制备方法对CuO/CeO_2-ZrO_2催化CO低温氧化活性的影响

采用微波加热分解法(一步法)和微波加热处理共沉淀+浸渍法(两步法)制备了CuO/CeO2-ZrO2催化剂,并对其进行了X射线衍射、低温氮气吸附/脱附和程序升温还原等表征,采用色谱流动法考察了催化剂的催化CO低温氧化性能.结果表明,一步法比两步法更有利于使催化剂表面CuO高度分散,CuO与CeO2-ZrO2间的相互作用更强,CuO更容易被还原,从而具有更高的催化CO氧化活性.与CeO2-ZrO2有相互作用的高分散和小颗粒CuO有利于催化剂活性的提高,与CeO2-ZrO2无相互作用的大颗粒CuO对催化剂的活性有抑制作用.     

CeO2-ZrO2-La2O3-Al2O3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR) and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Catalytic activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. They also have significant potential in industrial application because of their high performance and low cost.     

Nickel catalysts for the hydrodeoxygenation of biodiesel

A number of nickel and nickel-copper catalysts for the hydrodeoxygenation of fatty acid esters (biodiesel) were studied. The CeO₂ and ZrO₂ oxides and the CeO₂-ZrO₂ binary system were used as supports. The Ni-Cu/CeO₂-ZrO₂ catalyst exhibited the highest activity; it allowed us to quantitatively convert biodiesel into linear alkanes under mild conditions (290–320°C, 1.0 MPa). It was found that the selectivity of the formation of the main product (heptadecane) was 70–80%. The main correlations between the nature of catalysts and their activity under conditions of the target reaction were determined using temperature-programmed reduction, X-ray diffraction analysis, and electron microscopy. It was hypothesized that the high activity of Ni-Cu/CeO₂-ZrO₂ in the test reaction can be explained by the presence of a Ni_{1 − x} Cu _x (x = 0.2–0.3) solid solution as a constituent of the active component of the catalyst.     

CO oxidation over Au/CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> catalists: The effect of the support composition of the au-support interaction

The effect of the support composition on the Au-support interactions and its role in the creation of the activity of Au/CeO₂-ZrO₂ catalysts in CO oxidation has been studied. The CeO₂-ZrO₂ oxides and Au/CeO₂-ZrO₂ catalysts were synthesized, characterized by BET, XRD, HRTEM, AAS, TPR-H₂, and tested in CO oxidation. An approximate evaluation of the H₂ consumption for the surface reduction of the studied samples was estimated applying the model developed by Johnson and Mooi, which is based on the qualitative relationship between the amount of the capping oxygen and BET surface area. The sequence of the increasing percentage of O₂ atoms in the capping peak to the total Ce atoms follows the sequence of the decreasing Zr/Ce molar ratio in the sample. The activity of Au/CeO₂-ZrO₂ catalysts depends on the support composition and increases with the decrease in Zr/Ce molar ratio.     

Preparation,Characterization of CeO2-ZrO2 Composite Hollow Microspheres and Their Application as Electrocatalysis Materials for Hemoglobin in Biosensor

Composite hollow microspheres of CeO₂-ZrO₂ were prepared by using anionic PSA latex particles as template and then calcining the PSA core particles at 600°C. The samples were characterized by XRD, TEM, TG, SEM, EDS, and FT-IR spectra. The effects of the proportion of CeO₂ on the structure of the microspheres were also studied. Electrochemical assay showed that the CeO₂-ZrO₂ composite hollow spheres hydrided with chitosan could be used as a novel biosensing material to detect the direct electron transfer of hemoglobin.     

Colloidal properties of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols

CeO₂-ZrO₂ hydrosols are synthesized and the size, shape, phase composition, density, and electrophoretic mobility of particles are studied. The pH ranges of the stability of hydrosols and the thresholds of their fast coagulation in the presence of some electrolytes are determined. The nature of the aggregation stability of CeO₂-ZrO₂ hydrosols is discussed.     

Nanosized CeO2–SiO2, CeO2–TiO2, and CeO2–ZrO2 Mixed Oxides: Influence of Supporting Oxide on Thermal Stability and Oxygen Storage Properties of Ceria

The influence of SiO₂, TiO₂, and ZrO₂ on the structural and redox properties of CeO₂ were systematically investigated by various techniques namely, X-ray diffraction (XRD), Raman spectroscopy (RS), UV–Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HREM), BET surface area, and thermogravimetry methods. The effect of supporting oxides on the crystal modification of ceria was also mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahigh dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO₂–SiO₂ sample primarily consists of nanocrystalline CeO₂ on the amorphous SiO₂ surface. Both crystalline CeO₂ and TiO₂-anatase phases were noted in the case of CeO₂–TiO₂ sample. Formation of cubic Ce_0.75Zr_0.25O₂ and Ce_0.6Zr_0.4O₂ (at 1073 K) were observed in the case of CeO₂–ZrO₂ sample. The cell ‘a’ parameter estimations revealed an expansion of the ceria lattice in the case of CeO₂–TiO₂, while a contraction is noted in the case of CeO₂–ZrO₂. The DRS studies suggest that the supporting oxides significantly influence the band gap energy of CeO₂. Raman measurements disclose the presence of oxygen vacancies, lattice defects, and displacement of oxide ions from their normal lattice positions in the case of CeO₂–TiO₂ and CeO₂–ZrO₂ samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation states, Si(IV), Ti(IV), and Zr(IV) at the surface of the materials. Cerium is present in both Ce⁴⁺ and Ce³⁺ oxidation states. The HREM results reveal well-dispersed CeO₂ nanocrystals over the amorphous SiO₂ matrix in the case of CeO₂–SiO₂, isolated CeO₂ and TiO₂ (A) nanocrystals and some overlapping regions in the case of CeO₂–TiO₂, and nanosized CeO₂ and Ce–Zr oxides in the case of CeO₂–ZrO₂ sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO₂ is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of mixed oxides is more than that of pure CeO₂ and the CeO₂–ZrO₂ exhibits highest OSC.     

Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at room temperature

A procedure is developed for the synthesis of concentrated CeO₂-ZrO₂ hydrosols based on the peptization of a precipitate obtained by the hydrolysis of a cerium nitrate-zirconium oxynitrate mixture. The time intervals and optimum [H⁺]/[Me ⁿ⁺] molar ratios giving rise the formation of CeO₂-ZrO₂ hydrosols stable to aggregation with a narrow particle size distribution are established. The size, shape, density, and phase composition of the hydrosol particles are determined.     

Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide Over ZrO<Subscript>2</Subscript>-based Composite Oxide Catalysts

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO₂ as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO₂-ZrO₂, MnO₂-ZrO₂, CeO₂-ZrO₂, K₂O/TiO₂-ZrO₂, B₂O₃/TiO₂-ZrO₂ and CeO₂-ZrO₂/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO₂ as the soft oxidant.     

低贵金属Pt-Rh型三效催化剂空燃比性能的研究

研究了以浸渍法制备的低贵金属Pt-Rh型三效催化剂对C₃H₈, CO, NO的催化活性. 主要考察了CeO₂-ZrO₂和BaO的添加对催化剂空燃比性能的影响, 通过氧化反应、水气变换和蒸汽重整的性能研究, 探讨了催化剂三效工作窗口扩大的原因. 结果表明, 催化剂中只添加CeO₂-ZrO₂时即具有优异的水气变换性能, 蒸汽重整在250 ℃左右发生, 并且在450 ℃以下时C₃H₈的转化率一直保持在20%左右; BaO添加到含有CeO₂-ZrO₂的催化剂中对水气变换和蒸汽重整则有明显的促进作用, 能进一步扩大催化剂的三效工作窗口; 催化剂中只添加CeO₂-ZrO₂时, 能明显提高催化剂对CO的氧化反应活性, 但对C₃H₈的氧化反应的影响则不明显; BaO和CeO₂-ZrO₂同时存在于催化剂中时, 能进一步提高CO的氧化反应活性, 对C₃H₈的氧化反应则没有明显的促进作用.     

Temporal analysis of products (TAP) study on oxygen storage properties over Pt−Rh/CeO2 catalyst

The oxygen storage capacity of CeO₂, Ce_0.9Pr_0.1O₂, Pt?Rh/CeO₂ and Pt?Rh/Ce_0.9Pr_0.1O₂ was investigated by conventional GC pulse method and transient pulse techniques. It is shown that incorporation of PrO_y into CeO₂ matrix strongly promotes oxygen storage capacity (OSC) measured using the transient pulse technique. The improvement of OSC at low temperature is observed in Pt?Rh loaded onto CeO₂ and Ce?Pr catalysts.     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

Novel CeO2–CuO-decorated enzymatic lactate biosensors operating in low oxygen environments

The detection of the lactate level in blood plays a key role in diagnosis of some pathological conditions including cardiogenic or endotoxic shocks, respiratory failure, liver disease, systemic disorders, renal failure, and tissue hypoxia. Here, we described for the first time the use of a novel mixed metal oxide solution system to address the oxygen dependence challenge of first generation amperometric lactate biosensors. The biosensors were constructed using ceria-copper oxide (CeO₂–CuO) mixed metal oxide nanoparticles for lactate oxidase immobilization and as electrode material. The oxygen storage capacity (OSC, 492 μmol-O₂/g) of these metal oxides has the potential to reduce the oxygen dependency, and thus eliminate false results originated from the fluctuations in the oxygen concentration. In an effort to compare the performance of our novel sensor design, ceria nanoparticle decorated lactate sensors were also constructed. The enzymatic activity of the sensors were tested in oxygen-rich and oxygen-lean solutions. Our results showed that the OSC of the electrode material has a big influence on the activity of the biosensors in oxygen-lean environments. While the CeO₂ containing biosensor showed an almost 21% decrease in the sensitivity in a O₂-depleted solution, the CeO₂–CuO containing electrode, with a higher OSC value, experienced no drop in sensitivity when moving from oxygen-rich to oxygen-lean conditions. The CeO₂–CuO decorated sensor showed a high sensitivity (89.3 ± 4 μA mM⁻¹ cm⁻²), a wide linear range up to 0.6 mM, and a low limit of detection of 3.3 μM. The analytical response of the CeO₂–CuO decorated sensors was studied by detecting lactate in human serum with good selectivity and reliability. The results revealed that CeO₂–CuO containing sensors are promising candidates for continuous lactate detection.     

(CeO2)x-(La-Al2O3)1-x复合氧化物对柴油车尾气中可溶性有机成分的催化氧化

采用共沉淀法制备了一系列(CeO₂)_x-(La-Al₂O₃)_1-x复合氧化物(其中x为质量分数, x=0.00, 0.25, 0.50, 0.75, 1.00), 以其为催化剂. 采用热重-差热分析(TG-DTA)法模拟测试该系列催化剂对柴油车尾气中可溶性有机成分(SOF)的催化氧化性能. 结果表明, 当x=0.75时, 催化剂活性最高, 可使SOF在125℃起燃, 355℃完全转化. 并用低温N₂吸附-脱附, 储氧量(OSC)测试, X射线衍射(XRD), X射线光电子能谱(XPS)和H₂程序升温还原(H₂-TPR)等手段对催化剂进行了表征. 研究结果表明, 适量La 和Al 共掺杂增大了氧化铈的比表面积和催化剂中Ce³⁺所占的比例, 从而提高了催化剂对SOF的低温吸附能力和催化剂的储释放氧能力, 因而提高了催化剂对SOF的氧化活性. 所制备的(CeO₂)_0.75-(La-Al₂O₃)_0.25复合氧化物适合应用到柴油车尾气净化催化剂中.     

硫酸化对CeO2-ZrO2催化剂上NH3选择催化还原NO反应的影响

由发电厂等固定源和柴油机等移动源排放的一氧化氮(NO)造成的环境污染问题日益严重.随着严苛的排放法规出台,NO排放控制技术受到越来越多关注.NH3选择性催化还原(SCR)技术是目前去除NO应用最为广泛的方法之一.商业催化剂V2O5-WO3/TiO2在300–400℃温度窗口内显示出优越的NO去除效率,但仍存在一些问题,如钒氧化物的毒性以及在高温时形成N2O和SO3.因此,开发出低钒或无钒的新型催化剂是解决上述问题的关键.CeO2和含铈材料是重要的催化剂载体,具有良好的还原能力和氧存储功能,因而广泛应用于催化领域.CeO2添加到商用催化剂中不仅可以降低钒用量,而且可以提高催化剂抗碱金属中毒能力.CeO2-WO3催化剂在200℃以上时比商用催化剂具有更宽的温度窗口,并展现出较高的抗SO2和碱金属中毒能力.CeO2-ZrO2催化剂通过添加过渡金属元素可以提升其SCR活性,在较宽的温度窗口内具有较高的催化活性.废气中SO2可导致催化剂失活,在实际应用中催化剂硫中毒是较为常见的催化剂失效原因.通常情况下,锰基和铁基催化剂最容易硫中毒.然而CeO2催化剂在硫酸化处理后却展现出良好的SCR活性.催化剂硫酸化主要包括气相、液相和前驱体硫化三种方法.三种方法各有异同,但在催化剂表面形成的硫物种都是SO42–.硫酸化可以增强Ce基催化剂的SCR活性,但是对于硫化引起的催化剂表面酸性、氧化还原性以及NO吸附脱附性质的详细研究报道较少.本文通过液相法对CeO2-ZrO2(CeZr)催化剂进行了硫酸化.XRD结果表明,硫酸化并未对催化剂结晶结构产生影响.TPD和TPR结果表明,硫酸化后催化剂(S-CeZr)表面酸性增强,但抑制了其氧化性.通过原位红外光谱技术系统研究了催化剂在SCR反应过程中表面物种的变化,结果发现,CeZr和S-CeZr的催化机理相同,不同的SCR活性主要是由表面酸性和氧化性引起的.CeO2基催化剂在不同温度窗口遵循不同反应机理.CeZr催化剂具有较强的氧化还原性,使其对NO和NH3具有很强的氧化能力,所以其在低于200℃时具有较好的SCR活性.而S-CeZr催化剂具有更多的Br?nsted酸性位,导致NO不易吸附在催化剂表面,所以其在低温时SCR活性较差,但在高温时(>200℃)具有优良的SCR活性.通过SCR活性和反应机理研究,发现在高温时(>200℃),表面酸性尤其是强酸Br?nsted酸性位在SCR反应中起到决定性作用;而在低温时(<200℃),酸性位对NH3分子较强的键合作用导致NH3难以被氧化,所以较强的酸性位对SCR活性具有抑制作用,而氧化还原性在低温时对SCR反应起到主要作用.同时,在高温时,较高的氧化性可使NH3被O2直接氧化,导致N2选择性降低.     

Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at elevated temperature

A method for synthesizing aggregation-stable CeO₂-ZrO₂ hydrosols with different particle compositions is developed based on the peptization of hydrated oxide precipitates at elevated temperature. It is shown that, by varying heat treatment time, sols can be obtained with particles that have different degrees of crystallinity and sizes of no larger than 6 nm.     

Phase composition and catalytic properties of ZrO2 and CeO2-ZrO2 in the ketonization of pentanoic acid to 5-nonanone

The phase composition, microstructure, and catalytic properties of the samples of ZrO₂ and CeO₂-ZrO₂ calcined in air at 450–500°C in the ketonization reaction of pentanoic acid were studied. It was found that ZrO₂ of tetragonal and monoclinic modifications is characterized by sufficiently high activity and selectivity for 5-nonanone; the yield of 5-nonanone was 66.3–64.9%. The modification of zirconium dioxide with cerium oxide leads to the formation of a substitutional solid solution based on tetragonal ZrO₂. Upon the addition of CeO₂ in an optimum amount of 10 wt % to zirconium dioxide, an increase in the conversion of pentanoic acid was observed with the retention of high selectivity for the target product, which led to an increase in the yield of 5-nonanone to 73.3%. Based on the results of physicochemical studies performed by high-resolution transmission electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy, the physicochemical and catalytic properties of the test catalysts were compared.     

New In-situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors using a Novel Wet Collection System in a rf Inductively Coupled Thermal Plasma Reactor. Part 1: Reactor System and Sampling Probe

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO₂ powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO₂ powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO₂ formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO₂ formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO₂ were found.     

表面覆盖SiO2用于提高Pt-Pd/CeO2-ZrO2-Al2O3商用柴油机氧化型催化剂的抗硫性

向Pt-Pd/CeO₂-ZrO₂-Al₂O₃ （Pt-Pd/CZA）商用柴油机氧化型催化剂（DOC）中加入多孔SiO₂以提高其抗硫性. 使用多层涂覆法在Pt-Pd/CZA 催化剂表面覆盖一层多孔SiO₂,从而制得SiO₂/Pt-Pd/CeO₂-ZrO₂-Al₂O₃（SiO₂/Pt-Pd/CZA）抗硫DOC. 并使用扫描电子显微镜（SEM）,H₂程序升温还原（H₂-TPR）,氮气吸脱附,X射线能谱（EDX）和热重分析（TGA）等对其进行表征. SEM结果显示,SiO₂层以多孔形式均匀覆盖在催化剂表面. 氮气吸脱附结果表明,所添加的SiO₂的织构性质与Pt-Pd/CZA 催化剂的织构性质相似,因而表面覆盖的SiO₂并未明显改变Pt-Pd/CZA催化剂的比表面积和孔结构. H₂-TPR结果证实表面覆盖的SiO₂不影响Pt-Pd/CZA催化剂的还原性能. EDX和TGA结果说明表面覆盖SiO₂可以抑制硫物种在催化剂表面的形成及累积. 最终,本文所制备的SiO₂/Pt-Pd/CZA催化剂在保持Pt-Pd/CZA商用DOC的高活性及耐久性的同时有效提高了其抗硫性.     

贵金属对 NM/WO3-ZrO2 (NM = Ru, Rh 和 Pd) 催化乙烯直接氧化制乙酸反应的影响

 研究了负载 Ru, Rh 和 Pd 的 WO3-ZrO2 催化剂在乙烯直接氧化制乙酸反应中的催化性能. 结果显示, 负载的贵金属对催化剂的催化性能有非常重要的影响. Rh/WO3-ZrO2 催化剂具有最高的乙烯转化率, 而 Ru/WO3-ZrO2 催化剂对反应几乎没有活性. H2 化学吸附结果显示, 高的催化性能来源于高的金属分散度. Pd/WO3-ZrO2 催化剂显示了最高的乙酸选择性 (75%), 而其它两个催化剂的乙酸选择性都非常低 (~10%). 程序升温氧化和程序升温还原结果显示, 贵金属–O 键的键强对产物的选择性具有重要的影响. 弱的贵金属–O 键可以通过将氧插入到乙烯和/或乙醛中而有利于乙酸的生成, 而强的贵金属–O 键会导致乙烯完全氧化为 COx.