Study On Molybdenum-and Iron-Based Catalysts For CO₂ Hydrogenation

The environment was seriously affected by the continuously increased CO₂ emissions.A series of chemical processes for large-scale utilization of CO₂ have been studied for mitigating climate change.Among them,chemical products such as alcohols and hydrocarbons can be synthesized through the CO₂ hydrogenation process,which was of great significance in decreasing CO₂ emission to the atmosphere.Molybdenum carbide（Mo₂C）and Fe-based catalysts were active for CO₂ hydrogenation to alcohols or hydrocarbons.In this study,catalytic performance studies of CO₂hydrogenation over the Mo₂C-and Fe-based catalysts were conducted in fixed-bed reactor and autoclave,respectively.In addition,the physicochemical properties of Mo₂C-and Fe-based catalysts were analyzed through various characterization techniques.The results from this study prove that alcohol synthesis reactivity of Mo₂C-based catalysts was influenced byγ-Al₂O₃ as a carrier and different metals as promoters.Dispersion of Mo₂C can be effectively improved byγ-Al₂O₃.The reduction properties and CO₂ activation of Mo₂C-based catalysts were influenced by metallic promoters.Carbon chain growth activity was increased by Fe,while the CO₂ adsorption performance of Mo₂C-based catalysts was improved by alkali metal.The hydrogenation reactivity of Mo₂C was also moderately inhibited by alkali promoters.Effect of the molecular ratio of H₂ to CO₂ on the catalyst surface and the promotion effect of different metals were also investigated in this work.The alcohols synthesis results indicate that the best performance can be obtained after 50 h reaction likely due to the synergistic effect between promoter,active metal and the support.It was known that sintering was one of the main causes for the Fe catalyst deactivation in fixed-bed reactors due to high temperatures over300℃.Therefore,the relatively mild evaluation conditions for CO₂hydrogenation to hydrocarbons were carried out in autoclave.Effect of different promoters such as transition metals like Co,Ni and Cu,as well as alkali metals like Li,Na,K and Cs on the catalytic performance of CO₂hydrogenation to hydrocarbons were studied over the supported Fe-based catalyst.In addition,reaction conditions such as catalyst loading and reaction time on catalytic reactivity were also systematically investigated.The dispersion of active components was enhanced by different metal promoters,and the CO₂ adsorption and activation ability of the catalyst were thus improved,which affect the catalytic performance significantly.The catalysts promoted by both Co and K simultaneously yield the best activity for CO₂ hydrogenation to hydrocarbons.This study can potentially provide a potentially feasible theoretical ideas for catalyst designing of the CO₂ hydrogenation reactions.