Unusually High Selectivity to C₂₊ Alcohols on Bimetallic CoFe Catalysts During CO Hydrogenation

Abstract

Silica-supported cobalt and iron catalysts (10% Co and 5% or 1% Fe) were prepared and tested in a flow reactor in the hydrogenation of CO, using H₂/CO = 2:1 (molar) ratio in the feed, an overall pressure of 20 bar, and temperatures of 493, 513 and 533 K. Activity and product distribution were found to depend strongly on the composition of the catalysts. Thus, the Fe-free catalyst was selective toward C₅₊ formation (67% selectivity to C₅₊) and a low methanation rate, while the Co-free counterpart was less selective toward C₅₊, with a simultaneous increase in the formation of lighter fractions and alcohols. The behavior of the bimetallic CoFe catalysts was different. In the bimetallic CoFe10/5-c catalyst, selectivity to alcohols increased with respect to the monometallic Co10-c, and this was moderately high (15% to C₃₊ OH alcohols). In the bimetallic CoFe10/1-c sample, selectivity to alcohols was fairly high (29%), and ethanol reached the highest proportion (17%) among the alcohols. Surface and structural information concerning the activated catalysts, derived from X-ray diffraction, temperature-programmed reduction, Mössbauer, and photoelectron spectroscopy, revealed the appearance of a CoFe phase under the conditions employed during the catalyst activation. In the bimetallic cobalt–iron catalysts, this CoFe phase is suggested to be responsible for the rather high selectivity toward alcohol formation.