Enhanced formation of multi-branched isoparaffins in syngas conversion by ZnCrOx-MCM-22 composites

Direct syngas conversion to gasoline-range hydrocarbons particularly environmental-friendly, high octane number multi-branched isoparaffins attracts wide attention from both academia and industry but remains challenging. We report herein that ZnCrOx-HMCM-22 upon phosphorus modification enables selective syngas conversion to gasoline (C-5-C-11) with a selectivity of 77%. Following a simple hydrogenation in the same reactor, the fraction of isoparaffins among gasoline reaches 67%, particularly multi-branched isoparaffins as high as 27.5%, which is three times higher than that obtained by FTS-zeolites and four times higher than that in commercial 92# gasoline. This is attributed to the inhibited hydrogenation of olefins over the acid sites of phosphorus modified MCM-22 with weakened strength. Thus, methylation of olefins is significantly facilitated leading to formation of multi-branched isohydrocarbons. The fundamental understanding gained here will allow further optimization and development of catalysts for direct syngas conversion to high-quality gasoline.