The Catalytic Dehydrogenation of Conventional Chemicals using Unconventional Methods




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Catalytic dehydrogenation, or the selective removal of hydrogen from hydrocarbons, is an economically-driven process. In general, all dehydrogenation processes share the same two difficulties. First, non-oxidative dehydrogenation is difficult. C-H bonds are strong and the dehydrogenation process is endothermic, indicating both the kinetic and thermodynamic challenges of these reactions. Second, even if the kinetic and thermodynamic obstacles are overcome, only the partial dehydrogenation of the reactant molecule is usually desired. The complete removal of hydrogen from a hydrocarbon reactant is unwanted because it leads to the formation of catalyst-deactivating coke. Therefore, the key to unlocking selective dehydrogenation is finding an effective catalyst that rises above the activity challenges of the reaction, yet remains selective to the desired product. Recently, a class of catalysts known as single-atom alloys has attracted attention. These single-atom alloys consist of a highly active, isolated promoter atom that sits within the surface of a less-active host metal. A reactant would dissociate on the promoter atom and the resulting intermediates would diffuse away to the host metal, where it binds weaker and can desorb or undergo further chemistry. In our theory-driven work, we begin by examining the efficacy of these single-atom alloys. First, we find that they outperform the best literature monometallic catalyst in breaking the strong triple bond of N2, which is the rate-determining step of the Haber-Bosch process. We also determine that isolated palladium atoms in gold surfaces can actively and selectively dissociate methane for further upgrade in both non-oxidative and oxidative mechanisms. We then perform stability tests for all combinations of metals to determine which combinations are stable as single-atom alloys. Finally, we introduce a new paradigm that couples multi-faceted density functional theory and kinetic Monte Carlo to rationally design and optimize the size, shape, and promoter metals of a catalyst nanoparticle. As a case study, we examine the dehydrogenation of methanol to formaldehyde on silver and determine that small, cubic nanoparticles decorated with zinc or palladium promoters would optimize the reaction. Our paradigm can be extended to any catalytic reaction on metal surfaces and offers a bridge between computational and experimental catalysis.



Catalysis, Single atom alloys (SAA), Dehydrogenation, DFT, KMC


Portions of this document appear in: Do, Quan K., Hung-Vu Tran, Shengguang Wang, and Lars C. Grabow. "The Synergy of Dilute Pd and Surface Oxygen Species for Methane Upgrading on Au3Pd (111)." Energy Technology (2019).