Compositional dependence of Co- and Mo-supported beta zeolite for selective one-step hydrotreatment of methyl palmitate to produce bio jet fuel range hydrocarbons

Abstract

For producing a drop-in bio jet fuel, one-step hydrotreatment, which includes deoxygenation, isomerization and cracking in one step, is essential to overcome the typical biofuel drawbacks due to high oxygen content, out of jet fuel range hydrocarbons, and low isomerization degree. Herein, Co- or/and Mo-supported Beta(25) zeolites with various Co/Mo ratios were prepared as transition metal-supported zeolite catalysts without the need for sulfidation of conventional transition metal catalysts. Based on the catalyst characterization, the Co/Mo ratio alters the metal phase with the appearance of CoMoO₄ and the altered Co metal phase strongly influences the acidic properties of Beta(25) by the formation of Lewis (L) acid sites with different strengths as Co₃O₄ and CoMoO₄ for strong and weak L acid sites, respectively. The catalytic activities were investigated for hydrotreatment of methyl palmitate as a biofuel model compound of fatty acid methyl esters. Primarily, Co is required for deoxygenation and Mo suppresses overcracking to enhance the yield of jet fuel range hydrocarbons. The Co/Mo ratio plays an important role to improve the C₈–C₁₆ selectivity by modifying the acidic properties to inhibit excessive cracking. Co₅Mo₁₀/Beta(25) achieved the best catalytic performance with the conversion of 94.2%, C₈–C₁₆ selectivity of 89.7 wt%, and high isomer ratio of 83.8% in organic liquid product. This unique modification of acidic properties will find use in the design of optimal transition metal-supported zeolite catalysts for selective one-step hydrotreatment to produce bio jet fuel range hydrocarbons.