Impact of Copper on an Alkali Promoted Iron Fischer–Tropsch Catalyst

Abstract

Copper has traditionally been added to precipitated iron Fischer–Tropsch (FT) catalysts to facilitate reduction of Fe₂O₃ to zero valent iron during activation [M.E. Dry, in: J.R. Anderson and M. Boudart (eds), Catalysis Science and Technology, Vol. 1 (Springer-Verlag, New York, 1981) p. 179] by lowering the reduction temperature when activating with hydrogen, carbon monoxide or syngas [R.J. O'Brien et al., Catal. Today 36 (1997) 325]. This is particularly important when activating with hydrogen because metallic iron which is formed will sinter easily if the temperature is too high; however, it is not as critical when activating with carbon monoxide or syngas because iron carbides are formed and they are not as susceptible to sintering. The effect of copper on activity and selectivity has not been studied as thoroughly as its effect on catalyst activation. Kölbel reported that copper loadings less than 0.1% (weight % relative to iron) were sufficient to produce an active catalyst and that increased copper loading had no effect on FT activity [H. Kölbel and M. Ralek, Catal. Rev. Sci. Eng. 21 (1980) 225]. It has previously been shown that copper increases the activity of precipitated iron catalysts when operating at low temperature (<250°C) [2]. Bukur and Mukesh have reported that copper increases FT activity and water gas shift activity [D.B. Bukur et al., Ind. Eng. Chem. Res. 29 (1990) 194]. In addition, they reported that copper increased the average molecular weight of the product and increased hydrogenation of alkenes and isomerization of 1-alkenes. Soled et al., have reported that promotion with copper in conjunction with potassium increased FT activity but had little effect on alkene selectivity [S.L. Soled et al., Top. Catal. 2 (1995) 193]. Water gas shift activity and FT selectivity have been shown to depend on syngas conversion [A.P. Raje and B.H. Davis, Catal. Today 36 (1997) 335]. To determine the true impact of copper on FT selectivity and water gas shift activity comparisons should be done at similar conversion. No such study has been reported for the effects of copper. Herein are reported the effects of copper on FT activity and selectivity and water gas shift activity over a wide range of syngas conversions.