Sulfates of the refractory metals: crystal structure and thermal behavior of Nb2O2(SO4)3, MoO2(SO4), WO(SO4)2, and two modifications of Re2O5(SO4)2

The sulfates Nb(2)O(2)(SO(4))(3), MoO(2)(SO(4)), WO(SO(4))(2,) and two modifications of Re(2)O(5)(SO(4))(2) have been synthesized by the solvothermal reaction of NbCl(5), WOCl(4), Re(2)O(7)(H(2)O)(2), and MoO(3) with sulfuric acid/SO(3) mixtures at temperatures between 200 and 300 °C. Besides the X-ray crystal structure determination of all compounds, the thermal behavior was investigated using thermogravimetric studies. WO(SO(4))(2) (monoclinic, P2(1)/n, a = 7.453(1) ?, b = 11.8232(8) ?, c = 7.881(1) ?, β = 107.92(2)°, V = 660.7(1) ?(3), Z = 4) and both modifications of Re(2)O(5)(SO(4))(2) (I: orthorhombic, Pba2, a = 9.649(1) ?, b = 8.4260(8) ?, c = 5.9075(7) ?, V = 480.27(9) ?(3), Z = 2; II: orthorhombic, Pbcm, a = 7.1544(3) ?, b = 7.1619(3) ?, c = 16.8551(7) ?, V = 863.64(6) ?(3), Z = 4) are the first structurally characterized examples of tungsten and rhenium oxide sulfates. Their crystal structure contains layers of sulfate connected [W═O] moieties or [Re(2)O(5)] units, respectively. The cohesion between layers is realized through weak M-O contacts (343-380 pm). Nb(2)O(2)(SO(4))(3) (orthorhombic, Pna2(1), a = 9.9589(7) ?, b = 11.7983(7) ?, c = 8.6065(5) ?, V = 1011.3(1) ?(3), Z = 4) represents a new sulfate-richer niobium oxide sulfate. The crystal structure contains a three-dimensional network of sulfate connected [Nb═O] moieties. In MoO(2)(SO(4)) (monoclinic, I2/a, a = 8.5922(6) ?, b = 12.2951(6) ?, c = 25.671(2) ?, β = 94.567(9)°, V = 2703.4(3) ?(3), Z = 24) [MoO(2)] units are connected through sulfate ions to a three-dimensional network, which is pervaded by channels along [100] accommodating the terminal oxide ligands. In all compounds except WO(SO(4))(2), the metal ions are octahedrally coordinated by monodentate sulfate ions and oxide ligands forming short M═O bonds. In WO(SO(4))(2), the oxide ligand and two monodentate and two bidentate sulfate ions build a pentagonal bipyramid around W. The thermal stability of the sulfates decreases in the order Nb > Mo > W > Re; the residues formed during the decomposition are the corresponding oxides.     

SOx on ceria from adsorbed SO2

Results from first-principles calculations present a rather clear picture of the interaction of SO(2) with unreduced and partially reduced (111) and (110) surfaces of ceria. The Ce(3+)∕Ce(4+) redox couple, together with many oxidation states of S, give rise to a multitude of SO(x) species, with oxidation states from +III to +VI. SO(2) adsorbs either as a molecule or attaches via its S-atom to one or two surface oxygens to form sulfite (SO(3)(2-)) and sulfate (SO(4)(2-)) species, forming new S-O bonds but never any S-Ce bonds. Molecular adsorption is found on the (111) surface. SO(3)(2-) structures are found on both the (111) and (110) surfaces of both stoichiometric and partially reduced ceria. SO(4)(2-) structures are observed on the (110) surface together with the formation of two reduced Ce(3+) surface cations. SO(2) can also partially heal the ceria oxygen vacancies by weakening a S-O bond, when significant electron transfer from the surface (Ce4f) into the lowest unoccupied molecular orbital of the SO(2) adsorbate takes place and oxidizes the surface Ce(3+) cations. Furthermore, we propose a mechanism that could lead to monodentate sulfate formation at the (111) surface.     

CuO/Al2O3吸附SO2后氢再生及一体化回收硫磺

考察了添加Na助剂对CuO/Al2O3 的H2再生过程、硫磺产量及后续脱SO2过程活性的影响。结果表明,400℃再生温度下Na助剂添加后,CuO/Al2O3吸附剂的H2再生循环过程的硫磺产量及后续脱SO2过程硫容均变为添加前的1.3倍。Na助剂的添加明显增大吸附剂上载体Al2O3的硫化程度;且在Cu相和Na相共同存在情况下,吸附剂上生成的部分物质Al2(SO4)3在400℃以下即可被还原再生,从而明显提高了H2再生过程的硫磺产量和后续脱SO2硫容。     

Effect of CeO2 on the catalytic performance of Ni/Al2O3 for autothermal reforming of methane

The effect of promoter Ce on the catalytic performance of Ni/Al2O3 catalyst for autothermal reforming of methane to hydrogen was investigated. The catalysts were characterized by X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, and X-ray photoelectron spectroscopy （XPS）. The results indicated that the catalytic performance of the catalysts was improved with the addition of Ce. Ni/Ce30Al70Oδ showed the highest CH4 conversion in operation temperatures ranging from 650 ℃ to 850 ℃. At the same time, the decrease in H2/CO ratio with increasing reaction temperature was consistent with the fact that water-gas shift reaction was thermodynamically unfavorable at higher temperatures. The XRD result indicated that adding Ce to Ni/Al2O3 catalyst prevented the formation of NiAl2O4 and facilitated the formation of NiO. The formation of NiO increased the number of active sites, resulting in higher activity. Comparing the TPR profiles of Ni/Ce30Al70Oδ with Ni/Al2O3, it could be clearly observed that with the addition of Ce, the total reduction peak areas in the middle and low temperatures increased. It was most probably that the addition of Ce inhibited the stronger interaction between Ni and Al2O3 to form the phase of NiAl2O4, and favored the formation of the strong interaction between NiO species and CeO2. Therefore, the addition of Ce to the Ni/Al2O3 catalyst increased the active surface that promoted the activity of the catalyst.     

Characterization of O2-CeO2 interactions using in situ Raman spectroscopy and first-principle calculations.

Interactions between O(2) and CeO(2) are examined experimentally using in situ Raman spectroscopy and theoretically using density-functional slab-model calculations. Two distinct oxygen bands appear at 825 and 1131 cm(-1), corresponding to peroxo- and superoxo-like species, respectively, when partially reduced CeO(2) is exposed to 10 % O(2). Periodic density-functional theory (DFT) calculations aid the interpretation of spectroscopic observations and provide energetic and geometric information for the dioxygen species adsorbed on CeO(2). The O(2) adsorption energies on unreduced CeO(2) surfaces are endothermic (0.91相似文献   

V2O5-CeO2/TiO2-ZrO2催化剂表征及NH3还原NOx性能

商业选择性催化还原(SCR)催化剂V2O5-WO3(MoO3)/TiO2存在反应温度窗口窄(300–400 oC)和SO3转化率高等缺点,同时占催化剂总质量80%以上的载体TiO2比表面积小,热稳定性差.已有研究发现TiO2-ZrO2固溶体具有较大的比表面积和较强的表面酸性, TiO2与ZrO2的摩尔比为1：1时其比表面积达到最大. CeO2作为SCR催化剂的组成部分,由于其优良的储氧和放氧能力受到广泛关注.研究表明, CeO2-CuO, Ce/Ti-Si-Al和Mo2O3(Co2O3)/Ce-Zr等催化剂具有优良的SCR脱硝活性,同时对V2O5-WO3/TiO2催化剂进行CeO2改性,可提高催化剂的抗SO2中毒能力.实际烟气组分中同时存在SO2和H2O,必定会导致催化剂硫酸盐中毒,而目前对含Ce催化剂的硫酸盐中毒情况研究较少,因此开发新型高效脱硝催化剂十分必要.前期我们研究了xCeO2-3%V2O5/TiO2-ZrO2催化剂,发现CeO2可以显著拓宽脱硝温度窗口,同时增强催化剂酸性位点,但是V2O5含量较高时对环境及人体健康均有较大危害.本文采用共沉淀法制备摩尔比为1：1的TiO2-ZrO2固溶体,用浸渍法负载不同摩尔比的CeO2和1%的V2O5,得到一系列V-xCe/Ti-Zr催化剂,结合X射线衍射(XRD)、比表面积测试(BET)、高分辨透射电镜(HRTEM)、程序升温还原(H2-TPR)、原位漫反射红外光谱(in situ DRIFTS)和程序升温脱附(NH3-TPD)等手段分析催化剂的晶相、活性物质分散程度、氧化还原性质及表面酸性,在200–450 oC范围内考察Ce掺杂催化剂选择性催化还原NOx的脱硝活性,并在250 oC测试催化剂在NH3+NO+O2+SO2+H2O气氛中的脱硝活性,研究催化剂抗硫酸盐中毒能力.研究发现,CeO2掺杂可以拓宽脱硝反应活性窗口, V-0.2Ce/Ti-Zr (摩尔比Ce：Ti =0.2)表现出最优的脱硝性能,在250–350oC范围内脱硝效率均在92%以上,同时与前期研究结果对比发现CeO2含量较高时会导致高温段NOx转化率下降. XRD和HRTEM结果表明,ZrO2的添加可以显著降低载体TiO2的结晶度,复合氧化物TiO2-ZrO2呈无定形态, CeO2高度分散于载体之上,并且催化剂以单晶形式存在. H2-TPR结果表明,CeO2能显著提高催化剂的还原能力,主要的还原反应发生在CeO2的α(200–430oC)和β(430–600 oC)还原峰上,总体而言, V-0.2Ce/Ti-Zr表现出最大的氢气消耗量,即其还原性最强.低V2O5负载有利于较低温度SCR反应, V-0.3Ce/Ti-Zr的钒氧化物还原峰强度最大,其次是V-0.2Ce/Ti-Zr. NH3-TPD测试发现V2O5/TiO2主要存在中强酸及强酸,而V2O5/TiO2-ZrO2主要是弱酸, CeO2负载后随着其含量提高,弱酸强度增加.结合氨气原位漫反射红外光谱发现, CeO2可以增加催化剂Br?nsted和Lewis酸位数量,同时出现反应中间物–NH2, V2O5的负载量较高会抑制1660 cm–1处Br?nsted酸吸收峰的出现. BET结果发现, TiO2-ZrO2和V2O5/Ti-ZrO2比表面积分别可达255.73和143.77 m2/g, V2O5/TiO2仅为66.1 m2/g,表明ZrO2的添加可以显著增大催化剂比表面积,进而有利于SCR反应进行,沉积的氧化物进入载体孔道导致催化剂比表面积降低. V2O5-xCeO2/TiO2-ZrO2表现出较强的抗SO2中毒能力,但是在H2O存在条件下脱硝活性较差,可能是生成的硫酸铵盐及亚硫酸盐阻塞催化剂孔道所致. SO2和H2O停止通入后, V2O5-0.3CeO2/TiO2-ZrO2活性恢复至原有水平, V2O5-0.2CeO2/TiO2-ZrO2恢复至最初的84%.对中毒催化剂进行不同反应温度下的活性测试,发现V2O5-0.2CeO2/TiO2-ZrO2在中温段反应活性显著降低,可能是由于Ce(SO4)2的形成所致,由于V2O5-0.3CeO2/TiO2-ZrO2的Ce含量较高,其在此温度范围内活性依旧较高.两者在高温段NOx转化率均较高,推测是V2O5开始发挥活性组分作用的缘故.     

Theoretical study of CeO2 and Ce2O3 using a screened hybrid density functional

The predicted structures and electronic properties of CeO(2) and Ce(2)O(3) have been studied using conventional and hybrid density functional theory. The lattice constant and bulk modulus for CeO(2) from local (LSDA) functionals are in good agreement with experiment, while the lattice parameter from a generalized gradient approximation (GGA) is too long. This situation is reversed for Ce(2)O(3), where the LSDA lattice constant is much too short, while the GGA result is in reasonable agreement with experiment. Significantly, the screened hybrid HSE functional gives excellent agreement with experimental lattice constants for both CeO(2) and Ce(2)O(3). All methods give insulating ground states for CeO(2) with gaps for the 4f band lying between 1.7 eV (LSDA) and 3.3 eV (HSE) and 6-8 eV for the conduction band. For Ce(2)O(3) the local and GGA functionals predict a semimetallic ground state with small (0-0.3 eV) band gap but weak ferromagnetic coupling between the Ce(+3) centers. By contrast, the HSE functional gives an insulating ground state with a band gap of 3.2 eV and antiferromagnetic coupling. Overall, the hybrid HSE functional gives a consistent picture of both the structural and electronic properties of CeO(2) and Ce(2)O(3) while treating the 4f band consistently in both oxides.     

氨法选择性还原氮氧化物 V2O5/TiO2-PILC催化剂的抗硫性能

选择性催化还原(SCR)是目前去除氮氧化物最有效的方法之一. V2O5/TiO2催化剂被广泛应用于氨法选择性还原氮氧化物(NH3-SCR)反应,但该催化剂存在工作温度高(300–400oC)及 SO2氧化率高引起设备腐蚀和管路堵塞等问题,开发低温 SCR催化剂具有重要意义.过渡金属氧化物(如 Fe2O3, MnOx和 CuO等)催化剂用于低温SCR先后见诸文献报道,但这些催化剂在 SO2和 H2O存在下易失活.近年来柱撑黏土(PILC)引起科学家广泛关注, Yang等首次将 V2O5/TiO2-PILC催化剂应用于 NH3-SCR反应,发现其催化活性高于传统 V2O5/TiO2催化剂.柱撑黏土基催化剂在 NH3-SCR反应中也显示出良好抗硫性能,但 V2O5/TiO2-PILC催化剂的抗硫机理至今尚未见深入研究.因此我们制备了一系列 V2O5/TiO2-PILC催化剂,采用原位漫反射红外等方法详细研究了其抗硫性能较好的原因.
　　首先采用离子交换法制备出 TiO2-PILC载体,之后采用浸渍法制备了不同钒含量(质量分数x/%=0,3,4,5)的xV2O5/TiO2-PILC催化剂.同时,制备了传统 V2O5/TiO2和 V2O5-MoO3/TiO2催化剂作为对比.活性评价结果显示,4V/TiO2-PILC催化剂具有最高的催化活性,其催化性能与传统钒钛催化剂相当.在160oC时, NO转化率可达80%以上.同时,4V/TiO2-PILC催化剂还具有较宽的反应温度窗口,在260–500oC范围内, NO转化率保持在90%以上.向反应体系中加入0.05% SO2和10% H2O后,在低温(160oC以下)时所有催化剂的反应活性都有一定提高,可能是由于 SO2的加入提高了催化剂的表面酸性.继续升高温度,4V/TiO2和4V6Mo/TiO2催化剂活性均明显下降,而4V/TiO2-PILC催化剂的活性则未出现明显下降.原位漫反射红外光谱结果显示, SO2在三种催化剂表面的吸附以表面硫酸盐或亚硫酸盐物种以及离子态 SO42–物种形式存在,而在4V/TiO2-PILC催化剂表面离子态 SO42–物种的量最少. X射线光电子能谱及 O2程序升温脱附结果显示,在4V/TiO2-PILC催化剂上,表面吸附氧(Oads)的量最少.综合上述分析可以得出,在 SO2气氛下,离子态 SO42–物种在 SCR催化剂表面的累积可能是导致其失活的主要原因,而离子态 SO42–物种的形成可能与催化剂表面吸附氧的量有关.     

二维层状水合酸式硫酸铈H3O[Ce(SO4)2·(H2O)3]·H2O的水热合成与结构表征

镧系金属硫酸盐由于在稀土分离等方面具有重要的应用而受到广泛关注。但是，因其适于结构测定的单晶相对难以得到，迄今，关于稀土硫酸盐的结构报道仍然较少，且主要局限于水合硫酸盐和三元硫酸盐．近几年中，基于硫酸根与磷酸根在结构上的相似性，借鉴在水热／溶剂热体系中采用有机胺作模板剂大量合成具有空旷骨架结构的微孔磷酸盐的成功经验，以有机胺为模板剂合成具有空旷骨架结构的镧系金属硫酸盐的工作也已见诸报道．在这些化合物中，由于硫酸根配位方式的多样性和稀土元素配位数和配位构型的可调变性，展现出了一些有趣的结构特征．     

高效 CeO2-MnOx-Al2O3催化剂的制备、表征及催化消除 NO性能

机动车在给人类生活带来便利的同时,也造成了严重的大气污染.其尾气净化成为人们关注的焦点.一氧化氮(NO)、一氧化碳(CO)和碳氢化合物(HCs)是机动车尾气中的三大典型污染物,主要通过三效催化(TWC)技术进行脱除. TWC技术涉及几个重要的催化反应,其中 CO催化还原 NO由于能够同时消除 CO和 NO两种污染物而引起研究者的极大关注.研究表明,负载型贵金属催化剂在该反应中显示出优异的催化性能,但存在资源匮乏、价格昂贵以及热稳定性欠佳等不足.因此,低价、高效的过渡金属氧化物催化剂成为近年研究重点.稀土金属氧化物 CeO2由于具有良好的氧化还原性能、较高的储释氧容量以及丰富的表面氧空位而被广泛用于 CO催化还原 NO反应.研究表明,对 CeO2进行离子掺杂可进一步增大其比表面积,改善其氧化还原性能和储释氧容量.并且,我们在先前的研究中还发现,将具有多种可变价态的钛离子或锡离子掺入 CeO2晶格由于掺杂离子能与 Ce4+/Ce3+发生电子转移而更有利于改善 CeO2的理化性质.此外,锰氧化物(MnOx)在氧化还原气氛中容易实现不同价态之间的切换,从而在一些重要的氧化还原反应中表现出优异的催化性能.近年来,有研究者将 CeO2与 MnOx相结合制备了 CeO2-MnOx催化剂用于 NO消除、碳烟燃烧和挥发性有机物(VOCs)氧化等反应,并取得一些有意义的结果.然而,对于实际应用来说, CeO2-MnOx催化剂存在比表面积偏小等不足.众所周知,γ-Al2O3是一种常用的具有高比表面积和高热稳定性的催化剂载体材料,可有效增大催化剂比表面积.我们前期研究结果表明,通过共沉淀法将 Al3+掺入铈基复合氧化物的晶格相比于以γ-Al2O3为载体更有利于改善铈基复合氧化物的理化性质和催化性能.因此,我们通过简单的氨水反滴加共沉淀法制备了一系列 CeO2-MnOx-Al2O3(Ce：Mn：Al摩尔比=6：4：x,x =0.25,0.5,1,2)复合氧化物催化剂用于 CO催化还原 NO反应.并运用 X射线衍射、拉曼光谱、氮气物理吸附、氢气程序升温还原、X射线光电子能谱以及原位漫反射红外光谱等表征技术对上述催化剂进行了系统分析.重点考察了 Al3+掺杂量对 CeO2-MnOx-Al2O3复合氧化物催化剂理化性质和催化性能的影响.结果表明,在 CeO2-MnOx复合氧化物中掺入少量 Al3+会导致其晶粒尺寸减小,从而增大其比表面积和孔体积,并增加 Ce3+和 Mn4+的含量.比表面积和孔体积增大有助于催化剂与反应物分子之间充分接触; Ce3+和 Mn4+含量增加能分别促进 CO物种吸附以及吸附态 NO物种脱附、转化和解离.这些变化有利于提高 CeO2-MnOx复合氧化物在 CO催化还原 NO反应中的催化性能.最后,基于催化剂的理化性质表征及其催化性能评价,我们尝试提出了一个可能的催化反应机理,以进一步理解 CeO2-MnOx-Al2O3复合氧化物催化剂在 CO催化还原 NO反应中的优异性能.     

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     

Transformation of proton-conducting Perovskite-type into fluorite-type fast oxide ion electrolytes using a CO2 capture technique and their electrical properties

Fast oxide ion conducting Ce 1- x M x O 2-delta (M = In, Sm; x = 0.1, 0.2) and Ce 0.8Sm 0.05Ca 0.15O 1.825 were prepared from the corresponding perovskite-like structured materials with nominal chemical composition of BaCe 1- x M x O 3-delta and BaCe 0.8Sm 0.05Ca 0.15O 2.825, respectively, by reacting with CO 2 at 800 degrees C for 12 h. Powder X-ray diffraction (PXRD) analysis showed the formation of fluorite-type CeO 2 and BaCO 3 just after reaction with CO 2. The amount of CO 2 gained per ceramic gram was found to be consistent with the Ba content. The CO 2 reacted samples were washed with dilute HCl and water, and the resultant solid product was characterized structurally and electrically employing various solid-state characterization methods, including PXRD, and alternating current (ac) impedance spectroscopy. The lattice constant of presently prepared Ce 1- x M x O 2-delta and Ce 0.8Sm 0.05Ca 0. 15O 1.825 by a CO 2 capture technique follows the expected ionic radii trend. For example, In-doped Ce 0.9In 0.1O 1.95 (In (3+) (VIII) = 0.92 A) sample showed a fluorite-type cell constant of 5.398(1) A, which is lower than the parent CeO 2 (5.411 A, Ce (4+) (VIII) = 0.97 A). Our attempt to prepare single-phase In-doped CeO 2 samples at 800, 1000, and 1500 degrees C using the ceramic method was unsuccessful. However, we were able to prepare single-phase Ce 0.9In 0.1O 1.95 and Ce 0.8In 0.2O 1.9 by the CO 2 capture method from the corresponding barium perovskites. The PXRD studies showed that the In-doped samples are thermodynamically unstable above 800 degrees C. The ac electrical conductivity studies using Pt electrodes showed the presence of bulk, grain-boundary, and electrode contributions over the investigated temperature range in the frequency range of 10 (-2)-10 (7) Hz. The bulk ionic conductivity and activation energy for the electrical conductivity of presently prepared Sm- and (Sm + Ca)-doped CeO 2 samples shows conductivities similar to those of materials prepared by the ceramic method reported in the literature. For instance, the conductivity of Ce 0.8Sm 0.2O 1.9 using the CO 2 capture technique was determined to be 4.1 x 10 (-3) S/cm, and the conductivity of the same sample prepared using the ceramic method was 3.9 x 10 (-3) S/cm at 500 degrees C. The apparent activation energy of the area-specific polarization resistance for the symmetric cell (Sm,Sr)CoO 3- x |Ce 0.8Sm 0.2O 1.9|(Sm,Sr)CoO 3- x was determined to be 1 eV in air.     

Thermochemistry of Sr2Ce(1-x)Pr(x)O4 (x = 0, 0.2, 0.5, 0.8, and 1): variable-temperature and -atmosphere in-situ and ex-situ powder X-ray diffraction studies and their physical properties

A novel family of metal oxides with a chemical formula of Sr(2)Ce(1-x)Pr(x)O(4) (x = 0, 0.2, 0.5, 0.8, and 1) was developed as mixed oxide ion and electronic conductors for solid oxide fuel cells (SOFCs). All of the investigated samples were synthesized by the ceramic method at 1000 °C in air and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). Ex-situ PXRD reveals that the Sr(2)PbO(4)-type Sr(2)CeO(4) decomposes readily into a mixture of perovskite-type SrCeO(3) and rock-salt-type SrO at 1400 °C in air. Surprisingly, the decomposed products are converted back to the original Sr(2)PbO(4)-type Sr(2)CeO(4) phase at 800 °C in air, as confirmed by in-situ PXRD. Thermal decomposition is highly suppressed in Sr(2)Ce(1-x)Pr(x)O(4) compounds for Pr > 0, suggesting that Pr improves the thermal stability of the compounds. Rietveld analysis of PXRD and SAED supported that both Pr and Ce ions are located on the 2a site in Pbam (space group no. 55). The electrical transport mechanism could be correlated to the reduction of Pr and/or Ce ions and subsequent loss of oxide ions at elevated temperatures, as shown by TGA and in-situ PXRD. Conductivity increases with Pr content in Sr(2)Ce(1-x)Pr(x)O(4). The highest total conductivity of 1.24 × 10(-1) S cm(-1) was observed for Sr(2)Ce(0.2)Pr(0.8)O(4) at 663 °C in air.     

松散接触下 Au-Ce强相互作用对 Au/CeO2/3DOM Al2O3催化剂催化柴油炭烟燃烧活性的影响

与汽油发动机相比,柴油发动机具有热效率高、CO2排放低、寿命长、续航距离远和经济性好等优点,可大大缓解能源短缺,降低 CO2排放量.因此,机动车柴油化是当前发展趋势.然而,柴油发动机在使用过程中会排放大量炭烟颗粒物,对人体危害极大.因此,控制炭烟颗粒排放成为环境催化研究的重点之一.
　　炭烟颗粒物催化燃烧反应是典型的固(炭烟颗粒)-固(催化剂)-气(O2)多相催化反应.三维有序大孔氧化物(3DOM)具有大孔径和内部贯通的孔道结构,能有效提高炭烟颗粒与催化活性中心的接触性能.同时,纳米 Au颗粒在大孔氧化物表面的负载可有效提高催化剂本征活性,但纳米 Au颗粒催化剂热稳定性较差. CeO2具有较好的储放氧性能,可与贵金属活性组分发生相互作用,从而提高贵金属纳米颗粒的分散度和稳定性.因此,本文从柴油炭烟颗粒物催化燃烧反应本质出发,设计制备了高炭烟燃烧催化活性的3DOM氧化物担载 Au基催化剂,研究了 Au与 CeO2强相互作用对炭烟燃烧活性的影响.
　　采用胶体晶体模板法制备3DOM Al2O3载体,由微孔膜氨沉淀法制备 CeO2/3DOM Al2O3催化剂,以还原-沉积法制备 Au/3DOM Al2O3和 Au/CeO2/3DOM Al2O3催化剂,并利用扫描电镜、N2物理吸附-脱附、X射线衍射、透射电镜、紫外漫反射光谱、H2程序升温还原和 X射线光电子能谱等手段对催化剂形貌、比表面积、物理化学性质和氧化还原性进行了表征.结果表明,在 CeO2/3DOM Al2O3中, Al3+可进入到氧化铈晶格内,形成 Al-Ce-O固溶体,产生氧空位,这有利于氧物种转移.此外, Au/CeO2/3DOM Al2O3催化剂中 Au和 CeO2之间的强相互作用能增加 Au纳米颗粒表面活性氧物种数量,从而促进柴油炭烟燃烧反应.纳米颗粒 Au的担载使得催化柴油炭烟燃烧的起燃温度明显降低,其中 Au/CeO2/3DOM Al2O3催化剂表现出最高的催化活性,T10,T50和T90分别为273,364和412oC.     

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.     

纳米CeO2基固溶体催化柴油机碳颗粒物燃烧性能

采用柠檬酸溶胶鄄凝胶法制备CeO2基固溶体催化剂(Ce0.7Zr0.3O2-δ、Ce0.7Pr0.3O2-δ和Ce0.7Gd0.3O2-δ), 并考察了固溶体和三种常用载体(TiO2、SiO2和Al2O3)及其负载KNO3后的催化碳黑燃烧活性. 结果表明, CeO2基固溶体催化剂具有很高的催化燃烧活性, 其活性接近TiO2、SiO2和Al2O3负载30%KNO3催化剂的活性. 因为纳米CeO2基固溶体的形成, 提高了催化剂的抗烧结能力, 使氧更活泼, 从而提高氧化还原性能, 有利于碳颗粒燃烧. 由于CeO2基固溶体本身的高活性, 因此KNO3的添加不能明显提高CeO2基固溶体催化剂(尤其是Ce0.7Zr0.3O2-δ和Ce0.7Pr0.3O2-δ)的催化燃烧活性, 但KNO3能显著提高TiO2, SiO2和Al2O3的催化燃烧活性.     

Synergistic effect between NO2 and SO2 in their adsorption and reaction on gamma-alumina

Field measurements showed that there exists a correlation between nitrate and sulfate on mineral dust. In this work, the synergistic mechanism of adsorption and reaction between SO2 and NO2 on gamma-alumina was studied using in situ diffusion reflectance infrared Fourier spectroscopy (in situ DRIFTS) and temperature programmed desorption (TPD). The results revealed that the reaction pathway of NO2 adsorbed on alumina was altered in the presence of SO2. In the absence of SO2, nitrite was found to be an intermediate in the oxidation of NO2 to surface nitrate species. However, in the presence of SO2, the formation of nitrite was inhibited and a new intermediate, dinitrogen tetraoxide (N2O4), was observed. On the other hand, surface tetravalent sulfur species S(IV), including bisulfite and sulfite, were oxidized to sulfate in air condition when NO2 was present. The atmospheric implication of this synergistic effect was also discussed.     

Experimental study of the heterogeneous interaction of SO3 and H2O: formation of condensed phase molecular sulfuric acid hydrates

The interaction of SO(3) and H(2)O at low temperatures upon an inert surface has been studied with infrared spectroscopy and compared to the predictions of recent computational studies. At low temperatures and low water partial pressures, amorphous deposits of molecular H(2)SO(4) complexed with variable amounts of H(2)O in a ratio of between 1:1 and 2:1 are formed. Upon annealing, this material ejects water and converts first to a 1:1 H(2)SO(4).H(2)O complex and subsequently to anhydrous H(2)SO(4). Adding water to the amorphous molecular hydrate results in the formation of a new species, which on the basis of its thermal behavior and by comparison to theoretical predictions can be attributed to a molecular polymer with a repeat unit of (H(2)SO(4).(H(2)O)(2))(n)(). Implications of these observations for the initial stages of the formation of sulfate aerosol in the atmosphere and their surface reactivity are discussed.     

Hydrogen production from coke oven gas over LiNi/γ-Al2O3 catalyst modified by rare earth metal oxide in a membrane reactor

The performance of LiNi/r-Al2O3 catalysts modified by rare earth metal oxide (La2O3 or CeO2) packed on BCFNO membrane reactor was discussed for the partial oxidation of methane (POM) in coke oven gas (COG) at 875 ◦C. The NiO/r-Al2O3 catalysts with different amounts of La2O3 and CeO2 were prepared with the same preparation method and under the same condition in order to compare the reaction performance (oxygen permeation, CH4 conversion, H2 and CO selectivity) on the membrane reactor. The results show that the oxygen permeation flux increased significantly with LiNiREOx/r-Al2O3 (RE = La or Ce) catalysts by adding the element of rare earth especially the Ce during the POM in COG. Such as, the Li15wt%CeO29wt%NiO/ -Al2O3 catalyst with an oxygen permeation flux of 24.71 ml·cm−2·min−1 and a high CH4 conversion was obtained in 875 ◦C. The resulted high oxygen permeation flux may be due to the added Ce that inhibited the strong interaction between Ni and Al2O3 to form the NiAl2O4 phase. In addition, the introduction of Ce leads up to an important property of storing and releasing oxygen.     

NO-NH_3-O_2 reaction catalyzed by V_2O_5/AC at low temperatures——Effects of SO_2, V_2O_5 loading and reaction temperature

The effects of SO2, V2O5 loading and reaction temperature on the activity of activated carbon supported vanadium oxide catalyst have been studied for the reduction of NO with NH3 at low temperatures (150-250℃). It is found that SO2 significantly promotes the catalyst activity. Both V2O5 loading and reaction temperature are vital to the promoting effect of SO2. The catalysts with V2O5 loadings of 1 -5 weight percent have a positive effect on the promotion of SO2, while the catalysts with V2O5 loadings of above 7 weight percent have not such an effect or show a negative effect. At lower temperatures (<180℃) SO2 poisons the catalyst but at higher temperatures promotes it. The reason of the SO2 promotion was also discussed; it may results from the formation of SO42- on the catalyst surface, which increases the surface acidity and hence the catalytic activity.