Conclusion

In summary, we synthesized a series of intermetallic PtM- and Pt3M-type catalysts (M

= Sn, Pb, and Zn). The atomically-ordered intermetallic structures of these catalysts are elaborately correlated to their catalytic properties in the hydrogenation of 3-nitrostyrene. All PtM-type intermetallic compounds (IMCs) show high selectivity to 3-aminostyrene in the hydrogenation of 3-nitrostyrene, in contrast to pure Pt and Pt3M-type catalysts. Intermetallic

PtSn@mSiO2 is also highly selective for the hydrogenation of nitro group in nitroarenes in the

presence of bromo, iodo, formyl and methoxy groups. Kinetic studies over Pt, PtSn, and Pt3Sn

revealed that the hydrogenation pathways could be altered due to changes in the surface structure of IMCs. Intermetallic PtSn facilitates a unique non-Horiuti-Polanyi pathway, where

the elimination of Pt threefold site inhibits the H2 dissociative adsorption and, in turn, decreases

the reaction rate. DFT calculations and competitive reactions ascribe the high selectivity to the preferential adsorption of nitro groups in 3-nitrostyrene over intermetallic PtSn surfaces. This work demonstrates a molecular engineering of intermetallic structures to tune and elucidate the catalytic mechanism for selective hydrogenations. We anticipate that the geometric effect of IMCs in heterogeneous catalysis can be generalized to instruct the exploration of advanced intermetallic systems for heterogeneous catalysis.

3.6 Supporting Information

Figure S3.1. TEM images and HRTEM images of a), b) PtSn@mSiO2; c), d) Pt3Sn@mSiO2;

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Figure S3.2. PXRD patterns of a) Pt@mSiO2; b) Pt3Sn@mSiO2; c) PtSn@mSiO2; d)

Pt3Zn@mSiO2; e) PtZn@mSiO2; and f) PtPb@mSiO2 with corresponding standard patterns.

Figure S3.3. Surface structures of ideal a) Pt(111), b) Pt3Sn(111), (110) and (100), and c)

PtSn(112_0), (0001), and (112_1). Pt (white circles) and Sn atoms (yellow circles) are shown,

along with Pt threefold sites (red triangles and rhombus in b), fourfold sites, and bridge sites (red rectangle in c) and single Pt (circle in c).

Figure S3.4. CV spectra of H+ electro-reduction for intermetallic PtSn@mSiO2, Pt@mSiO2

and commercial Pt/Vulcan. H2 Electro-reaction of evolution (2H+ + 2e D H2) occurs at -0.2-

0.1 V region (vs. Ag/AgCl) for both forward and backward scans, and the subsequent H2

desorption and adsorption due to this electro-reaction occurs at ~ 0 V. In -0.2 ~ 0.1 V, commercial Pt/Vulcan and Pt@mSiO2 are both active for the H+ electro-reduction reaction.

Pt@mSiO2 has weaker peak intensity and some voltage shift compared to commercial

Pt/Vulcan, likely due to the large sizes of Pt@mSiO2 (14 nm) presenting low surface area-to-

volume ratio and less undercoordinated Pt at corner, edge and kink sites. Specifically, Pt@mSiO2 sample has two tails (~ 0 V) in forward and backward scans, corresponding the H2

adsorption and desorption. Intermetallic PtSn@mSiO2 shows only one tail as the backward

scan corresponding the desorption of H2 from the electro-reaction, but the absence of the

adsorption tail indicates a negligible H2 adsorption capability on PtSn surfaces in the liquid

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Figure S3.5. DFT results of 3-nitrostyrene adsorption on Pt(111) and PtSn(112_0) in different

configurations. Pt (Sn) in surfaces are given by light grey (brown) spheres; C, N, O and H atoms in 3-nitrostyrene are shown by small gray, blue, red and white spheres. Top (bottom) panel is the top (side) view.

Figure S3.6. For Pt@mSiO2: the dependence of reaction rate on a) 3-nitrostyrene (NS)

concentration, and b) H2 pressure. The slope is a) is 0.08, indicating a near zero reaction order,

and the slope in b) is -0.43. For PtSn@mSiO2: c) the dependence of reaction rate on 3-

nitrostyrene concentration, and d) H2 pressure. The slope in c) is 0.02, indicating a near zero

order reaction, and the slope in d) is -1.25, showing a near negative first reaction order to H2.

For Pt, nitrostyrene substrate varies from 50, 75, 100, 125, and 150 mg; H2 pressure ranges

from 10, 20, 30 and 40 bars. For PtSn, nitrostyrene substrate varies from 50, 75, and 100 mg; H2 pressure ranges from 20, 30, and 40. All other reaction conditions were controlled as the

same: 2 mL toluene as a solvent, 20 mg xylene as internal standard and 80 ˚C. The reaction rate was calculated at the initial reaction time.

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Figure S3.7. PXRD patterns of alloyed PtSn0.3@mSiO2 alloy (black curve, directly after

synthesis), and intermetallic Pt3Sn@mSiO2 (red curve, after annealing). The diffraction peaks

of alloy PtSn0.3 slightly shift to lower angle due to lattice expansion by addition of Sn. The

intermetallic Pt3Sn agrees well with the Pt3Sn standard. Intermetallic phase shifts more to the

lower angles in contrast to the alloy phase.

Figure S3.8. AP-XPS spectra of PtSn0.3@mSiO2 during in situ reductions. Pt stays as a metallic

state in both fresh and reduced samples. The fresh sample has SnOx peaks and transitions to

metallic state after high-temperature reduction. The SnOx on the fresh sample can be formed

during the sample handling. However, they may readily exist during the TEG reduction. Atomic Pt/Sn ratios of fresh, reduced in 300˚C, and reduced in 500 ˚C are respectively 1.33, 1.90 and 2.28.

Table S3.1. ICP results of all PtM@mSiO2 NPs (M=Sn, Zn, and Pb).

Entry Pt (wt.%) Secondary metal _(wt.%) Actual Pt/M in _{molar ratios}

Pt@mSiO2 46.0 – – PtSn@mSiO2 27.5 16.3 1.02 Pt3Sn@mSiO2 57.8 10.6 3.3 PtZn@mSiO2 41.9 12.7 1.1 Pt3Zn@mSiO2 43.0 4.3 3.3 PtPb@mSiO2 36.0 34.7 1.1

Table S3.2. Catalytic results of fresh and annealed PtSn0.3@mSiO2 for the selective

hydrogenation of 3-nitrostyrene.

Catalyst Time Conversion Selectivity

Entry (h) (%) 1 2 3 1 _PtSnFresh 0.3@mSiO2 1 3.2 >99 — — 9 63.3 >99 — — 2 _PtAnnealed 3Sn@mSiO2 0.5 >99 — — >99 1 >99 — — >99

a. Reaction condition: 1 mg catalyst, 50 mg 3-nitrostyrene, 20 mg xylene as internal standard, 2 mL toluene as solvent, 80 ˚C, and 20 bar H2.

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CHAPTER 4. NON-DISSOCIATION HYDROGENATION PATHWAY DRIVEN