Conversion of polycyclic aromatic hydrocarbons into key monoaromatic hydrocarbons through partial hydrogenation and ring-opening using MoOx-loaded beta zeolite catalyst

Abstract

This study demonstrates an efficient method for converting polycyclic aromatic hydrocarbons (PAHs) into key monoaromatic hydrocarbons (BTEX: benzene, toluene, ethylbenzene, and xylenes) via partial hydrogenation and ring-opening reactions using MoO_x nanocluster-loaded beta zeolite catalysts. The catalysts were prepared with various Mo loadings (1–20 wt%) and characterized by XRD, HAADF-STEM, N₂ adsorption, FTIR, NH₃ IRMS-TPD, and XAFS to elucidate Mo dispersion, oxidation states, and acid properties. At optimal Mo loading (10 wt%), MoO_x nanoclusters located mainly on external defect sites synergistically interacted with Brønsted acid sites on beta zeolite, activating H₂ molecules and promoting selective BTEX formation in tetralin conversion while suppressing side reactions such as ring contraction to methylindane and dehydrogenation to naphthalene. Conversion of 1-methylnaphthalene, naphthalene, and phenanthrene under high H₂ pressures revealed that MoO_x nanoclusters facilitated partial hydrogenation to tetralin derivatives, followed by mainly acid-catalyzed ring opening to BTEX. The higher BTEX yield from a mixture of 1-methylnaphthalene and naphthalene achieved 52.8 C-mol%. Although phenanthrene conversion was less efficient due to hydrogenation limitations, the results suggest the potential of MoO_x/beta zeolite as a non-precious-metal catalyst system for PAH valorization. This work provides the first detailed structural–activity relationship for MoO_x/beta zeolite catalysts in high-yield BTEX production from PAHs.