Datta Abheek, Deolka Shubham, Kumar Pawan, Ziadi Zakaria, Sasaki Toshio, Steinhauer Stephan, Singh Vidyadhar, Jian Nan, Danielson Eric, Porkovich Alexander James
Okinawa Institute of Science and Technology (OIST) Graduate University, 1919-1 Tancha, Onna-Son, Okinawa 904-0495, Japan.
Phys Chem Chem Phys. 2021 Jan 28;23(3):2063-2071. doi: 10.1039/d0cp05697a.
Interactions between oxide supports and noble metal nanoparticles (NPs) is an area of intense research interest across all fields of catalysis. Oxygen spillover, metal support interactions (MSIs) and charge transfer are among many mechanisms observed and proposed as to how NP-support interfaces assist and enhance catalysis. This work studies the migration of oxygen across the Pd NP-CuO nanowire (NW) interface and beyond. X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM) found an interaction between the Pd NP and CuO NW support, via the formation of PdO at the Pd-CuO interface. It was found, through in situ irradiation at high vacuum transmission electron microscopy (TEM), that oxygen enters the Pd NP lattice from the Pd-CuO interface via amorphization of the NP. Varying the amount of irradiation highlighted the different rates of amorphization of NPs, with full amorphization of a NP leading to the formation of an epitaxially driven PdO across the NPs. Interestingly, in situ heating in XPS observed a reduction to metallic Pd, found to be similarly amorphous during TEM investigation. On comparison with Pd supported on a non-reducible substrate - in which oxidation was found to proceed from the outer surface in, rather than the support interface (resulting in a PdO shell) - it is theorized that the oxidation and reduction of Pd on CuO forms a PdO NP surface full of Pd-PdO sites allowing for synergistic effects, of great use in the oxidation and hydrogenation of organic species.
氧化物载体与贵金属纳米颗粒（NPs）之间的相互作用是催化各个领域中研究兴趣浓厚的一个领域。氧溢流、金属-载体相互作用（MSIs）和电荷转移是众多已观察到并被提出的关于NP-载体界面如何辅助和增强催化作用的机制。这项工作研究了氧在Pd NP-CuO纳米线（NW）界面及以外的迁移情况。X射线光电子能谱（XPS）和开尔文探针力显微镜（KPFM）发现，通过在Pd-CuO界面形成PdO，Pd NP与CuO NW载体之间存在相互作用。通过在高真空透射电子显微镜（TEM）下的原位辐照发现，氧通过NP的非晶化从Pd-CuO界面进入Pd NP晶格。改变辐照量突出了NPs不同的非晶化速率，NP完全非晶化会导致在NP上形成外延驱动的PdO。有趣的是，XPS中的原位加热观察到还原为金属Pd，在TEM研究中发现其同样是非晶态的。与负载在不可还原衬底上的Pd相比（在这种情况下，氧化是从外表面向内进行，而不是从载体界面开始，导致形成PdO壳层），理论认为，CuO上Pd的氧化和还原形成了一个充满Pd-PdO位点的PdO NP表面，这有利于产生协同效应，在有机物种的氧化和氢化中具有很大用途。
