Research And Application Of Layered Double Hydroxides In Syngas Conversion

Fischer-Tropsch synthesis(FTS),derived from syngas(CO and H2),is used to produce liquid fuels and other high value-added chemicals.Due to the broad source of raw materials and variety of products,FTS has attracted wide attention.Catalysts often deactivate due to strongly exothermic reaction.Therefore,the design and development of low-temperature and high-efficiency catalysts has always been a hot spot in FTS field.Because of compositional flexibility,small crystal size and high surface area,layered double hydroxides(LDHs),also known as hydrotalcites,are considered to be suitable supports or catalysts.Hence,it is of practical application prospects to introduce Co into the LDHs material and further prepare FTS catalyst.In this paper,Co was used as the active component,Co-Al LDHs were prepared and delaminated to single lamellas to applied in aqueous-phase FTS.At the beginning,it was investigated whether the lamellas of Co-Al LDHs can catalyze the syngas conversion.These catalysts performed higher activity and greater oxygenated product selectivity than conventional supported cobalt-based catalysts.The products of Co-Al LDHs in aqueous phase FTS,prepared by different alkali auxiliaries(hexamethylenetetramine and sodium carbonate)and metal salt sources(N03-and SO42-),were in comparison.It was found that the ammonium ions resulted in significant decrease in activity.The hydrogen-lean surface,caused by the ammonium ions coverage,increased the selectivity of acetaldehyde.The presence of nitrate ions increased the selectivity of acetonitrile.The in-situ Raman characterization was used to investigate the evolution of the catalyst active phase in the reaction.By the comparison of catalyst reaction products with carbon deposition or not,the significant difference in selectivity of the products proved that Co2C phase helps increase the selectivity to C2 oxygenates.The catalyst product components prepared by different copper contents were investigated,it was proved the effect of copper in selectivity of ethanol.When Cu/Co was equal to 6.63/100(wt),the selectivity of ethanol was the highest.The selectivity of the C2 oxygenates was minimized.