Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Langmuir. 2010 Nov 2;26(21):16362-7. doi: 10.1021/la101690y.
We present an in situ study of the interaction of a bimetallic Rh(0.5)Pd(0.5) bulk crystal with O(2), CO, and NO using ambient pressure X-ray photoelectron spectroscopy (APXPS) and compare it to results for 15 nm nanoparticles with the same overall composition. The bulk crystal surface has less Rh present under both oxidizing and reducing conditions than the surface of nanoparticles under identical conditions. Segregation and oxidation/reduction proceeds faster and at lower temperature for nanoparticles than for the bulk crystal. The near surface of the Rh(0.5)Pd(0.5) bulk crystal after high temperature vacuum annealing is ca. 9% Rh measured by APXPS. Heating in 0.1 Torr O(2) to 350 °C increases the Rh surface composition to ca. 40%. The surface can then be reduced by heating in H(2) at 150 °C, leading to a chemically reduced surface with 30% Rh. Titration of CO by gas-phase O(2) from this Rh-rich surface proceeds at a much lower pressure than that on the Rh-deficient starting surface.
我们使用常压 X 射线光电子能谱 (APXPS) 对双金属 Rh(0.5)Pd(0.5)块状晶体与 O(2)、CO 和 NO 的相互作用进行了原位研究，并将其与具有相同整体组成的 15nm 纳米粒子的结果进行了比较。在氧化和还原条件下，块状晶体表面的 Rh 含量均低于相同条件下纳米粒子的表面含量。对于纳米粒子，相分离和氧化/还原的速度比块状晶体快，温度也更低。通过 APXPS 测量，高温真空退火后 Rh(0.5)Pd(0.5)块状晶体的近表面约有 9%的 Rh。在 0.1 托 O(2)中加热至 350°C 可将 Rh 表面组成增加至约 40%。然后可以通过在 150°C 下加热 H(2)将其还原，从而得到具有 30%Rh 的化学还原表面。富含 Rh 的表面通过气相 O(2)滴定 CO 的压力比 Rh 贫化起始表面低得多。
