Advanced Synthesis\nof Hierarchically Porous Zeolite\nCatalysts Utilizing Biomass Templates for the Catalytic Pyrolysis\nof Stearic Acid into Short-Chain Olefins

In this study, hierarchically porous ZSM-5 catalysts\nwere fabricated\nby one-pot assembling ZSM-5 particles onto diverse biomass templates\n(e.g., rice husk, tea seed husk, tung shell, and coconut shell), wherein\nthe biomass template was transformed into bio-SiO<sub>2</sub> or biochar\ndepending on the calcination conditions. The biotemplated ZSM-5 variants,\nincluding ZSM-5(RH), ZSM-5(TSH), ZSM-5(TS), and ZSM-5(CS), exhibited\nsignificantly improved deoxygenation performance, achieving ∼100.0%\ndeoxygenation efficiency as compared to the untemplated ZSM-5 catalyst\n(85.3%). Among them, the ZSM-5(TSH) catalyst exhibited the best performance,\naccompanied by 100% conversion, 99.6% deoxygenation rate, and 82.3%\nolefin selectivity. Interestingly, the product distribution over biotemplated\nZSM-5 was dominant C<sub>4</sub><sup>=</sup>-C<sub>8</sub><sup>=</sup> (selectivity of ∼100% in total olefins), while long-chain\nolefins (C<sub>9</sub><sup>=</sup>-C<sub>17</sub><sup>=</sup>) was\nthe major product (selectivity of 57.3%) over the untemplated ZSM-5.\nMoreover, molecular dynamics (MD) simulations revealed that biotemplated\nZSM-5 exhibited superior diffusion coefficients of stearic acid (reaction\nsubstrate) and anthracene (coke precursor) compared to the untemplated\nZSM-5, indicating higher self-diffusion rates and consequently superior\nactivity and stability in the catalytic pyrolysis reactions. Furthermore,\nin situ DRIFTS results showed stearic acid over ZSM-5(TSH) primarily\nwas converted to the C<sub>17</sub>H<sub>36</sub> intermediate mainly\nvia the decarboxylation route, followed by dehydrogenation pyrolysis\nand C–C breaking reactions into C<sub>4</sub><sup>=</sup>-C<sub>8</sub><sup>=</sup> products. Overall, this work developed an effective\nstrategy for manufacturing hierarchically porous zeolite catalysts\nusing biomass-derived bio-SiO<sub>2</sub> or biochar as the platform.