Hydrodeoxygenation of stearic acid on bimetallic Ni_xCu_1-x catalysts supported on ZrO₂

Several combinations of metals (mainly transition and noble metals) and the support (SiO₂, ZrO₂)^[1a] depending from the actual substrate (e.g. long chain fatty acids) have been presented already in the literature for hydrogenation/hydrodeoxygenation (HDO) reaction.^[1b] Hydrodeoxygenation of stearic acid (as a model compound of algae oil) to n-heptadecane on Ni/ZrO₂ proceeds via hydrodeoxygenation of stearic acid to 1-octadecanal with subsequent decarbonylation of the aldehyde to n-heptadecane (Figure 1). Within our study, we have investigated the impact of Cu on Ni/ZrO₂ based catalysts. It has been observed that the addition of Cu to Ni/ZrO₂ enhanced the total reaction rate. Cu/ZrO₂ was more active for the hydrodeoxygenation of stearic acid to aldehyde than Ni/ZrO₂. Decarbonylation of 1-octadecanal, which is in equilibrium with 1-octadecanol proceeded, however, with a much higher rate on Ni_xCu_1-x/ZrO₂ than compared to Ni/ZrO₂. The combination of the higher hydrodeoxygenation rate of the acid to the aldehyde or alcohol and the high rate of elimination of water on Ni or Ni_xCu_1-x lead to the superior properties of the new catalyst.