Ga-Ni modified MCM-41@HZSM-5 core-shell zeolite for catalytic fast pyrolysis of wheat straw to produce monocyclic aromatics

The HZSM-5 zeolite was modified through alkali treatment (NaOH) and metal loading (Ga, Ni), followed by constructing an MCM-41 layer to create a core–shell molecular sieve catalyst. With the feedstock of wheat straw, this work investigated the effects of various catalysts on pyrolysis product distribution and bio-oil composition with a tubular furnace and Py-GC/MS. The results showed that with the alkali-treated HZSM-5, the yield of monocyclic aromatic hydrocarbons (MAHs) in the bio-oil reached 40.35%, with an overall bio-oil yield of 21.16%. Metal-modified zeolites, exhibiting enhanced acidity, further optimized the bio-oil composition, producing an MAH yield of 61.48% and 27.31% bio-oil yield. Bimetal loading with Ga and Ni further enhanced MAH selectivity, delivering an MAH yield of 69.48% and a bio-oil yield of 27.79%. The synergy between Ga and Ni suppressed excessive aromatization and polymerization into polycyclic aromatic hydrocarbons (PAHs), favouring MAH formation. Constructing an MCM-41 layer further promotes the selectivity of MAHs. Compared to uncoated catalysts, those coated with MCM-41 significantly improved monocyclic aromatic yields, achieving the highest MAH yield of 83.61%.