La, Mn and Zn promoted microporous iron catalysts with high productivity and stability for Fischer-Tropsch synthesis

Abstract

Fischer-Tropsch synthesis is studied over precipitated Fe catalysts promoted with Mn, Zn and La metals. The results showed that there was a large increase in surface area and pore volume, and a sharp decrease in average pore size upon the addition of promoters. Catalyst productivity and rate of syngas converted as well as hydrocarbon yield increased with addition of promoters to Fe structure during precipitation step. Addition of metal promoters led catalyst samples of microporous structures with relatively high surface areas. This effect probably yielded catalysts with enhanced long-term activity and stability. Samples containing 10 % Zn and 5 % Mn exhibited the highest catalytic activity and stability. Increasing the loading of Zn from 5 to 10 wt% led to a noteworthy increase on yield and productivity as well as rate of syngas converted. The highest productivity was obtained for the sample containing 10 % Zn, highest yield was attained over the sample containing 5 % Mn. The results indicate that the selectivity to C-12-C-18 range was more pronounced for the catalyst promoted with Mn metal whereas alpha-olefins and higher molecular weight products were increased with the addition of 5 % Zn over Fe based catalysts. The decrease in temperature from 523 to 493 K resulted in an increase in heavy hydrocarbons and a significant decrease in gaseous and light hydrocarbons for Fe4Si5Mn catalyst.