High dispersed palladium nanoparticles with the size of about 3.8 nm confined within ZSM-5 zeolite catalyst (Pd/ZSM-5-IS) was successfully synthesized by in situ synthesis method based on azeotropic distillation assisted fabrication. Liquid phase selective hydrogenation of p -nitrophenol (PNP) to p -aminophenol (PAP) was chosen as model reactions to evaluate the catalytic behavior of the Pd/ZSM-5 catalysts. Thiophene and 4,6-dimethyldibenzothiophene were used as poisons to test their anti-poisoning ability. Pd/ZSM-5-IS catalyst exhibited higher catalytic activity in hydrogenation of PNP to PAP than sample prepared by impregnation method (Pd/ZSM-5-IM), which was mainly attributed to entering of Pd nanoparticles into the intracrystalline mesovoids of the ZSM-5 support for in situ method efficiently prevent active sites from loss and aggregation. In addition, Pd/ZSM-5-IS catalyst not only maintained high activity for five consecutive runs, but also showed high sulfur tolerance for the hydrogenation reactions. This simple and versatile method also can be extended to cover many kinds of other supported catalysts for broad applications in many other catalytic reactions in the future.
The biocathode bioelectrochemical system (bioc-BES) was used for p-nitrophenol (PNP) degradation with sodium bicarbonate as the carbon source. The PNP degradation efficiency in bioc-BES with applied voltage of 0.5 V reached 96.1% ± 0.5% within 72 h, which was much higher than that obtained in the biocathode BES without applied voltage (bioc-BES-NAP), open circuit biocathode BES (OC-bioc-BES) or abiotic cathode BES (abioc-BES). With the increase in the PNP concentration from 20 mg L−1 to 60 mg L−1, the PNP concentration of the effluent decreased from 21.66 ± 2.94 mg L−1 to 0.38 ± 0.1 mg L−1 in 48 h. The final reductive product of PNP was p-aminophenol (PAP) in the biocathode chamber. High-throughput 454 pyrosequencing showed that predominant populations in the biocathode biofilm of bioc-BES were affiliated with electrochemically active Delftia and Diaphorobacter, while Aminobacter was the predominant population in the biocathode biofilm of the bioc-BES-NAP and OC-bioc-BES. These results suggested that microbial electrocatalysis and electrochemically active bacteria on the cathodic electrode accelerated PNP degradation in the biocathode BES (bioc-BES). The biocathode BES will be a promising treatment technology for PNP-containing wastewater.
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