Controllable Synthesis and Acetylene Hydrogenation Performance of Supported Pd Nanowire and Cuboctahedron Catalysts
journal contributionposted on 03.08.2012, 00:00 by Yu-Fei He, Jun-Ting Feng, Yi-Yun Du, Dian-Qing Li
Supported Pd nanowire and cuboctahedron catalysts have been synthesized in an ethylene glycol–poly(vinylpyrrolidone)–KBr system using a precipitation–reduction method. KBr plays a critical role in controlling the morphology of Pd: with a variety of relatively low KBr concentrations, Pd nanowires with different lengths were obtained, but after adding sufficient KBr, shape evolution from nanowires to cuboctahedrons was observed. HRTEM images showed that the twisted Pd nanowires were actually composed of primary cuboctahedrons. Furthermore, lattice distortion was observed at interfacial regions, and the number of crystal boundaries increased with increasing length of the nanowires. The catalytic performance of the Pd materials was investigated in the selective hydrogenation of acetylene. The activities of the Pd nanowire catalysts were significantly higher than those of the cuboctahedron catalyst and gradually increased with the increasing number of crystal boundaries, indicating that the defect sites at crystal boundaries are more active owing to the exposure of larger numbers of Pd atoms. However, higher activity resulted in excessive hydrogenation and a decrease in ethylene selectivity. Therefore, the Pd cuboctahedron catalyst possessed higher selectivity. The relationship between crystal boundaries and catalytic performance was quantified, and the catalytic activity was found to increase linearly with an increasing number of crystal boundaries, whereas the trend in the selectivity was the reverse.