(689e) Non-Oxidative Dehydrogenation of Ethanol to Acetaldehyde and Hydrogen on Nickel-Gold Single Atom Alloys

The interest in non-oxidative dehydrogenation of ethanol towards acetaldehyde lies in two different factors. First, ethanol dehydrogenation is the first step to two other reactions of great industrial importance, ethanol steam reforming¹ and ethanol oxidation². Other than that, itself ethanol dehydrogenation yields acetaldehyde, an important commodity chemical, regarded as a building block in the chemical industry. Under non-oxidative conditions it also produces a highly desirable side product, hydrogen, and not water, which is the result of oxidative ethanol dehydrogenation. Copper-based catalysts are being used industrially for the oxidative reaction, despite suffering from sintering, leading to deactivation. Addition of low amounts of Ni has proven to be beneficial not only to the stability, but also to the catalytic activity³.

Au has been studied as an alternative to Cu, as it provides enhanced stability and exhibits 100% selectivity even at high temperatures. These benefits come at the cost of low conversion, as the catalyst is only active when in specific size⁴ and at elevated temperatures regardless of the support⁵. In our recent work⁶ we demonstrated how to successfully deposit single atoms of Ni in the Au surface, forming NiAu single atom alloys (SAAs). The addition of Ni isolated atoms prevented sintering of Au existing in either nanoparticles or nanoporous form. At the same time, it lowered the activation energy significantly (from 96±3 to 59±5 kJ/mol), while at the same time the high selectivity induced by Au was maintained even at high temperatures (280 ℃), at which point Ni forms cluster that catalyze the ethanol decomposition to CO, CH₄ and H₂.

In the present work, we aim to further study NiAu SAAs under the specific reaction. First, we confirm the atomic dispersion of Ni in Au surfaces via CO-DRIFTS and EXAFS on the fresh and used materials up to 250 ℃. PdAu SAAs, which have been recently reported as promising hydrogenation catalysts⁷ are also tested under similar reaction conditions for comparison. Unlike Ni, Pd atoms effect on the catalytic activity is not as equally apparent, as indicated by activation energy measurements and Ethanol DRIFTS. The effect of water as a potential co-catalyst has also been examined, as it had been reported to be successful in promoting the activity of other SAAs in dehydrogenation reactions, namely PdCu in methanol dehydrogenation⁸ and PtCu⁹ in formic acid dehydrogenation. Contrary to the latter, water does not activate ethanol at lower temperatures, only acting as a reactant at higher temperatures in the ethanol steam reforming reaction. Last, this work is aided by surface science techniques (TPD), as well as theoretical contributions (DFT), providing a deeper understanding of the system.

Acknowledgements: This material is based upon work supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE- SC0012573.

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