Efficient catalytic hydroconversion of phenolic-rich aromatic compounds from the extraction of coal tar residue to cyclanes over a β/M composite zeolite-supported Ni nanoparticles

Abstract

The separation of condensed aromatic compounds from coal tar residue (CTR), converted into cyclanes via catalytic hydroconversion (CHC) to produce essential blending components for coal-based jet fuel, represents a significant strategy for enhancing CTR's value. A highly efficient bifunctional catalyst was prepared by loading Ni nanoparticles (NNPs, ca. 10 %) on β/MCM-41 composite zeolite (β/M) and denoted as Ni_10%@β/M. CTR was sequentially extracted with acetone/carbon disulfide, petroleum ether, and petroleum ether/methanol (5 vol% H₂O) to obtain the soluble portion in methanol phase (PEEP_M). PEEP_M mainly consists of phenols (64.8 %) and arenes (18.9 %). It was conducted to CHC over Ni_10%@β/M at 160 °C for 16 h under 5 MPa of an initial hydrogen pressure (IHP) to obtain CHPEEP_M. The results indicate that the relative content of cyclanes in CHPEEP_M reaches as high as 93.4 %. In Ni_10%@β/M, abundant defects, hierarchical porous composite zeolite with strong Lewis acid sites and uniformly dispersed NNPs play crucial roles in removing heteroatoms and hydrogenating aromatic rings (ARs), respectively. Benzyloxybenzene (BOB) is a model compound with a >C-O- bridge bond and ARs, used to study the catalytic activity of Ni_10%@β/M. BOB was completely converted into cyclanes at 160 °C for 2 h under 5 MPa IHP. The high yield of polycyclic alkanes is related to the coupling between the active fragments formed after >C-O- cleavage and the main structure. The synergistic transfer of H···H, ^δ+H···H^δ-, and H⁺ generated by Ni_10%@β/M activation of H₂ is key to the hydrogenation of ARs via induced >C-O- bond cleavage, leading to the formation of saturated cyclanes.