Design And Sythesis Of Photothermal Dual-responsive Nanocatalysts And Their Fischer-tropsch Synthesis Catalytic Performance

Fischer-Tropsch synthesis?FTS?is a heterogeneous catalytic reaction that converts syngas?CO+H₂?into clean hydrocarbon liquid fuel in the presence of catalyst.Facing with the modern context of increasing energy demand,limited petroleum resources and the inability of large-scale renewable energy application in the short term,the development of Fischer-Tropsch synthesis technology,a way to efficiently convert coal,natural gas,biomass,and other carbon-containing resources into clean fuels,is of great practical significance for ensuring the energy security and reducing environmental pollution.How to improve the activity and rationally regulate the product distribution has always been the focus of FTS.In the past decades,researchers have done a lot of work in the design of catalysts,optimization of reactors,modulation of reaction conditions,etc.,and significant progress has been achieved.However,so far,Fischer-Tropsch reactions are conducted almost all under the excitation of thermal fields,and the enengy consumption is high.Photocatalytic technology,as a route to convert solar energy into chemical energy,has been widely used in energy and environmental fields due to its low-cost and environmentally friendly advantages.The mechanism of photocatalysis is very different from that of thermocatalysis,and photocatalysis can drive some reactions that are inaccessible by thermocatalysis.Based on the key problems of low activity,uncontrolled product distribution,and high energy consumption existed in Fischer-Tropsch synthesis reaction,we built a novel approach integrating photocatalysis and thermocatalysis in one system to drive FTS reaction in this dissertation.FTS performance under different reaction conditions over a series of self-prepared photothermal bifunctional catalysts was carried out to explore the feature and advantages of photothermal catalytic system,and then the correlation between the catalyst structure and catalytic performance was also discussed.The main results are listed as follows:?1?By selecting Ru with superior catalytic performance and high stability in conventional thermocatalytic FTS as active component,and TiO₂,ZnO,SiO₂ and SiC with considerably different intrinsic photo-responsibility as supports,we prepared a series of catalysts with different photo-responsive properties and then investigated their FTS performance under photothermocatalytic?UV and visible irradiation?and thermocatalytic condition respectively.The results showed that whether the catalyst can be excited by photoradiation is a prerequisite for the photothermal reaction,and the photothermal performance of the catalyst is closely related to the light absorption range and intensity of the catalyst.For photo-inert Ru/Si O₂ catalyst,the introduction of illumination had negligible effect on reaction performance;for UV-responsive Ru/TiO₂ and Ru/ZnO,the introduction of UV illumination apparently enhanced CO conversion and promoted the production of CO₂ and light paraffin,but visible illumination had no effect on their activity and selectivity;for Ru/SiC with both UV and visible light response,both UV and visible radiation affected catalytic activity and product selectivity,the change rule of which was consistent with that of Ru/Ti O₂and Ru/ZnO catalysts under UV photothermal conditions.Among these catalysts,Ru/TiO₂ possesed strongest UV light-absorption capacity and the effect of UV irradiation on performance of the catalyst is the most obvious.Especially,the CO conversion increased from 24.6%to 48.7%,the CO₂ selectivity increased from 2.6%to 7.2%,and the CH₄ selectivity increased from 15.6%to 20.0%.For the paraffin/olefin distribution in C₂-C₄,the ratio of paraffin increased from 54.3%to90.8%,correspondingly,and olefin decreased from 45.7%to 9.2%with the introduction of UV illumination.?2?The UV-responsive Co/TNT catalyst was prepared by loading thermal active component cobalt on one-dimensional tubular TiO₂ and their photothermocatalytic FTS performance was tested.The results show that CO conversion was obviously enhanced under ultraviolet illumination.Meanwhile,the product distribution also changed,including the decrease in CO₂ selectivity and the increase in light paraffin selectivity.Further studies showed that the promotion of CO conversion could be attributed to the transfer of photogenerated electron from TiO₂ semiconductor surface to metallic cobalt,while the change in product distribution was caused by both photochemical reaction and photocatalytic reaction.?3?A series of dual-support supported cobalt catalysts with different TiO₂contents?0%,5%,10%and 15%?were prepared using Al₂O₃ and TiO₂ composites as carriers and their FTS performance under photothermal and thermal conditions were studied.The results showed that TiO₂ component with less content is the decisive factor to stimulate the photocatalytic reaction.The introduction of UV illumination in this system also greatly increased the CO conversion,decreased CO₂ selectivity,and promoted the production of lower molecular weight paraffin.When the TiO₂ content is 5%,the promotion of CO conversion by UV illumination is the most obvious,reaching 68.8%.?4?On the basis of that the metal Cu can generate strong localized electromagnetic field and free electron under visible light excitation,three photothermal catalysts including Ru/Cu,Co/Cu-GO and Fe-Cu were designed and synthesized,and their photothermocatalytic FTS was conducted to improve the catalytic performance of traditional Ru,Co,and Fe catalysts.The results showed that although Cu can maintain the original metallic state during the reaction,the SPR copper-based photocatalytic material did not achieve the desired catalytic performance in FTS.The reason was analyzed and it is supposed that the photocatalytic activity of SPR metal copper can not be effectively exerted under high temperature and high pressure reaction conditions in FTS mainly owing to weaker light absorption ability and larger size of copper particles.