Study On Catalysts For Direct Hydrogenation Of CO ₂ To Light Olefins

Since the industrial revolution,the excessive use of fossil fuels has led to the continuous increase of carbon dioxide content in the atmosphere.The requirements of carbon neutrality and carbon dioxide emissions peak are imminent,and the transformation and utilization of carbon dioxide has become a hot spot,which has attracted the attention of all countries in the world.In this paper,Fe-based catalyst was used to catalyze the synthesis of low-carbon olefins by hydrogenation of CO₂,and the effects of reaction space velocity,pressure and temperature on the reaction performance of the catalyst were investigated.The effects of Fe content in the main catalyst,alkali metals,alkaline earth metals and rare earth metals as promoters on the reaction performance of the catalyst were studied.The effects of the content of Na,K and S as promoters on the catalyst were investigated.Finally,the catalyst with excellent performance was obtained,and its catalytic performance was evaluated for a long time.It was found that when the concentration of carrier promoter was10wt%,the catalyst calcined at high temperature had a bimodal structure with both large and small pores,and the macroporous structure could accommodate more carbon deposits generated during the reaction,thus making the catalyst have better performance.The space velocity of the reaction will affect the contact time of the raw catalyst,thus affecting the conversion of carbon dioxide and the selectivity of low-carbon olefins.The most suitable space velocity is 3000 h^-1and the pressure is 2 MPa.With the increase of temperature,the conversion of carbon dioxide and the selectivity of low-carbon olefins tend to increase.However,too high temperature will promote the RWGS reaction and produce more H₂O,which will affect the catalytic performance of the Fe active phase in the catalyst.The most suitable reaction temperature is 380℃.The experimental results show that Na and K promoters show excellent catalytic performance,and the addition of Na and K promoters can significantly change the conversion rate of CO₂,but compared with Na as promoter,adding K promoter can obtain higher selectivity of low-carbon olefins,and the most suitable mass ratio of K to Fe is 1.2.The addition of S is helpful to inhibit CO adsorption and promote H₂adsorption.With the addition of S,the selectivity of low-carbon olefins was improved when the conversion of CO₂decreased slightly,and the optimum mass ratio of S to Fe was 0.02.