Controllable Synthesis and Acetylene Hydrogenation Performance of Supported Pd Nanowire and Cuboctahedron Catalysts

Abstract

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.

Carbon-Modified Mesoporous Anatase/TiO2(B) Whisker for Enhanced Activity in Direct Synthesis of Hydrogen Peroxide by Palladium

“…Evidently, no extra diffraction peaks of carbon can be found in C-mb-TiO 2 , which implies that either the amount of carbon is too little or the generated carbon is amorphous [21]. In addition, the diffraction peaks for Pd are indistinguishable, which may be caused by the low content or good dispersion, as previously reported [22]. The bicrystalline structure was also confirmed by Raman spectra.…”

Recent advances in selective acetylene hydrogenation using palladium containing catalysts

“…This was attributed to the influence of hydride formation/decomposition (hydride decomposition occurred at lower temperature on nanocubes) and weaker ethylene adsorption on (100) faces [31]. He et al [32] explored the differences of Pd cuboctahedron and nanowires towards acetylene hydrogenation prepared by varying the amount of bromide added to the synthesis procedure. High resolution TEM images indicated that nanowires were composed of smaller cuboctahedra connected by different crystal faces.…”

“…Testing under competitive conditions demonstrated that nanowires were more active than the cuboctahedra although not as selective. The enhanced activity of the nanowires was attributed to a larger number of defect sites associated with the wire being composed of a number of smaller interconnecting cuboctahedra [32].…”

Improved catalytic performance of Pd/TiO2 in the selective hydrogenation of acetylene by using H2-treated sol–gel TiO2

“…In the selective hydrogenation of acetylene, Li et al [31] reported that the hydrogenation activity of the Pd nanowires increased because of the defect sites at crystal boundaries. In our previous work [32], a larger amount of Ti 3+ surface defects on the solvothermal-derived nanocrystalline TiO 2 was also found to result in a stronger interaction between Co and TiO 2 and then a higher Co dispersion.…”