Enhancing light olefin production by pre-cracking and acidity tuning over hierarchical La/ZSM-5@ASA composites

La/ZSM-5@ASA composites were developed by a stepwise assembly strategy. • La 3+ displaced the acidic protons and generated new BAS [Si-OLa(OH) 2 -Al]. • ASA overcoat passivated external surface acid sites and enabled pre-cracking. • Hierarchical La/ZSM-5@ASA shows high light-olefin selectivity in n -paraffin cracking. Catalytic cracking of surplus automotive fuels, heavy oil and waste plastics into light olefins is an efficient resource-reutilization strategy. Conventional ZSM-5 zeolites, however, suffer from limited light-olefin selectivity and coke-induced deactivation due to strong acidity and microporous constraints. Herein, a stepwise assembly strategy involving La modification and subsequent amorphous silica-alumina (ASA) overcoating was developed to construct core–shell catalysts with optimized acidity and diffusion. La modification modulated acid strength and distribution, and DFT calculations revealed it lowered the energy barrier of the rate-determining protonation step, promoting propylene formation. The ASA overcoat, applied via co-gelation, passivated external strong Brønsted acid sites and introduced open interfacial diffusion channels. This architecture enabled pre-cracking of reactants, promoting efficient C-C bond cleavage and suppressing secondary reactions. The optimized hierarchical La/ZSM-5@ASA(1:1) achieved 63.10% total ethylene and propylene selectivity in n -heptane cracking, outperforming ZSM-5 and 0.50La/ZSM-5 by 5.12% and 1.38%, respectively. This advantage is more pronounced for longer linear hydrocarbons, and the suppression of methane and coke precursors boosts atom utilization efficiency, indicating a carbon-economic cracking pathway.