Study On Preparation And Characteristion Of Nickel-based Composite Catalysts For Formic Acid Decomposition

In this work, a series of nickel-based composite catalysts for formic acid decomposition were designed and prepared, characterized and tested. The research aimed at eliminating formic acid resulted from N,N-dimethylformamide (DMF) hydrolysis in leather industry, focusing on the principle of catalytic decomposition of low concentration formic acid.Precipitation was employed to prepared nickel-based catalysts using Ni(NO₃)₂·6H₂O as main salt and ethanol-water mixture as solvent. Nano-size NiO was prepared with ultrasonic introduction. Then NiO was modified by adding citric acid to obtain Ni/NiO composite catalyst with good catalytic activity. Based upon those results, composite NiO/ZnO catalysts were prepared by doping metal oxide. Using formic acid catalytic decomposition as a characterization method, the catalyst preparing conditions were optimized step by step. In addition, the reaction routes and kinetics of the formic acid catalytic decomposition were primarily investigated.After comparing the catalytic activity of NiO, Ni/NiO and Ni/NiO/ZnO catalysts at respectively optimized preparation conditions, Ni/NiO/ZnO catalyst was chosen as the optimized catalyst for formic acid decomposition. For Ni/NiO/ZnO, The optimum preparing conditions were as follows: n(Zn):n(Ni)=1.5: 1, the precipitation temperature was 60℃, the aging for 4.0 h and calcined in N2 at 500℃for 3.0 h. In aqueous formic acid system with 0.05 mol·L^-1 formic acid initial concentration, formic acid can be decomposed completely in 1.0 h at 90℃with 1.8 g·L^-1 Ni/NiO/ZnO catalyst. In this case, dehydrogenation reaction dominated and the reaction order was zero with an apparent activatin energy of Ea=16.68 kJ·mol^-1. In DMF-Formic acid system, formic acid conversion rate can be up to 96% with 1.8 g·L^-1 Ni/NiO/ZnO catalyst in 1.0 h at 150℃, dehydrogenation and dehydration reaction reactions occurred at formic acid synchronously. The reaction order of dehydrogenation reaction was estimated to be 0.43 with Ea=45.87 kJ·mol^-1, and the reaction order of dehydration reaction was evaluated to be 0.47 with Ea=77.27 kJ·mol^-1.The as-prepared nickel-based catalysts may potentially applied to practical decompsition of formic acid, owing to many advantages such as high activity of catalytic decomposition for formic acid,simple process, low cost raw material and good catalytic activity.