Self-condensation of levulinic acid into bio-jet fuel precursors over acid zeolites: Elucidating the role of nature, strength and density of acid sites

The production of jet-fuel precursors from the aldol-dimerization of levulinic acid (LA) over acid zeolites is presented. Under solventless conditions, high LA conversion with selectivities to LA dimers > 90% are achieved. Chemisorption and spectroscopic analyses of the materials have revealed a cooperative effect between strong Bronsted (B-S) and strong Lewis (L-S) acid sites, which favors the selective formation of dimers. BEA structure is the most efficient owing to shape selectivity effect. H-Beta 19, having an optimum Bronsted to Lewis acid sites ratio and the adequate balance of B-S/L-S acid sites, displayed the best catalytic performance in terms of activity and selectivity to LA dimers. Under optimized reaction conditions H-Beta 19 achieved 79% LA conversion and > 98% selectivity. An analysis on the stability showed good reusability in consecutive reaction cycles. The small loss of activity, ascribed to the formation of organic deposits, can be reverted by calcination in air.