其性能研究

采用氨水 碳酸铵混合沉淀剂制备了低铈型铈锆钇三组分储氧材料. 采用X射线衍射、 BET、 氧脉冲吸附和H2程序升温还原(H2-TPR)等技术对材料的晶体结构、 比表面积、 孔结构、 储氧性能和还原性能进行了研究. 结果表明， 该材料经873 K焙烧4 h后比表面积达到116.8 m2/g, 孔容达到0.30 cm3/g, 经1 273 K老化10 h后, 比表面积和孔容仍然保持在68.1 m2/g和 0.22 cm3/g. 由XRD结果可知, 材料的物相组成为四方相的Zr0.84 Ce0.16 O2, 在热处理过程中物相结构稳定. 氧脉冲吸附和程序升温还原的结果表明, 材料储氧性能保持较好.     

氧化共沉淀法制备纳米级铈锆固溶体

采用改进的氧化共沉淀法制备了Ce0.5Zr0.5O2固溶体, 利用XRD和BET测定了其结构和比表面积. 采用H2的程序升温还原(TPR)研究铈锆固溶体的还原特性, 以考察它的低温还原特性. 改进的氧化共沉淀法制备的铈锆固溶体在550 ℃可形成立方相固溶体, 具有较大的比表面积和较小的晶粒度, 同时还具有良好的低温还原特性和较高的热稳定性, 经900 ℃焙烧6 h后比表面积达到34.37 m2*g-1.     

大比表面积铈锆氧化物固溶体的制备

采用共沉淀法制备铈、锆氧化物固溶体.发现以适当配比的(NH4)HCO3和NH3*H2O混合溶液作为沉淀剂,同时控制沉淀过成中的反应条件,所得到的沉淀在较低的温度(400 ℃)下焙烧即可形成铈、锆氧化物固溶体.该固溶体具有较大的比表面积和高的储氧能力.形成沉淀后添加适量表面活性剂,可进一步提高产品的比表面积而对其还原行为和储氧性能几乎无影响.对制得的氧化物以X-射线衍射、程序升温还原、氧的脉冲滴定和液氮物理吸附等方法进行了表征.     

不同铈添加量对CeO2-ZrO2-Al2O3材料性能的影响

采用共沉淀法制备了一系列不同铈添加量的CeO2-ZrO2-Al2O3(CZA)储氧材料,并通过XRD、低温N2吸附-脱附、氧脉冲吸附(OSC)和H2-TPR等手段进行了表征。XRD结果表明,在1 000和1 100℃高温焙烧后,当CeO2添加量为8%时样品具有最好的结构稳定性能。N2吸附-脱附结果表明,CeO2添加量为8%时样品具有最好的织构性能,1 000℃时,比表面积和孔容分别为:136.6 m2.g-1和0.38 mL.g-1;1 100℃时,比表面积和孔容分别为:83.7 m2.g-1和0.23 mL.g-1。OSC结果显示,CeO2添加量为8%时样品具有最大的储氧量,1 000℃和1 100℃分别为70μmol.g-1和31μmol.g-1。H2-TPR结果表明,CeO2添加量为8%时样品具有最佳的还原性能。     

沉淀方法对CeO2-ZrO2系储氧材料性能的影响

利用不同沉淀方法制备了一系列CeO2-ZrO2系储氧材料,并应用BET、XRD、TPR及其储氧性能测定等方法对储氧材料进行了研究.结果表明,不同的沉淀方法对样品的结构和性能有重要的影响.并流法可得到耐高温,储氧性能好,比表面积高的储氧材料;正滴法所得样品储氧量低但稳定,其比表面积抗老化性能差;反滴法所制备的样品储氧性能好,老化后比表面积较低.三种沉淀方法均可形成CeO2-ZrO2固溶体,材料的还原性能取决于比表面积,但与储氧性能无直接关系.     

水热法合成Ce0.67Zr0.33O0.2固溶体研究

采用两种不同前驱体通过水热法合成了Ce0.67Zr0.33O0.2固溶体,并通过XRD,BET,TPR等手段考察了样品的相结构,比表面及还原特性.结果表明,在180℃,12 h的水热条件下,以共沉淀产物为前驱体所制得的Ce0.67Zr0.33O0.2固溶体比表面积较高,但存在一定程度的相分离;以凝胶产物为前驱体制得的Ce0.67Zr0.33O0.2固溶体结构更完整,具有良好的还原特性及热稳定性.     

CeO_2-ZrO_2-Al_2O_3稀土储氧材料制备工艺的研究

采用化学沉淀法制备了系列CeO2-ZrO2-Al2O3稀土储氧材料,并用BET,XRD和储氧性能测定等表征手段考察了陈化时间、La2O3含量、反应pH和沉淀方式等工艺因素对CeO2-ZrO2-Al2O3比表面积、储氧性能和结构的影响。结果表明:当陈化时间为12 h,反应pH=10时,掺杂2%(质量分数)La2O3的CeO2-ZrO2-Al2O3样品在老化前后均具有很高比表面积和良好的储氧性能,并且pH为影响样品比表面积及热稳定性能的主要因素。与一步法沉淀相比,二步法制得的CeO2-ZrO2-Al2O3样品具有很高的热稳定性能,1050℃老化5 h后的样品比表面积高达46.4 m2.g-1,但储氧性能略差,这与Al2O3对CeO2-ZrO2的结构影响程度有关。     

水热法合成Ce0.67Zr0.33O0.2固溶体研究

采用两种不同前驱体通过水热法合成了Ce0.67Zr0.33O0.2固溶体,并通过XRD,BET,TPR等手段考察了样品的相结构,比表面及还原特性.结果表明,在180℃,12 h的水热条件下,以共沉淀产物为前驱体所制得的Ce0.67Zr0.33O0.2固溶体比表面积较高,但存在一定程度的相分离;以凝胶产物为前驱体制得的Ce0.67Zr0.33O0.2固溶体结构更完整,具有良好的还原特性及热稳定性.     

CeO2-ZrO2-Y2O3对Pt-Rh型三效催化剂性能的影响

采用共沉淀法技术制备了Ce0.35Zr0.55Y0.10固溶体,并对其进行了比表面积、储氧量的测试和XRD的表征.将其用于低贵金属Pt-Rh型三效催化剂的制备,考察了CeO2-ZrO2-Y2O3对三效催化剂性能的影响.结果表明,Ce0.35Zr0.55Y0.10具有与Ce0.50Zr0.50O2相似的立方结构和相近的储氧量,经高温(1000 ℃)后仍能保持较大的比表面积(38.66 m2·g-1).和含Ce0.50Zr0.50O2的三效催化剂相比,含CeO2-ZrO2-Y2O3的三效催化剂经高温老化后,C3H8,CO,NO仍具有较高的转化率和较低的起燃温度.     

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。     

Solution decomposition of the layered double hydroxide of Co with Fe: phase segregation of normal and inverse spinels

The nitrate-intercalated layered double hydroxide of Co with Fe decomposes on hydrothermal treatment to yield an oxide residue at a temperature as low as 180 degrees C. The oxide product is phase segregated into a Co(3)O(4)-type normal spinel and a CoFe(2)O(4)-type inverse spinel. Phase segregation is facilitated as decomposition in a solution medium takes place by dissolution of the precursor hydroxide followed by reprecipitation of the oxide phases. In contrast, thermal decomposition takes place at 400 degrees C. This temperature is inadequate to induce diffusion in the solid state whereby phase segregation into the thermodynamically stable individual spinels is suppressed. The result is a single-phase metastable mixed spinel oxide. This is rather uncommon in that a hydrothermal treatment yields thermodynamically stable products where as thermal decomposition yields a metastable product.     

In situ X-ray absorption spectroscopy study of Si(1-x)Ge(x)O2 dissolution and germanium aqueous speciation under hydrothermal conditions

The dissolution of Si(1-x)Ge(x)O(2) solid solutions under hydrothermal conditions was studied by in situ X-ray absorption spectroscopy. Experiments were performed at the Ge K-edge using a high-pressure cell mounted on the FAME beamline of the European Synchrotron Radiation Facility. Spectra in both transmission and fluorescence mode were collected in isobaric conditions (100 and 150 MPa) up to 475 °C. The local atomic structure around the Ge atom was investigated as a function of the temperature and in pure water and sodium hydroxide solutions. In pure water, the solubility of the cristobalite-type Si(0.8)Ge(0.2)O(2) increases with the temperature and the Ge atom is in 4-fold coordination. In a sodium hydroxide aqueous solution, a complex between Ge and Na atoms forms and gives rise to precipitation of sodium germanates. Under these conditions, the Ge content in the solution decreases with increasing temperature. These results show that a sodium hydroxide aqueous solution, usually used for quartz crystal growth, is not suitable for Ge-containing crystals. The dissolution kinetics and phase transformation of the solid solution were studied as a function of the atomic fraction of Ge. Ge-rich solid solutions dissolve and transform to stable phases faster than Ge-poorer composition, giving rise to important variations of the Ge content in solution.     

Easy Room Temperature Synthesis of High Surface Area Anatase Nanowires with Different Morphologies

Anatase nanowires were synthesized in solution by using a simple mixing of titanium diisopropoxide bis(acetylacetonate), lactic acid and sodium hydroxide at room temperature. We discuss effects of reaction parameters and post treatment (annealing) on the nanowire morphology, surface area, and crystallinity, as well as the competing morphology directing effects of lactic acid and sodium hydroxide. Then the room temperature nanowires were directly grown onto fluoride doped tin oxide (FTO) glass to form photoanodes. Photoelectrochemical measurements of the different nanowires were performed and compared to conventional nanowires produced by high temperature synthesis. Clearly the nanowires introduced in this work show a significant increase in the maximum photocurrent, compared to classic hydrothermal nanowire layers.     

Hydrothermal synthesis of tungsten molybdenum mixed oxides

The phase composition, particle size, and morphology of ultrafine products recovered as a result of hydrothermal treatment of precursor solutions were studied. The precursor solutions were prepared by ion exchange and contained various proportions of tungsten and molybdenum. When tungsten percentages in the precursor solution were 20–95 mol %, the major synthesis product was a mixed oxide (substitutional solid solution (W, Mo)O₃ · 1/3H₂O based on the structure of crystal hydrate WO₃ · 1/3H₂O). When the tungsten percentage was 5 mol %, the product was (W, Mo)O₃ solid solution with the structure of orthorhombic MoO₃. Particle shapes and sizes (ranging from 20 to 8 000 nm) were dictated by the proportion between tungsten and molybdenum compounds in the precursor solution and by the method used to prepare the precursor.     

Topochemical synthesis of cobalt oxide-based porous nanostructures for high-performance lithium-ion batteries

Two kinds of topochemical conversion routes from cobalt hydroxide precursors to cobalt oxide-based porous nanostructures are presented: pyrolysis in air and hydrothermal treatment by the Kirkendall diffusion effect. These cobalt hydroxide precursors were synthesized by a simple hydrothermal approach with sodium acetate as mineralizer at 200 °C. Detailed proof indicates that the process of cobalt hydroxide precursor growth is dominated by a nucleation, dissolution, renucleation, growth, and exfoliation mechanism. By the topochemical conversion processes several Co(3)O(4) nanostructures, such as cobalt oxide-coated cobalt hydroxide carbonate nanowires, cobalt oxide nanotubes, hollow cobalt oxide spheres, and porous cobalt oxide nanowires, have been synthesized. The obtained Co(3)O(4) nanostructures have also been evaluated as the anode materials in lithium-ion batteries. It was found that the as-prepared Co(3)O(4) nanostructures exhibited high reversible capacity and good cycle performance due to their porous structure and small size.     

氧化镁两步法制备阻燃型氢氧化镁

以氯化镁焙烧生成的氧化镁为原料,采用两步法即先水化后水热的方法制备出六方片状氢氧化镁。考察了水化时间、水热时间和温度及水热添加剂氢氧化钠浓度对氢氧化镁材料形貌的影响。研究表明,水化时间超过3h,氧化镁水化率基本不变,水热温度越高对晶体形貌改善越大,水热时间的延长可促进晶体粒径及厚度的增加,但是对晶体的宽厚比改变不大。水热添加剂氢氧化钠浓度的增加可明显地提高晶体结晶度,减小晶体微观内应变,提高粉体分散性。     

氧化镁两步法制备阻燃型氢氧化镁

以氯化镁焙烧生成的氧化镁为原料,采用两步法即先水化后水热的方法制备出六方片状氢氧化镁。考察了水化时间、水热时间和温度及水热添加剂氢氧化钠浓度对氢氧化镁材料形貌的影响。研究表明,水化时间超过3 h,氧化镁水化率基本不变,水热温度越高对晶体形貌改善越大,水热时间的延长可促进晶体粒径及厚度的增加,但是对晶体的宽厚比改变不大。水热添加剂氢氧化钠浓度的增加可明显地提高晶体结晶度,减小晶体微观内应变,提高粉体分散性。     

微波水热改性制备S_2O_8~(2-)/Fe_2O_3-SiO_2固体酸及催化性能

对共沉淀法得到的Fe2O3-SiO2混合氧化物前驱物进行微波水热改性处理,经浸渍(NH4)2S2O8后再焙烧得S2O82-/Fe2O3-SiO2固体酸催化剂。用XRD、TEM、N2气吸附/脱附及化学分析方法对其进行了表征,用乙酸/丁醇酯化催化反应评估固体酸的催化性能,并与通常条件下制得的催化剂进行了比较。结果显示,引入SiO2会延迟Fe2O3晶体的形成与长大;对前驱物用250W的微波水热改性处理1.5h,制得的固体酸具有适中的比表面积、均匀的孔径分布,含硫量为6.02%,比表面积为37.1m2/g。该固体酸对乙酸丁醇酯化反应有很高的催化活性,催化酯化反应3h,乙酸的转化率高达97.7%。     

Low temperature deposition of TiO2 layers from nanoparticle containing suspensions synthesized by microwave hydrothermal treatment

In this paper, we present a microwave-assisted, hydrothermal method for the synthesis of TiO₂ suspensions. These were obtained from Ti⁴⁺ aqueous precursor solutions using titanium-isopropoxide with EDTA and triethanolamine or tetraethylammonium hydroxide by applying a microwave treatment at temperatures between 100 and 140 °C. The influence of the ligands, pH, reaction temperature and time on the particle size and crystallinity was investigated and discussed. A selection of the TiO₂ suspensions was deposited on glass substrates using piezoelectric driven ink-jet printing. The rheological properties of the suspensions were evaluated against the relevant criteria for ink-jet printing and their jetting behavior was analyzed. The ink-jet printed layers were heated at temperatures between 150 and 500 °C to create transparent titanium oxide layers. The photocatalytic activity of the finally obtained layers was analyzed by following the decomposition of a methylene blue solution under UV illumination. The presence of preformed titania nanoparticles makes it possible to obtain photocatalytic active coatings at reduced heating temperatures. This can widen the application range of these functional layers to heat-sensitive substrates such as polymers. The influence of the heat treatment temperature on the film roughness, thickness and photocatalytic activity was also studied.     

制备方法对MnOx-CeO2催化剂理化性质及低温NH3-SCR脱硝性能的影响

随着人们环保意识的增强,氮氧化物(NOx)的危害引起广泛关注.NOx作为首要的大气污染物之一,主要来源于以燃煤电厂为代表的固定源和以机动车为代表的移动源.它不仅能够导致酸雨和光化学烟雾,而且还是PM2.5的重要前驱体,严重危害人类健康和植物生长.因此,NOx的治理迫在眉睫.研究表明,氨选择性催化还原(NH3-SCR)技术是控制固定源NOx排放最经济有效的方法.商业化V2O5-WO3/TiO2和V2O5-MoO3/TiO2脱硝催化剂的最佳工作温度窗口为300?400℃.因此,NH3-SCR脱硝设施通常安装在除尘器和脱硫装置之前以满足最佳工作温度需要.然而,在这种情况下,脱硝催化剂容易因烟气中的飞灰和含硫化合物堵塞、中毒而失活.此外,对于老电厂增加脱硝设施的改造工程,在除尘器和脱硫装置之前没有足够的空间用于安装脱硝设施.因此,开发环境友好型低温NH3-SCR脱硝催化剂显得尤为重要,因为它可以直接安装在除尘器和脱硫装置之后,从而有效减缓脱硝催化剂失活,有利于改造工程的施工.研究表明,锰基催化剂由于其优异的氧化还原性能和氧迁移能力有利于氧化NO为NO2,促进反应沿着"快速NH3-SCR"途径进行,从而表现出优异的低温脱硝性能.然而,其N2选择性、抗水性能和工作温度窗口还有待改善.因此,开发既具有高催化活性又具有宽工作温度窗口、优异抗水性能以及理想N2选择性的低温脱硝催化剂仍是一个富有挑战性的课题.二氧化铈(CeO2)由于具有优异的氧化还原性能、良好的储/释氧能力、丰富的氧空位以及Ce4+/Ce3+的轻易切换而被广泛用于NH3-SCR反应.因此,将锰氧化物(MnOx)与CeO2相结合而制备的MnOx-CeO2催化剂可能会表现出优异的低温脱硝性能.而催化剂的理化性质和催化性能还强烈地依赖于其制备方法.因此,本文采用不同方法(机械混合法、浸渍法、水热法、共沉淀法以及溶胶-凝胶法)制备了一系列MnOx-CeO2催化剂用于低温NH3-SCR反应,并运用X射线衍射(XRD)、拉曼光谱(Raman)、氮气物理吸附、氢气程序升温还原(H2-TPR)、氨气程序升温脱附(NH3-TPD)、X射线光电子能谱(XPS)以及原位漫反射红外光谱(in situ DRIFTS)等表征技术对催化剂进行了系统分析.重点考察了制备方法对MnOx-CeO2催化剂理化性质和催化性能的影响.结果表明,低温脱硝性能有如下顺序:水热法>溶胶-凝胶法>共沉淀法>浸渍法>机械混合法.这与催化剂表面Ce3+和Mn4+含量、氧空位和表面吸附氧物种浓度以及酸量和酸强度顺序一致.这些性质都与MnOx和CeO2之间的电子相互作用(即Mn3++Ce4+?Mn4++Ce3+)密切相关.特别是水热法制备的MnOx-CeO2催化剂(MnCe-HTM)由于Mnn+掺入到CeO2晶格形成铈基固溶体(含Mn-O-Ce结构)以及水热过程中的高温高压环境加强了MnOx和CeO2之间的电子相互作用,从而表现出优异的理化性质、最佳的低温脱硝性能以及理想的抗水性能.