The comparison of Co, Ni, Mo, CoMo and NiMo sulfided catalysts in rapeseed oil hydrodeoxygenation

Abstract

The Al₂O₃ supported monometallic Co, Ni and Mo and bimetallic CoMo and NiMo catalysts were compared in rapeseed oil hydrodeoxygenation (HDO) reaction after in situ sulfidation. The reaction was described by five pseudo-first order rate constants (k ₁–k ₅) for the simplified reaction scheme: triglycerides (Tgs) to octadecane (k ₁); Tgs to oxygenates (Oxs; i.e., sum of fatty acids, fatty alcohols, and esters of fatty acids and fatty alcohols) (k ₂); Tgs to heptadecane (k ₃); Oxs to octadecane (k ₄), and Oxs to heptadecane (k ₅). The empirical pseudo-first order rate constant of the hydrocarbons (Hcs) product formation (k _Hc ) increased in the order Ni/Al₂O₃ ~ Co/Al₂O₃ < CoMo/Al₂O₃ ~ Mo/Al₂O₃ ≪ NiMo/Al₂O₃ showing hence a significant synergy between Ni and Mo. All monometallic catalysts exhibited k ₁ and k ₃ practically zero and the reaction proceeded essentially through the formation of the oxygenated reaction intermediates (high k ₂). The Co/Al₂O₃ and Ni/Al₂O₃ catalyzed selectively hydrodecarboxylation (HDC) of fatty acids (high k ₅). Over Mo/Al₂O₃, the HDO pathway, however, was nearly the exclusive one (high k₄). CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts yielded both HDO and HDC products suggesting partial synergy in the relative selectivity HDO/HDC between Co(Ni) and Mo.