Hong Jiang,Songlin Xue,Yefei Liu,Weihong Xing,Rizhi Chen
The Pd@ZIF-L catalysts with uniform crosshair-star shape and a size of about 20 μm were synthesized by an assembly method, in which a two-dimensional layered zeolitic imidazolate framework-L (ZIF-L) was used as the support to immobilize Pd nanoparticles . Their catalytic activities were evaluated by the catalytic reduction of p -nitrophenol to p -aminophenol. The results highlight that the physical-chemical and catalytic properties of the Pd@ZIF-L catalysts are greatly affected by the synthesis temperature. The temperature variation can make the catalysts transform from two-dimensional flakes to zero-dimensional spheres. High temperature is beneficial for increasing Pd loading and encapsulating Pd nanoparticles within the ZIF-L matrix. However, under the temperature larger than 30 °C, the dense dia(Zn) structures are formed. Increasing Pd loading in the Pd@ZIF-L catalysts leads to a significantly higher p -nitrophenol conversion. The relative dense structure of the as-synthesized catalysts makes p -nitrophenol access the active centers difficultly and a lower catalytic activity is observed. These findings would aid the development of high-performance Pd@ZIF-L catalysts.
Hong Jiang,Songlin Xue,Yefei Liu,Rizhi Chen,Weihong Xing
The Pd@ZIF-L catalysts with uniform crosshair-star shape and a size of about 20 μm were fabricated by an assembly method that enables the crystallization of ZIF-L in water with the presence of polyvinylpyrrolidone (PVP)-stabilized Pd nanoparticles (NPs). The physical and catalytic properties of the Pd@ZIF-L catalysts are greatly affected by the molar ratios of 2-methylimidazole (2-MeIM)/Zn2+ and PVP/Zn2+. Their catalytic activities were evaluated by the catalytic reduction of p-nitrophenol to p-aminophenol. The results indicate that a lower molar ratio of 2-MeIM/Zn2+ is beneficial for the increase of Pd loading and p-nitrophenol conversion, but a suitable molar ratio (≥20) of 2-MeIM/Zn2+ is helpful to the crystallization of ZIF-L and the encapsulation of the Pd NPs within the ZIF-L framework. The Pd@ZIF-L catalyst synthesized at a lower PVP/Zn2+ molar ratio has higher Pd loading and p-nitrophenol conversion due to the easy adsorption of PVP–Pd NPs onto the ZIF-L surfaces. This work would aid the development of high-performance Pd@ZIF-L catalysts.
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