Design,Preparation And Performance Of High-efficiency Photothermal Catalyst For Fischer-tropsch Synthesis

Fischer-Tropsch synthesis is a reaction to convert syngas?CO and H₂?into multi-carbon organic compounds under high temperature and high pressure.However,the catalytic products exhibit a wide distribution of carbon atoms,low selectivity and a high proportion of methane.The photothermocatalytic reaction provides an approach that the photothermal catalyst directly converts the ultraviolet,visible and infrared parts in the sunlight to thermal energy,which makes the catalyst heat itself and thereby induce the catalytic reaction.Although the investigation of photothermal catalysis is still at a early stage,compared with the conventional photocatalysis and thermocatalysis,it has exhibited excellent advantages in the reactivity and selectivity.In this thesis,the Fe-based catalysts is designed and synthesized to apply in the photothermocatalytic Fischer-Tropsch synthesis,which aims to lower the energy consumption and improve the selectivity for organic product.The main results and conclusions are as below.1.The Fe₂O₃ with alkali-mental electron assistant loading is designed as the initial catalyst that can serve in the Fischer-Tropsch synthesis under light irradiation and low pressure?55 kPa?.The effect of light-to-thermal conversion to supply thermal energy and the low reaction pressure can significantly reduce the energy consumption.The effect of alkali-mental electron assistant K⁺over catalyst surface on catalytic performance was studied in detail.The K⁺can suppress the activation of H over the active component of catalyst and thus is beneficial for the C-C coupling.The results indicate that,the proper loading amount of K⁺increased the proportion of the multi-carbon products obviously;however,overloading of K⁺caused rapid carbon deposition on the surface of the catalyst,which thereby strongly inhibited the activity of the catalyst and meanwhile remarkably increased the content of methane in the product.2.The photoactivation method is designed to control the phase transformation of Fe₂O₃,which can modulate the proportion and exposed facet of the active component of iron carbide and therefore enhance the selectivity for the multi-carbon products.Because the?-Fe₂O₃ and?-Fe₂O₃ as the initial catalysts exhibited excellent selectivity and activity,respectively,the photoactivation method and the reaction atmosphere in activation process were used to prepare different complex phases of?/?-Fe₂O₃,which is expected to realize an overall optimal of selectivity and activity.The results indicate that the modulation of complex phases of?/?-Fe₂O₃ could control the proportion and exposed facet of Fe5C2 active component formed in the reaction,and therefore,ensured a relatively high activity and meanwhile a significantly improved selectivity for multi-carbon products.An optimal sample achieved a high selectivity of 71.9%for light olefin?C₂⁼-C₄⁼alkenes?,which obviously exceeded the limitation of 57%in ASF distribution model;under this optimal selectivity,the conversion percentage of CO reached 28.8%.In the photothermal catalytic Fischer-Tropsch synthesis,for the first time,this thesis adopts the electronic assistant and the photoactivation method adjusting active component to significantly enhance the selectivity of multi-carbon products.The results herein demonstrate that the design and synthesis of high-efficient photothermal catalyst is one of the effective strategies to realize the low-energy-consumption,high-efficient,and high-selectivity Fischer-Tropsch synthesis.