Hydrodeoxygenation of Methyl Heptanoate over Noble Metal Catalysts: Catalyst Screening and Reaction Network

Hydrodeoxygenation (HDO) of methyl heptanoate was performed over zirconia-supported mono- and bimetallic Rh and Pt catalysts in a batch reactor. The Rh/ZrO₂ catalyst gave the highest conversion and selectivity toward hydrocarbons (dominantly hexane) at 250 °C and 8 MPa of H₂. The formation of alkenes was not detected due to high hydrogenation activity of the noble metal catalysts. Furthermore, a complete reaction network for the HDO of methyl heptanoate over Rh/ZrO₂ was proposed on the basis of the HDO experiments with reaction intermediates, such as heptanoic acid, heptanal, and heptanol. It was proposed that heptanoic acid originated from the direct hydrogenolysis of methyl heptanoate. The prevailing reaction pathway to hexane was suggested to be decarbonylation reaction from either heptanoic acid or heptanal. Heptanal was highly reactive on Rh catalyst in the presence of H₂. The effect of reaction temperature on the HDO of methyl heptanoate over Rh/ZrO₂ was also investigated. Increasing temperature significantly improved the conversion of methyl heptanoate and the selectivity toward hydrocarbons.