Study On The Catalytic Performance And Mechanism Of Shale Gas Reforming With CO₂

The development of shale has been one area of research focus with the large consumption of oil-gas resources.Meanwhile,the global warming makes it necessary to reduece CO₂.Producing syngas with proper H₂/CO by reforming of shale gas and CO₂（DRS）can not only realize the utilization of resource,but also deal with two kinds of greenhouse gases,which makes it an ideal way.CH₄ and C₂H₆ are the two main composition of shale gas.The study on catalytic DRM is more mature than DRE and DRS,which is barely reported.Hence,it’s important to produce scientific datas of experiment and theory.Based on the scarce study,the catalytic DRS performance was studied in this paper.The specific work was as follows:Firstly,Ce modified Ni based catalysts with different weight ratioof Ni and Ce were developed to study the performance of DRS on the fixed bed system.Some characterization methods were also used to explore the catalytic mechanisms of the catalysts during DRS process.Results showed that the reforming performance increased with temperarture due to its strong endothermic character,and 800^oC was the best temperature.C₂H₆ showed a better reforming performance than CH₄.The catalytic performance was different with different weight ratio of Ni and Ce.The catalyst containing 5wt%Ni and 5wt%Ce possessed the best catalytic performance and carbon-resistence in DRS process.The catalytic mechanisms were proposed by exploreing the structure and character of the catalysts:the strong interaction between Ni and Ce enhanced the catalytic performance,of which the solid solution Ni-CeOx was the key to prduce the redox couples and site defects.Secondly,based on the developed catalyst in the last chapter,the influences of different composition of shale gas and CO₂ excess coefficient on the catalytic performance were studied.And the deactivation mechanism was also investigated by exploring carbon deposition in different reaction conditions.Results showed that the existence of C₂H₆ reduced the conversion of CH₄ but increased the selectivity of syngas,showing the superiority of DRS than DRM when the temperature was low.But it’s not aperant in higher temperature.Overall,the yield of syngas during DRS was higher than DRM because the existence of C₂H₆ makes positive effect in reforming process.The carbon deposition produced during DRM was most filamentous,which was easy to remove and no harm to catalyst.But they entwined with each other,leading to the decrease of the active metal dispersion.The destruction of active structure was the main reacon of the decrease of cataltitic performance when the filamentous carbon was much.There are three kinds of carbon deposition during DRE:filamentous carbon,upright fibre carbon and embedded carbon,which covered the active sites and were hard to remove.This was the main reason of the decrease of cataltitic performance.The excess CO₂can remove active carbon and improve the stability.Further,in order to reveal the catalytic mechanisms and the interacrion between gas compositions,producing theoretical foundation for the experiments,the CASTEP software based on density functional theory（DFT）was used to calculate the catalytic mechanism.The surface properties of the catalyst were judged from the perspective of electron transfer and molecular adsorption performance.The combination way of Ni/Ce/O and the higher gradient of electron distribution density was the key for the better catalytic performance of solid solution Ni-CeOx.The adsorbability of CH₄ and C₂H₆ on the surface of Ni-CeOx was stronger than that of Ni,and the co-absorbabilty of CH₄ and C₂H₆ was also much stronger than singe adsorbability of CH₄ or C₂H_6.The caiculation produced theoretical basis for the experimental phenomenon.The results in this paper provide an experimental and theoretical standard for catalytic DRS area.