SEARCH · Search NASA
Results for “C3N4”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Thermally Stable Co@C3N4 Single-Atom Catalysts for CO Oxidation: Atomic-Level Insights into Structure and Activity
Single Co atoms supported on C3N4 (Co@C3N4) have demonstrated high activity and selectivity in photocatalysis. However, the investigation of structure–function relationships and reaction mechanisms under photocatalytic conditions is very challenging due to the complex conditions of light absorption, charge transfer, and catalysis. In this study, we employed thermal CO oxidation as a prototypical probe reaction to benchmark the intrinsic catalytic performance and track the active-site evolution of Co@C3N4. Single Co atoms were identified and shown to be the catalytically active sites for CO oxidation based on control experiments and isotope-labeling experiments. The Co sites remained atomically dispersed before, during, and after the reaction with temperatures up to 400 °C, as established by in situ X-ray absorption fine structure (XAFS) combined with density functional theory (DFT), FDMNES simulations, and dynamic-time-warping (DTW)-assisted X-ray absorption near edge structure (XANES) matching. Together with theoretical calculations, the integrated analysis reveals a stable coordination environment under reaction conditions, which correlates with sustained activity, establishing Co@C3N4 single-atom catalysts as thermally stable CO oxidation catalysts. Beyond these findings, the current study provides a workflow for unambiguously assigning active sites in Co@C3N4 for thermal CO oxidation. This workflow will aid the understanding of their behavior in photocatalysis in the future, where light-driven dynamics obscure direct structure–function links. Notably, this study provides fundamental insights for the rational design of robust single-atom catalysts and a foundation for the broader application of Co@C3N4 catalysts in oxidation reactions.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of two C3N4 sheets oriented in the (0, 0, 1) direction. C4+ is bonded in a trigonal planar geometry to three N3- atoms. There is two shorter (1.33 Å) and one longer (1.46 Å) C–N bond length. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms. In the second N3- site, N3- is bonded in a bent 120 degrees geometry to two equivalent C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three C3N4 sheets oriented in the (0, 0, 1) direction. C4+ is bonded in a trigonal planar geometry to three N3- atoms. There is two shorter (1.33 Å) and one longer (1.46 Å) C–N bond length. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a bent 120 degrees geometry to two equivalent C4+ atoms. In the second N3- site, N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. C4+ is bonded to four N3- atoms to form corner-sharing CN4 tetrahedra. There is three shorter (1.46 Å) and one longer (1.47 Å) C–N bond length. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms. In the second N3- site, N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the cubic I-43d space group. The structure is three-dimensional. C4+ is bonded to four equivalent N3- atoms to form corner-sharing CN4 tetrahedra. All C–N bond lengths are 1.47 Å. N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 is Hausmannite structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded to four equivalent N3- atoms to form corner-sharing CN4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. All C–N bond lengths are 1.54 Å. In the second C4+ site, C4+ is bonded to six equivalent N3- atoms to form CN6 octahedra that share corners with six equivalent CN4 tetrahedra and edges with six equivalent CN6 octahedra. All C–N bond lengths are 1.66 Å. N3- is bonded in a distorted rectangular see-saw-like geometry to four C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the cubic P-43m space group. The structure is three-dimensional. C4+ is bonded to four equivalent N3- atoms to form corner-sharing CN4 tetrahedra. All C–N bond lengths are 1.49 Å. N3- is bonded in a trigonal non-coplanar geometry to three equivalent C4+ atoms.
Materials Data on C3N4 by Materials Project
C3N4 crystallizes in the trigonal P31c space group. The structure is three-dimensional. there are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded to four N3- atoms to form corner-sharing CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.44–1.49 Å. In the second C4+ site, C4+ is bonded to four N3- atoms to form corner-sharing CN4 tetrahedra. All C–N bond lengths are 1.46 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to three equivalent C4+ atoms. In the second N3- site, N3- is bonded in a trigonal non-coplanar geometry to three equivalent C4+ atoms. In the third N3- site, N3- is bonded in a trigonal planar geometry to three C4+ atoms. In the fourth N3- site, N3- is bonded in a trigonal planar geometry to three C4+ atoms.
Materials Data on FeAg3H6(C3N4)2 by Materials Project
Fe(Ag(CN)3)2Ag(NH3)2 crystallizes in the monoclinic Cc space group. The structure is zero-dimensional and consists of four iron molecules, four Ag(CN)3 clusters, and four Ag(NH3)2 clusters. In each Ag(CN)3 cluster, there are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to four N3- atoms to form edge-sharing AgN4 tetrahedra. There are a spread of Ag–N bond distances ranging from 2.15–2.50 Å. In the second Ag1+ site, Ag1+ is bonded to four N3- atoms to form distorted edge-sharing AgN4 tetrahedra. There are a spread of Ag–N bond distances ranging from 2.17–2.54 Å. There are six inequivalent C2+ sites. In the first C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the second C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the third C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the fourth C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the fifth C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. In the sixth C2+ site, C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.18 Å. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded in a 3-coordinate geometry to two Ag1+ and one C2+ atom. In the second N3- site, N3- is bonded in a 1-coordinate geometry to two Ag1+ and one C2+ atom. In the third N3- site, N3- is bonded in a distorted linear geometry to one Ag1+ and one C2+ atom. In the fourth N3- site, N3- is bonded in a distorted bent 150 degrees geometry to one Ag1+ and one C2+ atom. In the fifth N3- site, N3- is bonded in a distorted linear geometry to one Ag1+ and one C2+ atom. In the sixth N3- site, N3- is bonded in a 2-coordinate geometry to one Ag1+ and one C2+ atom. In each Ag(NH3)2 cluster, Ag1+ is bonded in a distorted linear geometry to two N3- atoms. There are one shorter (2.13 Å) and one longer (2.17 Å) Ag–N bond lengths. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Ag1+ and three H1+ atoms. All N–H bond lengths are 1.02 Å. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one Ag1+ and three H1+ atoms. There is two shorter (1.02 Å) and one longer (1.03 Å) N–H bond length. There are six inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one N3- atom.
Single Copper Atoms Enhance Photoconductivity in g-C3N4
Explore the source record for details and available documents.
Ru Single Atoms on One-Dimensional CF@g-C 3 N 4 Hierarchy as Highly Stable Catalysts for Aqueous Levulinic Acid Hydrogenation
Herein, we report a stable catalyst with Ru single atoms anchored on a one-dimensional carbon fiber@graphitic carbon nitride hierarchy, by assembling wet wipes composed of fiber-derived carbon fiber (CF), melamine-derived graphitic carbon nitride (g-C3N4) and RuCl3 before NaBH4 reduction. The atomically dispersed Ru species (3.0 wt%) are tightly attached via N-coordination provided by exterior g-C3N4 nanosheets, and further stabilized by the interior mesoporous CF. The obtained CF@g-C3N4–Ru SAs catalyst can be cycled six times without notable leaching of Ru or loss of GVL yield in the acidic media. This catalyst is more stable than Ru nanoparticles supported on CF@g-C3N4, as well as Ru single atoms anchored on CF and g-C3N4, and proves to be one of the most efficient metal catalysts for aqueous LA hydrogenation to γ-valerolactone (GVL). The isolated Ru atoms by strong N-coordination, and their enhanced electron/mass transfer afforded by the one-dimensional hierarchy, can be responsible for the excellent durability of CF@g-C3N4–Ru SAs under harsh reaction conditions.
Understanding the Origin of Negative Temperature Dependence and Activity of N-Coordinated Cobalt Sites During Ethylene Dimerization
The on-demand production of short-chain linear alpha olefins (LAOs; C4-C8) via C2H4 dimerization and oligomerization is industrially attractive, prompting extensive research on designing active, selective, and stable catalysts for industrial use. Cobalt supported on ammoniated carbon (Co(NH3)x/C) catalysts have shown remarkable activity and selectivity in this process. However, critical aspects such as the active phase, active site structure, the role of the catalyst support, cobalt loading effects, and the inverse correlation of the reaction rate with temperature remain inadequately understood. This study systematically explores these factors using a combination of steady-state differential catalytic tests, in situ molecular characterization including diffuse reflectance UV-Vis (DR-UV-Vis), Infrared, and Raman spectroscopies, and ex situ X-ray diffraction (XRD) and high annular aberration-corrected dark field transmission electron microscopy (HAADF-STEM). Various supports (SiO2, Al2O3, NH4-ZSM-5, g-C3N4, and C) and cobalt loadings (1.0-3.0 Co nm-2) were studied to determine the optimal catalyst composition and identify the active phase and sites. Carbon-supported catalysts uniquely produce C4-8 LAOs during C2H4 dimerization, with site-time-yield remaining constant (~10-3 s-1) for 1.0-4.0 Co nm-2 at prolonged reaction times (24-48?h time-on-stream). At higher loadings of 6.0 Co nm-2, the formation of crystalline CoO and Co3O4 phases reduces catalytic activity and LAO selectivity. Our findings show that active catalysts lack crystalline cobalt oxides and instead feature dispersed Co2+ sites, tetra-coordinated to a mix of N/NH3 and O/H2O ligands, which catalyze C2H4 dimerization via the Cossee-Arlman mechanism, exhibiting 1st order dependence on C2H4 concentration. The observed inverse rate-temperature correlation is attributed to compensation effects (i.e., presence of Cremer-Constable relationship) linked to changes in adsorption enthalpic and entropic factors.
The presence of Ru metal modifies the behavior of deuterium bound to pyridinic nitrogen in doped graphene-like materials
We used a combination of x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) to investigate how the presence of a ruthenium (Ru) metal substrate modifies the N-D bond strength of the pyridinic nitrogen species in nitrogen (N)-doped graphene (Gr) on Ru(0001) compared to metal-free highly-oriented pyrolytic graphite (HOPG) substrate. The N-dopants were introduced through low-energy N+/N2+ irradiation. N is embedded in the carbon materials in two predominant configurations: as graphitic N (GN: N substituted in the hexagonal C lattice) and pyridinic N (PN: substitutional N adjacent to a C vacancy). XPS data showed that upon atomic deuterium (D) exposure at 220 K, the PN peak shifted to a higher binding energy by +1.2 eV for HOPG and +1.0 eV for N-doped graphene on Ru(0001), while the GN peak remained unchanged, indicating that the D atoms bound solely to pyridinic N. 85% of PN sites on HOPG can be saturated with D atoms, whereas only ~30% of pyridinic N sites are able to bind D atoms in N-doped Gr/Ru(0001). Our DFT analysis shows that this difference is due to the coordination of PN to Ru atoms, which necessitates bond cleavage of the N-Ru interaction prior to D atom adsorption. D begins desorbing from N-HOPG at ~573 K and is fully desorbed by ~973 K, whereas desorption from N-doped graphene on Ru(0001) begins at ~290 K, with complete desorption observed at ~700 K, indicating that the Ru metal weakens the N-D bond strength. We also studied a high-surface-area, layered, and porous N-doped carbon material, internally labeled NC900, which was synthesized by pyrolysis of glucose and graphitic carbon nitride (g-C3N4) at 1173 K. D exposure caused a +1.1 eV PN peak shift in NC900, with no change in the GN peak. Moreover, the NC900 exhibited the same desorption behavior as HOPG, demonstrating that well-defined model systems can effectively capture the behavior of more complex N-doped carbon materials.