Study On The Effects Of Pyrolysis Temperature And Reduction Atmosphere On The Iron-based MOFs Mediated Catalysts For Fischer-Tropsch Synthesis

It is the key point to improve C₅₊selectivity in Fischer-Tropsch synthesis(FTS)process since the products are widely distributed.For traditional catalysts,high selectivity is often at the expense of reduced CO conversion rate.Therefore,it is of great significance to improve C₅₊selectivity without reducing CO conversion rate.For this purpose,new kinds of catalysts are expected to be studied.In this paper,the Fe@C catalysts were successfully synthesized through direct pyrolysis of Fe-MIL-88B with MOFs structure at high temperature over 600 ^oC.Upon pyrolysis,transformation from needle-like precursor to highly porous sponge shaped crystals were observed.As a result,the reduced catalysts show high Fe species dispersion coupled at very high Fe loading from 62%to 66%.Furthermore,temperature effects(600,700&800 ^oC)on textural properties and FTS performance were studied.The catalyst Fe@C-F-800 being pyrolyzed at 800 ^oC achieved an exceptionally high C₅₊hydrocarbon selectivity near 90%with high reaction stability.Meanwhile,catalyst Fe@C-F-700 showed high CO conversion among catalysts that can be credited to the presence of Fe₅C₂ carbide phase which is a known active phase for FTS system.Conversely,we managed to reduce methane selectivity to extremely low value i.e.2.44%.So,this approach strongly demonstrate that the MOFs derived Fe-based catalysts are potential for high C₅₊selectivity toward FTS without successive reduction of CO conversion.Catalyst activation is an important and influencing step while determining FTS activity.Taking into account the crucialness of how reduction atmosphere effects the FTS product selectivity,stability,catalytic activity,textural and morphological properties,MOFs mediated Fe-based catalyst(Fe@C)reduced under five different reduction atmospheres i.e.R-1(pure CO),R-2(H₂/CO=1/4),R-3(H₂/CO=1/2),R-4(H₂/CO=4)and R-5(pure hydrogen)and then tested under several characterization(SEM,TEM,PXRD,N₂ physisorption,Raman and TG)to unravel the facts behind differently reduced catalysts and how they take part in FTS catalytic reaction.However,R-1 seen to give highest catalytic activity among all other catalysts while other yielded more stable reaction coupled to low activity.Furthermore,experiments were performed to prepare highly uniform MOFs derived Iron-based catalysts by simply adding a surfactant(PVP)that were up to the expectation as analyzed by SEM but further we tested its activity that was not satisfactory.Moreover,higher BET surface area of principle precursor estimated from N2 physisorption,decreased upon increasing PVP amount during precursor synthesis that suggest the decreased FTS activity might be due to plummeted surface area.