Brief introduction of the results
The basic understanding of the synergistic effect of bimetallic catalysts is of great significance in heterogeneous catalysis, but how to accurately construct homogeneous bimetallic sites still faces great challenges. Based on this,Professor Qin Yong and Associate Professor Ren Yujing of Northwestern Polytechnical University, Haifeng Qi of Leibniz Institute of Catalysis in Germany, Na Yang of University of Electronic Science and Technology of China, etcIn this paper, we report an efficient method for the construction of a dual-single-atom catalyst, which anchors the Pt single atom by modifying the Fe1-N4 single atomic site on the surface of nanodiamond (ND).
The presence of PT1-Fe1 bi-monoatomic sites (denoted as PT1-Fe1 ND) on the surface of nanodiamonds was confirmed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) image analysis, X-ray absorption fine structure (XAFS) spectral simulation and X-ray photoelectron spectroscopy (XPS) spectral fitting.
The test found that the synergistic catalysis of chemically selective hydrogenation of nitroaromatic hydrocarbons was revealed at the atomic level using this Pt1-Fe1 dual site. Combined with the experimental results and density functional theory (DFT) calculations, the hydrogen is activated at the Pt1-Fe1 site, and the nitro group is preferentially adsorbed and activated at the Fe1 site. Although the hydrogen activation ability of the Pt1-Fe1 site against the Pt NP counterpart was slightly poor, the vertical adsorption configuration of the nitro group on the Fe1 site and the strong adsorption energy made it easier for the Pt1-Fe1 site to selectively activate the nitro group.
The synergistic effect on the Pt1-Fe1 dual site results in a record catalytic performance for nitroaromatic hydrogenation with a turnover frequency (TOF) of 31 s-1, the selectivity is close to 100%, and the substrate adaptability reaches 24 kinds. This discovery not only promotes the application of bi-monoatomic catalysts in selective hydrogenation, but also opens up a new way to explore the nature of cocatalysis at the atomic level.
Background:
Supported metal catalysts (SMCs) play an important role in the fields of chemical industry, energy conversion and environmental protection. At present, the study of synergistic catalysis of SMCs has become one of the hot topics in the field of heterogeneous catalysis. Although the synergy between *** and non-*** oxides has made great progress in the hydrogenation of C-O, revealing the nature of synergistic catalysis is still a difficult obstacle to overcome due to the inevitable coexistence of multiple metal sites in traditional SMCS.
Compared with traditional SMCS, the geometric isolation of metal species in single-atom catalysts eliminates the influence of various active site structures such as step sites, angular sites, and step sites. By further selectively anchoring another metal single atom to a single atom catalyst to precisely construct the hetero-nuclear M1-M'1 double single atomic site, the researchers were able to reveal the fundamental role of cocatalysis at the atomic level. However, the "bottom-up" synthesis strategy has limited operability for the construction of hetero-nuclear M1-M'1 dual sites.
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Preparation and characterization
For the first time, the authors anchored the PT single-atom precursor (PTCL62-) by modifying the surface of nanodiamond (ND) with Fe1-N4 single-atomic site (FeΔ+) for self-confinement surface reactions. The ferric phthalocyanine (Fe-PC) precursor was impregnated on the surface of the ND and then treated in AR at 400 to load the Fe1-N4 monoatomic site on the surface of the ND. Then, the PT precursor (PTCL62-) was loaded on the surface of Fe1 Nd by a simple electrostatic adsorption method and reduced at 250. Inductively coupled plasma (ICP) measurements showed that the PT1-Fe1 ND sample (201 wt.% pt and 100 wt.% Fe) and PTNP ND samples (199 wt.% pt) is close to the theoretical value.
Figure 1Schematic diagram of the preparation of the PT1-Fe1 ND catalyst and Haadf-STEM images
Figure 2Ac-HAADF-STEM images and coordination environment characterization of PT1-Fe1 ND, FE1 ND, and PTNP NDATR-IR characterization
Attenuated Total Reflection Infrared (ATR-IR) spectroscopy was performed using a Thermo Scientific Nicolet IS50 spectrometer equipped with a mercury-cadmium tellurium (MCT) detector with a resolution of 4 cm-1. Before the experiment, the samples were dispersed in ethanol, sonicated for 1 h, and then the suspension was dropped onto the surface of the diamond crystals on the instrument at 65 and dried at 100 for 4 h. Before collecting data, the background spectrum is recorded.
Then, to obtain a signal to adsorb the substrate, droplets of the substrate are added to the surface of the catalyst. H2 microcalorific measurements are made by BT215 heat flux calorimeters, which are connected to gas handling and volumetric systems, are carried out with MKS Baratron capacitance pressure gauges for precision pressure measurements. The ultimate dynamic vacuum of the microthermal system has been calculated to be 10-7 torr.
Figure 3Electronic structures of Pt1-Fe1 ND, Fe1 ND, and PTNP ND samples
Figure 4Kinetic experiments on p-nb hydrogenation on PT1-Fe1 ND and PTNP ND catalystsAIMD simulation
Through ab initio molecular dynamics (AIMD) simulations, the authors theoretically investigated the stability of the PT1-Fe1 double monoatomic bite. The configuration of N3-Pt1-Fe1-N3 on graphitic carbon surface was optimized by density functional theory (DFT) calculation, which was derived from the results of HAADF-STEM and Exafs. Under the condition of 353 K, a systematic AIMD simulation of the N3-PT1-FE1-N3 model was carried out within 10 ps to clarify its dynamic stability.
The results show that the structure of N3-Pt1-Fe1-N3 does not undergo structural failure during the whole simulation process, and the energy and temperature of the system remain stable, which is consistent with the stability experimental results. More importantly, from the radial distribution function (RDF) results of AIMD simulation, it is found that the Fe and Pt atoms in the N3-Pt1-Fe1-N3 structure have a bond length of 1., respectively96 and 2The 3 n atoms of 01 are directly coordinated and in 2There were 32 obvious PT-Fe coordination sites, which proved the theoretical coordination environment of N3-Fe-Pt1 and N3-PT-Fe1 at the Fe1 and Pt1 monoatomic sites.
Figure 5AIMD simulationTheoretical calculations
Adsorption and activation of H2 on Pt1-Fe1, dissociation of H2 molecules at Pt1-Fe1 dual site, and its dissociation reaction barrier (050 eV) was slightly higher than the dissociation reaction barrier on the surface of PT(111), indicating that PT1-Fe1 was more difficult to activate the H2 molecule. The optimized adsorption structure of P-Nb on the surface of PT(111), including planar configuration and vertical configuration, indicates that P-Nb tends to adsorb on the surface of Pt in planar structure. For the N3-Pt1-Fe1-N3 structure, the Fe1 site in Pt1-Fe1 preferentially adsorbs the -NO2 group in the vertical configuration of the P-Nb molecule. For the dual sites, both Fe1-Fe1 and Pt1-Pt1 can dissociate H2, but the adsorption of Fe1-Fe1 by P-Nb molecule is too strong, and the adsorption of Pt1-Pt1 is too weak.
The results showed that Fe1, Pt1, Fe1-Fe1 and Pt1-Pt1 sites were not conducive to the selective hydrogenation of P-Nb. Therefore, the PT1-Fe1 ND di-monoatomic catalyst exhibits excellent catalytic performance for the selective hydrogenation of nitroaromatic hydrocarbons. For the N3-Pt1-Fe1-N3 structure, there were 14 intermediate states (IMS) and 6 transition states (TSS) in the P-Nb hydrogenation reaction, and it was found that its surface had stronger nitrohydrogenation activity than that of PT (111). The vertical adsorption configuration of the nitro group on Fe1 and the strong adsorption energy make it easier for N3-Pt1-Fe1-N3 to activate the nitro group, resulting in excellent catalytic performance and excellent substrate adaptability.
Figure 6Mechanism of catalytic hydrogenation process
Bibliographic information
atomic insights into synergistic nitroarene hydrogenation over nanodiamond-supported pt1-fe1 dual-single-atom catalyst. angew. chem. int. ed.,