Activation of noble metals on metal-carbide surfaces: novel catalysts for CO oxidation, desulfurization and hydrogenation reactions.
Activation of noble metals on metal-carbide surfaces: novel catalysts for CO oxidation, desulfurization and hydrogenation reactions.
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DOI：
10.1039/c1cp22738f
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发表时间：
2012-01
期刊：
影响因子：
--
通讯作者：
J. Rodríguez;F. Illas
中科院分区：
文献类型：
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作者：
J. Rodríguez;F. Illas
这篇前瞻性文章的重点是高活性催化剂的物理和化学性质的CO氧化，脱硫和加氢反应所产生的沉积贵金属上的金属碳化物表面。为了使这些新型催化剂的结构-反应性关系合理化，需要定义明确的系统。利用高分辨光电子能谱、扫描隧道显微镜（STM）和第一性原理周期密度泛函（DF）计算研究了第9、10和11族金属与MC（001）（M = Ti，Zr，V，Mo）表面的相互作用. DF计算给出的吸附能范围为2 eV（Cu，Ag，Au）至6 eV（Co，Rh，Ir）。STM图像显示，Au、Cu、Ni和Pt在很低覆盖度时在碳化物基体上形成二维岛状结构，在中等覆盖度和较大覆盖度时形成三维岛状结构。在许多系统中，DF计算的结果指向的admetal-C键的优先形成与显着的电子扰动的admetal。TiC（001）和ZrC（001）将部分电子密度转移到吸附金属上，促进吸附原子与电子受体分子（CO、O（2）、C（2）H（4）、SO（2）、噻吩等）的键合。例如，Cu/TiC（001）和Au/TiC（001）体系能够在低至150 K的温度下裂解SO（2）的两个S-O键，显示出比TiC（001）或块体铜和金的扩展表面大得多的反应性。在低于200 K的温度下，Au/TiC能够解离O（2），并进行2CO + O（2）→ 2CO（2）反应。此外，尽管TiC（001）或Au（111）的加氢脱硫性能非常差，但Au/TiC（001）表面显示出比常规Ni/MoS（x）催化剂更高的噻吩加氢脱硫活性。通常，Au/TiC系统比通过在氧化物表面上沉积Au纳米颗粒产生的系统更具有化学活性。因此，金属碳化物是用于增强贵金属的化学反应性的优良载体。
This perspective article focuses on the physical and chemical properties of highly active catalysts for CO oxidation, desulfurization and hydrogenation reactions generated by depositing noble metals on metal-carbide surfaces. To rationalize structure-reactivity relationships for these novel catalysts, well-defined systems are required. High-resolution photoemission, scanning tunneling microscopy (STM) and first-principles periodic density-functional (DF) calculations have been used to study the interaction of metals of Groups 9, 10 and 11 with MC(001) (M = Ti, Zr, V, Mo) surfaces. DF calculations give adsorption energies that range from 2 eV (Cu, Ag, Au) to 6 eV (Co, Rh, Ir). STM images show that Au, Cu, Ni and Pt grow on the carbide substrates forming two-dimensional islands at very low coverage, and three-dimensional islands at medium and large coverages. In many systems, the results of DF calculations point to the preferential formation of admetal-C bonds with significant electronic perturbations in the admetal. TiC(001) and ZrC(001) transfer some electron density to the admetals facilitating bonding of the adatom with electron-acceptor molecules (CO, O(2), C(2)H(4), SO(2), thiophene, etc.). For example, the Cu/TiC(001) and Au/TiC(001) systems are able to cleave both S-O bonds of SO(2) at a temperature as low as 150 K, displaying a reactivity much larger than that of TiC(001) or extended surfaces of bulk copper and gold. At temperatures below 200 K, Au/TiC is able to dissociate O(2) and perform the 2CO + O(2)→ 2CO(2) reaction. Furthermore, in spite of the very poor hydrodesulfurization performance of TiC(001) or Au(111), a Au/TiC(001) surface displays an activity for the hydrodesulfurization of thiophene higher than that of conventional Ni/MoS(x) catalysts. In general, the Au/TiC system is more chemically active than systems generated by depositing Au nanoparticles on oxide surfaces. Thus, metal carbides are excellent supports for enhancing the chemical reactivity of noble metals.