Synthesis Of Transition Metal Nanocomposites For Catalytic Hydrogenation Of Nitrophenol

As one of the most representative pollutants in industrial wastewater, 4-nitrophenol(4-NP) has a great threat to the environment due to its high toxicity, potential carcinogenic and mutagenic hazards. Recently, the catalytic hydrogenation of 4-NP is considered to be the most efficient, green and economical approach because the catalytic reduction product 4-aminophenol(4-AP) is an important chemical and pharmaceutical intermediates, which shows the potential development prospects. It is the key point to develop a highly effective, stable and inexpensive catalyst for catalytic hydrogenation of 4-NP compounds in aqueous solutions under mild condition. Based on the present research status, Ag-SiO2, Ag@CeO2 and CoNi/rGO nanocomposites(NCs) were synthesized and characterized, and investgated with their catalytic performance for the catalytic hydrogenation reaction of 4-NP in this thesis. The main contents are as follows:Ag-SiO2 NCs with “plum-pudding” structure were one-pot synthesized in a nonylphenol polyoxyethylene ether/cyclohexane reverse micelle system with AgNO3 aqueous solution. The obtained results demonstrated that ultrafine Ag nanoparticles(NPs) with size of ~2 nm were well dispersed in SiO2 nanosphere(~28 nm). In comparison with SiO2, free Ag NPs and supported Ag/SiO2 catalyst, the Ag-SiO2 NCs showed superior catalytic activity for the catalytic hydrogenation of 4-NP with a turnover frequency(TOF) of 489.0 h-1 at room temperature, which was higher than those of many reported metal catalysts. The activation energy of Ag-SiO2 NCs was estimated to be about 34.4 kJ mol-1 and it also exhibited good durability for recycle tests. Moreover, the Ag-SiO2 NCs also showed superior catalytic activity for the catalytic hydrogenation reactions of 2-nitrophenol and 3-nitrophenol.In order to further improve the stability of Ag-based catalysts, Ag@CeO2 NCs with core-shell structure were successfully synthesized by the combination of the reverse micelle technique and the redox reaction. The characterized results of Ag@CeO2 NCs showed that Ag NPs with diameter of 3~7 nm were surrounded by CeO2. Compared to CeO2, free Ag NPs and Ag/CeO2, the as-synthesized Ag@CeO2 NCs exhibited a better catalytic activity for the hydrogenation reactions of 4-NP and 2-nitroaniline with the TOF value of 138.7 h-1 and 109.8 h-1, respectively. Moreover, the Ag@CeO2 NCs showed good activity stability even after ten cycle tests. These results indicated that the Ag@CeO2 NCs exhibited superior durability as compared to the previous Ag-SiO2 NCs and other reported catalysts.Concerning the limited resources and expensive price of noble metal, the development of efficient and economical non-noble catalysts is of great importance for the practical application. CoNi NPs supported on reduced graphene oxide(CoNi/rGO NCs) with low crystallinity were synthesized via a facile one-step co-reduction synthetic route with NaBH4 and NH3BH3 as co-reductants. The bimetallic catalysts showed a higher catalytic performance than the monometallic counterparts for the hydrogenation of 4-NP, especially for Co0.5Ni0.5/rGO NCs showing better catalytic activity. Compared to crystal structure of Co0.5Ni0.5/rGO-N and Co0.5Ni0.5/rGO-annealed NCs, Co0.5Ni0.5/rGO NCs with lower crystallinity exhibited superior catalytic performance with a TOF value of 38.82 h-1. The activation energy of Co0.5Ni0.5/rGO NCs for the reduction of 4-NP was calculated to be 27.0 kJ mol-1. Moreover, the Co0.5Ni0.5/rGO NCs showed good durability for the hydrogenation of 4-NP after five runs.