Encapsulation Ni in HZSM-5 for catalytic hydropyrolysis of biomass to light aromatics

Ni-encapsulated (Ni@HZ5) and Ni-incorporated (xNi/HZ5) zeolites were prepared via one-pot hydrothermal synthesis and impregnation method, respectively, and further employed for hydroconversion of pyrolytic volatiles of spent coffee grounds into benzene, toluene, ethylbenzene, xylene, naphthalene (BTEXN) in a drop tube reactor under H2 atmosphere. The properties of metallic Ni species on Ni@HZ5, xNi/HZ5 and Ni/Al2O3 were comparably characterized. Ni@HZ5 displayed superior selectivity for BTEXN production among those catalysts, especially for B and T. Metallic Ni species encapsulated MFI-type framework plays crucial roles in enhancing aromatics selectivity, promoting oligomerization, cyclization and aromatization of small molecular hydrocarbons in channels. On the contrary, Ni species presented on the external zeolite surface is in favor of hydrocracking and hydrogenolysis of macromolecular pyrolytic fragments. It also exhibited high coke content containing "soft" and "hard" coke, which was mainly caused by metallic particles sintering. An important difference was proposed in the effect of Ni species on reaction pathway for catalytic upgrading of volatiles to BTEXN. The configured Ni@HZ5 inhibits sintering and has potential of enhancing BTEXN by catalytic hydropyrolysis of biomass.