Catalytic deoxygenation of fatty acids via ketonization and α-carbon scissions over layered alkali titanate catalysts under N2

Abstract

The ketonization of fatty acid with subsequent McLafferty rearrangement of the fatty ketone allows the deoxygenation to hydrocarbons. Here, we report the cascade reaction of palmitic acid (C₁₆) to hydrocarbons (≤C₁₄) over lepidocrocite-type alkali titanate K_0.8Zn_0.4Ti_1.6O₄, K_0.8Mg_0.4Ti_1.6O₄, and K_0.8Li_0.27Ti_1.73O₄ and the reassembled TiO₂ catalysts at ≤400 °C under atmospheric N₂ in a continuous fixed-bed flow reactor. The C₁₆ acid is coupled to C₃₁ ketone prior to the scissions mostly to a C₁₇ methyl ketone and C₁₄ hydrocarbons (i.e., the McLafferty rearrangement). The hydrocarbons yield increases with temperature and is proportional to partial charge at the O atom, suggesting that basic sites are responsible for C₃₁ ketone scissions. The layered alkali titanate catalysts with two-dimensional (2D) space inhibit diffusion of the ketone primarily formed and promote its scissions to hydrocarbons within the confined space. Otherwise, low hydrocarbons yield (but high ketone yield) is obtained over TiO₂ and the Mg/Al mixed oxide catalysts possessing no interlayer space. Meanwhile, the semi-batch experiment with pre-intercalated palmitic acid favors a direct deoxygenation, demonstrating the essential role of reaction mode toward ketone scission reaction pathway. Over K_0.8Li_0.27Ti_1.73O₄, the complete palmitic acid conversion leads to ∼47% hydrocarbons yield, equivalent to ∼80% reduction of the oxygen content in the feed under N₂.