Study On The Synthesis And Catalytic Performance Of Ni-supported Catalysts In 4-nitrophenol Reduction

P-nitrophenol（4-NP）was one of aromatic nitrogenous compounds,which was a persistent and harmful organic pollutant and widely existed in various industrial and agricultural wastewater.4-NP had been classified as a“priority control pollutant”by the US Environmental Protection Agency for significant damage to human health and natural environment caused by only its trace amounts in the mid-70s.The reduction of 4-NP to p-aminophenol（4-AP）by Na BH₄ was an environmentally friendly,economical and effective treatment method.The BH₄^-eventually became BO₂^-in catalytic reaction,which posed a negligible threat to the ecosystem.Catalysts were needed to promote the reaction due to the slow reduction rate,which was responsible for the research focus on efficient 4-NPS reduction catalyst.Often,noble metal catalyst with high activity suffered from some disadvantages such as high cost and difficult recovery.Therefore,cheap metal catalysts were deemed as promising for large-scale industrial application,among of which Ni catalysts were more widely concerned.In this paper,graphene supported Ni catalysts（x Ni/PGO）and chainlike ZSM-5 zeolite supported Ni catalysts（Ni/x ZSM-5）were prepared by thermal exfoliation method and impregnation method,respectively for the 4-NP hydrogenation reaction.The effects of Ni loading and preparation method on the structure and reactivity of the catalyst were discussed,and the structure-activity relationships of the catalysts were revealed.The main research contents and results are as follows:（1）xNi/PGO catalysts with different Ni loading were prepared by thermal exfoliation method using graphene oxide and Ni（NO₃）₂?6H₂O as starting materials.Highly dispersed Ni catalysts was obtained and the introduction of Ni precursor improved the stripping degree of graphene.When the Ni loading was 15 wt%,the specific surface area of the 15Ni/PGO catalyst reached 215 m²?g^-1,in which the graphene thickness was only 0.76 nm,and the size of nickel nanoparticle was only 2.5 nm.During the thermal exfoliation process,the binding energy of oxygen-containing functional groups on graphene was reduced by the introduction of Ni species,which facilitated the decomposition and removal of oxygen-containing functional groups and thus help to the exfoliation of graphene along with good dispersion of Ni nanoparticles on the surface of graphene.（2）The 4-NP reduction activity of x Ni/PGO catalyst increased firstly and then decreased with the increasing of Ni loading.As the Ni loading reached 15wt%,the reduction activity reached the maximum,in which the TOF value was 0.153 min^-1,the conversion rate got up to91.80%,and the reaction rate constant（k）was 0.183 at the reaction time of 16 min.Obviously30Ni/PGO was superior to other cheap metal catalysts that reported in the literature.（3）The ZSM-5 molecular sieves with different Si/Al molar ratio（25,30,50 and 70）were synthesized by hydrothermal method.It was founded that the ZSM-5 zeolite exhibited chainlike structure（ZSM-5-L）as the Si/Al ratio was equal to or higher than 30,while the ZSM-5exhibited cubic bulk structure（ZSM-5）when the Si/Al ratio was 25.In addition,the Ni particle size decreased first and then increased with the increase of Si/Al ratio and Ni/30ZSM-5-L owned the smallest grain size of 5.41 nm.（4）The catalytic results of 4-NP reduction showed that chainlike Ni/x ZSM-5-L catalysts were superior to cubic stacked Ni/25ZSM-5 and the activity of chainlike Ni/x ZSM-5-L increased firstly and then decreased with the increased of Si/Al molar ratio.Ni/30ZSM-5-L displayed the highest reduction activity to 4-NP,in which the TOF value was 0.152 min^-1,the conversion rate got up to 94.89%,and the reaction rate constant（k）was 0.40 at the reaction time of 7 min.The results were attributed to the improved dispersion of Ni nanoparticles by the enhancement of interaction between the Ni species and ZSM-5,which was derived from the increased acidity in the chainlike ZSM-5-L zeolites.