Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany.
Phys Chem Chem Phys. 2011 Oct 6;13(37):16800-10. doi: 10.1039/c1cp21677e. Epub 2011 Aug 22.
The heat of adsorption and sticking probability of CO on well-defined Pd nanoparticles were measured as a function of particle size using single crystal adsorption microcalorimetry. Pd particles of different average sizes ranging from 120 to 4900 atoms per particle (or from 1.8 to 8 nm) and Pd(111) were used that were supported on a model in situ grown Fe(3)O(4)/Pt(111) oxide film. To precisely quantify the adsorption energies, the reflectivities of the investigated model surfaces were measured as a function of the thickness of the Fe(3)O(4) oxide layer and the amount of deposited Pd. A substantial decrease of the binding energy of CO was found with decreasing particle size. Initial heat of adsorption obtained on the virtually adsorbate-free surface was observed to be reduced by about 20-40 kJ mol(-1) on the smallest 1.8 nm sized Pd particles as compared to the larger Pd clusters and the extended Pd(111) single crystal surface. This effect is discussed in terms of the size-dependent properties of the Pd nanoparticles. The CO adsorption kinetics indicates a strong enhancement of the adsorbate flux onto the metal particles due to a capture zone effect, which involves trapping of adsorbates on the support and diffusion to metal clusters. The CO adsorption rate was found to be enhanced by a factor of ∼8 for the smallest 1.8 nm sized particles and by ∼1.4 for the particles of 7-8 nm size.
采用单晶吸附量热法，研究了 CO 在具有明确结构的 Pd 纳米粒子上的吸附热和吸附几率如何随粒子尺寸而变化。我们使用了不同平均粒径（120 至 4900 个原子/粒子，或 1.8 至 8nm）的 Pd 粒子和负载在原位生长的 Fe3O4/Pt(111) 氧化物薄膜上的 Pd(111)。为了准确地定量吸附能，我们测量了所研究模型表面的反射率如何随 Fe3O4 氧化物层的厚度和沉积的 Pd 量而变化。发现 CO 的结合能随粒子尺寸的减小而显著降低。与较大的 Pd 团簇和扩展的 Pd(111)单晶表面相比，在最小的 1.8nm 尺寸的 Pd 粒子上，实际上不存在吸附质的表面上初始吸附热降低了约 20-40kJ/mol。这种效应是根据 Pd 纳米粒子的尺寸相关特性来讨论的。CO 的吸附动力学表明，由于捕获区效应，吸附质向金属颗粒的通量大大增强，其中涉及到吸附质在载体上的捕获和向金属团簇的扩散。我们发现，对于最小的 1.8nm 尺寸的粒子，CO 的吸附速率提高了约 8 倍，对于 7-8nm 尺寸的粒子，提高了约 1.4 倍。
