Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Phys Chem Chem Phys. 2012 Aug 7;14(29):10207-14. doi: 10.1039/c2cp41601h. Epub 2012 Jun 25.
We have investigated surface CO oxidation on "inverse catalysts" composed of SnO(x) nanostructures supported on Pt(111) using X-ray photoelectron spectroscopy (XPS), low-energy ion scattering spectroscopy (LEISS) and temperature-programmed desorption (TPD). Nanostructures of SnO(x) were prepared by depositing Sn on Pt(111) pre-covered by NO(2) layers at low temperatures. XPS data show that the SnO(x) nanoparticles are highly reduced with Sn(II)O being the dominant oxide species, but the relative concentration of Sn(II) in the SnO(x) nanoparticles decreases with increasing Sn coverage. We find that the most active SnO(x)/Pt(111) surface for CO oxidation has smallest SnO(x) coverage. Increasing the surface coverage of SnO(x) reduces CO oxidation activity and eventually suppresses it altogether. The study suggests that reduced Sn(II)O, rather than Sn(IV)O(2), is responsible for surface CO oxidation. The occurrence of a non-CO oxidation reaction path involving reduced Sn(II)O species at higher SnO(x) coverages accounts for the decreased CO oxidation activity. From these results, we conclude that the efficacy of CO oxidation is strongly dependent on the availability of reduced tin oxide sites at the Pt-SnO(x) interface, as well as unique chemical properties of the SnO(x) nanoparticles.
我们使用 X 射线光电子能谱（XPS）、低能离子散射谱（LEISS）和程序升温脱附（TPD）研究了负载在 Pt(111) 上的 SnO(x)纳米结构的“反催化剂”上的表面 CO 氧化。SnO(x)纳米结构是通过在预先覆盖有 NO(2)层的 Pt(111)上低温沉积 Sn 制备的。XPS 数据表明，SnO(x)纳米颗粒高度还原，Sn(II)O 是主要的氧化物物种，但 Sn(II)在 SnO(x)纳米颗粒中的相对浓度随 Sn 覆盖度的增加而降低。我们发现，对 CO 氧化最活跃的 SnO(x)/Pt(111)表面具有最小的 SnO(x)覆盖度。增加 SnO(x)的表面覆盖率会降低 CO 氧化活性，最终完全抑制 CO 氧化。研究表明，还原的 Sn(II)O 而不是 Sn(IV)O(2)是表面 CO 氧化的原因。在较高的 SnO(x)覆盖率下，涉及还原的 Sn(II)O 物种的非 CO 氧化反应途径的发生，导致 CO 氧化活性降低。根据这些结果，我们得出结论，CO 氧化的效果强烈依赖于 Pt-SnO(x)界面上还原的氧化锡位点的可用性，以及 SnO(x)纳米颗粒的独特化学性质。
