Direct Synthesis of Isoparaffin-rich Gasoline from Syngas

Isoparaffins are preferred components of high-quality gasoline because they are much more environmentally friendly as octane number contributors than olefins or aromatics. We report here an unprecedentedly high ratio of isoparaffins/normal paraffins (iso/n-paraffin ratio) of 48 in the one-step synthesis of gasoline-range hydrocarbons from syngas, enabled by a ZnAlOx-SAPO-11 composite catalyst. Infrared characterization of SAPO-11 upon the adsorption of 2,6-DTBPy and a cracking reaction of 1,3,5-TIPB demonstrate that the iso/n-paraffin ratio is almost linearly correlated with the concentration of external acid sites and the sites located near the pore mouths. In particular, the formation of multi-branched isomers, which generally exhibit a higher octane number, is significantly facilitated. A 150 h time-on-stream test indicates rather stable activity in syngas-to-gasoline. These findings provide a general approach for tuning the gasoline quality by modulating the acid site distribution of zeolites (zeotypes), that is, the concentration of external acid sites.