Preparation and optimization of mixed iron cobalt oxide catalysts for conversion of synthesis gas to light olefins

摘要

Iron cobalt oxides were prepared using co-precipitation procedure and studied for the conversion of synthesis gas to light olefins.In particular,the effect of a range of preparation variables such as the precipitate ageing time and [Fe]/[Co] molar ratio of the precipitation solution were investigated in detail.The preparation procedure and also the optimum preparation conditions were identified with respect to the catalyst activity for the hydrogenation of carbon monoxide.The results are interpreted in terms of the structure of the active catalyst and it has been generally concluded that the catalyst containing 40% Fe/60% Co -on molar basis -and aged for 2 h,is the most active catalyst for the conversion of synthesis gas to ethylene and propylene.The effect of different promoters and supports along with loadings of optimum support and promoter on the activity and selectivity of this catalyst are studied.It was found that the catalyst containing 40% Fe/60% Co/15 wt.% SiO_2/1.5 wt.% K is an optimum modified catalyst and gave the best activity and selectivity.The activity and selectivity of all prepared catalysts have been studied in a fixed bed micro reactor in a range of reactor temperatures using synthesis gas with different H_2/CO molar feed ratios.The lifetime of optimum catalyst for 72 h has been tested under the optimum reaction conditions and the catalyst was found to be highly stable.Characterization of both precursors and calcined catalysts by X-ray diffraction and scanning electron microscopy showed that the precipitate ageing time and also the [Fe]/[Co] ratio of the precipitation solution influenced the catalyst precursor structure and morphology.