CexPr1-xO2-δ复合氧化物的XRD和Raman表征

CeO2是重要的催化材料,在三效催化剂中起着特别重要的作用。CeO2通过Ce3 和Ce4 之间的高效氧化还原循环产生储氧和释放氧的能力,在三效催化剂中起到“氧缓冲器”的作用[1~3]。但是在850℃以上焙烧CeO2容易发生烧结并和γ-Al2O3相互反应生成CeAlO3[4],使储氧能力降低,影响了它在     

焙烧温度对复合储氧材料性能的影响

自上世纪80年代初期以来,稀土铈氧化物(CeO2)作为一种储氧材料已在汽车三效催化剂(TWC)中得到了广泛应用。众所周知,CeO2在富氧和富燃条件下有储氧和释放氧的功能,CeO2在缺氧条件下可通过Ce4 转化成Ce3 而释放出氧气,在富氧条件下Ce3 又可氧化成Ce4 而吸收氧,即2CeO2(Ce2O3 1/2     

Pd-O/CeO_2纳米管催化苯酚氧化羰基化反应

以碳纳米管(CNTs)为模板,采用液相沉积-水热法制备了管状纳米氧化铈(Ce O2-NT).利用X射线衍射、透射电镜和N2等温吸附-脱附技术对其结构进行了表征,所得Ce O2-NT外径~25 nm,长度大于300 nm,管壁由粒径4–9 nm的Ce O2晶粒组成,比表面积为108.8 m2/g.以其为载体制备了Pd-O/Ce O2-NT催化剂,程序升温还原结果发现,该催化剂表面氧在低温下即可被还原,具有较高的活性.将Pd-O/Ce O2-NT用于催化苯酚氧化羰基化反应,催化剂活性和碳酸二苯酯(DPC)选择性均高于零维CeO 2负载的Pd-O/Ce O2-P催化剂.在优化的条件下,苯酚转化率为67.7%,DPC选择性为93.3%.但该催化剂再次使用时活性下降明显,这是由于Pd-O/Ce O2-NT的管状结构在反应过程中被破坏,并且活性组分Pd流失所致.     

铈锰氧化物对二氯甲烷催化氧化性能的研究

采用溶胶-凝胶法制备了系列Ce1-xMnxO2催化剂,运用BET,XRD,Raman,XPS和H2-TPR等方法对催化剂进行了表征。并考察了催化剂对CH2C l2催化氧化的性能。XRD结果表明,催化剂中Ce的加入可以有效抑制催化剂晶粒变大,且有部分Mn离子进入CeO2骨架中形成了固溶体;而XPS结果表明,催化剂中Mn物种以+3和+4价存在。H2-TPR结果表明,催化剂中Ce的加入降低了MnOx中晶格氧的还原温度。反应活性结果表明,Ce1-xMnxO2系列催化剂较纯CeO2,MnOx催化活性好,其本征活性顺序为Ce0.8Mn0.2O2Ce0.6Mn0.4O2Ce0.5Mn0.5O2Ce0.4Mn0.6O2Ce0.2Mn0.8O2CeO2MnOx。这可能是由于Ce的添加提高了催化剂中MnOx晶格氧的活泼程度,进而影响反应性能。     

Pt/Ce0.6Zr0.4O2催化剂在水煤气变换反应中的电导研究

采用浸渍法制备了不同载体(Ce0.6Zr0.4O2,CeO2和ZrO2)负载的Pt基水煤气变换反应(WGSR)催化剂, 并对其进行了活性评价. 利用X射线衍射(XRD), 程序升温还原(TPR)和原位电导等技术对样品进行了表征. 结果表明, Ce0.6Zr0.4O2固溶体具有比CeO2更高的氧转移能力, 因此促进了Pt/Ce0.6Zr0.4O2催化剂的WGSR活性.     

Pd/Ce0.8Zr0.15La0.05Oδ整体催化剂甲苯催化燃烧性能的研究

采用一次浸渍法分别制备了 Pd/Ce0.8Zr0.15La0.05Oδ及Pd/Ce0.8Zr0.2O2整体式蜂窝陶瓷催化剂,考察了不同温度焙烧的两类整体催化剂甲苯催化燃烧性能.通过X射线粉末衍射(XRD)、比表面积、拉曼光谱(Raman)、程序升温还原(H2-TPR)、PdO分散度等表征结果与催化活性进行关联.结果表明,随着焙烧温度升高,催化剂比表面积下降,Raman图谱CeO2及PdO峰强度增加,H2-TPR中Ce4+还原峰向高温方向移动,同时PdO分散度下降,相应甲苯催化氧化活性下降.与CeO0.8Zr0.2O2涂层催化剂相比,La3+掺杂催化剂在高温焙烧时,其比表面积下降较小,Raman光谱表明其氧缺位比铈锆涂层催化剂多,H2TPR谱图中Ce4+还原峰低约60～80℃,PdO分散度亦比末掺杂催化剂高.1000℃焙烧下的甲苯氧化反应活性远高于未掺杂催化剂,说明镧的掺杂提高了铈锆涂层催化剂的高温反应活性及热稳定性.     

添加稀土氧化物助剂的CeO2-ZrO2固溶体的储氧性及热稳定性研究

大多数工业催化剂都是在稳定的操作条件下进行的,然而汽车尾气净化催化剂却被暴露在大气中,使用条件经常变化,尤其是空燃比(A/F)的变化,直接影响了对氧敏感的三效催化剂的氧化和还原性能[1].CeO2则是一种具有储氧/释氧能力的催化材料,它作为助剂加入三效催化剂中,可在贫况下储存氧(以Ce4+存在)利于NOx的还原,在富况下释放氧(以Ce3+存在),利于HC、CO的氧化,从而提高了催化剂的活性.然而,CeO2 的储氧性通常局限在表面上,当温度超过400℃以上时,其比表面积降低从而引起储氧性能急剧下降,直接影响催化剂的性能和寿命.     

CeO2-MnOx催化剂上氯乙烯有机废气的催化燃烧

采用柠檬酸(CA)溶胶-凝胶法制备了不同Mn:(Ce+Mn)摩尔比的CeO2-MnOx催化剂,以氯乙烯有机废气的催化燃烧为模型反应,考察了催化剂制备条件和反应条件对于CeO2-MnOx催化剂性能的影响,并用N2吸附、X射线衍射(XRD)和H2程序升温还原(H2-TPR)对催化剂进行了表征.结果表明,CeO2-MnOx催化剂上氯乙烯燃烧反应产物只有HCl,H2O和CO2,没有检测到其他氯代烃和氯气等副产物.当CA:Mn:Ce=0.3:0.50:0.50时,所制备的CeO2-MnOx催化剂活性最高,对于较宽的空速范围(10000～30000h-1)和较宽的浓度范围(0.05%～0.15%),低浓度氯乙烯的催化燃烧反应具有较好的操作弹性.其中当氯乙烯浓度为0.1%,空速为15000h-1时,起燃温度T50=110oC,完全转化温度T99=220oC.XRD和H2-TPR结果表明,在CeO2-MnOx催化剂中只出现立方相萤石结构CeO2的特征衍射峰,没有出现MnOx物种的特征衍射峰;Mn离子进入CeO2晶格形成的Ce-Mn-O固溶体,有利于提高催化剂表面的活性氧物种的活性,乃至催化剂活性.     

Ce-OMS-2催化苯甲醇液相氧化制苯甲醛

采用回流法合成氧化锰八面体分子筛(OMS-2),并采用浸渍法负载Ce制备Ce-OMS-2催化剂,以分子氧为氧化剂考察了催化剂对苯甲醇液相氧化制苯甲醛的活性。当Ce含量为30%(质量分数)时,Ce-OMS-2催化剂的活性最高。100℃下反应1 h时,苯甲醇转化率为50.3%,催化剂的质量比活性达10.1 mmol.(g.h)-1。采用X射线衍射(XRD)、透射电镜(TEM)、X射线光电子能谱(XPS)、红外光谱(FT-IR)、程序升温还原(H2-TPR)对催化剂进行了表征。结果表明:所制备的催化剂具有结晶良好的八面体结构,当Ce含量小于30%时,Ce以高分散形式存在,但当Ce含量大于30%时,将出现聚集态CeO2结晶;高分散CeO2促进了OMS-2中MnOx的还原,改善了活性中心的电子传递,从而显著提高了催化剂活性。     

Pt/CexZr1-xO2催化剂上丙烷完全氧化性能研究

采用沉淀法制备了ZrO2,CeO2和Ce0.7Zr0.3O2载体,并用浸渍法制备负载型Pt催化剂。考察了500和900℃焙烧催化剂的丙烷完全氧化性能和水汽对丙烷氧化反应的影响。对于500℃焙烧的催化剂,催化剂的丙烷氧化活性顺序为:Pt/ZrO2-500>Pt/CeO2-500>Pt/Ce0.7Zr0.3O2-500;而经900℃焙烧的催化剂活性顺序为:Pt/ZrO2-900>Pt/Ce0.7Zr0.3O2-900>Pt/CeO2-900。反应气氛中水汽的存在对两种Pt/ZrO2催化剂的活性均有抑制作用(T50温度均提高了10~15℃);而对于Pt/CeO2-500催化剂有抑制作用(T50温度提高10℃),但对Pt/CeO2-900催化剂活性有促进作用(T50温度下降25℃);对于两种Pt/Ce0.7Zr0.3O2催化剂活性具有促进作用(T50温度均下降5~25℃)。表征结果表明催化剂的活性与其表面Pt物种价态密切相关,催化剂表面上Pt0物种有利于活性的提高。Pt/Ce0.7Zr0.3O2-500催化剂中只含有氧化态Pt物种(Pt^2+),而Pt/Ce0.7Zr0.3O2-900催化剂中则含有部分金属态Pt物种,因此其活性高于Pt/Ce0.7Zr0.3O2-500催化剂。     

Effect of cerium addition on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

The effect of cerium addition on the catalytic performance of propane dehydrogenation over PtSnNa/ZSM-5 catalyst has been investigated by reaction tests and some physicochemical characterization such as XRD,BET,TEM,XPS,NH 3-TPD,H 2 chemisorption,TPR and TPO techniques.It has been found that with suitable amount of cerium addition,the platinum dispersion increased,while the carbon deposition tended to be eliminated easily.In these cases,the presence of cerium could not only realize the better distribution of metallic particles on the support,but also strengthen the interactions between Sn species and the support.Additionally,XPS spectra confirmed that more amounts of tin could exist in oxidized form,which was advantageous to the reaction.In our experiments,PtSnNaCe(1.1 wt%)/ZSM-5 catalyst exhibited the best catalytic performance.After running the reaction for 750 h,propane conversion was maintained higher than 30% with the corresponding selectivity to propylene of about 97%.     

A theoretical study of the rotational distribution of no resulting from dissociation of HNO

The activity of an iron-base catalyst modified by molybdenum and cerium for CO shift reaction was investigated in a flow microcatalytic reactor. The results show that the activity of the modified catalyst is obviously improved. The surface behavior of Fe−Mo−Ce catalyst and the role of molybdenum and cerium in the catalyst are discussed.     

预硫化处理对Ce-TiO2催化剂NH3-SCR反应活性影响及其反应机理研究

通过对Ce-TiO2催化剂进行SO2+O2气氛下的不同时间的预硫化处理并用于NH3-SCR反应,研究了Ce-TiO2催化剂物化特性随预硫化时间的演变规律,以及预硫化对中低温活性及NH3-SCR反应路径的影响。结果表明Ce-TiO2催化剂表面氧化铈的硫酸化相当迅速,在预硫化处理0.5h后,几乎所有的表面氧化铈都被硫酸盐化形成硫酸铈,随着硫酸化时间的增加到1h和1.5h,Ce-TiO2催化剂上沉积的硫缓慢增加。活性测试表明预硫化后的催化剂对SCR活性的抑制作用随着反应温度的提高而减弱,结合NO-DRIFT、NH3-DRIFT等多种原位表征,结果表明预硫化后低温NH3-SCR活性大幅降低是由于生成硫酸铈后催化剂氧化还原能力大幅削弱,E-R反应路径严重受阻。随着反应温度的升高,SCR活性逐渐不受硫酸铈沉积的影响,一方面,氧化还原性能的提高导致E-R反应路径逐渐恢复;另一方面,硫酸铈的生成促进了NO的活化,增强了L-H反应路径,两者共同导致了预硫化后较高的中温NH3-SCR活性。     

Preparation of Ammonium Cerium Phosphate via Low-heating Solid State Reaction and Its Catalysis for Benzyl Acetate Synthesis

Ammonium cerium phosphate was prepared with (NH₄)₃PO₄·3H₂O and Ce(SO₄)₂·4H₂O as raw materials and PEG‐400 as surfactant via a solid state reaction at low‐heating temperature. The characterization result of XRD indicates that the molecular formula of the product was (NH₄)₂Ce(PO₄)₂·H₂O. The synthesis of benzyl acetate was carried out with H₂SO₄/ammonium cerium phosphate as catalyst, and uniform experimental design as well as data mining technology was applied to the experiments, in which the effect of the reaction time, the molar ratio of acid to alcohol and the amount of catalyst on the conversion yield of acetic acid were studied. When benzalcohol was 0.10 mol, under the optimal reaction conditions, i.e. reaction time of 174 min, 2.02 of molar ratio of acid to alcohol and 0.5 g of catalyst, the esterification rate of acetic acid was 97.9%. The ammonium cerium phosphate had potential for industry application since it not only was feasible and simple in synthesis technics, but also had good catalysis activity for the synthesis of benzyl acetate.     

微波辅助催化氧化苯高性能催化剂实验研究

采用传统浸渍法制备分子筛负载过渡金属和稀土元素催化剂,通过微波辅助催化氧化苯性能实验考察其催化活性。研究表明,天津科密欧的5A分子筛为优良的催化剂载体,分子筛负载铜-锰-铈催化剂对苯的完全燃烧温度为230℃,铜(Cu)锰(Mn)双金属催化剂中晶相与非晶相Cu_1.5Mn_1.5O₄尖晶石提高了催化剂的催化活性,稀土铈(Ce)的助催化效果显著;30 h的连续性实验表明,Cu-Mn-Ce/分子筛催化剂具有良好的稳定性和高的催化活性。催化剂的比表面积和表面形貌表征表明,催化剂比表面积和孔径受高温煅烧和氧化反应而增大,从而有助于苯的吸附与氧化降解;X射线衍射表明,实验前后分子筛结构未发生明显变化,铜锰主要以二价和三价的氧化物形态分布于催化剂表面。     

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al_2O_3 and Pd/(Al_2O_3 MO_x)(M=Ca,La,Ce) palladium catalysts in the reaction of complete oxidation of methane are presented in this study.The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide.Then they were impregnated with palladium nitrate solution.The catalysts with unmodified alumina had a high surface area.The activity and thermal stability of the alumina- supported catalyst was also very high.The introduction of calcium,lanthanum,or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method.These modifiers decreased the activity of palladium catalysts,and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al_2O_3.The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.     

Use of an efficient polystyrene‐supported cerium catalyst for one‐pot multicomponent synthesis of spiro‐piperidine derivatives and click reactions in green solvent

One‐pot multicomponent reactions are very demanding in synthetic organic chemistry. Here we report a new polystyrene‐supported cerium catalyst (PS‐Ce‐amtp) obtained via an easy two‐step procedure, which was thoroughly characterized using various techniques. PS‐Ce‐amtp catalyses the environmentally benign one‐pot multicomponent synthesis of spiro‐piperidine derivatives through the reaction of substituted aniline, cyclic active methylene compound and formaldehyde at room temperature. The catalyst also exhibits excellent catalytic activity in one‐pot synthesis of 1,4‐disubstituted 1,2,3‐triazoles via click reaction between in situ generated azides (derived from anilines and amines) and terminal alkynes. The catalyst can be recovered easily after reaction and reused five times without significant loss in its catalytic activity. The advantageous features of this catalyst are atom economy, operational simplicity, short reaction times, easy handling and high recycling efficiency.     

Synthesis and characterization of CeFeO3 photocatalyst used in photocatalytic bleaching of gentian violet

Ternary oxides have been used as effective photocatalyst for carrying out number of chemical reactions. Method of preparation has major effect on the performance of these mixed oxide catalysts. In the present work, cerium iron oxide catalyst was synthesized using co-precipitation method and specific heating cycle. Synthesized catalyst was characterized using X-ray diffraction patterns. Photocatalytic degradation on gentian violet dye was observed using this catalyst and progress of the reaction was monitored spectrophotometrically. The effect of variation of different parameters like concentration of gentian violet, pH, amount of semiconductor and light intensity was also studied. A tentative mechanism for the photocatalytic bleaching of gentian violet has been proposed.     

Partial oxidation of 4-tert-butyltoluene catalyzed by homogeneous cobalt and cerium acetate catalysts in the Br-/H2O2/acetic acid system: insights into selectivity and mechanism

The partial oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde by hydrogen peroxide in glacial acetic acid, catalyzed by bromide ions in combination with cobalt(II) acetate or cerium(III) acetate, has been studied in detail. Based on the observed differences in reaction rates and product distributions for the different catalysts, a reaction mechanism involving two independent pathways is proposed. After the initial formation of a benzylic radical species, either oxidation of this intermediate by the metal catalyst or reaction with bromine generated in situ occurs, depending on which catalyst is used. The first pathway leads to the exclusive formation of 4-tert-butylbenzaldehyde, whereas reaction of the radical intermediate with bromine leads to formation of the observed side products 4-tert-butylbenzyl bromide and its hydrolysis and solvolysis products 4-tert-butylbenzyl alcohol and 4-tert-butylbenzyl acetate, respectively. The cobalt(II) catalysts Co(OAc)(2) and Co(acac)(2) are able to quickly oxidize the radical intermediate, thereby largely preventing the bromination reaction (i.e., side-product formation) from occurring, and yield the aldehyde product with 75-80 % selectivity. In contrast, the cerium catalyst studied here exhibits an aldehyde selectivity of around 50 % due to the competing bromination reaction. Addition of extra hydrogen peroxide leads to an increased product yield of 72 % (cerium(III) acetate) or 58 % (cobalt(II) acetate). Product inhibition and the presence of increasing amounts of water in the reaction mixture do not play a role in the observed low incremental yields.     

Exploitation the unique acidity of novel cerium-tungstate catalysts in the preparation of indole derivatives under eco-friendly acid catalyzed Fischer indole reaction protocol

Solid acidic cerium tungstate catalysts containing different molar ratios of cerium and tungstate were prepared by direct solvothermal methodology. The structure of the prepared catalysts was deeply studied and confirmed based on different characterization techniques such as DTA-TGA, FTIR, Raman spectra, XRD and N₂ adsorption measurements. Moreover, FTIR and TPD of chemically adsorbed pyridine techniques were conducted to fully address the nature and the strength of the acidic sites of the prepared catalysts. The study showed that at a lower molar ratio of tungstate, the catalyst contains cerium oxide phase and slight participation of cerium tungstate phase, which gradually increases with further increase of tungstate molar ratio. This phase change was also accompanied by a noticeable change in the thermal stability, surface area and acidic properties of the prepared catalysts. Additionally, the techniques used to study the acidic properties showed an excellent enhancement in the acidic centers. It was also noted that the strength of these acidic centers reached the maximum in the case of using tungstate: cerium molar ratio 2:1 (CeW2.0) catalyst, and slightly decreased thereafter. By exploiting the acidic properties of the prepared catalysts, a series of indole derivatives were synthesized via the Fischer indole synthesis strategy. The results also showed that ～100% of indole derivatives were obtained using 0.02 g catalyst at 80 °C after 2 h only. Moreover, the Reuse experiment demonstrated the possibility of recycling and reusing the catalyst through many cycles with high efficiency, indicating its wonderful constancy and reusability.