Preparation Of Metal Nickel-based Catalysts And Their Catalytic Activity Evaluation

The catalysts play an important role in the modern chemical industry. As a universalcatalyst, nickel-based catalysts have a variety of excellent properties, such as low price,high catalytic activity and stability, and have been widely applied in such chemicalprocesses as hydrogenation, dehydrogenation, oxidation, dehalogenation, desulphurization,etc. On the other hand, hydrolysis of sodium borohydride （NaBH₄）, as a new hydrogenproduction process, is considered to be a safe, highly effective hydrogen productiontechnology. High-purity hydrogen gas can be controllably released from the alkalineNaBH₄solution in the presence of catalysts. As a part of the project supported by theNational Natural Science Foundation of China （21076063）, the preparation,characterization and evaluation of the catalytic activity of as-prepared Ni-based catalystsfor hydrogen generation from NaBH₄hydrolysis have been studied in this dissertation.The main results are summarized as follows:1. The multi-shaped nickel catalysts have been successfully prepared via hydrothermalreduction method using hydrazine hydrate（N₂H₄H₂O）, sodium hypophosphite（NaH₂PO₂H₂O） and ethylene glycol（C2H₄（OH）2） as reductants and PVP as structure-directing agent and stabilizer. These nickel catalysts have been characterized by XRD,SEM and TEM, and the impact of surfactants, reaction time, reaction temperature andreductants were investigated. Meanwhile, the formation mechanism of the products wassuggested. The results show that the chain, spherical, dendritic, hexagonal, meshy andhexagonal nickel microstructures could be respectively obtained using NaH₂PO₂H₂O,N₂H₄H₂O and C2H₄（OH）2as reductants.2. Hexagonal FeNi₃double metal nano-sheets, whose mean diameter is about50nm to100nm, have been successfully synthesized using N₂H₄H₂O as reductants via a PVP-assisted hydrothermal process in alkaline solution. The alloys were analyzed by XRD, andTEM methods, and the main factors that affect the morphologies of the product was studied. The formation mechanism of the alloys were also discussed. It is shown thatNaOH and PVP play an important role in growth process of hexagonal alloy FeNi₃nano-sheets.3. Fe2O3and NiO oxides were respectively synthesized by the hydrothermal technique,and the commercial4A molecular sieve were served as catalyst carriers. The supportedcatalyst, Ni/Fe₃O₄, Ni/NiO and Ni/SM4A, were successfully prepared using the in-situreduction method, and characterized by XRD. The results show that Fe2O3oxide as thesupport is not stable and easily changed into Fe₃O₄in part.4. The as-prepared catalysts were used in the process of NaBH₄hydrolysis, and themain influencing factors such as NaBH₄concentration, NaOH concentration andtemperature for the NaBH₄hydrolysis process were studied. The results show that the rateof hydrogen production descends with NaBH₄and NaOH concentration increasing, butascengds with temperature rising in the whole process. The concentrations of NaBH₄andNaOH are all kept at5%, and the temperature at30℃are considered to be the bestconditions. In addition, the morphology, carriers and loading also have great influence onthe rate of hydrogen production. The catalytic activity of the Ni catalysts for the NaBH₄hydrolysis was investigated by measuring the rate of hydrogen production, and thesequence of catalytic activity for the above catalysts is as follows: Ni/Fe₃O₄> Ni/SM4A>FeNi₃> hexagonal nickel> spherical nickel> meshy nickel> Ni/NiO.