Four types of palladium (Pd) nanoparticles were prepared from the systems containing PdCl2 or Na2PdCl4 with or without the assistance of poly(vinylpyrrolidone) (PVP). Two types of Pd nanoparticles obtained in the absence of PVP were obviously larger than those synthesized with the assistance of PVP. The former large Pd particles showed typical features in cyclic voltammetry in H2SO4 solution, whereas two types of small Pd nanoparticles did not. However, small nanoparticles treated first in an electrochemical way in 0.5 M KOH solution displayed the adsorption and desorption peaks similar to those of typical Pd-modified electrodes in H2SO4 solution. Large Pd nanoparticles from the PdCl2 synthesis system showed a catalytic specific current of 629 mA/mg in the electrocatalysis of ethanol, whereas large particles from the Na2PdCl4 system showed a current of 262 mA/mg. The maximum catalytic currents of small Pd nanoparticles without surface cleaning treatment were 1382 and 1019 mA/mg for samples from the Na2PdCl4 and PdCl2 systems, respectively, higher than those being treated in KOH solution first, and the electrocatalytic stability of the two untreated samples was better. However, small nanoparticles after the electrochemical treatment can reach the maximum catalytic current faster. The synthesis and structure–property relation of four types of Pd nanoparticles have been discussed and analyzed on the basis of systematically experimental data.
Weining Sun,Xiaofeng Lu,Yan Tong,Junyu Lei,Guangdi Nie,Ce Wang
In this report, a palladium/polypyrrole/polyacrylonitrile (Pd/PPy/PAN) composite nanofiber membranes was synthesized by a one-pot redox polymerization process between pyrrole monomers and Na2PdCl4 in the presence of electrospun PAN nanofibers, without the introduction of any other surfactants or reductants. The as-prepared Pd/PPy/PAN nanofiber membrane exhibited good catalytic performance towards hydrogen generation from the hydrolysis of ammonia borane (AB). The apparent activation energy (Ea) was calculated to be about 33.5 kJ mol−1. In addition, the Pd nanoparticles (Pd NPs) were encapsulated in PPy layers on the surface of the PAN nanofibers, enabling the catalyst to be stable against poisoning and easily separated from the suspension system. The catalytic activity does not weaken after five cycles. This study indicated that the obtained Pd/PPy/PAN composite nanofiber membrane could be applied as an alternative in exploring new catalysts for hydrogen generation, as hydrogen is an important fuel as a clean power source.
Graphical Nitrogen-doped graphene nanoshells supporting palladium nanoparticles (Pd/N-GNS) have been developed as a superior catalyst for the N -allylation reaction. Experimental results and DFT calculations reveal strong metal–support interactions between the pyridinic N and palladium species, which significantly boost the catalytic efficiency and stability of the catalyst. In this study, nitrogen-doped graphene nanoshells (N-GNS) were developed to support palladium nanoparticles (Pd/N-GNS) as an efficient and recyclable catalyst for the N -allylation reaction. N-GNS was synthesized through a facile hard-template method by using petroleum asphalt, followed by nitrogen doping by thermal annealing with urea, the contents and species of which could be altered by the calcination temperature. Palladium nanoparticles (Pd NPs) with an average diameter of 3.3 nm were homogeneously deposited onto the N-GNS support through a mild solvent-growth approach. The Pd/N-GNS exhibited a superior activity towards the N -allylation reaction, 6-fold higher than that of the pristine graphene nanoshells supporting the palladium catalyst. The Pd/N-GNS could be recycled several times without activity deterioration and metal leaching. The catalytic activity showed a linear correlation relationship with the pyridinic N content. Experimental and theoretical studies reveal strong metal–support interactions between the pyridinic N and palladium species, which can downsize the Pd NPs, modulate the electronic properties, and promote the adsorption of reactant, thereby significantly boosting the catalytic efficiency and stability for the N -allylation process. The present work could help unravel the roles of nitrogen-doped carbon supports and provides a feasible strategy to rationally design superior palladium catalysts for chemical transformations.
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