Production of bio-oils from the catalytic pyrolysis of neem sawdust: Comparative study of versatile zeolite parameters

Catalytic fast pyrolysis (CFP) is promising in converting biomass into renewable bio-oils, wherein zeolites play a critical role in bio-oil upgrading. Although it is widely known that zeolite properties (e.g., morphology, acidity, metal modification) determine bio-oil quality, studies on their uniformly comparative effect are limited and hinders a precise design of efficient zeolite catalyst for biomass CFP. Herein, the CFP of neem sawdust was catalyzed by fourteen ZSM-5 zeolites with different structural parameters. The separate impacts of zeolite morphologies (0.2, 0.5, 1, 3 μm), acidity (Si/Al = 25, 50, 100, 200), loaded metal types (Ni, Zn, Co, Ce), and metal loadings (1, 2, 5, 8 wt%) on bio-oil production were initially studied in detail. Then, their relative contributions in regulating bio-oil yield and hydrocarbon selectivity were compared. Results showed that nanosized ZSM-5 with a higher Si/Al ratio improved bio-oil yield, while metal modification had a greater impact on hydrocarbon selectivity. The nanosized 2NiO_x/ZSM-5 with a Si/Al ratio of 50 and a NiO_x loading of 2 wt% was superior in producing a maximized bio-oil yield and a satisfactory hydrocarbon selectivity. To shed light on future zeolite catalyst design, a pyrolysis mechanism was proposed for neem sawdust over ZSM-5 with varied parameters.