Dual-atom Pt heterogeneous catalyst with excellent catalytic performances for the selective hydrogenation and epoxidation

Atomically monodispersed heterogeneous catalysts with uniform active sites and high atom utilization efficiency are ideal heterogeneous catalytic materials. Designing such type of catalysts, however, remains a formidable challenge. Herein, using a wet-chemical method, we successfully achieved a mesoporous graphitic carbon nitride (mpg-C3N4) supported dual-atom Pt2 catalyst, which exhibited excellent catalytic performance for the highly selective hydrogenation of nitrobenzene to aniline. The conversion of ˃99% is significantly superior to the corresponding values of mpg-C3N4-supported single Pt atoms and ultra-small Pt nanoparticles (~2 nm). First-principles calculations revealed that the excellent and unique catalytic performance of the Pt2 species originates from the facile H2 dissociation induced by the diatomic characteristics of Pt and the easy desorption of the aniline product. The produced Pt2/mpg-C3N4 samples are versatile and can be applied in catalyzing other important reactions, such as the selective hydrogenation of benzaldehyde and the epoxidation of styrene.

To confirm the existence and the consequence of the incomplete focusing "problem", we have compared the different images that were collected within the same region of the sample but with the focus of the imaging constantly changed (Supplementary Figure 6). It can be seen that under different focusing conditions, isolated dots can indeed be imaged as paired dots. For example, with the focusing condition changed, the two isolated bright dots in the areas marked as "1" and "2" in the Supplementary Figure 6a  Supplementary Figure 11. The two-dimensional projection of three-dimensional sample along the incident beam direction in the AC HAADF-STEM characterization.
In Supplementary Figure 10a, there was paried bright dots (marked in the green rectangle) observed in the AC HAADF-STEM image of the Pt1/mpg-C3N4 sample. Very probably, this feature come from two Pt single atoms, which were far away from each other in the three-dimensional space, but happened to be very close when being projected onto a certain two-dimensional plane, as shown in the Supplementary Scheme S1. This is because the AC HAADF-STEM image only represents a two-dimensional projection of a three-dimensional sample along the incident beam direction. It should be noted that the emergence of such situation is very rare. Besides, since there was no Pt-Pt path observed in the EXAFS measurements for the Pt1/mpg-C3N4 sample, we could exclude the existence of the Pt2 species in the Pt1/mpg-C3N4 sample.
Supplementary Figure 12. FT EXAFS fitting spectrum of Pt1/mpg-C3N4 at R space. The inset is a schematic model of the Pt1/g-C3N4 system. The teal, gray, blue, and red spheres represent the Pt, C, N, and O atoms, respectively.
Supplementary Figure 14. Side view of Pt2/g-C3N4 structure, showing the distortion of the g-C3N4 substrate with obvious undulations. The teal, gray, and blue spheres represent the Pt, C, and N atoms, respectively.
Supplementary Figure 15. Selected Pt2 configurations (without the involvement of oxygen) on the g-C3N4 substrate obtained from the first-principles simulations Supplementary Figure 16. Selected Pt2-O2 configurations (upon the associative adsorption of O2) on the g-C3N4 substrate obtained from the first-principles simulations.
Supplementary Figure 17. TEM image of Pt NPs/mpg-C3N4 before the reaction.
Supplementary Figure 20. AC HAADF-STEM image of the Pt1/mpg-C3N4 after the reaction.
Supplementary Figure 21. TEM image of Pt NPs/mpg-C3N4 after the reaction.
Supplementary  Supplementary Figure 30. Reaction pathway and computational energy profile of the hydrogenation of benzaldehyde on the Pt2/g-C3N4 catalyst. The label S0 represents the initial state and the subsequent labels S1 -S6 represent a series of intermediate states.
The labels TS1 and TS2 represent a series of transition states. Here, only the key structures, i.e., the Pt2 catalytic system as well as the adsorbate bound on it, are shown. The information regarding reactant molecules which have not been adsorbed and/or product molecules which have been desorbed are labelled in the Supplementary Figure 27. The teal, gray, blue, red, and white spheres represent the Pt, C, N, O, and H atoms, respectively.
Supplementary Table 3. Imaginary frequencies of the transition states for the energy profile of the nitrobenzene hydrogenation on Pt2/g-C3N4 as shown in Fig. 4