Study On The CO₂ Reforming Of Methane For Syngas Production Over Ni Based Catalysts

The reforming of methane with CO2 (DRM) provides a pathway for comprehensive utilization of CH4 and CO2. Dry reforming of CH4, which uses both CH4 and CO2 as reactants, is a potential method to utilize the greenhouse gases in the atmosphere. So, the DRM process is a very attractive reaction in terms of both the academic study of syngas production and industrial utilization.It is known that transition metal carbides show chemical properties similar to those of noble metals. Herein, we prepared Ni modified carbide catalyst based on the following idea: the activation of methane can be promoted due to the presence of nickel and carbon dioxide is activated by the transition metal carbides. By adjusting the molar ratio of nickel to carbide, a catalytic oxidation-carbonation cycle could be established over Ni modified carbide catalyst. On the other side, plasma technology, as an effective molecular activation approach, has been applied to the conversion of CH4 and CO2. However, it is difficult for plasma to control the selectivity of product. In order to obtain a new technology for DRM which has both high reaction activity and selectivity, we combine the plasma and catalytic activation for DRM.The main results presented in the dissertation have been summarized as followings:(1) At atmospheric pressure, Mo2C catalyst has poor activity and stability for DRM. However, Ni-Mo2C catalyst has stable DRM activity and stability at atmospheric pressure. The conversions of reactants and selectivities to products do not change within the range of time tested (35 h), which is the best results for DRM over carbide catalyst at atmospheric pressure.(2) The role of nickel in Ni-Mo2C catalyst for DRM is investigated. The deactivation of Mo2C catalyst in DRM is due to bulk oxidation by CO2, indicating that the rate of CO2 dissociation is faster than that of CH4 dissociation over Mo2C catalyst. Due to the addition of Ni, the dissociation of CH4 can be significantly enhanced. Accordingly, the oxygen species form CO2 dissociation could be timely consumed by reacting with carbon species generated from CH4 dissociation. Thus, the catalytic cycle of oxidation-carbonation could be established over the Ni-Mo2C catalyst.(3) In-situ synthesis of nickel modified molybdenum carbide catalyst during dry reforming of methane was investigated. Ni-Mo2C catalyst can be in-situ synthesized in CH4/CO2 feed for DRM at 800℃using NiMoOx as precursor. Compared with Ni-Mo2C catalyst synthesized in CH4/H2 mixture by traditional method, the in-situ synthesized Ni-Mo2C catalyst still exhibited stable DRM activity at atmospheric pressure. Combined with the results of characterization, we studied the mechanism of in-situ carbonzation and the role of nickel in the in-situ carbinzation process. (4) The synergistic effect between DBD plasma and Cu-Ni/γ-Al2O3 catalyst for DRM was studied. In the pure plasma process, the DRM reaction depends strongly on the input power, total flow rate and CH4/CO2 ratio. The addition of argon as dilute gas in the feed was found to greatly improve the reaction. The presence of catalyst in the plasma region greatly improved the DRM process. Both activity and selectivity were enhanced by combination of plasma with catalyst. A synergistic effect was obtained over Cu-Ni/γ-Al2O3 catalyst in DBD plasma.