Hydrodeoxygenation of stearic acid to produce green diesel over alumina supported CoMo catalysts: Role of Co/Mo mole ratio

Abstract

Alumina-supported CoMo catalyst is a potential alternative to the precious metal-based counterpart for hydrodeoxygenation (HDO) of stearic acid to diesel-range hydrocarbons. The mole ratio of individual metals in bimetallic catalysts plays a vital role in forming various catalytically active species. This study thus elucidates the impact of the Co/Mo mole ratio on the efficacy of CoMo catalysts. The CoMo catalysts showed superior catalytic activity compared to the Co due to the synergistic interaction and CoMo alloy formation. The Mo, Co, and mixed metal oxide were observed in calcined CoMo catalysts. For 4.1 mmol metals per g of alumina, Mo and Co oxides were increased with increasing Mo and Co content, respectively. However, CoMoO₄ was increased by increasing Mo loading up to 2.4 mmol. Conversely, the reduced CoMo catalysts were gradually enriched with CoMo alloy with increasing Co content up to 2.4 mmol and slightly declined at 3.1 mmol Co. The reaction follows the HDO mechanism over CoMo alloy and Co oxide resulting in C₁₈ hydrocarbon formation. The CoMo catalysts displayed enhanced catalytic performance at elevated temperatures and metal loadings, with insignificant effect on the alkane selectivity. The experimental results were also correlated by a suitable kinetic model.