Molecular sieve-confined Pt-FeOx catalysts achieve highly efficient reversible hydrogen cycle of methylcyclohexane-toluene

Professor Qiming Sun of Soochow University and Researcher Manyi Yang of Nanjing University successfully achieved confined loading of highly dispersed Pt-FeO_x nanoparticles within nanosheet molecular sieves. This catalyst exhibited excellent catalytic performance in the dehydrogenation of methylcyclohexane and the hydrogenation of toluene, realizing hydrogen energy storage and release mediated by the "methylcyclohexane-toluene" reaction. The study shows that the Pt-FeO_x catalyst possesses excellent mass transfer performance; the introduction of FeO_x not only significantly lowers the activation energy barrier of the CH bond in methylcyclohexane but also regulates the formation of electron-rich Pt active sites to promote toluene desorption, while effectively inhibiting the aggregation and sintering of Pt nanoparticles, thereby significantly improving the structural and reaction stability of the catalyst. This work demonstrates the application potential of nanosheet molecular sieve-confined metal catalysts in organic liquid hydrogen storage reactions, contributing to the rational design and development of efficient catalytic systems for hydrogen energy technologies. The article was published as an open access Research Article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.

Background information:

Organic liquid hydrogen storage technology enables safe, efficient, and reversible hydrogen storage and transportation at ambient temperature and pressure, and is highly compatible with existing energy infrastructure, making it a key approach to overcome the bottlenecks in large-scale hydrogen storage and transportation. Among these technologies, the methylcyclohexane-toluene system has attracted significant attention due to its high hydrogen storage density and chemical stability, providing a feasible solution for safe and efficient hydrogen storage cycling through reversible hydrogenation and dehydrogenation processes. However, traditional supported metal catalysts struggle to simultaneously and efficiently catalyze the dehydrogenation of methylcyclohexane and the hydrogenation of toluene, and are prone to problems such as carbon deposition, organic adsorption, and metal particle agglomeration under high-temperature reaction conditions, leading to decreased activity and insufficient stability. Therefore, designing and constructing efficient and stable supported metal catalysts to achieve reversible hydrogen storage and release in the methylcyclohexane-toluene system has become an important research direction in the field of hydrogen storage and transportation catalysis. Nanosheet molecular sieves, with their regular pore structure, high specific surface area, and short diffusion paths, serve as ideal supports for confining and stabilizing metal catalysts. Applying it to the "methylcyclohexane-toluene" system is expected to improve mass transfer efficiency, inhibit the aggregation of active components, and overcome the limitations of existing catalytic systems in terms of activity and stability.

Highlights of this article:

To address the aforementioned key challenges, this study employed an equal-volume impregnation method to construct a series of highly dispersed Pt-FeO_x nanoparticle catalytic systems confined within nanosheet molecular sieves. The nanosheet molecular sieves, with their high specific surface area and abundant silanol sites, effectively promoted the high dispersion and stable anchoring of Pt-FeO_x nanoparticles. Simultaneously, their ultrathin sheet structure significantly shortened the diffusion path between reactant and product molecules, reducing mass transfer resistance during the catalytic reaction. The results show that the introduction of FeO_x species not only significantly improved the anti-sintering stability of Pt nanoparticles but also effectively lowered the activation barrier of the CH bonds in methylcyclohexane and increased the electron density of Pt sites, thereby promoting the rapid desorption of toluene. Thanks to the confinement effect of molecular sieves and the synergistic effect of "metal-metal oxide", this highly dispersed Pt-FeO_x catalyst has a hydrogen production rate of up to 3965 mmol(H₂)/g(Pt)/min (350℃) in the dehydrogenation reaction of methylcyclohexane. At the same time, it also shows excellent performance in the hydrogenation reaction of toluene, realizing efficient and reversible hydrogen storage and hydrogen release cycle based on the "methylcyclohexane-toluene" system.

Summary and Outlook:

In summary, this study constructed highly dispersed Pt-FeO_x nanoparticles confined within nanosheet molecular sieves, which exhibited excellent catalytic performance in both methylcyclohexane dehydrogenation and toluene hydrogenation reactions, realizing reversible hydrogen storage and release mediated by "methylcyclohexane-toluene". This provides a reference for the design and synthesis of efficient and stable organic liquid hydrogen storage catalysts.

The relevant research findings were published as a Research Article in CCS Chemistry. Dr. Chengxu Li, a postdoctoral researcher at Soochow University, and Yuanxin Gu, a research assistant at Nanjing University, are co-first authors of this paper, with Professor Qiming Sun and Researcher Manyi Yang as corresponding authors. This work was supported by the National Natural Science Foundation of China.

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About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem.

About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/.