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CO oxidation on Pd(100) vs. PdO(sqrt5xsqrt5)R27^o: First-Principles Kinetic Phase Diagrams and Bistability Conditions  [PDF]
Max J. Hoffmann,Karsten Reuter
Physics , 2013, DOI: 10.1007/s11244-013-0172-5
Abstract: We present first-principles kinetic Monte Carlo (1p-kMC) simulations addressing the CO oxidation reaction at Pd(100) for gas-phase conditions ranging from ultra-high vacuum (UHV) to ambient pressures and elevated temperatures. For the latter technologically relevant regime there is a long-standing debate regarding the nature of the active surface. The pristine metallic surface, an ultra-thin (sqrt5xsqrt5)R27^o PdO(101) surface oxide, and thicker oxide layers have each been suggested as the active state. We investigate these hypotheses with 1p-kMC simulations focusing on either the Pd(100) surface or the PdO(101) surface oxide and intriguingly obtain a range of (T, p)-conditions where both terminations appear metastable. The predicted bistability regime nicely ties in with oscillatory behavior reported experimentally by Hendriksen and coworkers [Catal. Today 105, 234 (2005)]. Within this regime we find that both surface terminations exhibit very similar intrinsic reactivity, which puts doubts on attempts to assign the catalytic function to just one active state.
CO oxidation on Pd(100) at technologically relevant pressure conditions: A first-principles kinetic Monte Carlo study  [PDF]
Jutta Rogal,Karsten Reuter,Matthias Scheffler
Physics , 2008, DOI: 10.1103/PhysRevB.77.155410
Abstract: The possible importance of oxide formation for the catalytic activity of transition metals in heterogenous oxidation catalysis has evoked a lively discussion over the recent years. On the more noble transition metals (like Pd, Pt or Ag) the low stability of the common bulk oxides suggests primarily sub-nanometer thin oxide films, so-called surface oxides, as potential candidates that may be stabilized under gas phase conditions representative of technological oxidation catalysis. We address this issue for the Pd(100) model catalyst surface with first-principles kinetic Monte Carlo (kMC) simulations that assess the stability of the well-characterized (sqrt{5} x sqrt{5})R27 surface oxide during steady-state CO oxidation. Our results show that at ambient pressure conditions the surface oxide is stabilized at the surface up to CO:O2 partial pressure ratios just around the catalytically most relevant stoichiometric feeds (p(CO):p(O2) = 2:1). The precise value depends sensitively on temperature, so that both local pressure and temperature fluctuations may induce a continuous formation and decomposition of oxidic phases during steady-state operation under ambient stoichiometric conditions.
Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study  [PDF]
K. Kusakabe,K. Harada,Y. Ikuno,H. Nagara
Physics , 2009, DOI: 10.1088/0953-8984/21/48/485003
Abstract: Stable oxygen sites on a PdO film over a Pd(100) thin structures with a (sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the first-principles electronic structure calculations with the generalized gradient approximation. The adsorbed monatomic oxygen goes to a site bridging two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom between the two stable sites is evaluated using the nudged elastic band method, where an energy barrier for a translational motion of the adsorbed oxygen may become sim 0.45 eV, which is low enough to allow fluxionality of the surface oxygen at high temperatures. The oxygen fluxionality is allowed by existence of 2-fold-coordinated Pd atoms on the PdO film, whose local structure has similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling. Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by the PdO film, we conclude that there may happen continual redox reactions mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the influx of NO_x and CO continues, and when the reaction cycle is kept on a well-designed oxygen surface.
pd/v2o5薄膜的氢气敏感性质研究  [PDF]
余海湖,史勇2,吴银伟2,黄金山2
武汉理工大学学报 , 2010,
Abstract: ?采用磁控溅射法制备了不同厚度的pd/v?2o?5双层复合薄膜,采用紫外?可见光分光光度计研究了薄膜的氢气敏感性质,原位测量了薄膜的激光拉曼光谱并分析了薄膜的氢气敏感机理。结果表明,复合薄膜v?2o?5(280nm)/pd(30nm)对氢气的敏感性质较好,对0.01%h?2?n?2有响应,在4%h?2?n?2标气中,在560nm处透过率的相对变化值达到25%。拉曼光谱分析结果表明,pd/v?2o?5薄膜在与氢气作用过程中,pd膜主要起催化作用,氢原子扩散到v?2o?5层,v??5+?转变为v??4+?,导致pd/v?2o?5薄膜的透过率发生变化。
Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures  [PDF]
E. Lundgren,A. Stierle,M. Todorova,J. Gustafson,A. Mikkelsen,J. Rogal,K. Reuter,J. N. Andersen,H. Dosch,M. Scheffler
Physics , 2003, DOI: 10.1103/PhysRevLett.92.046101
Abstract: The oxidation of the Pd(100) surface at oxygen pressures in the 10^-6 to 10^3 mbar range and temperatures up to 1000 K has been studied in-situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions we either observe a thin sqrt(5) x sqrt(5) R27 surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.
Multi-Lattice Kinetic Monte Carlo Simulations from First-Principles: Reduction of the Pd(100) Surface Oxide by CO  [PDF]
Max J. Hoffmann,Matthias Scheffler,Karsten Reuter
Physics , 2015, DOI: 10.1021/cs501352t
Abstract: We present a multi-lattice kinetic Monte Carlo (kMC) approach that efficiently describes the atomistic dynamics of morphological transitions between commensurate structures at crystal surfaces. As an example we study the reduction of a $(\sqrt{5}\times \sqrt{5})R27^{\circ}$ PdO(101) overlayer on Pd(100) in a CO atmosphere. Extensive density-functional theory calculations are used to establish an atomistic pathway for the oxide reduction process. First-principles multi-lattice kMC simulations on the basis of this pathway fully reproduce the experimental temperature dependence of the reduction rate [Fernandes et al., Surf. Sci. 2014, 621, 31-39] and highlight the crucial role of elementary processes special to the boundary between oxide and metal domains.
配合物[Pd(L)(trp)]Cl·5H_2O(L=phen,5-NO_2phen)的合成、抗癌活性及其DNA作用研究  [PDF]
高恩君,刘祁涛
化学学报 , 2002,
Abstract: 合成了两个混合配体配合物[Pd(phen)(trp)]Cl·5H_2O(1)和[Pd(5-NO_2phen)(trp)]Cl·5H_2O(2)(其中phen=1,10-phenanthroline,5-NO_2phen=5-nitro-1,10-phenanthroline,trp=L-tryptophan)。配合物对肺腺癌细胞AGZY-83a均具有一定的杀伤活性,IC_(50)值分别为158.5μg/mL和大于293.0μg/mL。荧光法测定配合物与鱼精DNA的结合常数(K)分别为6.36*10~6和3.64*10~6。荧光光谱、紫外可见光谱和粘度法证实配合物主要以插入方式与DNA结合。
多孔Pd/α-Al2O3活性膜上1,5-环辛二烯选择加氢  [PDF]
周永华,叶红齐,Reinhard SCHOMACKER
催化学报 , 2007,
Abstract: ?利用微乳液及浸渍技术制备了多孔Pd/α-Al2O3催化活性膜.利用透射电镜、扫描电镜和X射线衍射对微乳液中及α-Al2O3陶瓷膜孔结构中纳米Pd颗粒的形貌和分布进行了表征.分析结果表明,通过浸渍技术,微乳液中的纳米Pd颗粒以几百纳米大小的晶体形态均匀负载于陶瓷膜孔中.在“催化接触器”型膜反应器中,以1,5-环辛二烯催化加氢为模型反应,考察了多孔Pd/α-Al2O3膜的活性与选择性,并与Pd-聚丙烯酸(PAA)有机催化膜反应器、悬浮床反应器和固定床反应器中的催化性能进行了比较.结果表明,Pd/α-Al2O3膜反应器的催化活性与目的产物1-环辛烯的选择性远高于Pd-PAA有机膜反应器和固定床反应器.Pd/α-Al2O3膜反应器在强化传质和消除孔内扩散方面效果显著,这与Pd在陶瓷膜孔中的分布及反应物在膜反应器中的高速流动有关.
Pd/Al2O3膜的制备及其对1,5-环辛二烯加氢的催化性能  [PDF]
周永华,叶红齐,Reinhard SCHOMCKER
催化学报 , 2007,
Abstract: ?利用微乳液浸渍技术制备了负载型Pd/Al2O3膜,并用扫描电镜和原子吸收光谱对微乳液中的纳米Pd颗粒及其在Al2O3陶瓷膜载体上的形貌、分布和负载量进行了表征.在"催化接触器"型膜反应器中,以1,5-环辛二烯(COD)加氢作为模型反应考察了Pd/Al2O3膜的催化性能.结果表明,采用微乳液技术制备Pd/Al2O3膜时,Pd负载量、浸渍操作方式、焙烧温度和载体孔径对Pd/Al2O3膜的催化性能有一定影响.要获得对COD加氢反应的高催化活性和较高的中间产物环辛烯选择性,优化的Pd/Al2O3膜制备条件为:缓慢析出Pd纳米颗粒,同时采用循环浸渍方式,焙烧温度300℃,膜载体孔径1.9μm.
Effect of SO2 on the performance of Ag-Pd/Al2O3 for the selective catalytic reduction of NOx with C2H5OH
XIE Shu-xi,YU Yun-bo,WANG Jin,HE Hong,
XIE Shu-xi
,YU Yun-bo,WANG Jin,HE Hong

环境科学学报(英文版) , 2006,
Abstract: The influence of SO2 on the performance of Ag-Pd/Al2O3 for the selective catalytic reduction (SCR) of NOx with C2H5OH was investigated experimentally. The activity test results suggest that Ag-Pd/Al2O3 shows a small activity loss in the presence of SO2 when using C2H5OH as a reductant. In situ DRIFTS spectra show that the activity loss originates from the formation of surface sulphate species on the Ag-Pd/Al2O3. The surface sulphate species formation inhibits the formation of nitrate, whereas hardly changes the partial oxidation of C2H5OH. Compared with the NOx reduction by C3H6, an obvious suppression of the surface sulphate species formation was observed by DRIFTS experiment when using C2H5OH as a reductant. This phenomenon reveals the better catalytic performance and strong SO2 tolerance of Ag-Pd/Al2O3-C2H5OH system.
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