The Study Of Fe@C Catalysts For Alcohol Synthesis From CO₂ Hydrogenation

The goal of"carbon neutrality"and"peak carbon emissions"has brought the use of carbon dioxide（CO₂）into focus again.Catalytic conversion of CO₂ to alcohols and other high value-added chemicals via hydrogenation reaction was an effective way to improve carbon efficiency.The development of high efficiency nano-catalyst is the key factor in this important process.Due to the excellent activity in reverse water gas shift reaction and strong C-C coupling capacity,Fe-based catalysts are often used to catalyze CO₂ hydrogenation to olefin or oxide.In addition,Fe species can be used as promoter to increase the selectivity of long chain alcohols for Cu and In based catalysts in CO₂hydrogenation reaction.On Fe-based catalysts,CO₂ is firstly converted into CO via reverse water gas shift reaction;and oxygenates products were produced via Fischer-Tropsch synthesis process.However,Fe species are often carbonized into different types of iron carbide during the reaction process,which brings great difficulties to the study of the structure-activity relationship of catalysts.Therefore,clarifying the properties of various iron carbide species in CO₂ reaction process is of great significance to understand the structure-activity relationship of multi-component catalysts containing Fe species.In this thesis,Fe₃C@C catalyst precursor was prepared by melting method,different kinds of iron carbide species were obtained by changing the pretreatment conditions of this catalyst precursor,and their CO₂ hydrogenation performance were investigated.In order to further improve the selectivity of low carbon alcohols,Cu and In were added as promoters,and their effects on the performance of catalysts were also investigated.The detailed work is shown as follows:1.Fe@C catalyst was firstly prepared by melting method,and the iron carbide phase of the catalyst was modified by controlling pretreatment conditions.It is found thatθ-Fe₃C phase has higher CO₂ hydrogenation activity and lower methane selectivity.Besides,θ-Fe₃C is very stable in the reaction process.Andε-Fe₂C has high methanol yield together with high selectivity of methane.The activity and methanol selectivity on χ-Fe₅C₂ phase were relatively low,while its methane selectivity was high.2.xCu55Fe@C and 1In55Fe@C catalysts were synthesized by melting method,and the 20%Cu/55Fe@C catalyst was prepared by melting-impregnation method,in this sample,the 20 wt.%Cu was loaded by impregnation method.Characterization results showed that Cu could effectively promote the reduction of Fe@C catalyst.After280℃,the catalytic activity of 10Cu55Fe@C was higher than that 1Cu55Fe@C,and under the conditions of 300℃,2 MPa,the STY（Space Time Yield）value of methanol on 10Cu55Fe@C catalyst was apparently higher(123.1μmol/g_cat/h).The catalyst impregnated with Cu has the same problem as the x Cu55Fe@C catalyst prepared by melting method,the carbon dioxide conversions were low.However,the STY of methanol on 20%Cu/55Fe@C catalyst(194.6μmol/g_cat/h)was higher than x Cu55Fe@C catalysts.As to 1In55Fe@C and 1Cu55Fe@C catalysts,their catalytic activities were both lower,but the STY of methanol was high(313.6μmol/g_cat/h).