Introducing Co-O Moiety to Co-N-C Single-Atom Catalyst for Ethylbenzene Dehydrogenation

While single-atom catalysts (SACs) have been extensively studied as a type of high-atom-efficiency heterogeneous catalyst, their reaction stability under high temperature reductive atmosphere is yet to be addressed. In this work, we introduced a Co-O moiety to Co-N-C SACs by employing glutamic acid as both a N,O-bidentate ligand of Co(II) and a source for N-doped carbon. After undergoing pyrolysis in N-2 at 900 degrees C, the complex transformed into the CoN3O1-OH2 structure and subsequently to the CoN3O1 structure upon being submitted to a high temperature reaction due to leaving out a weakly adsorbed water molecule, which was unambiguously identified by X-ray absorption spectroscopy combined with density functional theory calculations. The resulting CoN3O1 structure exhibited satisfactory activity and stability for ethylbenzene dehydrogenation at 550 degrees C, giving rise to a steady conversion rate of 4.7 mmol(EB)center dot g(cat)(-1).h(-1) and 192.9 mmol(EB)center dot g(metal)(-1).h(-1), which was 74.2 times higher than that of Co3O4 and more than twice as high as those of Co NPs and O-free Co-N-4 counterparts, manifesting the catalytically active role of the Co-O moiety. Intrinsic to alkane dehydrogenation, the initial activity decay was also observed for CoN3O1 SAC, which could be attributed to coking and loss of the ketonic carbonyl group on the N-doped carbon surface. The characterizations of the used catalyst after 30 h revealed that the CoN3O1 structure was well preserved without any aggregation of the Co species caused by the reduction of Co-N or C-O moieties, demonstrating the robustness of the CoN3O1 structure under a high-temperature reductive atmosphere. This work provides a route to the rational design of both active and stable SACs operating at high temperatures and in a reductive atmosphere.