Effective regulation of Ga active species in mesoporous ZSM-5 for catalytic upgrading of coal pyrolysis volatiles

Abstract

Quality improvement of pyrolysis tar with yield increasing of high value-added components is highly desired for coal utilization. Herein, Ga-impregnated mesoporous ZSM-5 (Ga/MZ5) directed by organosilane surfactant of [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC) is used as a catalyst for the catalytic upgrading of coal pyrolysis volatiles. Effective regulation by reduction and reduction/reoxidation promotes a secondary dispersion of gallium species from external surface deposition to micropore permeation. The comprehensive evaluation of catalytic upgrading performance indicates that the designedly regulated gallium species (mainly Ga+, GaH2+ and GaO+), feasible balance of Brønsted and Lewis active sites and mesopore diffusion superiority effectively contribute the yield increasing of both light-fraction (MLF/MTar) and target products of BTEXN (benzene, toluene, ethylbenzene, xylene and naphthalene). The optimal catalyst of Ga/MZ5_R/O exhibited the highest value of MLF/MTar (88 %) and highest yield of BTEXN (31.84 mg.g−1), which are 173 and 589 % higher than non-catalytic single pyrolysis and 133 and 280 % higher than those over the conventional Ga-impregnated ZSM-5 (Ga/Z5). Moreover, the possible reaction networks towards high value-added products of BTEXN based on the positive conversion of polycyclic aromatic hydrocarbons (PAHs), phenols, and other oxygen-containing compounds (abbreviated as PPO) is further proposed.