Elucidation of reaction network of higher alcohol synthesis over modified FT catalysts by probe molecule experiments

Abstract

The reaction network of higher alcohol synthesis over a CuFe/ZrO₂ modified FT catalyst was investigated by the probe molecule technique, and the influence of various probe molecules (alkane, alcohol, aldehyde and olefin) on the catalytic performance was evaluated in detail. Alcohol selectivity and CO conversion remained almost constant when alkane was used as the probe molecule. However, the products shifted to higher carbon number significantly due to the alleviation of the retention of heavy products by the extraction of the added alkane. When alcohol was introduced into the reaction system, a considerable amount of esters with unique structures was formed with the formula RCO₂R′, where R′ is the alkyl group from the added alcohol, and such esters followed ASF distribution with a similar chain propagation factor to that of the corresponding higher alcohols. With the addition of aldehyde as the probe molecule, most of the added aldehyde was directly hydrogenated to the corresponding alcohol, but a considerable amount of esters was also detected in the reaction products, which could be attributed to the reaction between the surface acyls adsorbed from the introduced aldehyde molecules and the alcohols synthesized by syngas. The added 1-olefins were directly hydrogenated to the corresponding paraffins, incorporated into the growing carbon chain to form higher products or transformed into alcohols with one more carbon number by CO insertion reaction. Based on these results, the catalytic mechanism and reaction network of higher alcohol synthesis over a modified FT catalyst were discussed.