Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
ChemSusChem. 2012 Jan 9;5(1):140-8. doi: 10.1002/cssc.201100491.
A method, based on self assembly, for preparing core-shell nanostructures that are dispersible in organic solvents is demonstrated for Pd and Pt cores with CeO(2), TiO(2), and ZrO(2) shells. Transmission electron microscopy (TEM) of these nanostructures confirmed the formation of distinct metal cores, approximately 2 nm in diameter, surrounded by amorphous oxide shells. Functional catalysts were prepared by dispersing the nanostructures onto an Al(2)O(3) support; and vibrational spectra of adsorbed CO, together with adsorption uptakes, were used to demonstrate the accessibility of the metal core to CO and the porous nature of the oxide shell. Measurements of water-gas-shift (WGS) rates demonstrated that these catalysts exhibit activities similar to that of conventional supported catalysts despite having lower metal dispersions. Pd-based CeO(2) and TiO(2) core-shell catalysts exhibit significant transient deactivation, which is probably caused by a decrease in the exposed metal surface area due to the ease of reduction of the shells. Alternatively, Pt-based analogous core-shell catalysts do not exhibit such a transient decrease. Both Pd- and Pt-based ZrO(2) core-shell catalysts deactivate at a significantly lower rate due to the less reducible nature of the ZrO(2) shell.
一种基于自组装的方法，用于制备可分散在有机溶剂中的核壳纳米结构，该方法适用于 Pd 和 Pt 核与 CeO(2)、TiO(2) 和 ZrO(2)壳。这些纳米结构的透射电子显微镜 (TEM) 证实了明显的金属核的形成，直径约为 2nm，周围是无定形氧化物壳。通过将纳米结构分散在 Al(2)O(3)载体上制备了功能催化剂；吸附 CO 的振动光谱以及吸附量用于证明金属核对 CO 的可及性和氧化物壳的多孔性质。水煤气变换 (WGS) 速率的测量表明，尽管这些催化剂的金属分散度较低，但它们的活性与传统负载型催化剂相似。基于 Pd 的 CeO(2)和 TiO(2)核壳催化剂表现出显著的瞬态失活，这可能是由于壳层易于还原导致暴露的金属表面积减少所致。相比之下，基于 Pt 的类似核壳催化剂则不会表现出这种瞬态减少。由于 ZrO(2)壳层的还原性质较差，基于 Pd 和 Pt 的 ZrO(2)核壳催化剂的失活速率要低得多。
