Structural,textural and catalytic properties of pure and Li-doped NiO/Al2O3 and CuO/Al2O3 catalysts

Pure and Li-doped NiO/Al₂O₃ and CuO/Al₂O₃ catalysts were prepared to contain 2, 4 and 8 wt.% of Ni and Cu, respectively. The structural properties were determined using DTA, XRD and FTIR techniques, and the textural properties of the catalysts were determined from their adsorption–desorption isotherms of nitrogen at 77 K. The chemisorption of hydrogen at 473–823 K with the pre-reduced catalysts was measured. The data obtained allowed the determination of the metal surface area, S (m²/g); the percentage of metal distribution, R; and the diameter of metal crystallite, d (nm). The amount of surface acidity, measured in mmol/g, was determined from the amount of chemisorbed pyridine necessary to completely inhibit the catalytic dehydration (DHD) of isopropanol. The conversion of isopropanol at 533–623 K was investigated using the micro-catalytic pulse technique. DTA, XRD and FTIR indicated that NiO and CuO exist as separate phases with crystallite sizes too small to be detected. No evidence has been gathered to indicate the existence of an aluminate phase.With the increase of metal loading, the surface area decreased whereas the total pore volume and the mean pore radius increased. Conversion of iso-propanol to propene proceeded via (DHD) on surface acid sites, and conversion of isopropanol to acetone proceeded via dehydrogenation (DHG) on redox sites. DHD and DHG exhibited first-order kinetics, and the rates of both reactions increased with temperature, with the latter being more temperature-dependent.     

焙烧温度对非负载Ni-Mo-Al2O3催化剂加氢脱氧性能的影响

采用热分解硝酸镍和钼酸铵的方法制备了Ni-Mo-Al2O3非负载催化剂。分别以乙酸、苯酚为探针分子,在连续流动固定床反应器上评价了催化剂的加氢脱氧活性,并采用XRD、BET、XRD、EDS等技术对催化剂进行了表征,着重考察了焙烧温度对催化剂的晶态结构、表面元素相对含量及催化性能的影响。结果表明,随着焙烧温度的升高,催化剂的比表面积增大,晶化程度提高,焙烧温度550℃时,催化剂表面Ni、Mo、Al的比例达到最优,并具有最好的加氢脱氧活性。在250℃、0.4 MPa条件下,乙酸的脱氧率达到96.0%;在200℃、0.3 MPa条件下,苯酚的脱氧率达到96.8%。     

Propane oxidation with chemically bound oxygen on Pt/TiO2/Al2O3 and Pt/CeO2/Al2O3 catalysts

Possible mechanisms are suggested for propane oxidation on Pt/TiO₂/Al₂O₃ and Pt/CeO₂/Al₂O₃ catalysts in the cyclic reactant supply mode. As compared to the steady-state process, the process conducted as catalyst oxidation-reduction cycles results in a very different product composition: it is more selective toward partial oxidation products and yields much smaller amounts of complete oxidation products. It is established by isothermal and temperature-programmed oxygen desorption that, under the reaction conditions examined, the oxygen desorbed from the catalyst surface into the gas phase makes a negligible contribution to propane oxidation. It is proved by XPS that propane oxidation is due to the chemically bound oxygen of the catalyst. The hypothetical mechanism of the process includes propane activation on Pt followed by the transfer of the activated species to the oxygen-storing component (TiO₂ or CeO₂), where the intermediates are oxidized by chemically bound oxygen.     

CeO2对CuO／Al2O3分散状态及催化性能的影响

用色谱－液反流动法技术,考察了ＣｕＯ催化剂对ＣＯ的性及添加ＣｅＯ２对催化活性的影响,并运用ＸＲＤ,ＴＰＲ和ＸＰＳ技术,研究了催化剂的物相结构和还原牧场 生。实验结果表明,ＣｅＯ２的添加增加了ＣｕＯ的分散性,使ＣｕＯ的特征衍射峰消失,从而改善了催化剂的氧化活性。     

CeO2和Pd在Ni/γ-Al2O3催化剂中的助剂作用

采用脉冲微反技术研究了添加n型半导体氧化物CeO2及贵金属Pd对Ni/γ-Al2O3催化剂上CH4积炭/CO2消炭反应性能的影响,并运用BET、TPR、CO2-TPSR及氢吸附等技术对催化剂进行了表征.结果表明,n型半导体氧化物CeO2的添加可以降低Ni/γ-Al2O3催化剂上CH4裂解积炭活性,提高CO2消炭活性,添加少量贵金属Pd可以进一步改变载体Al2O3、助剂CeO2和活性组分Ni之间的相互作用,从而改善Ni/γ-Al2O3催化剂的抗积炭性能.通过Ni-Ce-Pd/γ-Al2O3催化剂上CH4积炭/CO2消炭模型对上述作用机制作出了新的解释.     

CeO2/Al2O3珠光材料的制备研究

以单晶片状氧化铝为基材,硝酸铈为铈源,NaOH为沉淀剂,采用液相沉积包覆法制备了氧化铈包覆片状氧化铝珠光材料。系统讨论了制备过程中溶液pH值、反应温度、铈盐种类以及铈盐滴加速率等条件对包覆效果的影响,使用X-射线衍射、金相显微镜和扫描电镜对包覆产物和煅烧产物进行了表征分析。实验结果表明最优反应条件为体系pH值为7.5,反应温度为75℃,加料速度为0.4～0.8 mL/min,煅烧温度为760℃时,反应生成的氢氧化铈能以纳米级颗粒形式均匀细密地包覆在片状氧化铝表面,煅烧后制得的CeO_2/Al_2O_3珠光材料产物的CeO_2包覆率可达25%,且具有良好的光学效果。     

Pt/Al2O3和Pt/CeO2/Al2O3催化甲烷部分氧化制合成气反应

研究了Pt/Al₂O₃和Pt/CeO₂/Al₂O₃对甲烷部分氧化制合成气反应的催化活性,发现Pt/CeO₂/Al₂O₃显示了更高的甲烷转化率和合成气选择性.用H₂-TPR、H₂-TPD、SEM-EDX和XRD等技术对催化剂进行了表征.CeO₂和Pt相互作用促进Pt在催化剂表面的分散,抑制Pt在催化剂表面的迁移;降低了催化剂的燃烧活性,提高了催化剂的部分氧化活性和选择性,可避免因催化剂床层局部温度过高而导致催化剂活性下降或失活,提高了催化剂的稳定性.同时,CeO₂通过促进水汽变换反应使反应体系迅速达到平衡,提高了催化剂对H₂的选择性.     

Al2O3掺杂对CeO2基固体电解质性能的影响

利用四探针电阻测量法、 SEM等手段研究了CeO2基固体电解质材料中掺杂Al2O3后的性能变化. 实验发现, 加入的Al2O3分布在晶界处, 将会导致裂纹偏转, 可以显著增加CeO2基材料的强度, 最大弯曲强度对应的Al2O3添加剂量为3 mol%. 另外, 掺杂Al2O3后由于热膨胀系数的差异, 在CeO2中引入压缩性应力, 可以抑制裂纹的进一步扩展. 加入Al2O3还具有显著的促进烧结作用, 但使电导率降低.     

CuO／CeO2和CuO／Al2O3催化剂的催化性能

本文以ＣＯ氧化为模式反应考察了ＣｅＯ２和Ａｌ２Ｏ３负载氧化铜催化剂的氧化活性，运用ＸＲＤ和ＴＰＲ技术研究了催化剂的还原性能和物相结构，结果表明：载体性质对负载ＣｕＯ催化剂的ＣＯ氧化活性有很大影响，ＣｕＯ／ＣｅＯ２催化剂活性明显高于ＣｕＯ／Ａｌ２Ｏ３催化剂．催化剂的还原特性随载体不同而不同．同时发现，热处理对催化剂铜物种的存在形式，晶粒大小、还原特性及其催化活性有明显影响，ＣｕＯ／Ａｌ２Ｏ３催化剂活性下降的主要因素是生成了活性较低的ＣｕＡｌ２Ｏ４相，而ＣｕＯ／ＣｅＯ２催化剂活性下降是由于ＣｕＯ和ＣｅＯ２发生烧结，晶粒变大     

Monolayer dispersion of NiO in NiO/Al2O3 catalysts probed by positronium atom

NiO/Al(2)O(3) catalysts with different NiO loadings were prepared by impregnation method. The monolayer dispersion capacity of NiO is determined to be about 9 wt.% through XRD quantitative phase analysis. Positron lifetime spectra measured for NiO/Al(2)O(3) catalysts comprise two long and two short lifetime components, where the long lifetimes τ(3) and τ(4) correspond to ortho-positronium (o-Ps) annihilation in microvoids and large pores, respectively. With increasing loading of NiO from 0 to 9 wt.%, τ(4) drops drastically from 88 to 38 ns. However, when the NiO loading is higher than 9 wt.%, τ(4) shows a slower decrease. Variation of λ(4) (1/τ(4)) as a function of the NiO content can be well fitted by two straight lines with different slopes. The relative intensity of τ(4) also shows a fast decrease followed by a slow decrease for the NiO content lower and higher than 9 wt.%, respectively. The coincidence Doppler broadening measurements reveal a continuous increase of S parameter with increasing NiO loading up to 9 wt.% and then a decrease afterwards. This is due to the variation in intensity of the narrow component contributed by the annihilation of para-positronium (p-Ps). Our results show that the annihilation behavior of positronium is very sensitive to the dispersion state of NiO on the surface of γ-Al(2)O(3). When the NiO loading is lower than monolayer dispersion capacity, spin conversion of positronium induced by NiO is the dominant effect, which causes decrease of the longest lifetime and its intensity but increase of the narrow component intensity. After the NiO loading is higher than monolayer dispersion capacity, the spin conversion effect becomes weaker and inhibition of positronium formation by NiO is strengthened, which results in decrease of both the long lifetime intensity and the narrow component intensity. The reaction rate constant is determined to be (1.50 ± 0.04) × 10(10) g mol(-1) s(-1) and (3.43 ± 0.20) × 10(9) g mol(-1) s(-1) for NiO content below and above monolayer dispersion capacity, respectively.     

The physicochemical properties of the LiCl-CeCl3-H2O ternary system

The density, viscosity, refractive index, heat conductivity, heat capacity, and freezing temperature of the LiCl-CeCl₃-H₂O ternary system were experimentally determined over the lithium and cerium chloride concentration ranges 13–20 and 8–14 wt %, respectively, and the temperature range ?50–35°C. The densities and viscosities of the LiCl-CeCl₃-H₂O ternary system were calculated by various methods from the properties of binary solutions. The calculation results were compared with the experimental data. The possibilities and shortcomings of each of the methods used are discussed.     

甲烷部分氧化制合成气反应Pt/Al_2O_3和Pt/CeO2/Al_2O_3催化剂的研究(英文)

研究了Ｐｔ／Ａｌ２Ｏ３和Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３催化剂对甲烷部分氧化制合成气反应的催化活性，发现Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３显示了比Ｐｔ／Ａｌ２Ｏ３更高的甲烷转化率和合成气选择性。用Ｈ２ＴＰＲ，Ｈ２ＴＰＤ，ＳＥＭ和ＸＲＤ等手段和技术对催化剂进行了表征。ＣｅＯ２与Ｐｔ之间存在较强的相互作用（ＳＭＳＩ），这种作用促进了Ｐｔ在催化剂表面的分散，抑制了Ｐｔ在催化剂表面的迁移，大大降低了催化剂在反应中的完全燃烧活性，提高了催化剂的部分氧化活性和选择性，避免了因催化剂床层局部温度过高而导致催化剂活性下降或失活，提高了催化剂的稳定性。同时，在反应过程中，ＣｅＯ２通过促进水蒸气变换反应（ＷＧＳＲ）的进行使反应体系迅速达到平衡，提高了催化剂对Ｈ２的选择性。     

CeO2改性的Pd/Al2O3催化剂在加氢脱硫反应中的抗硫性能

采用浸渍法制备CeO2改性的Pd/Al2O3催化剂,以噻吩加氢脱硫为探针反应,考察了Pd/Al2O3 和Pd-CeO2/Al2O3催化剂的活性和抗硫性能,并运用CO吸附、FT-IR、TG等分析测试技术研究表征了催化剂性质. 结果表明,Pd-CeO2/Al2O3催化剂比Pd /Al2O3催化剂具有较低的硫化度. 在连续反应中,Pd-CeO2/Al2O3催化剂的抗硫失活能力较强. CeO2的加入导致了Pd-S键能的减弱,在Pd-CeO2/Al2O3催化剂上H2S主要吸附在CeO2上而不是Pd原子上. Pd-CeO2/Al2O3抗硫能力的提高是由于Pd-Ce结合导致Pd缺电子状态,减少了Pd的硫化失活而引起. CeO2对H2S的竞争吸附造成与CeO2结合作用的Pd处于较低的H2S分压,减少了Pd失活的几率.     

CeO2纳米层对多层载体x-CeO2/3DOM Al2O3负载纳米Au催化剂催化柴油炭烟燃烧活性的影响

与汽油车相比,柴油车具有CO2排放低、寿命长和经济性好等优点,所以近年来受到广泛关注并被大量使用.但是,柴油车在使用过程中会产生大量炭烟颗粒物(PM),对大气环境和人类健康造成很大威胁.因此,开展这方面的基础研究具有重要的科学意义及环境保护意义.催化柴油炭烟燃烧反应是一个气-固-固多相深度氧化反应,由于PM的粒径远大于传统催化剂,导致PM不能进入催化剂孔道内部,造成催化剂活性比表面积利用率较低.设计并制备大孔径的三维有序大孔结构(3DOM)的催化剂,能够减小反应扩散阻力,增加催化剂与炭烟颗粒物的有效接触,加快反应进行.另外,可以通过在3DOM氧化物表面担载其它活性组分,提高催化剂的氧化还原性能,进而提高其活性.CeO2有很好的储放氧性能,在柴油车尾气净化催化剂中较为常见,但是单一的CeO2热稳定性较差,高温下容易烧结,使得比表面积减小,并且失去储氧能力,造成催化剂失活.文献中较常见的解决办法是在CeO2中掺杂其它阳离子,如Zr4+,Pr3+,Al3+,La3+及Y3+等离子,以提高CeO2的抗高温烧结能力.此外,研究报道的催化剂对催化柴油炭烟颗粒物燃烧的峰值温度已经远低于炭烟颗粒物的自燃温度,但是对颗粒物的起燃温度仍普遍较高.我们前期研究结果表明,担载纳米Au颗粒催化剂能够显著降低炭烟燃烧的起燃温度.本文采用胶体晶体模板法制备了3DOM Al2O3载体,利用微孔膜-氨沉淀法担载不同量的活性组分CeO2,制备出一种负载型x-CeO2/3DOM Al2O3催化剂,它既可减少稀土元素用量,降低成本,又因为Al2O3的机械强度较高,还能保证催化剂的机械强度足够好.为了进一步降低催化剂催化炭烟燃烧的起燃温度,利用还原沉积法在多层载体x-CeO2/3DOM Al2O3上负载纳米Au催化剂,制备出不同厚度的CeO2纳米层负载Au催化剂(Au/x-CeO2/3DOM Al2O3).利用X射线衍射、扫描电镜、透射电镜、H2程序升温还原和O2程序升温脱附等方法研究了催化剂的结构及物化性质与催化剂活性之间的关系,提出了消除PM反应的可能机理.结果表明,Al3+离子能够部分进入到CeO2中,形成Al-Ce固溶体.由于Al离子半径小于Ce离子,Al3+掺杂后能引起CeO2晶格发生畸变,产生大量缺陷,形成大量氧空位,促进晶格氧的移动,从而使催化剂具有更大的储放氧能力.在Au/x-CeO2/3DOM Al2O3催化剂中,CeO2担载量过高时,氧化铈纳米层较厚,活性组分容易烧结,不利于催化剂活性提高;而CeO2担载量过低,则CeO2纳米层较稀薄,催化剂的氧化还原性能受限,催化剂活性也不高.因此,CeO2的担载量应适当.此外,Au和CeO2之间的强相互作用能够增加Au纳米颗粒表面活性氧物种的数量,从而促进柴油炭烟燃烧反应.活性测试结果表明,担载纳米Au颗粒后,催化剂催化柴油炭烟燃烧的起燃温度均明显降低,在所制备的系列催化剂中Au/20％CeO2/3DOM Al2O3催化剂展示了最高的催化活性,T10,T50和T90分别为267,372和426 oC.     

不同硅铝比的SAPO-41分子筛物化性质及催化性能研究

磷酸硅铝分子筛（SAPO）因其温和的酸性分布和合适的孔道结构，在很多烃类反应中表现出了较好的催化性能。在二甲苯的异构化反应中，也有少量关于SAPO分子筛的应用报道，但相关的报道主要集中于SAPO-5、SAPO-11和SAPO-31，对于SAPO-41的二甲苯异构化性能的报道较少。     

Study on the NaNp/CpTiCl3/Al2O3-SiO2 system

CpTiCl(3)/Al(2)O(3)-SiO(2)/NaNp (Cp=cyclopentadienyl, Np=naphthenide anion) system was obtained by a reduction of cyclopentadienyl titanium[IV] complexes supported on alumina-silica gels with sodium naphthenide in dinitrogen or argon atmospheres. The yield of the reduction reactions and the yield of dinitrogen fixation by the systems reduced in dinitrogen depend on the kind of phases which are present on alumina-silica gel surfaces according to their composition. On hydrolysis the nitrogen titanium complexes obtained liberated ammonia. The highest yields of these reactions, above 70% calculated as NH(3)/Ti ratio, were obtained for the systems containing in the carriers 10-, 60-wt%, of Al(2)O(3) and SiO(2Deg) of aerosil type. This relatively high activity was achieved with surface titanium complexes obtained by a reaction of CpTiCl(3) with isolated surface hydroxyl groups of neutral properties present on these gels. The EPR method was used to investigate the titanium[III] complexes formed during reduction of the systems. The signals obtained helped in discussion concerning the way in which titanium complexes undergo transformations during the reactions studied.     

Study on the NaNp/Al2O3-SiO2 system

Sodium naphthenide (NaNp) deposited on aluminosilicate gels yields systems that exhibit signals in EPR spectra, the multiplicity, g values, and intensities of which depend on the gel composition. The symmetrical singlets (I) of a g(1) value of 2.00 were assigned to the complexed naphthalene anion radicals on the centers occurring on the surfaces of the alumina and silica phases of the gels studied. Those radicals complexed on surface Lewis acid sites are of hard acid/hard base type according to Pearson theory, and are bonded to the sites by ionic forces. The asymmetrical singlets (II) described by the value g(2)=1.95 were assigned to naphthalene anion radicals, which are complexed by the centers of the aluminosilicate phase of the gels studied. Those radicals, complexed on surface Lewis acid sites of this phase, are of soft acid/soft base type and are bonded to the sites by covalent bonds. The highest intensity of the singlet (I) was recorded for the system containing alumina gel. The highest intensity of the singlet (II) was recorded for the system containing Al(2)O(3) in 30 wt%. The structures of Lewis acid sites on aluminosilicate phases are postulated to be different from those on alumina or silica phases.