The position effect caused by the matching of reactants molecules in fenton-like single-atom catalysts
Research background
Single-atom catalysts (SACs) have unique properties such as high metal atomic utilization rate, adjustable coordination environment, and strong metal-carrier interaction, which make them widely used in electrocatalysis, chemical synthesis, environmental remediation and other fields. Over the past few years, efforts have been made to increase atomic site density to increase their catalytic activity in various catalytic reactions. In principle, as the position density increases to a certain extent, the internal atom dispersion of the metal will become tighter and form adjacent atoms. However, when reactant molecules co-adsorb at adjacent active sites, this bit spacing effect may not be suitable for other catalytic systems, and its adsorption structure may change when the adjacent active site spacing changes. Therefore, a further understanding of this position distance effect of catalytic action other than oxygen reduction reactions is critical for designing efficient dense SACs for various reactions. Understanding the locus interaction properties of single-atom catalysts (SAC), especially dense SAC, is critical for their application in a variety of catalytic reactions.
Synopsis
Based on this, academicians Li Yadong of Tsinghua University, Wang Dingsheng, and Zhang Hui of Wuhan University collaborated to report the site distance effect, which emphasized that the degree of matching the distance of adjacent copper atoms (denoted as dCu1-Cu1) with the molecular size of the reactant perdisulfate (PDS) determines the Fenton-like reactivity on the carbon-loaded SAC. The dCu1-Cu1 optimized in the 5-6 Å range matches the molecular size of the PDS and has a TOF value nearly twice that of dCu1-Cu1 beyond this range, enabling record-breaking kinetics for the oxidation of emerging organic pollutants. Further studies have shown that this site distance effect stems from the PDS adsorption change to a bi-site structure at cu1-Cu1 site when dCu1-Cu1 decreases by 5-6 Å, significantly enhancing interfacial charge transfer, resulting in the most efficient catalyst for PDS activation. The paper was published in Anglo Chem. Int. Ed.
Highlights of this article
Experimental and theoretical results have shown that dCu1-Cu1 has a significant effect on Fenton-like reactivity.
2. This new range effect announces a change in the adsorption structure of reactants at adjacent active sites with different ranges, emphasizing the importance of the distance matching the size of the reactants molecules in saCs.
3. This work provides insight into how well the active center distance matches the reactant molecule at the atomic level, rather than determining the position density of the single-atom catalytic reaction activity, which adds new knowledge to the sound design of efficient SACs in other applications.
Graphic and text analysis
HAADF-STEM,XANES
Figure 1. Regulation and characterization of dCu1-Cu1 structure of Cu1/NG.
Cu1/NG is a synthetic method by chemical vapor deposition (CVD). By adjusting the amount of metal salts, a series of catalysts with different bit densities were synthesized. AC-HAADF-STEM images show that 1.0% of Cu1/NG samples consist mainly of individual Cu atoms. When the mass load of copper increases to 2.9%, some adjacent copper atoms appear. The portion of adjacent Cu atoms of dCu1-Cu1 in the range of 5–6Å is marked with a red dotted rectangle. This distance is consistent with the distance in the optimized structural model. The corresponding energy dispersive X-ray spectroscopy (EDS) plot shows that C, N, and Cu elements are evenly distributed across all catalysts. The local atomic structure of Cu atoms in Cu1/NG catalysts was further studied by X-ray absorption fine structure spectroscopy (XAFS). The valence state of the Cu atom in Cu1/NG is between 0 and +2. The newly formed adjacent Cu atoms induce charge redistribution, thereby enriching the charge density of the Cu atoms.
XPS,EXAFS,DFT
Figure 2. Atomic structure analysis.
XPS results confirmed the presence of C, N and Cu elements in all Cu1/NG samples. The fitting results showed that the coordination numbers of cu in the first coordination ball in 0.2, 1.0, 2.9 and 5.0% Cu1/NG were 4.1, 4.1, 4.0 and 3.9, respectively. However, since Cu-N or Cu-C bonds are still difficult to distinguish from XAFS analysis, density functional theory (DFT) calculations are further performed to determine an optimized structural model of Cu1/NG. Among the various structures, the formation energy of the cu-N4 configuration of the atom Cu embedded in the graphene lattice is the lowest, indicating that the Cu species in Cu1/NG exist mainly in the form of Cu-N4. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) shows that although the Metal Bit Densities of cu1/NG samples differ, they all form CuN4 atomic bits.
Catalytic results
Figure 3. dCu1-Cu1 has excellent Fenton-like reactivity.
The researchers evaluated the Fenton-like reactivity of the Cu1/NG catalyst by removing bisphenol A (BPA) through PDS activation. Of the catalysts prepared with different Cu densities, 2.9% of Cu1/NG had the highest catalytic activity, where ultra-fast removal of BPA was achieved within 5 min by activating PDS. Comparing the relationship between catalyst activity and Cu-N4 sites, it was found that the opposite of the results pursued by most previous studies to finally support metals in SAC to enhance catalytic capacity were found. Therefore, a new determinant of the position distance rather than the position density effect of the Fenton reactivity is proposed. This location distance effect is not only applicable to PDS, but can also be extended to other oxidizing agents. Compared with the literature results, the k-value of 2.9% Cu1/NG exceeded all catalysts for PDS activation and the most advanced SAC for Fenton-like reactions reported to date. The inheritance distance of the adjacent atoms of the catalyst after the cycle is well maintained, indicating that the stability of 2.9% Cu1/NG is good.
EPR,Raman
Figure 4. Identification of reactive oxygen species and active sites.
Rapid removal of BPA is a catalytic oxidation process in a 2.9% Cu1/NG/PDS system where rapid removal of BPA is achieved through an electron transfer mechanism without producing free radicals and 1O2. As a result of this non-free radical process, the 2.9% Cu1/NG/PDS system exhibits significant substrate specificity for the removal of multiple contaminants, where contaminants with electron-giving groups are more susceptible to oxidation. A good linear correlation between lnkobs and the half-wave potentials of different contaminants was observed, suggesting that selective oxidation is primarily due to the single-electron oxidation potential of contaminants. At the same time, the electron transfer oxidation process enables the system to resist common anions and a variety of real water matrices, indicating that Cu1/NG has good practical application prospects.
DFT
Figure 5. Experimental and theoretical calculations verify the adsorption structure changes.
To understand this site distance effect, a DFT calculation was performed. Four related models of Cu-N4, 2Cu-N4, Cu2-N6 and N-G were established, representing 1.0%, 2.9%, 5.0% Cu1/NG and NG, respectively. Calculations show that PDS adsorption at 2.9% Cu1/NG is much stronger than other catalysts. Therefore, this novel locus distance effect that increases Cu1/NG activity by 2.9% may be mainly due to the formation of bilocal adsorption on adjacent Cu atoms. For 2.9% Cu1/NG, when a certain number of Cu atoms are blocked by DMP, bilocal adsorption may be destroyed immediately, and the oxidation rate of BPA drops sharply. Conversely, as DMP continues to increase, the toxicification of DMP to Cu1 sites with a maximum dCu1-Cu1 ratio of more than 5-6 Å increases linearly, suggesting that there is only one type of adsorption in these catalysts, namely single-point adsorption. Therefore, the site distance effect of altering the adsorption structure of PDS on Cu1-Cu1 sites with different dCu1-Cu1 to increase Fenton-like reactivity was co-confirmed. To further reveal the nature of the superior performance of bilocal adsorption between PDS and 2Cu-N4, the projection crystal orbital Hamilton layout (pCOHP) was used to analyze the interaction between the metal center and the PDS. The results showed that bilocal adsorption caused by the site distance effect could enhance the interaction between PDS and Cu sites and promote their charge transfer, resulting in excellent activity of 2.9% Cu1/NG for PDS activation.
The main calculation and test methods of the study
- Synchrotron radiation X-ray absorption spectroscopy (XAFS)
- First Principles DFT Computation (VASP)
- Field testing | In situ aberration correction transmission electron microscopy (JEOL JEM-ARM200F)
Do synchrotron radiation find easy scientific research
- Synchrotron radiation X-ray absorption spectroscopy (XAFS)
Do aberration electron microscopy to find easy scientific research
- Cryo-transmission electron microscopy (FEI Titan Krios)
- Double-ball aberration correction transmission electron microscopy (FEI Themis Z)
- Field testing | In situ aberration correction transmission electron microscopy (JEOL JEM-ARM200F)
- Field testing | In situ ambient spherical aberration correction transmission electron microscope (FEI Titan ETEM G2)
Do calculations find easy scientific research
- First Principles DFT Computation (VASP)
- Molecular Dynamics Simulation (Gromacs)
- Molecular Dynamics (LAMMPS)
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