One-pot solvent-free sequential synthesis of high-density polycycloalkanes fuels from lignin-derivatives over laminated NbOPO₄ catalyst

Upgrading lignocellulose biomass to renewable fuels is essential to achieve carbon neutrality. However, the multiple synthetic, and purification steps as well as the employment of solvents in the production of renewable fuel inhibit the overall yields and cause the waste of energy and resources. Herein, a new catalytic strategy for one-pot solvent-free sequential synthesis (OSS) of perhydrofluorene and dicyclohexylmethane was developed from lignin-derivatives. A two-dimensional layered nanosheet niobium phosphate (NbOPO4-IB) catalyst was fabricated to efficiently integrate the alkylation of phenol and benzyl alcohol and sequential hydrodeoxygenation with a cocatalyst of Ru/C. The high crystalline NbOPO4 phase and the lamellar morphology contributes to the large specific surface area to expose more active sites, especially more Bronsted acid sites. The NbOPO4-IB catalyst with a suitable Bronsted/Lewis acid ratio of 1.49 favors the selectivity of fuel precursors benzyl phenol in the alkylation and also provides the appropriate acid strength to promote hydrodeoxygenation activity. NbOPO4IB also shows good reusability. Excessive phenol plays a vital role in promoting the alkylation reaction by dissolving the intermediates, and then into cyclohexane to enhance the H2 dissolution in the hydrodeoxygenation. A possible mechanism of OSS from lignin-derivatives into polycycloalkanes over the cocatalysts was proposed.