Diethylamine-assisted stepwise desilication of HZSM-5 for aromatic selective upgrading of bio-oil from biomass fast pyrolysis

Constructing hierarchical zeolites that simultaneously retain crystallinity, microporosity and accessible acidity remains challenging for catalytic upgrading of bio-oil. Herein, a stepwise strategy combining TPAOH pre-structuring and diethylamine (DEA)-assisted alkali treatment was developed to regulate HZSM-5 desilication. Especially, DEA moderated framework dissolution, enabling progressive mesopore development while preserving the MFI crystallinity, microporosity, and acidity. The optimized catalyst, prepared with 0.2 M NaOH for 2 h in the presence of DEA, showed the best balance between pore structure and acidity, with the V meso / V micro ratio increasing from 0.19 for Z5 to 1.31. During the upgrading of bio-oil from fast pyrolysis of Monster-TUAT-1 # genetically modified rice straw (MOS), it decreased the relative peak area for ketone from 42.73% without a catalyst to 8.19% while giving a relative peak area of 53.37% for aromatics and a deoxygenation level of 62.56%. Monocyclic aromatic hydrocarbons accounted for 79.69% of the aromatic fraction. Across the catalyst series, aromatic formation and deoxygenation peaked at moderate treatment severity. Mesopore development improved accessibility whereas excessive desilication reduced microporosity as well as the measured strong acidity, indicating that the performance depended on balancing transport and acidity rather than maximizing mesopore volume alone. Model compound and literature analyses support the initial conversion of bulky oxygenates on accessible external/mesoporous domains, followed by shape-selective aromatization of smaller intermediates within micropores. The catalyst retained 89.32% of its initial aromatic relative peak area after five cycles with reduced coke accumulation. This strategy offers a practical route to construct framework-preserved hierarchical zeolites for more efficient and durable upgrading of bio-oil.