> ## Content Index > Fetch the complete content index at: https://research-pop.com/llms.txt > Use this file to discover other available public pages before exploring further. # MIT-led team uses gallium-modified ZSM-5 to steer polyolefin hydrocracking toward propane - URL: https://research-pop.com/mit-led-team-uses-gallium-modified-zsm-5-to-steer-polyolefin-hydrocracking-toward-propane/ - Published: 2026-10-26T13:21:11.000Z - Updated: 2026-10-26T13:21:11.000Z - Author: ResearchPOP ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-26-at-14.16.47.png) Source: [https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c06722/5457813/Gallium-Containing-ZSM-5-Zeolites-Improve](https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c06722/5457813/Gallium-Containing-ZSM-5-Zeolites-Improve?ref=research-pop.com) ## At a glance Adding gallium oxide to ZSM-5 can shift polyolefin hydrocracking toward propane and butanes while maintaining polymer conversion. Researchers from MIT, SLAC National Accelerator Laboratory, the National Laboratory of the Rockies and the BOTTLE Consortium connect this effect to extra-framework GaOₓ located close to the zeolite’s acid sites. The optimized catalyst contained 3 wt% Ga deposited by incipient wetness impregnation. Under benchmark batch conditions of 240 °C for 16 h, with an initial H₂ pressure of 40 barg at room temperature, combined C₃–C₄ selectivity was approximately 85 c-wt% for PE and HDPE. Here, c-wt% expresses selectivity on a carbon-mass basis. Longer experiments brought propane selectivity close to 60 c-wt%, while combined propane and butane selectivity reached 87 c-wt% at complete solids conversion. Catalyst comparisons show that gallium’s location, coordination and effect on acidity matter together. Increasing the proportion of reduced Ga did not improve propane selectivity. ## Background Polyethylene and polypropylene contain long chains of carbon–carbon bonds. Hydrocracking breaks these chains into smaller hydrocarbons in the presence of hydrogen. Producing a narrow range of useful molecules requires control over both the initial chain cleavage and the subsequent reactions of the fragments. Zeolites provide acidic environments that support carbocation chemistry, including rearrangement and β-scission, in which a carbon–carbon bond breaks near the positively charged centre. Their pores also influence which intermediates can form and react. Hydrogen helps convert unsaturated fragments into saturated products, but the balance between cracking and hydrogenation determines whether the products remain relatively heavy or undergo further conversion to light hydrocarbons. ZSM-5 already favors comparatively narrow distributions of light products. A metal modifier can change this distribution by influencing hydrogen activation, acidity or intermediate conversion. Those effects are not always beneficial: additional metal sites can introduce competing pathways or terminate cracking before the desired products form. Gallium-containing zeolites offer several possible environments, from Ga incorporated into the framework to extra-framework oxide species. The study uses these structural differences to investigate how gallium can reinforce ZSM-5’s selectivity toward propane and butanes. ## Research question Which metal or metal-oxide modifier can increase C₃–C₄ selectivity during polyolefin hydrocracking without sacrificing conversion? For gallium, which combination of location, dispersion, oxidation state and acidity produces the enhancement, and how does it change the sequence of reactions leading to light alkanes? ## Inside the study The researchers began by comparing Pt, Pt–Sn, SnOₓ, ZnOₓ and GaOₓ supported on ZSM-5 with a Si/Al ratio of 11.5\. The benchmark experiment used 700 mg of model polyethylene and 46 mg of catalyst at 240 °C for 16 h, with a 40 barg H₂ fill at room temperature. Pt lowered both solids conversion and propane selectivity. Adding Sn to Pt did not reverse that behavior, while SnOₓ and ZnOₓ provided no improvement in propane selectivity. GaOₓ produced a different response: at 3 wt% Ga, solids conversion remained approximately 66%, while propane selectivity increased by about 19 percentage points on the reported carbon-mass basis. Meanwhile, C₆+ selectivity fell from 16 to 5 c-wt%, indicating that the gain in light products came largely at the expense of heavier hydrocarbons. Support comparisons showed that total acid-site density was insufficient to explain the result. ZSM-5 with a higher Si/Al ratio retained substantial activity but produced a different product distribution. Amorphous silica–alumina with a similar measured total acid-site density was largely inactive under the benchmark conditions. These comparisons point to the combined importance of acid properties and the zeolite pore environment. The location of gallium proved equally important. Hydrothermally synthesized Ga-ZSM-5, containing predominantly framework Ga, reached only 27% solids conversion and favored heavier products. GaOₓ on silica was largely inactive. Physically mixing that material with ZSM-5 reproduced the behavior of the parent zeolite rather than the selectivity of directly modified GaOₓ/ZSM-5. Preparation methods further distinguished the catalysts. Solid-state ion exchange generated larger, less dispersed GaOₓ species and gave intermediate performance. Incipient wetness impregnation produced the strongest propane-selectivity enhancement. Together, these controls support the need for extra-framework GaOₓ in close proximity to zeolite acid sites. Characterization showed that gallium deposition also changed the acidic environment. At 3 wt% Ga, the total measured acid-site density decreased from 1,275 to 911 μmol g⁻¹, and the Brønsted-to-Lewis acid-site ratio declined. X-ray absorption measurements identified Ga³⁺ as the dominant state in the fresh catalyst, while depth-resolved XPS and STEM-EDS placed much of the Ga near the external zeolite surface. Under reaction-relevant conditions, operando X-ray absorption detected predominantly tetrahedrally coordinated oxidic Ga alongside a minority Ga¹⁺ population. The measurements establish that multiple Ga environments coexist during operation; they do not isolate one oxidation state as the sole source of the selectivity enhancement. Reaction-time experiments then examined how the products developed. GaOₓ/ZSM-5 reached approximately 50 c-wt% propane selectivity after 8 h and approached 60 c-wt% after 32 h. At complete solids conversion, propane and butanes together accounted for 87 c-wt%. Propane selectivity on the parent zeolite depended more strongly on conversion, consistent with slower secondary cracking of heavier intermediates. Continuous-flow experiments with n-dodecane provided a complementary view at approximately 5% conversion. The parent ZSM-5 produced more olefinic and higher-carbon-number intermediates, whereas GaOₓ/ZSM-5 favored C₃ and C₄ hydrocarbons. The authors interpret this comparison as evidence that gallium modification promotes light-alkane formation earlier in the reaction network. A reductive pretreatment at 400 °C tested whether further changes to Ga could improve performance. It increased the estimated Ga¹⁺ population, moved Ga deeper into the material and raised the concentration of strong Lewis acid sites from 199 to 346 μmol g⁻¹. Propane selectivity nevertheless decreased by about 10 percentage points on the carbon-mass basis. Because reduction altered several properties simultaneously, the result cannot be assigned to oxidation state alone. Finally, the catalyst was evaluated with model PE, PP, LDPE and HDPE. The propane-selectivity enhancement persisted across this substrate set, with combined C₃–C₄ selectivity above 80 c-wt%. PE and HDPE each gave approximately 85 c-wt% combined propane and butane selectivity under the 16 h benchmark conditions. ## Takeaways and outlook The study identifies a specific arrangement of gallium and zeolite acidity that favors light-alkane production. Directly deposited extra-framework GaOₓ, concentrated near the zeolite exterior and close to acid sites, shifts the reaction network toward propane and butanes while preserving conversion under the benchmark conditions. The pretreatment experiment illustrates why catalyst optimization must consider several properties together. A larger reduced-Ga population, greater penetration into the zeolite and stronger Lewis acidity coincided with lower propane selectivity. The effective catalyst therefore depends on the balance among these features. The next mechanistic challenge is to vary gallium’s coordination, location and influence on acidity independently. Longer catalyst-lifetime studies and tests with more complex waste feeds would help establish whether the same selectivity can be maintained beyond the controlled polyolefin substrates examined here. ## About the researchers Anna E. Brenner is the first author, and Yuriy Román-Leshkov is the corresponding author, both at MIT. The MIT team also includes Faisal H. Alshafei, Juliana Lu-Yang, Marcos G. Farpón, Bowei Liu, Rachita Rana and Griffin Drake. Ozge D. Bozkurt, Colum O’Leary, Arun Asundi and Simon R. Bare are affiliated with SLAC National Accelerator Laboratory and the BOTTLE Consortium. Gregg T. Beckham is affiliated with the National Laboratory of the Rockies and the BOTTLE Consortium. ## Original research Anna E. Brenner; Faisal H. Alshafei; Juliana Lu-Yang; Ozge D. Bozkurt; Marcos G. Farpón; Colum O’Leary; Arun Asundi; Bowei Liu; Rachita Rana; Griffin Drake; Simon R. Bare; Gregg T. Beckham; Yuriy Román-Leshkov. “Gallium-Containing ZSM-5 Zeolites Improve Hydrocracking Selectivity to Propane.” *ACS Catalysis* (2026). Original paper: [https://doi.org/10.1021/acscatal.6c06722](https://doi.org/10.1021/acscatal.6c06722?ref=research-pop.com) --- ## Research POP Notes This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. If you identify any inaccuracies or have concerns regarding the content, figures or attribution, please contact us at [team.researchpop@gmail.com](mailto:team.researchpop@gmail.com). 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