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catalyst - PowerPoint PPT Presentation


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Pt nanoparticles ( Pt NPs ). catalyst. hydrogen storage media. d ~ 1 - 10 2 nm. electrodes for fuel cells. Electron states of Pt atoms on the surface of Pt NPs are remarkable !. 195 Pt NMR of Pt NPs depends on. ・ molecular size ・ chemisorbed molecules. Solid-state 195 Pt NMR.

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Presentation Transcript
slide1

Ptnanoparticles(Pt NPs)

catalyst

hydrogen

storage media

d ~ 1 - 102 nm

electrodes for fuel cells

Electron states of Pt atoms on

the surface of Pt NPs are remarkable !

195Pt NMR of Pt NPsdepends on

・molecular size

・chemisorbed molecules

slide2

Solid-state 195Pt NMR

Peak positions of

Pt compounds

commercial Pt NPs

a few MHz

Pt complex

bulk Pt

(chemical shift)

(Knight shift)

The spins excited

by conventional π/2 pulses

(a few hundred kHz, at most)

H2PtCl6

H2PtI6

(standard)

[PtF6]2-

1.08

1.10

1.12

1.14

B0/ν0 (kG/MHz)

Point-by-point plots of

the peak area of the spin echoes

on variable-field

B0/ν0 (kG/MHz)

slide3

a home-built probe

Instruments (in Kyoto University)

variable-field cryogen-free magnet

controller

PC

amplifier

OPENCORE NMR spectrometer[2][3]

slide4

195Pt NMR of Pt NPs

cubo-octahedral

PtNPs

bulk Pt (n = ∞)

195PtNMR of Pt NPs

surface (n = 0)

subsurface(n = 1)

sub-subsurface

(n = 2)

K1

Kbulk

K0

K2

B0/ν0 (kG/MHz)

slide5

The NMR layer model for Pt NPs

the thickness of each Pt layer

0.23 nm

phenomenological

NMR layer model[4][5]

healing length

m×0.23 nm

Kbulk: the Knight shift on bulk Pt metal

K0: the Knight shift on the surface Pt atoms

Kn: the Knight shift on the nth Pt layer

n: layer number

m: healing factor

n×0.23 nm

surface

bulk moiety

the additional effect of hybridization of 5d and 6s band

core polarization by

5d conduction electron

electron configuration of

Pt atom: 6s25d8

→low 5d electron DOS at Fermi energy

→high 5d electron DOS at Fermi energy

slide6

all d~ 2-3 nm

1.08

1.08

1.10

1.10

1.12

1.12

1.14

1.14

B0/ν0 (kG/MHz)

B0/ν0 (kG/MHz)

195Pt NMRof Pt NPs protected by n-alkylthiols(1)

C6

surface

Pt-complex

(H2Pt(OH)6) ?

surface

C10

Pt complex ?

slide7

C18

Pt complex ?

1.08

1.08

1.10

1.10

1.12

1.12

1.14

1.14

B0/ν0 (kG/MHz)

B0/ν0 (kG/MHz)

195Pt NMRof Pt NPs protected by n-alkylthiols (2)

surface

C12

Pt-complex ?

surface