Authors:

Maxwell K Bartlett

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About Paper:

Abundant natural gas (~90% methane) found in isolated shale gas reservoirs is often flared due to high transportation costs and lack of technologies to transform methane into useful products, emitting ~500 million tons of CO2 per year, exacerbating detrimental greenhouse gas effects. Methane dehydroaromatization (DHA) is an oxygen-free reaction that produce benzene and H2, catalyzed by molybdenum active sites supported onto zeolites. Zeolites are aluminosilicate crystalline materials that influence rates, selectivities and stability for methane DHA. Specifically, the chabazite (CHA) framework is promising for methane DHA due to its improved long-term stability during reaction-regeneration cycles. However, chabazite's small pore openings (?4 Å) impose diffusion limitations and its large internal cavities (?8 Å) promote carbon (i.e., coke) deposition, decreasing benzene selectivity. We seek to alleviate diffusional constraints by synthesizing CHA materials containing mesoporous voids, allowing for higher benzene selectivity and reduced coking. Al-substituted CHA was synthesized according to literature references and treated in air at 300, 400, and 450? (1 h). Then, CHA zeolites were exposed to alkaline treatment with 0.4 M NaOH (aq.) at varying contact times (30, 60 minutes). Treated samples were characterized using powder X-ray diffraction (XRD), Ar adsorption isotherms (87 K), and elemental analysis (ICP). XRD peaks evidence that CHA crystallinity does not change significantly after the alkaline treatment. Moreover, Ar isotherms evidence increasing air-treatment temperature and alkaline-treatment time leads to higher density of mesopores. These post-synthetic protocols provide a method to systematically investigate the effect of morphological changes on diffusivity and benzene selectivity for methane DHA. Keywords: [no keywords provided]

Source:

Purdue University / 2025

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Co-authors:

Maxwell K Bartlett