Design,Construction And Performance Of Catalysts For Carbon Dioxide Reforming Of Methane

CO₂?dry?reforming of methane?DRM?has attracted much attention from academia and industry in recent years for its broad applications in effectively utilizing natural gas,taking advantage of industrial exhaust gas and greenhouse gas,and solving the increasing environmental problems.Aiming at solving the shortcomings of the current DRM catalysts,this dissertation developed novel catalyst system and preparation method,which improved the activity and stability of catalysts for DRM reaction.Further study for the traditional Ni-based catalyst was also performed.The results could provide some ideas and experience for catalysts design and are summarized as follows:?1?The monometallic Mo₂N and bimetallic Ni₃Mo₃N and Co₃Mo₃N nitrides were used as new catalysts for the DRM reaction.It was found that the Mo₂N,Ni₃Mo₃N and Co₃Mo₃N were all active species for the reaction.Compared to the single metal nitride catalyst Mo₂N,the bimetallic nitride catalysts Ni₃Mo₃N and Co₃Mo₃N showed better activity,stability and oxidation resistance.The addition ofmetal?Ni or Co?into the interstice of Mo₂N could construct the atomic level contact among the bimetal centers,leading to the enhanced methane dissociation ability,the changed chemical environment of metal active centers and subsequently the synergistic effect between different metal species in bimetallic nitride catalyst.The adsorption centers of bimetallic nitrides shifted to higher temperature range,helping provide more reactant molecules adsorbed on catalyst surface under high reaction temperature of 800?,which was conducive to the improvement of catalytic activity.In addition,Co₃Mo₃N exhibited the highest activity and stability among the three samples due to the synergistic effect between the Mo and interstitial metal Co in the interstitial structure,the equal adsorption capacity and consumption rate of C0₂ and CH₄ and their increment on the catalyst surface at the reaction temperature,as well as the possible reactants conversion balance on the active centers.The Co₃Mo₃N catalyst could be considered as a competitive candidate in the DRM reaction.?2?By using support phase transformation induction phenomenon and active metal atoms migration effect,a novel preparation strategy for highly efficient and stable Ni-based catalysts was developed.A series of highly dispersed,strongly anchored nano-sized Ni-based supported catalysts were prepared using metal oxides and metallic oxyacid salt such as Ti0₂,Zr0₂ and CaSiO₃,and the natural layered mineral material?Kaolinite?as supports.By controlling the structural rearrangement induced by carrier phase transition and active component reduction simultaneously,the size of active metal was reduced and the metal dispersion was improved,which further improved the activity of the catalyst.Meanwhile,the metal-support interaction was enhanced,which could provide a strong anchoring effect for active metal particles on the surface of carrier,improving the metal migration resistance ability of catalyst at high temperature.As a result,the stability of the catalyst was improved significantly.In addition,the effectiveness of the method for active component loading over Ni/Ti0₂-TB catalyst was investigated.It was found that the new method was effective for the metal loading between 5%and 1₃%.For the metal loading lower than ₃%or higher than 15%,the advantages of the new method were not obvious.?3?The effect of reduction temperature of active metal species on the running stability of Ni/Al₂O₃ catalyst was studied.It was found that under the reduction temperature,the metal dispersion was inscreased.The catalyst of 650? reduction can be stable for ₂000 h on stream.The stability of this Ni/Al₂O₃ catalyst was the highest among the reported Ni/Al₂O₃ catalyst up till now.?4?The promotion effects of different rare earth oxides?La,Ce,Pr,Nd and Sm?on the Co/Al-PILM catalysts with Al-pillared montmorillonite support were systematically studied.It was found that the particle size of active metal species,metal dispersion,reducibility,the catalytic activity and the carbon deposition were all affected by lanthanides promotion.Moreover,the distribution of different rare earth elements on the catalysts surface was significantly different,and this difference will affect the interaction between active metal and rare earth,which subsequently influence the metal-support interaction of the catalysts.