Isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles to regulate selectivity in 4-nitrophenylacetylene hydrogenation

Noble metals play a momentous role in heterogeneous catalysis but still face a huge challenge in selectivity control. Herein, we report isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles as an effective strategy to optimize the selectivity of Pt catalysts. Contiguous Pt atoms are isolated into single atoms and Pt-Zn intermetallic nanoparticles are formed which are supported on hollow nitrogen-doped carbon nanotubes (PtZn/HNCNT), as confirmed by aberration-corrected high-resolution transmission electron microscopy and X-ray absorption spectrometry measurements. Interestingly, this PtZn/HNCNT catalyst promotes the hydrogenation of 4-nitrophenylacetylene to 4-aminophenylacetylene with a much higher conversion ( > 99%) and selectivity (99%) than the comparison samples with Pt isolated-single-atomic-sites (Pt/HNCNT) and Pt nanoparticles (Pt/CN). Further density functional theory (DFT) calculations disclose that the positive Zn atoms assist the adsorption of nitro group and Pt-Zn intermetallic nanoparticles facilitate the hydrogenation on nitro group kinetically.


Supplementary Information
Han et al.
without acid washing process. The polydopamine nanospheres were prepared according to literature 1 . The average diameter is around 200 nm.

Synthesis of PdZn/HNCNT.
The PdZn/HNCNT was obtained by a similar procedure to PtZn/HNCNT except that the Na2PdCl4 instead of H2PtCl6.

Characterization of products
Product 2a was isolated by flash column chromatography on silica gel with petroleum ether/ethyl acetate as eluent. As a known compound, the product 2a is characterized by comparison of their 1 H NMR and 13 C NMR spectroscopic data with those reported in the literature. All chemical shifts (δ) are reported in ppm and coupling constants (J) in Hz. All chemical shifts were reported relative to tetramethylsilane (0 ppm for 1 H), and CDCl3 (77.16 ppm for 13 C), respectively. CO FTIR characterizations were carried out on a Brucker Tenser II in situ infrared spectrometer with MCT detector using a home-made cell. The samples were pretreated with H2/Ar at 200 o C for 1 h. After cooling down to room temperature (20 o C) and flushing with Ar for 20 min, the background spectrum was collected. Then, CO gas was introduced into the sample holder for 30 min. The sample was flushing with Ar and spectra were collected every 15 s. 4 The catalyst was centrifuged out and washed with ethanol for several times. After drying in oven at 80 o C, it was reused directly.

XAFS measurements:
The X-ray absorption find structure spectra (Pt L3-edge and Zn Kedge) were collected at BL1W1B station in Beijing Synchrotron Radiation Facility (BSRF).
The data were collected in fluorescence excitation mode using a Lytle detector. All samples were pelletized as disks of 13 mm diameter using graphite powder as a binder.

XAFS Analysis and Results:
The acquired EXAFS data were processed according to the standard procedures using the ATHENA module implemented in the IFEFFIT software packages. The EXAFS spectra were gained by subtracting the post-edge background from the overall absorption and then normalizing with respect to the edge-jump step.
Subsequently, the χ(k) data were Fourier transformed to real (R) space using a hanning windows (dk=1.0 Å -1 ) to separate the EXAFS contributions from different coordination shells. Least-squares curve parameter fitting was carried out using the ARTEMIS module of IFEFFIT software packages to obtain the quantitative structural parameters around central atoms.

Computational details.
The calculations were performed ultilizing the plane-wave pseodopotential method in the framework of density functional theory (DFT). The ion core and valence electron interaction was described by Vanderbilt-type ultrasoft pseudopotential. The electron exchange-correlation effects were described by the generalized gradient approximation (GGA) in the form of Perdew-Burke-Ernzerh (PBE) functional 2 . All spin-polarized density functional theory (DFT) calculations were performed on the Cambridge serial total energy package (CASTEP) program 3 . The role of the van der Waals (vdw) force should not be ignored in the considered systems. Hence, the dispersion correction included DFT-D method was used 4 . The plane-wave cutoff enrgy was set to 350 eV. The convergence thresholds between optimization cycles for energy change and maximum force were set as 10 -5 eV/atom and 0.03 eV/Å, respectively.
Surfaces were modeled using p(5×5) and p(3×4) unit cells for Pt(111) and  Using the above calculation method, the bulk PtZn was firstly optimized, obtaining the following lattice constants: a=b=4.026 Å, c=3.450 Å. The calculation results are well consistent with the XRD measurements: a=b=4.025 Å, c=3.491 Å. These calculation results indicate that the calculation models and method in the present work are reasonable.         The left configuration is more stable.   C.N. is the coordination number; R is interatomic distance (the bond length between central atoms and surrounding coordination atoms); σ 2 is Debye-Waller factor (a measure of thermal and static disorder in absorber-scatterer distances); R factor is used to value the goodness of the fitting.