Study On W_xC Supported Rh-Based Catalysts For Synthesis Of Oxygenates From Syngas

Syngas(CO/H2)catalytic conversion to produce clean liquid fuels and high value-added chemicals is an important process for the conversion and utilization of carbon-based energy and resources,including coal-based.Among them,the synthesis of oxygen-containing compounds from syngas,which retains the oxygen atoms of CO in the product,has higher atomic efficiency.Moreover,oxygenates can be used in many fields,which are of great significance to alleviate China’s crude oil shortage and ensure energy security,and are currently the most promising alternatives of petroleum-based fuels.In the study,it has been found that the catalysts for the one-step synthesis of oxygenates from syngas generally have low activity and poor selectivity,and the inevitable catalyst deactivation caused by metal sintering and carbon deposition.To get deeper insights into the two key scientific issues about activity and stability of the catalysts,we choose CO hydrogenation into high alcohols(HAs)as the target reaction.A series of Rh/WxC@CS(CS stands for carbon spheres)with different phase compositions by controlling the extent of carburization and RhFe-WxC@C/CNTs(CNTs stands for carbon nanotubes)will be synthesized.On the one hand,transition-metal carbides(TMCs)possess the strong metal-support interaction and the cleavage of C-O bond assisted by hydrogen.On the other hand,anchoring effects are induced by the defect-rich CNTs.Furthermore,amorphous carbon produced by carburization exert limitation and anchoring of WxC nanoparticles(NPs)and provide carbon source for the loss of carbon from WxC NPs under the reaction conditions.The optimal conditions of carbonrization was set as 850℃ for 3 h under 5%H2/N2 through the reactivity of syngas to higher alcohols synthesis.For the RhFe-WxC@C/CNTs,the optimal contents of WxC and Fe were 10 wt%and 5 wt%,respectively.After reduction at 300℃ it showed the best catalytic performance under the reaction conditions of T=220℃,P=2.0 MPa,GHSV=4000 mL/(g·h),n(H2)/n(CO)=2:1.The conversion rate of CO is 10.7%,the selectivity of hydrocarbons,C2+-OH and CO2 are 45.9%,25.5%,and 0.6%successively.Under the best reaction conditions,the RhFe-WxC@C/CNTs catalyst exhibited excellent durability at 100 h,except for a short induction period during the first 20 h.So,it demonstrated the superior long-term stability.Throuth the structure-performance corrections,it was found that the W2C phase is closely related to the formation of oxygenates;the introduction of the transition metal tungsten carbide enhances the interaction between the metal and the carrier,which is beneficial to obtain highly dispersed active centers and effectively avoid the catalyst sintering;carbon nanotubes can further disperse and rivet active centers;the addition of Fe is beneficial to obtain a higher molar fraction of Rh+.The RhFe-WxC@C/CNTs catalyst has better performance.The above promotion mechanism are conducive to the improvement of the activity,selectivity and stability in the target reaction of syngas to oxygenates synthesis...