Nickel Nanoparticles Loaded In Microporous Supports As The Catalysts For The Reaction Of CO₂ Methanation

Supported metal catalysts play an important role in the field of catalysis,which have attracted much attention.The most important advantage of the supported metal catalysts is that the active component can be well dispersed on the support,which can increase the utilization of the materials.Nowadays the main drawback of the metal catalysts is that the metal nanoparticles tend to aggregate or sinter during the reaction,and thus it results in fast deactivation.Aiming at this problem,three-dimensional ordered microporous carbon and microporous zeolite are used as the supports,and metal nickel nanoparticles are loaded into the micropores.We propose to use the confinement of micropores within supports to prevent metal nanoparticles aggregation and improve catalytic performance.The following three aspects are discussed:1.Using Y zeolite as template,furfuryl alcohol and propylene as carbon source,a three-dimensional ordered microporous carbon(3DOC)is prepared by chemical vapor deposition(CVD).Then Ni is loaded into the micropores of 3DOC by incipient wetness impregnation method.Through a series of characterizations such as XRD,FT-IR,BET,SEM and TEM,we found the 3DOC with a three-dimensional ordered microporous structure can provide a large specific surface area for the active component nickel.The performance of the catalyst was investigated by carbon dioxide methanation.And the results show the optimal reaction temperature of Ni@3DOC catalyst is 400℃,and the optimal content of Ni is 15 wt%.Under such conditions,the conversion rate of CO2 is about 50%and the selectivity of CH4 can reach about 96%,the activity of Ni@3DOC catalyst remains stable within 30 hours.2.Using TEOS as silicon source,TPAOH as template,and the metal complex[Ni(NH2CH2CH2NH2)2](NO3)2 as precursor,Ni(OH)2@S-1 is synthesized by in-situ hydrothermal synthesis method.Through a series of characterizations such as XRD,BET,SEM and TEM,we found that Ni clusters are well dispersed in the channels of MFI zeolite.The performance of the catalyst was investigated by carbon dioxide methanation.And the results of carbon dioxide methanation show the optimal reaction temperature of Ni(OH)2@S-1 catalyst is 700℃,the optimal reaction temperature is 400℃,and the optimal content of Ni is 4 wt%.Under such conditions,the conversion rate of CO2 is about 50%and the selectivity of CH4 can reach about 90%,and the activity of Ni@3DOC catalyst remains stable within 20 hours.3.For comparison purpose,three commercial carbon nanomaterials such as carbon nanotubes(CNTs),carbon black(BP2000)and activated carbon(AC)are tested as the supports,and Ni@CNTs,Ni@BP2000 and Ni@AC are obtained by impregnation method.The performance of three catalysts were investigated by carbon dioxide methanation and compared with the previously prepared Ni@3DOC and Ni(OH)2@S-1 catalysts.The results show that among these catalysts,15 wt%Ni@3DOC has the best performance,the conversion rate of CO2 is about 50%and the selectivity of CH4 is about 96%,and its activity remains stable within 30 hours.The reason for this result is that the larger specific surface area of 3DOC can improve the dispersibility of the active component,and its highly ordered microporous structure can restrain the migration of metal Ni particles,therefore the performance of the catalyst is improved.In summary,we successfully prepared two kinds of supported metal catalysts Ni@3DOC and Ni(OH)2@S-1 by using three-dimensional ordered microporous carbon and microporous zeolite as supports.Both of them exhibit excellent catalytic properties in the carbon dioxide methanation.The research results in this thesis show the advantages of microporous materials as supports in the field of catalysis.First,they can provide a larger specific surface area for the active component and improve the dispersion of the metal nanoparticles.Second,the highly ordered microporous structure can play a space-limited role and inhibit the aggregation and sintering of the metal nanoparticles,thus increasing the catalytic activity while extending the life of catalyst.