| With the increasing use of fossil fuels worldwide,C02 emissions are increasing day by day,the resulting greenhouse effect is causing untold damage to our earth.Controlling CO2 emissions is the fundamental solution to the greenhouse effect,and the most radical solution is to use non-fossil clean energy sources.However,based on current technology and high energy demand,it will take a long time to abolish fossil fuels.Therefore,the reuse of CO2 is the focus of governments and researchers.Many kinds of CO2 chemical conversion technologies have been developed,including electrocatalytic CO2 reduction,simulated photosynthesis CO2 conversion,CO2 catalytic synthesis and catalytic hydrogenation reaction.But from the perspective of large-scale industrial application.Converting the syngas(CO and H2)obtained from CH4-CO2 reforming reaction by F-T reaction to get other chemicals,which is the best way to realize CO2 recovery and reuse.CH4 and CO2 are both high stable molecules,so the CH4-CO2 reforming reaction should be carried out at high temperature.The core is the development of high performance catalyst,there are several key scientific problems in the study of catalyst:(1)Preventing the agglomeration and sintering of metal active site under high temperature reaction to prepare CH4-CO2 reforming catalyst with high thermal stability.(2)To prevent the formation of carbon deposite in the CH4-CO2 reforming reaction,and to explore the the condition and mechanism for generating carbon.(3)The structure-activity relationship of high thermal stability catalyst was investigated to direct the design and synthesis of the catalyst.In this paper,the high thermal stability catalysts for CH4-CO2 reforming reaction are studied in the following aspects:(1)By encapsulating NiCo nanoparticle to SiO2 nanosphere,a uniform core-shell sturcture catalyst was obtained,the stabilization effect of SiO2 shell on catalyst and the catalytic effect of NiCo alloy on catalytic performance were described.(2)Al2O3/Ni/Al2O3 sandwich structure catalysts were obtained by combining wet impregnation method and ALD method,the relationship between Al2O3 film and catalytic activity&stability was investigated.(3)The Stober method,the impregnation method and the sol gel method were used together to prepare the Ti02/Ni/TiO2 sandwich structure catalyst.By the characterization and activity test,the structure-activity relationship of catalyst was preliminarily discussed.(4)The Ni@SiO2 core-shell structure catalyst and the RuCoMn composite oxide catalyst were combined,the CH4-CO2 reforming reaction was catalyzed by Ni@SiO2 catalyst,then the F-T reaction was catalyzed by RuCoMn catalyst to realize one-pot CO2 conversion to low carbon olefin,and the synergistic effect of catalyst was also described.1.NiCo@Si02 core-shell structure catalystWhen the reaction temperature reaches 800°C,the activity of Ni&Co is very high.However,it is easy to agglomerate sintering,which leads to the inactivation of the catalyst,and the increase of the particle size will also aggravate the surface carbon deposit and further accelerate the inactivation.We have solved this problem by the method of inert silica nanosphere encapsulation.We found that NiCo@SiO2 core-shell structure catalyst has a better thermal stability in 800°C than in the support NiCo/SiO2 catalyst.For NiCo@SiO2 catalyst,the conversion of CH4 and CO2 are close to 100%and no other product at 800°C.In addition,the catalyst can stay stable for 1000 h under 800°C without obvious inactivation which demonstrate that the core-shell structure is a high thermal-stable structure.In addition,we found that the alloy NiCo catalyst had higher conversion and better thermal stability than the mono-metal Ni&Co catalyst.2.Al2O3/Ni/Al2O3 sandwich structure catalystA novel Al2O3/Ni/Al2O3 sandwich structure catalyst was prepared by combining chemical method(wet impregnation)and physical method(atomic layer deposition).The catalyst showed good reforming activity and excellent thermal stability for DRM reaction at the reaction temperature of 800°C which can stay stable for more than 400 h.The high thermal stability of the catalyst can be attributed to the double interactions of Ni with y-Al2O3 support and the Al2O3-film,which could effectively inhibit Ni agglomeration at high temperature and the subsequent carbon deposition.Other metal sandwich catalysts could also be designed in this way,which may offer more opportunities for their industrial application under harsh conditions.3.Ti02/Ni/Ti02 sandwich structure catalystBy replacing the support,the Al2O3/Ni/Al2O3 sandwich structure catalyst was expanded to the TiO2/Ni/TiO2 sandwich structure catalyst.The TiO2 nanosphere with size about 1000 nm were obtained by hydrolysis method.Then the Ni/TiO2 support catalyst was prepared by the wet impregnation method to load the Ni on TiO2 nanosphere.Finally,the TiO2 film was hydrolyzed and deposited on the surface of Ni/TiO2 supported catalyst by sol-gel method to generate the Ti02/Ni/TiO2 sandwich structure catalyst.Based on the characterization and DRM reaction activity test,the relationship between catalyst structure and effect was preliminarily explored.4.One-pot CO2 conversion to low carbon olefin by tandem reactionThe high thermal stability catalyst was used in the CH4-CO2 reforming reaction.By the F-T synthesis reaction,the syngas was converted into lower olefins,which can realize the one-pot conversion of CO2 to lower olefins.The Ni@SiO2 core-shell structure catalyst was used as DRM reaction catalyst,the syngas generated from DRM reaction was converted to lower olefins through F-T reaction catalyzed by the RuCoMn composite oxide catalyst synthesized by chemical coprecipitation which show high selectivity to lower olefins.The reaction mechanism and the synergistic effect of catalysts were analyzed,the influence of catalyst composition on performance was also explored,it is found that the addition of Ru can effectively improve the reduction of Co in the catalyst,thus improving the F-T activity. |
