红外光谱研究甲烷和氧与SrO-La2O3/CaO表面的相互作用

在甲烷氧化偶联（ＯＣＭ）反应条件下，用原位红外光谱研究ＳｒＯ－Ｌａ２Ｏ３／ＣａＯ催化剂，结果表明，晶格氧使甲深度氧化，Ｌａ２Ｏ３和ＣａＯ具有活泼的晶格氧，ＳｒＯ的晶格氧比较稳定，气相氧通过催化剂表面消耗掉的晶格氧，加速甲烷了深度氧化，另一方面，催化剂表面的碳酸根物种在氧气氛下分解，在Ｌａ２Ｏ３和ＬＣ催化剂中，催化剂表面Ｌａ２Ｏ２（ＣＯ３）的分解形成配位不饱和的晶格氧Ｏ＾２－，并为气相氧吸附提供氧空     

CO2选择性氧化甲烷制C2烃催化剂La2O3/ZnO的氧化还原和CO2吸附性能

Ｌａ２Ｏ３／ＺｎＯ催化剂体系在以二氧化碳作为氧化剂的甲烷氧化偶联反应中具有很高的Ｃ２烃选择性和稳定性．采用ＣＯ２－ＴＰＤ－ＭＳ和ＴＰＲ技术考察了Ｌａ２Ｏ３／ＺｎＯ对ＣＯ２的吸附性质及其氧化还原行为．结果表明：（１）Ｌａ２Ｏ３／ＺｎＯ催化剂体系存在着强、弱两种碱中心，其中弱碱中心数量随样品中Ｌａ２Ｏ３含量增加而减少，强碱中心强度随样品中Ｌａ２Ｏ３含量增加而增强．（２）由于组分相互作用，高温下，Ｌａ２Ｏ３／ＺｎＯ易产生晶格氧空位，使之对ＣＯ２的吸附增强，吸附后的ＣＯ２与晶格氧作用形成立方晶型Ｌａ２Ｏ２ＣＯ３．（３）Ｌａ２Ｏ３／ＺｎＯ表面的Ｌａ３＋和Ｚｎ２＋可以部分被还原，由于组分间的相互作用，使得二者的还原都较单一组分存在时更难．（４）Ｈ２－ＣＯ２－Ｈ２氧化还原循环实验表明，Ｌａ２Ｏ３／ＺｎＯ表面被部分还原后，ＣＯ２可以将部分被还原的表面再氧化．在此基础上对Ｌａ２Ｏ３／ＺｎＯ催化剂上甲烷与ＣＯ２转化为Ｃ２烃的机制也进行了讨论．     

La2O3对Ni-Mo/γ-Al2O3催化剂CO和CO2甲烷化的影响

采用浸渍法制备了一系列Ｎｉ－Ｍｏ－Ｌａ／γ－Ａｌ２Ｏ３催化剂并测定了催化剂的ＣＯ和ＣＯ２甲 化活性采用ＴＥＭ,ＸＰＳ和ＣＯ化学吸附等手段研究了表面性质。结果表明,Ｌａ２Ｏ３的咖入提高了Ｎｉ－Ｍｏ／γ／Ａｌ２Ｏ３催化剂的ＣＯ和ＣＯ２甲烷化活性,增加了催化剂中Ｎｉ的分散度,活性表面积及催化剂表面Ｎｉ原子的浓度,降低了电子结合能。     

含氧化镧的甲烷的氧化偶联催化剂的一些特性

利用ＤＴＡ、ＴＰＤ－ＭＳ、ＸＲＤ、ＴＰＲ及ＴＰＳＲ－ＭＳ等手段对Ｌａ２Ｏ３和含Ｌａ２Ｏ３的甲烷氧化偶联催化剂进行了研究。实验发现含Ｌａ２Ｏ３的催化剂的一个特点是其容易吸水，此时，催化剂中除含Ｌａ２Ｏ３外，还有Ｌａ（ＯＨ）３及Ｌａ２Ｏ３ＣＯ２存在。ＴＰＲ及ＴＰＳＲ结果表明了催化剂的起始氢气还原温度与纯甲烷的程序升温反应开始温度的致性，这说明催化剂的晶格氧参与了甲烷的活化过程。不同的氧化物由于其晶格氧     

Mo—La2O3模拟阴极的高温XPS／AES研究：Ⅱ.激活过程中La的变化？…

选用片状样品考察Ｍｏ－Ｌａ２Ｏ３阴极激活过程，侧重分析Ｌａ的存在状态和变化对热发射的影响。对高温ＸＰＳ实验结果的分析证实，激活过程Ｌａ的化学价态发生了改变，伴随大量晶格氧的分离，Ｌａ２Ｏ３变成了缺氧化合物ＬａＯｘ，即形成了超额的Ｌａ；修正的Ａｇｅｒ参数等变化趋势与上述相符。ＬａＯｘ具有较低的逸出功是由于氧缺位的存在，氧缺位对电子发射起到积极影响。激活过程促使Ｌａ，Ｏ离子的价电子态密度增加，配位不饱     

Ba—La2O3催化剂的表面碱性,活性氧种对甲烷氧化偶联的影响

利用ＣＯ２－ＴＰＤ技术考察了Ｂａ－Ｌａ２Ｏ３系催化剂的表面碱性，实验发现，催化剂表面仅有单一的强碱位或中碱位时，其催化性能均较差。只有表面的中碱位与强碱位以适当量共同存在的样品（６％Ｂａ－Ｌａ２Ｏ３），才能获得好的催化活性和Ｃ２选择性。此碱性特征可能有利于表面活性位的产生。同时利用ＸＲＤ和ＸＰＳ等技术分别对体相结构和表面氧物种进行了研究。结果表明，Ｂａ－Ｌａ２Ｏ３系催化剂表面存在Ｏ２＾２－离子，但     

含氧化镧的甲烷氧化偶联催化剂的一些特性

利用ＤＴＡ、ＴＰＤ－ＭＳ、ＸＲＤ、ＴＰＲ及ＴＰＳＲ－ＭＳ等手段对Ｌａ＿２Ｏ＿３和含Ｌａ＿２Ｏ＿３的甲烷氧化偶联催化剂进行了研究。实验发现含Ｌａ＿２Ｏ＿３的催化剂的一个特点是其容易吸水，此时，催化剂中除含Ｌａ＿２Ｏ＿３外，还有Ｌａ（ＯＨ）＿３及Ｌａ＿２Ｏ＿３ＣＯ＿２存在。ＴＰＲ及ＴＰＳＲ结果表明了催化剂的起始氢气还原温度与纯甲烷的程序升温反应开始温度的一致性，这说明催化剂的晶格氧参与了甲烷的活化过程。不同的氧化物由于其晶格氧的活性不同，因而其活化甲烷的温度不同。Ｌａ＿２Ｏ＿３中的晶格氧非常活泼，它在７３０℃时即可以与甲烷或与Ｈ＿２反应而本身被还原。甲烷和氧气共进料时的程序升温反应（ＴＰＳＲ－ＭＳ）表明甲烷氧化偶联反应中Ｃ＿２烃的选择性有一最佳温度范围。     

Mo-La2O3模拟阴极的高温XPS/AES研究Ⅱ.激活过程中La的变化及对发射的影响

选用片状样品考察ＭｏＬａ２Ｏ３ 阴极激活过程， 侧重分析Ｌａ 的存在状态和变化对热发射的影响。对高温ＸＰＳ实验结果的分析证实， 激活过程Ｌａ 的化学价态发生了改变， 伴随大量晶格氧的分离，Ｌａ２Ｏ３变成了缺氧化合物ＬａＯｘ（ｘ＜３／２） ， 即形成了超额的金属Ｌａ； 修正的Ａｕｇｅｒ 参数等变化趋势与上述相符。ＬａＯｘ 具有较低的逸出功是由于氧缺位的存在， 氧缺位对电子发射起到积极影响。激活过程促使Ｌａ，Ｏ离子的价电子态密度增加， 配位不饱和的Ｌａ 离子外层６ ｓ 高能价电子易形成电子发射， 即这一变化过程对热电子发射具有积极作用。     

氧化镧催化剂上甲烷氧化偶联—不同制备方法的比较

本文研究了５种不同制法的Ｌａ＿２Ｏ＿３对甲烷氧化偶联的催化性能，其Ｃ＿２选择性和Ｃ＿２收率的相对顺序为：Ｌａ＿２Ｏ＿３（１）＞Ｌａ＿２Ｏ＿３（２）＞Ｌａ＿２Ｏ＿３（４）＞Ｌａ＿２Ｏ＿３（５）＞Ｌａ＿２Ｏ＿３（３）。并运用ＸＲＵ、ＸＰＳ、ＣＯ＿２－ＴＰＤ、ＮＨ＿３－ＴＰＤ和ＩＰＡ转化反应等技术分别对催化剂的体相结构和表面性质，表面酸碱性进行了测定。结果表明，由于制备方法的不同，导致了Ｌａ＿２Ｏ＿３晶体表面结构的差异，这是影响催化性能的主要原因。同时还发现，催化剂的活性和Ｃ＿２选择性与表面酸碱性存在着相依性，Ｌａ＿２Ｏ＿３表面的总碱位数与总酸位数的比值，与其催化性能有较好的直接对应关系。     

甲烷氧化偶联催化剂ThO_2－La_2O_3／BaCO_3上活性氧物种研究

本文运用电子顺磁共振（ＥＰＲ）技术研究了Ｏ２在甲烷氧化偶联催化剂ＴｈＯ２，Ｌａ２Ｏ３／ＢａＣＯ３及ＴｈＯ２－Ｌａ２Ｏ３／ＢａＣＯ３上的吸附．通过对这三种催化剂上生成的Ｏ２超氧离子性质的比较，并与其催化活性相关联，发现ＴｈＯ２的掺杂使Ｏ２离子的ｇｚｚ值向低场方向移动，这可能有利于Ｏ２离子在升温过程中向Ｏ２离子的转化，从而使ＴｈＯ２－Ｌａ２Ｏ３／ＢａＣＯ３的催化活性和选择性有明显的提高．本文还考察了ＣＯ２对Ｏ２离子的影响．     

Periodic density functional theory study of methane activation over La(2)O(3): activity of O(2-), O(-), O(2)(2-), oxygen point defect,and Sr(2+)-doped surface sites

Results of gradient-corrected periodic density functional theory calculations are reported for hydrogen abstraction from methane at O(s)(2-), O(s)(-), O(2)(s)(2-) point defect, and Sr(2+)-doped surface sites on La(2)O(3)(001). The results show that the anionic O(s)(-) species is the most active surface oxygen site. The overall reaction energy to activate methane at an O(s)(-) site to form a surface hydroxyl group and gas-phase (*)CH(3) radical is 8.2 kcal/mol, with an activation barrier of 10.1 kcal/mol. The binding energy of hydrogen at an site O(s)(-) is -102 kcal/mol. An oxygen site with similar activity can be generated by doping strontium into the oxide by a direct Sr(2+)/La(3+) exchange at the surface. The O(-)-like nature of the surface site is reflected in a calculated hydrogen binding energy of -109.7 kcal/mol. Calculations indicate that surface peroxide (O(2(s))(2-)) sites can be generated by adsorption of O(2) at surface oxygen vacancies, as well as by dissociative adsorption of O(2) across the closed-shell oxide surface of La(2)O(3)(001). The overall reaction energy and apparent activation barrier for the latter pathway are calculated to be only 12.1 and 33.0 kcal/mol, respectively. Irrespective of the route to peroxide formation, the O(2)(s)(2-) intermediate is characterized by a bent orientation with respect to the surface and an O-O bond length of 1.47 A; both attributes are consistent with structural features characteristic of classical peroxides. We found surface peroxide sites to be slightly less favorable for H-abstraction from methane than the O(s)(-) species, with DeltaE(rxn)(CH(4)) = 39.3 kcal/mol, E(act) = 47.3 kcal/mol, and DeltaE(ads)(H) = -71.5 kcal/mol. A possible mechanism for oxidative coupling of methane over La(2)O(3)(001) involving surface peroxides as the active oxygen source is suggested.     

A theoretic insight into the catalytic activity promotion of CeO2 surfaces by Mn doping

In this paper, we investigated the primary reduction and oxygen replenishing processes over Mn substitutionally doped CeO(2)(111) surfaces by density functional theory with the on-site Coulomb correction (DFT + U). The results indicated that Mn doping could make the surface much more reducible and the adsorbed O(2) could be effectively activated to form superoxo (O(2)(-)) and/or peroxo species (O(2)(2-)). The Mn doping induced the Mn 3d-O 2p gap state instead of Ce 4f acting as an electrons acceptor and donor during the first oxygen vacancy formation and O(2) replenishing, which helped to lower the formation energy of the first and second oxygen vacancies to -0.46 eV and 1.40 eV, respectively. In contrast, the formation energy of a single oxygen vacancy in the pure ceria surface was 2.08 eV and only peroxo species were identified as the O(2) molecule adsorbed. Our work provides a theoretical and electronic insight into the catalytic redox processes of Mn doped ceria surfaces, which may help to understand the enhanced catalytic performances of MnO(x)-CeO(2) oxides, as reported in previous experimental works.     

Probing water interactions and vacancy production on gadolinia-doped ceria surfaces using electron stimulated desorption

Polycrystalline gadolinia-doped ceria (GDC) surfaces were studied using low-energy (5-400 eV) electron stimulated desorption (ESD). H(+), O(+), and H(3)O(+) were the primary cationic desorption products with H(+) as the dominant channel. H(+), H(3)O(+), and O(+) have a 22 eV threshold followed by a yield change around 40 eV. H(+) also has an additional yield change approximately 75 eV and O(+) has an additional change approximately 150 eV. The O(+) ESD yield change approximately 150 eV may indicate bond breaking of Gd-O and the involvement of oxygen vacancies. The H(+) and H(3)O(+) threshold data collectively indicate the presence of hydroxyl groups and chemisorbed water molecules on the GDC surfaces. ESD temperature dependence measurements show that the interaction of water with GDC surface defect sites, mainly oxygen vacancies, influences the desorption of H(+), O(+), and H(3)O(+). The temperature dependence of the O(+) ESD at 400 eV incident electron energy yields a 0.21 eV activation energy. This is close to the energy needed for oxygen vacancy production next to a pair of Ce(3+) on a CeO(2) surface. These results may indicate a correlation between the O(+) ESD yield and oxygen vacancy density on GDC surfaces and a potential correlation of O(+) ESD and GDC ionic conductivity.     

Vanadium oxides on aluminum oxide supports. 1. Surface termination and reducibility of vanadia films on alpha-Al2O3(0001)

Using density functional theory and statistical thermodynamics, we obtained the phase diagram of thin VnOm films of varying thickness (approximately 2-6 A, 1-6 vanadium layers) supported on alpha-Al2O3(0001). Depending on the temperature, oxygen pressure, and vanadium concentration, films with different thickness and termination may form. In ultrahigh vacuum (UHV), at room temperature and for low vanadium concentrations, an ultrathin (1 x 1) O=V-terminated film is most stable. As more vanadium is supplied, the thickest possible films form. Their structures and terminations correspond to previous findings for the (0001) surface of bulk V2O3 [Kresse et al., Surf. Sci. 2004, 555, 118]. The presence of surface vanadyl (O=V) groups is a prevalent feature. They are stable up to at least 800 K in UHV. Vanadyl oxygen atoms induce a V(2p) core-level shift of about 2 eV on the surface V atoms. The reducibility of the supported films is characterized by the energy of oxygen defect formation. For the stable structures, the results vary between 4.11 and 3.59 eV per 1/2O2. In contrast, oxygen removal from the V2O5(001) surface is much easier (1.93 eV). This provides a possible explanation for the lower catalytic activity of vanadium oxides supported on alumina compared to that of crystalline vanadia particles.     

高色纯度高热稳定性红色荧光粉Sr3La2Ge3O12:Sm^3+的合成及其性能

通过高温固相法合成了一系列Sr3La2-xGe3O12:xSm^3+(0≤x≤0.04)红色荧光粉,并对样品的形貌、元素组成、晶体结构、发光性能及热稳定性进行了探究。结果表明:样品Sr3La2Ge3O12:xSm^3+为较宽尺寸分布的颗粒,且结构中仅含有Sr、La、Ge、O、Sm等元素。样品Sr3La1.97Ge3O12:0.03Sm^3+的Rietveld结构精修图与实测XRD图完全吻合,具有六方晶系结构。漫反射测试结果显示基质Sr3La2Ge3O12的带宽为5.54 eV,属于宽带隙材料。在404 nm激发下,样品Sr3La2-xGe3O12:xSm^3+(0≤x≤0.04)的最大发射峰位于601nm处,属于Sm^3+的6H5/2→4L13/2能级跃迁。此外,样品Sr3La1.97Ge3O12:0.03Sm^3+的发光性能最佳,其CIE色坐标为(0.5321,0.4601),色纯度高达94.2%,在298-473 K范围内具有较好的热稳定性,测试温度达到423 K时发射强度仍为室温时的81.6%。     

氧化铜表面臭氧分解路径及表面氧物种生成机理研究

基于密度泛函理论（DFT）计算研究了O3在完整和具有氧空位的CuO(111)表面吸附的吸附位、吸附结构、吸附能和电子转移情况,比较了O3在完整表面和具有氧空位的表面分解的路径和能垒,分析了氧空位和表面吸附氧的生成机理。结果表明,在完整CuO表面,O3分子通过化学吸附或物理吸附表面结合,吸附能最高为-1.22eV（构型bri(2)）。O3在具有氧空位的CuO表面均为化学吸附,吸附能最高为-2.95eV（构型ovbri(3)）,显著高于完整表面的吸附能。O3吸附后,Cu吸附位的电荷密度减小,O3中的O原子附近的电荷密度显著增强,电荷从CuO表面转移到O3,并形成Cu-O离子键。O3分解后形成了超氧物种,提高了表面的氧化活性。在完整表面,以构型bri(2)为起始构型的路径反应能垒最低,为0.52eV;O2*在完整表面的脱附所需要的最低能量为0.42eV,形成氧空位的O2*脱附能为2.06eV。在具有氧空位的表面,O3分解的反应能垒为0.30eV（构型ovbri(1)）和0.12eV（构型ovbri(3)）,均低于完整表面的反应能垒;分解形成的O2*的最低脱附能也低于完整表面,为0.27eV。可见,氧空位的形成提高了吸附能,降低了反应能垒,使O3分子更容易吸附在CuO表面,并加快了O3的催化分解。     

氧存在下钙钛矿LaCoO3硫化过程的XPS研究

 采用XPS,XRD和TEM对含氧气氛下钙钛矿LaCoO3硫化活化过程中不同阶段的催化剂进行了表征分析．在硫化初期,经SO2预中毒后,吸附氧种不存在,Co2p3／2结合能发生明显的位移,La3d的XPS双峰变得不明显,同时出现不稳态的S4＋物种,表明催化剂LaCoO3被SO2的强吸附所覆盖;催化剂LaCoO3仍为钙钛结构并没有新的物相产生,SO2中毒仅在催化剂表面进行．在进一步的硫化活化过程中,出现吸附氧物种,Co出现三种价态,分别对应于LaCoO3,Co3O4和CoSO4,La3d的XPS双峰变得特别明显,同时催化剂表面出现S2－物种和S6＋物种．可以认为,在含氧气氛下硫化LaCoO3的过程中,SO2预中毒为进一步硫化提供硫物种,吸附氧物种保证硫化过程中钙钛矿结构不会被完全破坏．     

Adsorption of atomic and molecular oxygen on the LaMnO3(001) surface: ab initio supercell calculations and thermodynamics

We present and discuss the results of ab initio DFT plane-wave supercell calculations of the atomic and molecular oxygen adsorption and diffusion on the LaMnO(3) (001) surface which serves as a model material for a cathode of solid oxide fuel cells. The dissociative adsorption of O(2) molecules from the gas phase is energetically favorable on surface Mn ions even on a defect-free surface. The surface migration energy for adsorbed O ions is found to be quite high, 2.0 eV. We predict that the adsorbed O atoms could penetrate the electrode first plane when much more mobile surface oxygen vacancies (migration energy of 0.69 eV) approach the O ions strongly bound to the surface Mn ions. The formation of the O vacancy near the O atom adsorbed atop surface Mn ion leads to an increase of the O-Mn binding energy by 0.74 eV whereas the drop of this adsorbed O atom into a vacancy possesses no energy barrier. Ab initio thermodynamics predicts that at typical SOFC operation temperatures (approximately 1200 K) the MnO(2) (001) surface with adsorbed O atoms is the most stable in a very wide range of oxygen gas pressures (above 10(-2) atm).     

Synergistic effects in La/N codoped TiO2 anatase (101) surface correlated with enhanced visible-light photocatalytic activity

The interaction between implanted La, substitutional N, and an oxygen vacancy at TiO(2) anatase (101) surface has been investigated by means of first-principles density function theory calculations to investigate the origin of enhanced visible-light photocatalytic activity of La/N-codoped anatase observed in experiments. Our calculations suggest that both the adsorptive and substitutional La-doped TiO(2) anatase (101) surfaces are probably defective configurations in experiments. The h-Cave-adsorbed La doping decreases the formation energy for the substitutional N implantation and vice versa, while the charge compensation effects do not take effect between the adsorptive La and substitutional N dopants, resulting in some partially occupied states in the band gap acting as traps of the photoexcited electrons. The Ti(5c)-substituted La doping decreases the energy required for the substitutional N implantation, and the substitutional La and N codoping promotes the formation of an oxygen vacancy, which migrates from the O(sb-3c) site at the inner layer toward the surface O(b) site. For the substitutional La/N-codoped (Ti(5c)_O(3c-down)) surface, the charge compensation between the substitutional La and substitutional N leads to the formation of two isolated occupied N(s)-O π* impurity levels in the gap, while the excitation energy from the higher impurity level to the CBM decreases by about 0.89 eV. After further considering an oxygen vacancy on the Ti(5c)_O(3c-down) surface, the two electrons on the double donor levels (O(b) vacancy) passivate the same amount of holes on the acceptor levels (substitutional La and N), forming the acceptor-donor-acceptor compensation pair, which provides a reasonable mechanism for the enhanced visible-light photocatalytic activity of La/N codoped TiO(2) anatase. This knowledge may aid the further design and construction of new effective visible-light photocatalysts.