Müller Patrick, Hejral Uta, Rütt Uta, Stierle Andreas
Deutsches Elektronen Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany.
Phys Chem Chem Phys. 2014 Jul 21;16(27):13866-74. doi: 10.1039/c4cp01271b. Epub 2014 Jun 4.
Alloy nanoparticles on oxide supports are widely used as heterogeneous catalysts in reactions involving oxygen. Here we discuss the oxidation behavior of Pd-Rh alloy nanoparticles on MgAl2O4(001) supports with a particle diameter from 6-11 nm. As an In situ tool, we employed high energy grazing incidence X-ray diffraction at a photon energy of 85 keV. We find that physical vapor deposited Pd-Rh nanoparticles grow epitaxially on MgAl2O4(001) with a truncated octahedral shape over the whole concentration range. During our systematic oxidation experiments performed at 670 K in the pressure range from 10(-3) to 0.1 mbar, we observe for Rh containing nanoparticles the formation of two different Rh oxide phases, namely RhO2 and a spinel-like Rh3O4 phase. PdO formation is only observed for pure Pd nanoparticles. This oxidation induced segregation behavior is also reflected in the oxidation induced enlargement of the average nanoparticle lattice parameter towards to value for pure Pd. Our results have ramifications for the phase separation behavior of alloy nanocatalysts under varying reducing and oxidizing environments.
氧化物载体上的合金纳米颗粒被广泛用作涉及氧气的反应中的多相催化剂。在此，我们讨论了粒径为6 - 11 nm的MgAl2O4(001)载体上Pd - Rh合金纳米颗粒的氧化行为。作为一种原位工具，我们采用了光子能量为85 keV的高能掠入射X射线衍射。我们发现，物理气相沉积的Pd - Rh纳米颗粒在整个浓度范围内以截顶八面体形状外延生长在MgAl2O4(001)上。在670 K、压力范围为10(-3)至0.1 mbar的系统氧化实验中，我们观察到含Rh的纳米颗粒形成了两种不同的Rh氧化物相，即RhO2和类尖晶石Rh3O4相。仅在纯Pd纳米颗粒中观察到PdO的形成。这种氧化诱导的偏析行为也反映在氧化诱导的平均纳米颗粒晶格参数向纯Pd值增大的过程中。我们的结果对合金纳米催化剂在不同还原和氧化环境下的相分离行为具有重要意义。
