The nature of CO adsorption on Pdn/TiO2(110) (n = 1, 2, 7, 20) has been examined using temperature-programmed desorption (TPD), temperature-dependent helium ion scattering (TD-ISS), and X-ray photoelectron spectroscopy (XPS). All samples contain the same number of Pd atoms (0.10 ML-equivalent) deposited as different size clusters. The TPD and TD-ISS show that CO binds in two types of sites associated with the Pd clusters. The most stable sites are on top of the Pd clusters (“on-top” sites), however, there are also less stable sites, in which CO is bound in association with, but not on top of the Pd (“peripheral” sites). For saturation CO coverage over a fixed atomic concentration of Pd (present in the form of Pdn clusters of varying size), the population of CO in peripheral sites decreases with increasing cluster size, while the on-top site population is size-independent. This is consistent with what geometric considerations would predict for the density of the two types of sites, provided the clusters adsorb predominantly as 2D islands, which ISS results suggest to be the case. The XPS analysis indicates that CO-Pd binding is dominated by π-backbonding to the Pdn clusters. The results also show evidence for efficient support-mediated adsorption (reverse-spillover) of CO initially impinging on TiO2 to binding sites associated with the Pd clusters.

1.
H.
Conrad
,
G.
Ertl
, and
J.
Kueppers
,
Surf. Sci.
76
,
323
(
1978
).
2.
T.
Schalow
,
B.
Brandt
,
D. E.
Starr
,
M.
Laurin
,
S. K.
Shaikhutdinov
,
S.
Schauermann
,
J.
Libuda
, and
H.-J.
Freund
,
Phys. Chem. Chem. Phys.
9
,
1347
(
2007
).
3.
S.
Shaikhutdinov
,
M.
Heemeier
,
J.
Hoffmann
,
I.
Meusel
,
B.
Richter
,
M.
Bäumer
,
H.
Kuhlenbeck
,
J.
Libuda
,
H.-J.
Freund
,
R.
Oldman
,
S. D.
Jackson
,
C.
Konvicka
,
M.
Schmid
, and
P.
Varga
,
Surf. Sci.
501
,
270
(
2002
).
4.
S.
Kunz
,
F. F.
Schweinberger
,
V.
Habibpour
,
M.
Rottgen
,
C.
Harding
,
M.
Arenz
, and
U.
Heiz
,
J. Phys. Chem. C
114
,
1651
(
2010
).
5.
S. M.
McClure
and
D. W.
Goodman
,
Chem. Phys. Lett.
469
,
1
(
2009
).
6.
W. E.
Kaden
,
W. A.
Kunkel
,
M.
Kane
,
F. S.
Roberts
, and
S. L.
Anderson
,
J. Am. Chem. Soc.
132
,
13097
(
2010
).
7.
W. E.
Kaden
,
T.
Wu
,
W. A.
Kunkel
, and
S. L.
Anderson
,
Science
326
,
826
(
2009
).
8.
M.
Gadgil
and
S.
Kulshreshtha
,
J. Mol. Catal. A: Chem.
95
,
211
(
1995
).
9.
M.
Gadgil
and
S.
Kulshreshtha
,
J. Solid State Chem.
111
,
357
(
1994
).
10.
T.
Engel
and
G.
Ertl
,
Chem. Phys. Lett.
54
,
95
(
1978
).
11.
T.
Engel
and
G.
Ertl
,
J. Chem. Phys.
69
,
1267
(
1978
).
12.
I. Z.
Jones
,
R. A.
Bennett
, and
M.
Bowker
,
Surf. Sci.
439
,
235
(
1999
).
13.
G. A.
Kok
,
A.
Noordermeer
, and
B. E.
Nieuwenhuys
,
Surf. Sci.
135
,
65
(
1983
).
14.
C. J.
Harding
,
S.
Kunz
,
V.
Habibpour
,
V.
Teslenko
,
M.
Arenz
, and
U.
Heiz
,
J. Catal.
255
,
234
(
2008
).
15.
C. J.
Harding
,
S.
Kunz
,
V.
Habibpour
, and
U.
Heiz
,
Chem. Phys. Lett.
461
,
235
(
2008
).
16.
M.
Bowker
and
E.
Fourre
,
Appl. Surf. Sci.
254
,
4225
(
2008
).
17.
I.
Stara
and
V.
Matolin
,
Surf. Sci.
313
,
99
(
1994
).
18.
V.
Matolin
,
I.
Stara
,
N.
Tsud
, and
V.
Johanek
,
Prog. Surf. Sci.
67
,
167
(
2001
).
19.
V.
Matolin
,
I.
Jungwirthova
, and
E.
Tomkova
,
Prog. Surf. Sci.
35
,
175
(
1990
).
20.
J.
Fischer-Wolfarth
,
J.
Farmer
,
J.
Flores-Camacho
,
A.
Genest
,
I.
Yudanov
,
N.
Rosch
,
C.
Campbell
,
S.
Schauermann
, and
H.-J.
Freund
,
Phys. Rev. B
81
,
241416
(
2010
).
21.
A. S.
Woerz
,
K.
Judai
,
S.
Abbet
, and
U.
Heiz
,
J. Am. Chem. Soc.
125
,
7964
(
2003
).
22.
U.
Landman
,
B.
Yoon
,
C.
Zhang
,
U.
Heiz
, and
M.
Arenz
,
Top. Catal.
44
,
145
(
2007
).
23.
S.
Vajda
,
R. E.
Winans
,
J. W.
Elam
,
B.
Lee
,
M. J.
Pellin
,
S.
Seifert
,
G. Y.
Tikhonov
, and
N. A.
Tomczyk
,
Top. Catal.
39
,
161
(
2006
).
24.
S.
Lee
,
L. M.
Molina
,
M.
Lopez
,
J. A.
Alonso
,
B.
Hammer
,
B.
Lee
,
S.
Seifert
,
R. E.
Winans
,
J. W.
Elam
,
M. J.
Pellin
, and
S.
Vajda
,
Angew. Chem., Int. Ed.
48
,
1467
(
2009
).
25.
S.
Vajda
,
M. J.
Pellin
,
J. P.
Greeley
,
C. L.
Marshall
,
L. A.
Curtiss
,
G. A.
Ballentine
,
J. W.
Elam
,
S.
Catillon Mucherie
,
P. C.
Redfern
,
F.
Mehmood
, and
P.
Zapol
,
Nature Mater.
8
,
213
(
2009
).
26.
S. K.
Buratto
,
M. T.
Bowers
,
H.
Metiu
,
M.
Manard
,
X.
Tong
,
L.
Benz
,
P.
Kemper
, and
S.
Chretien
,
Chem. Phys. Solid Surf.
12
,
151
(
2007
).
27.
J. G.
Wang
and
B.
Hammer
,
Phys. Rev. Lett.
97
,
136107
(
2006
).
28.
S.
Chretien
,
S. K.
Buratto
, and
H.
Metiu
,
Curr. Opin. Solid State Mater. Sci.
11
,
62
(
2008
).
29.
A.
Vijay
,
G.
Mills
, and
H.
Metiu
,
J. Chem. Phys.
118
,
6536
(
2003
).
30.
M.
Bowker
,
P.
Stone
,
R.
Bennett
, and
N.
Perkins
,
Surf. Sci.
497
,
155
(
2002
).
31.
M.
Boudart
,
J. Mol. Catal. A: Chem.
138
,
319
(
1999
).
32.
M.
Boudart
,
M. A.
Vannice
, and
J. E.
Benson
,
Z. Phys. Chem.
64
,
171
(
1969
).
33.
C. R.
Henry
,
C.
Chapon
, and
C.
Duriez
,
J. Chem. Phys.
95
,
700
(
1991
).
34.
F.
Rumpf
,
H.
Poppa
, and
M.
Boudart
,
Langmuir
4
,
722
(
1988
).
35.
T.
Dellwig
,
J.
Hartmann
,
J.
Libuda
,
I.
Meusel
,
G.
Rupprechter
,
H.
Unterhalt
, and
H.-J
Freund
,
J. Mol. Catal. A: Chem.
162
,
51
(
2000
).
36.
W. C.
Conner
and
J. L.
Falconer
,
Chem. Rev.
95
,
759
(
1995
).
37.
W. E.
Kaden
,
W. A.
Kunkel
, and
S. L.
Anderson
,
J. Chem. Phys.
131
,
114701
(
2009
).
38.
M.
Aizawa
,
S.
Lee
, and
S. L.
Anderson
,
Surf. Sci.
542
,
253
(
2003
).
39.
A.
Linsebigler
,
G.
Lu
, and
J. T.
Yates
,
J. Chem. Phys.
103
,
9438
(
1995
).
40.
K. J.
Boyd
,
A.
Lapicki
,
M.
Aizawa
, and
S. L.
Anderson
,
Rev. Sci. Instrum.
69
,
4106
(
1998
).
41.
S.
Lee
,
C.
Fan
,
T.
Wu
, and
S. L.
Anderson
,
J. Chem. Phys.
123
,
124710
(
2005
).
42.
M.
Aizawa
,
S.
Lee
, and
S. L.
Anderson
,
J. Chem. Phys.
117
,
5001
(
2002
).
43.
U.
Diebold
,
M.
Li
,
O.
Dulub
,
E. L. D.
Hebenstreit
, and
W.
Hebenstreit
,
Surf. Rev. Lett.
7
,
613
(
2000
).
44.
W. S.
Epling
,
C. H. F.
Peden
,
M. A.
Henderson
, and
U.
Diebold
,
Surf. Sci.
412/413
,
333
(
1998
).
45.
T.
Wu
,
W. E.
Kaden
, and
S. L.
Anderson
,
J. Phys. Chem. C
112
,
9006
(
2008
).
46.
D.
Matthey
,
J. G.
Wang
,
S.
Wendt
,
J.
Matthiesen
,
R.
Schaub
,
E.
Lagsgaard
,
B.
Hammer
, and
F.
Besenbacher
,
Science
315
,
1692
(
2007
).
47.
L. Q.
Wang
,
K. F.
Ferris
,
A. N.
Shultz
,
D. R.
Baer
, and
M. H.
Englehard
,
Surf. Sci.
344
,
237
(
1995
).
48.
Q.
Guo
,
S.
Lee
, and
D. W.
Goodman
,
Surf. Sci.
437
,
38
(
1999
).
49.
A. J.
Muscat
and
R. J.
Madix
,
J. Phys. Chem.
100
,
9807
(
1996
).
50.
See supplementary material at http://dx.doi.org/10.1063/1.4721625 for a description of the sources of error present when calculating absolute correction factors for CO/Pdn TPD, validation of our simulation procedure via fitting of well understood reference data, and a description of our ISS methodology.
51.
T.
Engel
,
J. Chem. Phys.
69
,
373
(
1978
).
52.
C. T.
Campbell
,
G.
Ertl
,
H.
Kuipers
, and
J.
Segner
,
Surf. Sci.
107
,
207
(
1981
).
53.
X.
Guo
and
J.
Yates
,
J. Chem. Phys.
90
,
6761
(
1989
).
54.
J.
Libuda
,
I.
Meusel
,
J.
Hoffmann
,
L.
Piccolo
,
C. R.
Henry
, and
H.-J.
Freund
,
J. Chem. Phys.
114
,
4669
(
2001
).
55.
M. A.
Roettgen
,
S.
Abbet
,
K.
Judai
,
J.-M.
Antonietti
,
A. S.
Woerz
,
M.
Arenz
,
C. R.
Henry
, and
U.
Heiz
,
J. Am. Chem. Soc.
129
,
9635
(
2007
).
56.
J.
Libuda
,
A.
Sandell
,
M.
Baumer
, and
H.-J.
Freund
,
Chem. Phys. Lett.
240
,
429
(
1995
).
57.
S.
Wendt
,
R.
Schaub
,
J.
Matthiesen
,
E. K.
Vestergaard
,
E.
Wahlstrom
,
M. D.
Rasmussen
,
P.
Thorstrup
,
L. M.
Molina
,
E.
Lægsgaard
,
I.
Stensgaard
,
B.
Hammer
, and
F.
Besenbacher
,
Surf. Sci.
598
,
226
(
2005
).
58.
J. F.
Ziegler
, “
The Stopping and Range of Ions in Matter
” computer program available from www.srim.org (
2008
).
59.
T.
Kravchuk
,
V. A.
Esaulov
,
A.
Hoffman
, and
R. C.
Monreal
,
Nucl. Instrum. Methods Phys. Res. B
232
,
27
(
2005
).
60.
R. C.
Monreal
,
L.
Guillemot
, and
V. A.
Esaulov
,
J. Phys.: Condens. Matter
15
,
1165
(
2003
).
61.
J. W.
Rabalais
,
Principles and Applications of Ion Scattering Spectrometry: Surface Chemical and Structural Analysis
(
Wiley
,
New York
,
2003
).
62.
Handbook of X-Ray Photoelectron Spectroscopy: Physical Electronics
, edited by
J. F.
Moulder
,
W. F.
Stickle
,
P. E.
Sobol
,
K. D.
Bomben
,
J. J.
Chastain
, and
R. C.
King
(
Eden Prairie
,
Minnesota
,
1995
).
63.
H. M.
Ajo
,
V. A.
Bondzie
, and
C. T.
Campbell
,
Catal. Lett.
78
,
359
(
2002
).
64.
A.
Sandell
,
J.
Libuda
,
P. A.
Brühwiler
,
S.
Andersson
,
A. J.
Maxwell
,
M.
Bäumer
,
N.
Mårtensson
, and
H. J.
Freund
,
J. Vac. Sci. Technol. A
14
,
1546
(
1996
).
65.
P.
Liu
, private communication.

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