Enhancing the tar removal efficiency and gas production for the pyrolysis of biomass through the nickel-based hollow zeolite

Using metal-zeolite catalysts to improve the catalytic efficiency for tar cracking during biomass pyrolysis has attracted a lot of attention of scholars. Herein, the Ni@ZSM-5 catalyst with a hollow structure encapsulating Ni metal was synthesized by hydrothermal-recrystallization. The properties of the catalysts were evaluated by a series of characterization and compared with the solid ZSM-5 as well as nickel loaded ZSM-5. Through TEM observation, it was found that a regular cavity was constructed inside ZSM-5 with Ni particles encapsulated in it successfully. The unique hollow structure facilitated Ni@ZSM-5 owning greater Brønsted acidity and coke resistance, presenting a great activity and stability in tar catalytic cracking. The microporous shell prevented the sintering and loss of Ni significantly. Tar removal efficiency reached 92.2 %, and remained around 90 % after 10 cycles. Pyrolysis gas yield increased by 27.2 %, simultaneously. The reasons for excellent catalyst performance was analyzed as well as the potential evolutionary mechanism for tar molecule over Ni@ZSM-5. The utilization of this unique catalyst provides a reference in the field of biomass utilization.