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 N2 at 900 °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 °C, giving rise to a steady conversion rate of 4.7 mmolEB·gcat–1·h–1 and 192.9 mmolEB·gmetal–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–N4 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.