Controlling partial and deep hydrogenation of naphthalene over supported metal phosphides: kinetic and DFT insights into Ni2P/Al2O3 and MoP/Al2O3

Selective hydrogenation of polycyclic aromatic hydrocarbons is vital for fuel upgrading and hydrogen-donor solvent synthesis, whereas precise regulation between partial and deep hydrogenation pathways remains a long-standing challenge. Herein, Al 2 O 3 -supported Ni 2 P and MoP catalysts with identical nominal loading were fabricated via a spatially confined phosphorization route and comparatively investigated for naphthalene hydrogenation. Under identical conditions (320 °C, 4 MPa H 2 ), Ni 2 P /Al 2 O 3 preferentially catalyzed deep hydrogenation: it delivered 92.8 % naphthalene conversion with 89.7 % selectivity toward decalin. By contrast, MoP/Al 2 O 3 dominated partial saturation, affording 90.6 % naphthalene conversion and 94.9 % tetralin selectivity. Apparent kinetic measurements revealed close activation energies for initial naphthalene consumption over the two catalysts (61.16 and 65.36 kJ mol −1 , reflecting similar activity for the first-ring hydrogenation. Nevertheless, the activation energy for subsequent tetralin hydrogenation differed markedly, reaching 91.59 kJ mol −1 on MoP/Al 2 O 3 versus 66.44 kJ mol −1 on Ni 2 P/Al 2 O 3 . Consistently, DFT calculations confirmed similar energy barriers for naphthalene conversion to tetralin on Ni 2 P(0 0 1) and MoP(1 0 1), while MoP(1 0 1) possessed significantly elevated energy barriers for late-stage hydrogenation. Combined experimental and theoretical evidence identifies secondary hydrogenation of tetralin as the selectivity-determining step. This work offers clear mechanistic insights into tuning the formation of tetralin and decalin over transition metal phosphide catalysts.