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

Abstract

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.

Design of Single-Atom Catalysts and Tracking Their Fate Using Operando and Advanced X-ray Spectroscopic Tools

“…Soft X-rays are often used to probe K-edges of light elements like C (283 eV), N (402 eV), or O (532 eV). For single atom catalysts, this offers the possibility to get complementary information on the surrounding ligands that basically comes from the support. , Also, L- and M-edges of many elements are accessible only with tender X-rays, such as the L 3 -edges of Rh (3004 eV), Pd (3173 eV) or Ag (3351 eV). Such near-edge X-ray absorption fine structure (NEXAFS) spectra often yield more structural information as the excited electrons are stronger influenced by valence electrons than the energetically deeper lying K-shell electrons.…”

Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single-atom Cu/O Lewis pair for acetylene hydrochlorination

“…To further con rm this optimum Cu−cis−N 2 C 2 Cl−O1 con guration, we performed XANES modeling based on Finite Difference Method Near Edge Structure (FDMNES) calculation, which was usually reported to identify the metal single−atom coordination structure of M−N−C. 49 Figure 4f showed that the experimental simulation spectra presented a relatively satisfactory agreement on the basis of the Cu−cis−N 2 C 2 Cl−O1 model. Moreover, the corresponding differential charge density analysis discovered that when the epoxide group existed in the vicinal location of Cu−cis−N 2 C 2 Cl center, the charge state of single−atom Cu became more positive due to the inductive effect of oxygen atom in functional epoxide group, in agreement with the previous report 37 (Figure 4g and Figure 4h).…”

Coordination Engineering of Defective Cobalt–Nitrogen–Carbon Electrocatalysts with Graphene Quantum Dots for Boosting Oxygen Reduction Reaction

“…[ 46 ] In the Fourier‐transformed k 3‐weighted extended X‐ray absorption fine structure (EXAFS) spectra (Figure 3h), G‐CoNOC shows a relatively broad peak at a distance of 1–2 Å caused by the backscattering of light atoms of N and O, which can be ascribed to the CoN/O first coordination shell. [ 47 ] Moreover, the EXAFS fitting result confirm that the first shell of the Co atom is approximately coordinated to two N atoms and two O atoms, implying the formation of the CoN 2 O 2 bonds in G‐CoNOC (Figure 3i; Table S4, Supporting Information).…”