Study Of Nickel-based Catalysts For Oxidative Dehydrogenation Of Ethane To Ethylene

In this thesis, the appropriate catalysts for oxidative dehydrogenation of ethane (ODHE) were chosen through the results of catalytic activity evaluation in a fixed-bed micro-reactor. The parameters of catalyst preparation and reaction condition were also identified. The influences of the preparation methods of catalyst as well as the addition promoter of Ce on the catalytic performance were also investigated. The results show that:(1) The Ni-based catalysts show a good catalytic performance of ODHE for the ethylene production. With the Ni loading of 17 wt%, the calcination temperature of 550℃, the reaction temperature rang of 500℃⁶00℃, the space velocity of 12000 ml/(g ·h) and the reactants ratio of C₂H₆: O₂: He = 2: 1: 9, the C₂H₄ selectivity and yield were both above 60% and 20%, respectively.(2) Three types of NiO/ γ -Al₂O₃ catalysts with the same Ni loading [ω (Ni) =17%] were prepared by hydrothermal treatment method, impregnation method and solid-state exchange method respectively. The catalysts prepared by impregnation method showed the optimized reaction activity. The active species were studied by XRD, XPS and H2-TG. It was found that the easily reducible NiO microcrystalline and the 'surface spinel' NiAl₂O₄ are the active species for ODHE. The active species on the impregnated catalysts were easily reducible and uniformly distributed on the surface of support, and the interaction between the active species and support is moderate, thus resulted in relatively higher activity and selectivity for ODE. The different oxygen species were investigated by O2-TPD-MS, the results imply that the non-stoichiometric oxygen species (O₂^-, O^-and O₂^2-) is the high selectivity oxygen species for ODHE reaction.(3) The selective oxidative activity of ODHE at low temperature was enhanced with the addition of promoter CeC>2 in the catalyst, but the addition was not helpful to the selective oxidation at high temperature. The distribution of Ni species on the catalyst surface as well as the existing conditions of oxygen species was characterized by XRD, TPR and XPS. The results show that the addition of CeC>2 promoter decreases the interaction between Ni species and support, enhances the distribution of Ni species on the catalyst surface, and increases the density of crystal oxygen on the catalyst surface, therefore the reaction activity of ODHE under low temperature is improved. On the other hand, higher CeO2 addition would lead to the its sintering, or go into the bulk of the catalyst, or cover the catalyst surface, so the interaction with Ni species would be reduced, and the catalytic activity decreased because of the aggregation of Ni crystalline on the catalyst surface.