There is a critical need for better utilizing methane, an important and abundant resource and the second most prevalent greenhouse gas. Activating methane at low enough temperatures in a selective manner is a key aspect to take advantage of the large amount of natural gas extracted, and to reduce emissions and the detrimental effect on the environment of unwanted leaks. Palladium is accepted as the most active metal in breaking methane’s C-H bonds at low temperatures. Unfortunately, Pd, an expensive noble metal, has to be utilized to the best possible extent and must be even more active and stable under typical conditions to provide chemicals and combust methane. Promoting Pd with Earth-abundant transition metals is a promising solution to optimizing Pd utilization and increasing its stability. Conventional catalyst synthesis, such as co-impregnation processes, lack control over active phase size and composition, and promoter-active phase interface, and as a consequence it is difficult to correlate structure with activity. To gain a fundamental understanding of Pd-promoter interactions and design highly active, selective and stable methane activation catalysts, control over active phase size, composition and Pd-promoter interface is essential.<br/>In this study, we demonstrate a novel and general approach to synthesizing monodisperse palladium-based bimetallic nanocrystals promoted with transition metals (V, Mn, Fe, Co, Ni, Zn and Sn). Excellent control over size, shape and composition is demonstrated, providing a library of highly uniform materials. TEM and complimentary spectroscopies (EFTEM and EDX) demonstrate an unprecedented control over size and composition, all with a single synthesis protocol. Control over nucleation and precursors decomposition is crucial to the quality of the final materials. The nanocrystals are used as precursors for heterogeneous catalysts. Materials calcined up to 850C demonstrate the improved thermal stability of bimetallic systems as compared to a Pd monometallic sample. Detailed catalytic characterization of the Pd-promoted bimetallic catalysts highlights the improved activity, selectivity and stability for methane activation reactions, such as methane complete combustion and reforming, and a clear correlation between structure and activity, demonstrating the promise of such systems to improve current catalytic systems and to increase much needed fundamental understanding of the activation of an abundant resource like methane.

Synthesis and compositional control in highly uniform palladium-based bimetallic nanocrystals for catalytic methane activation

253rd National Meeting (2017)

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