Activation of Copper Species on Carbon Nitride for Enhanced Activity in the Arylation of Amines

Abstract

We report the promoting effect of graphitic carbon nitride in Cu-catalyzed N-arylation. The abundance of pyridinic coordination sites in this host permits the adsorption of copper iodide from the reaction medium. The key to achieving high activity is to confine active Cu species on the surface, which is accomplished by introducing atomically-dispersed metal dopants to block diffusion into the bulk. The alternative route of incorporating metal during the synthesis of graphitic carbon nitride is ineffective as Cu is thermodynamically more stable in inactive subsurface positions. A combination of X-ray absorption, X-ray photoelectron, and electron paramagnetic resonance spectroscopy, density functional theory, and Kinetic Monte Carlo simulations is employed to determine the location and associated geometry as well as the electronic structure of metal centers. N-arylation activity correlates to the surface coverage by copper, which varies during the reaction due to an interplay between site formation via adsorption from the reaction medium and deactivation by diffusion into the bulk of the material, and is highest when an Fe dopant is used that hinders movement through the lattice.

Precursor Nuclearity and Ligand Effects in Atomically‐Dispersed Heterogeneous Iron Catalysts for Alkyne Semi‐Hydrogenation

“…Even in instances, where the barriers for surface ensemble formation are low (Fe 1 /MCN and Fe 2 /MCN), this configuration is furthermore compromised in terms of stability, due to the thermodynamic tendency for the metal to percolate to inactive interlayer positions (FeÀ i, inset d Figure 1c). [28] The surface iron content determined through XPS reveals metal depletion over the single-atom catalyst (0.1 wt.%) with respect to bulk contents and is therefore in agreement with DFT results. Samples from cluster precursors, and with nanoparticles, in turn, show smaller differences between bulk and surface iron concentration (0.4-0.47 wt.%) (Table 1).…”

“…The computational results indicate that the complete removal of ligands leading to bare Fe ensembles as active surface species, either in the form of single atom, dimers, or trimers (Fe−s, Fe 2 −s, Fe 3 −s, insets c, g, j Figure 1c) is unlikely. Even in instances, where the barriers for surface ensemble formation are low (Fe 1 /MCN and Fe 2 /MCN), this configuration is furthermore compromised in terms of stability, due to the thermodynamic tendency for the metal to percolate to inactive interlayer positions (Fe−i, inset d Figure 1c) [28] . The surface iron content determined through XPS reveals metal depletion over the single‐atom catalyst (0.1 wt.%) with respect to bulk contents and is therefore in agreement with DFT results.…”

Visible‐Light Promoted C–O Bond Formation with an Integrated Carbon Nitride–Nickel Heterogeneous Photocatalyst

“…The recovered heterogeneous material could be reused for further cycles to give coupling product 3 with no need of re‐addition of any of the catalytic components (Ni or mpg‐CN x ) and without loss of activity up to three cycles after which a slower rate of coupling was observed (Figure 2). The decrease in rate/activity could be due to an overall leaching of 20 % Ni from Ni‐mpg‐CN x after the fourth recycling or migration of surface‐activated Ni species to the bulk (Table S1) [38] . The recovered material displayed unchanged spectroscopic features and pXRD diffraction pattern (Figure 1).…”

Visualizing single atom dynamics in heterogeneous catalysis using analytical in situ environmental scanning transmission electron microscopy

“…ETEM with EELS has been employed to study gas compositions in gas-catalyst studies [47]. High-resolution STEM with EDX has been used to study enhanced activity of supported copper in the arylation of amines [48]. Catalyst nanostructural modifications induced by electronic metal–support interaction effects have been reported [49].…”