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 K0.8Zn0.4Ti1.6O4, K0.8Mg0.4Ti1.6O4, and K0.8Li0.27Ti1.73O4 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 K0.8Li0.27Ti1.73O4, the complete palmitic acid conversion leads to ∼47% hydrocarbons yield, equivalent to ∼80% reduction of the oxygen content in the feed under N2.