Upgrading of palmitic acid to iso-alkanes over bi-functional Mo/ZSM-22 catalysts

Abstract

Bi-functional Mo/ZSM-22 catalysts were designed to upgrade palmitic acid and further to isomerize n-alkanes. Besides the effects on acidity, H⁺ cations might be beneficial for the distribution of MoO_x particles, the higher surface Mo/Si ratio and the greater surface Mo⁴⁺ content of bi-functional Mo/ZSM-22 catalysts. In the upgrading of palmitic acid, strong acid sites of catalysts were proven to favor hydrodecarbonylation (HDC), isomerization and cracking. Mo⁶⁺ (or MoO₃) preferred to support the HDC reaction, whereas Mo⁴⁺ (or MoO₂) suitably improved the hydrodeoxygenation (HDO) reaction without carbon atom loss. That is, the Mo⁴⁺/Mo⁶⁺ ratio of Mo/ZSM-22 catalysts significantly influenced HDO/HDC selectivity. More importantly the improvement in HDO rather than HDC with the complete conversion of palmitic acid, could significantly decrease the negative effects of strong acid sites (such as HDC and cracking) to facilitate isomerization of n-alkanes to afford more branched alkanes with a higher iso-alkanes/n-alkanes ratio.