Decoding the Kinetic Complexity of Pt-Catalyzed n-Butane Dehydrogenation by Machine Learning and Microkinetic Analysis

n-Butane dehydrogenation to butene and butadiene has recently gained increasing attention owing to the exploitation and development of shale gas as well as the rapid growth in the demand for synthetic rubber worldwide. In this work, the full n-butane dehydrogenation reaction network involving 568 elementary steps on Pt is established by using a chemical informatics approach to loop over all of the atoms and chemical bonds in n-butane. By combining density functional theory (DFT) calculations, the Morgan molecular fingerprint method, and machine learning techniques, we have identified 208 elementary steps that contribute to the kinetically important reaction network, which presents some general guidelines for the formulation of mechanisms of great complexity. A detailed microkinetic analysis that ensures thermodynamic consistency is then performed, without and with the presence of H2 cofeeding, to assess the n-butane catalytic activity and butene selectivity. It turns out that in the absence of H2, the high coverages of the coke precursors give rise to a low catalytic activity due to the occupancy of a large number of active sites. The turnover frequencies for n-butane consumption and butene production rise rapidly as the H2/n-C4H10 ratio goes up from 0 to 1.33. Meanwhile, the selectivity toward 1-butene increases as well, whereas the selectivities toward 2-butene and 1,3-butadiene are not sensitive to the H2 partial pressure. The flux analysis reveals that the dominant reaction pathways for 1-butene and 2-butene follow the reverse Horiuti–Polanyi mechanism, and the byproducts are formed primarily by the C–C bond cleavage in CH3CCHC*. The C–H bond activation in n-butane is identified by the sensitivity analysis as the rate-limiting step for the overall reaction while the selectivities toward butenes are found to be controlled dominantly by the ease with which n-butane can be activated and how readily butenes can be deeply dehydrogenated.