Nanophase-separated Ni3Nb as an automobile exhaust catalyst† †Electronic supplementary information (ESI) available: Demonstration procedure, experimental and characterization details. See DOI: 10.1039/c6sc05473k Click here for additional data file. Click here for additional data file.

Nanophase-separated Ni3Nb alloy exhibited higher performance than traditional Pt catalysts toward the remediation of automobile exhaust.


Supporting Information
Title:
6 Figure S3: HAXPES spectrum in the Nb 3d region for the nanophase-separated Ni 3 Nb.7 Figure S4: HAXPES spectrum in the Ni 2p region for the nanophase-separated Ni 3 Nb. 8 Figure S5: pXRD profile for the Ni 3 Nb material exposed to the reactant gas. 9 Guide to a supporting movie 14 Electronic Supplementary Material (ESI) for Chemical Science. This journal is © The Royal Society of Chemistry 2017 photon energy of 5.95 keV at the undulator beamline BL15XU of SPring-8, Japan. The HAXPES measurements were conducted at room temperature under UHV using a hemispherical electron energy analyser (VG SCIENTA R4000). The total energy resolution was set to 220 meV. The binding energy was referenced to the Fermi edge of a Au thin film. We

Catalytic tests
The NO remediation performance of the different catalysts was evaluated with a gascirculation reactor and a fixed-bed flow reactor. Aliquots consisting of 50 mg and 500 mg of the powder samples were introduced into the reaction tubes (4 mm in diameter) of the gascirculation reactor and the fixed-bed flow reactor, respectively. Aliquots consisting of a 10 kPa mixture of NO+CO gas (NO:CO=1:1) and a 100 kPa mixture of NO+CO+He gas (NO:CO:He=1:1:98 or NO:CO:O 2 :He=2:4:1:93; feeding rate = 5 cm 3 min −1 ; space velocity = 30000 h -1 ) were used for the gas-circulation and fixed-bed flow tests, respectively. The composition of the effluent gas was monitored using a gas chromatograph (Shimadzu G8-A) and a FTIR spectrometer equipped with a gas cell unit (Shimadzu Prestige 21).

Surface-chemistry analyses
The number of active Ni sites on the Ni 3 Nb surface was determined by CO chemisorption with an automatized chemisorption apparatus (Autochem, Micromeritics  Figure S1. Powder X-ray diffraction (pXRD) profiles for different Ni intermetallics.

Figures
pXRD profiles for Ni 3 Ti, Ni 3 Nb, Ni 3 B and Ni 3 Sn. Simulated pXRD patterns are presented as blue bars. The simulated patterns are consistent with the experimentally acquired pXRD profiles, indicating that the synthesized intermetallics are uniformly ordered in the desired phases.

Figure S2. Hard X-ray photoemission (HAXPES) spectra for different Ni intermetallics.
The HAXPES spectra for Ni, Ni 3 B, Ni 3 Al and Ni 3 Sn show sharp Ni 3d emission peaks right below the Fermi level (Binding Energy = 0.0 eV). By contrast, the spectrum for neither Ni 3 Ti nor Ni 3 Nb shows Ni 3d emission peaks due to hybridization between the Ni 3d orbital and the Ti 3d-or Nb 4d orbitals.

Figure S3. HAXPES spectrum in the Nb 3d region for the Ni 3 Nb catalyst.
The Ni 3 Nb catalyst was exposed to the reactant gas (NO:CO = 1:1; total pressure = 10 kPa) at 400 °C for 1 hr, forming a nanophase-separated structure on the surface. The HAXPES spectra for Nb metal and Nb 2 O 5 are presented as references. The Nb 3d emissions from the Nb n+ cations in the nanophase-separated Ni 3 Nb had lower binding energies than those from Nb 5+ 2 O 5 , indicating that the nanophase-separated structure consists of oxygen-deficient NbO x (x < 5/2). The HAXPES spectra for Ni metal and NiO are presented as references. Figure S5. pXRD profile for the nanophase-separated Ni 3 Nb catalyst.
The Ni 3 Nb catalyst was exposed to a He-balanced reactant gas (NO:CO:He = 1:1:98) at 400 °C for 550 hrs. The pXRD profiles for the as-prepared Ni 3 Nb, Ni, NiO and Nb 2 O 5 are presented as references.

Figure S6. Annular-dark-field image (left) and bright-field image of the nanophaseseparated Ni 3 Nb.
The Ni 3 Nb sample was exposed to the reactant gas (NO:CO = 1:1; total pressure = 10 kPa) at 400 °C for 1 hr.

Figure S7. Cross-section TEM images of the nanophase-separated Ni 3 Nb.
The images correspond to the Ni 3 Nb catalysts after 1 hr of exposure (top) and after 550 hrs of exposure (bottom) to the He-balanced reactant gas (NO:CO:He = 1:1:98; 400 °C; see the text).
[1] T. Tanabe, Microscopy 2011, 60, 35. Catalytic activity of Nb 2 O 5 -supported Ni nanoparticles at different temperatures. Each of the NO-remediation activty data was evaluated at 50 min. after the catalyst was exposed to the simulated exhaust gas. Note that the NO-remediation activity evaluated at 425 o C in decreasing temperature was lower than that in increasing temperature, indicating that the catalyst was degraded during the catalytic reactions up to 525 o C.