Hydrogen adsorption on Ru/ZrO2 studied by FT-IR

Article abstract of DOI:10.1021/jp9842852

Hydrogen adsorbed on Ru/ZrO₂ was studied by FT-IR (Fourier transform infrared) spectroscopy. While the Ru-H (Ru-D) species was not observed, the H₂O (D₂O)-like species was formed by H₂ (D₂) introduction on ZrO₂. The H₂O (D₂O)-like species was characterized by a band at around 1600 (1190) cm^-1 due to the bending mode and by a broad band at 2500-3800 (2000-2700) cm^-1 attributed to the stretching mode. The H₂O (D₂O)-like species was stable under evacuation at 300 K, but desorbed as H₂ (D₂) at 370 K. The H₂O (D₂O)-like species was considered to be produced by spillover of hydrogen (deuterium) atoms dissociatively adsorbed on Ru particles to react with the surface lattice oxygen atoms of ZrO₂. The heat of formation and the activation energy of the H₂O (D₂O)-like species formation from H₂ (D₂) were 134 ± 11 (172 ± 11) kJ mol^-1 and 28.6 ± 3.2 (36.6 ± 5.6) kJ mol^-1, respectively. The difference between the H₂O-like species and adsorbed H₂O molecules on Ru/ZrO₂ was also examined.

Full text of DOI:10.1021/jp9842852

J. Phys. Chem. B 1999, 103, 3229-3234
3229
Hydrogen Adsorption on Ru/ZrO2 Studied by FT-IR
Hiroyuki Ishikawa, Junko N. Kondo, and Kazunari Domen*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
ReceiVed: October 30, 1998; In Final Form: February 4, 1999
Hydrogen adsorbed on Ru/ZrO2 was studied by FT-IR (Fourier transform infrared) spectroscopy. While the
Ru-H (Ru-D) species was not observed, the H2O (D2O)-like species was formed by H2 (D2) introduction
on ZrO2. The H2O (D2O)-like species was characterized by a band at around 1600 (1190) cm-1 due to the
bending mode and by a broad band at 2500-3800 (2000-2700) cm-1 attributed to the stretching mode. The
H2O (D2O)-like species was stable under evacuation at 300 K, but desorbed as H2 (D2) at 370 K. The H2O
(D2O)-like species was considered to be produced by spillover of hydrogen (deuterium) atoms dissociatively
adsorbed on Ru particles to react with the surface lattice oxygen atoms of ZrO2. The heat of formation and
the activation energy of the H2O (D2O)-like species formation from H2 (D2) were 134 ( 11 (172 ( 11) kJ
mol-1 and 28.6 ( 3.2 (36.6 ( 5.6) kJ mol-1, respectively. The difference between the H2O-like species and
adsorbed H2O molecules on Ru/ZrO2 was also examined.
Introduction
clusters. A peak of on-top H on Ru surface should appear at
1800-2000 cm-1 when it is compared to IR bands of cluster
In recent years, the role of the spillover has been recognized
in many heterogeneous catalysis reactions.1 Spillover may be
regarded as a special case of surface migration of adsorbed
species. A definition of spillover has been proposed as “Spillover
involves the transport of an active species which is adsorbed
or formed on a first phase onto another phase that does not
adsorb to form the species under the same condition”.2 Various
kinds of studies on spillover have been reported: methods for
characterization, spillover effects in catalysis, simulation and
modeling of spillover, and so on.1
Ru compounds such as H2Ru(CO)422 and H2Ru(CO)2(PPh3)2.22
Similarly, peaks of bridging and 3-fold H on Ru surface are
expected to appear at 1250-1600 cm-1 and near 1000 cm-1
22,23
by comparison with those of H4Ru4(CO)12
and H2Ru6-
(CO)18,24 respectively.
Adsorbed hydrogen species on various supported metals such
as Pt/Al2O3 (2120 and -2060 cm-1),25 Ir/Al2O3 (2120 and
-2050 cm-1),26 Ni/Al2O3 (1880 cm-1),27 and Ni/SiO2 (1880
cm-1 27
) were observed by IR. However, details of the behavior
of adsorbed hydrogen and reactivity of the hydrogen species
on supported metals have not been clarified. In this study, we
examined the adsorbed hydrogen species on Ru/ZrO2 and their
behavior under various conditions by FT-IR and TPD (temper-
ature-programmed desorption). It was revealed that the Ru-H
species was not observed by IR and the hydrogen adsorption
species on ZrO2 of Ru/ZrO2 were very different from that on
the bare ZrO2.
The present authors have studied the activation process of
H2 as well as hydrogenation of ethene3-7 and CO8,9 over ZrO2
by FT-IR. In this study, ZrO2 loading with Ru was used in order
to examine the H2 adsorption and the spillover.
Ruthenium is known to be a good catalyst for FT (Fischer-
Tropsch) synthesis10,11 and ammonia synthesis.12-15 Supported
Ru catalysts also showed one of the highest activities for
methane production from carbon monoxide and hydrogen.16
Although there is a report17 on the intermediate for FT synthesis
on Ru, details of this reaction have not yet been thoroughly
clarified. On Ru single-crystal surfaces, H atoms adsorbed on
3-fold sites were observed by HREELS (high-resolution electron
energy loss spectroscopy); Ru(001) (1113 and 847 cm-1),18
(1137 and 823 cm-1),19 and Ru(110) (1136, 1031, and 685
cm-1).20 On the other hand, many hydrogen species adsorbed
on on-top (1880, 1801, and 1717 cm-1),15 (1870 and 1760
cm-1),21 bridging (1550 and 1330 cm-1),15,21 and 3-fold (1120
Experimental Section
The Ru/ZrO2 catalyst was prepared from the Ru3(CO)12
precursor according to the refs 14 and 15. ZrO2 was prepared
by calcination of ZrO(OH)2 in air at 973 K for 4 h. The prepared
ZrO2 was confirmed to have monoclinic crystal structure by
XRD (X-ray powder diffraction). ZrO2 (BET surface area, 34
m2 g-1) was calcined in air at 673 K for 4 h and then
immediately impregnated with Ru3(CO)12 in the stirred THF
(tetrahydrofran) solution at room temperature for 6 h. The
solvent (THF) was removed by a rotary evaporator at room
temperature, and then the sample was heated to decarbonylate
at 673 K for 1 h under evacuation (ca. 10-3 Torr; 1 Torr )
133.3 Pa). An amount of 2.0 wt % of ruthenium was loaded
onto ZrO2. Then, the dried sample was pressed to a self-
supported IR disk (20 mm diameter, 60 mg) in air. The
pretreatment of the sample was reduction by circulated H2 (200
Torr) at 673 K for 1.5 h with a liquid nitrogen trap and
evacuation at 673 K for 1 h. For D2 adsorption, the sample was
and 933 cm-1 15
) sites of Ru particles supported on MgO were
reported by transmission FT-IR. We expected that if the
hydrogen species adsorbed both on Ru and on ZrO2 of Ru/ZrO2
could be observed, information about the dynamic behavior of
adsorbed hydrogen could be obtained.
Generally, IR peaks of metal-H species can be assigned by
comparison with IR and Raman bands of organometallic hydride
* Author to whom correspondence should be addressed. Telephone: 81-
45-924-5238. Fax: 81-45-924-5282. E-mail: kdomen@res.titech.ac.jp.
10.1021/jp9842852 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/02/1999

3230 J. Phys. Chem. B, Vol. 103, No. 16, 1999
Ishikawa et al.
Figure 2. FT-IR spectrum measured after exposure of H2 and D2 (1:1
ratio, total 57.0 Torr) mixed gas to Ru/ZrO2 at 473 K for 10 min.
stretching mode of bridged Ru2H species by comparison with
the IR band (1605 cm-1) of cluster compound (H4Ru4(CO)12).29
To make an assignment on the 1600-cm-1 band, the isotopic
experiment was carried out. A mixture of H2 and D2 (1:1 ratio,
total 57.0 Torr) was introduced on Ru/ZrO2 at 473 K for 10
min. The IR spectrum was observed as shown in Figure 2. If
the peak at around 1600 cm-1 in Figure 1 is due to atomic H
species on Zr or Ru, two peaks due to Zr-H or Ru-H and
Zr-D or Ru-D species should be observed from the H2 and
D2 mixture. However, three bands appeared at 1604, 1411, and
1186 cm-1 in Figure 2. This excluded the assignment of the
Figure 1. FT-IR spectra of hydrogen adsorbed on Ru/ZrO2 under 100
Torr of H2 at (a) 293 K, (b) 323 K, (c) 343 K, (d) 373 K, (e) 433 K,
and (f) 466 K. H2 was introduced at 123 K and gradually warmed in
the presence of H2.
band at around 1600 cm-1
to Zr-H or Ru-H species. The
prereduced in a similar way with D2. H2 or D2 was introduced
through a Pd tube to eliminate contamination such as O2 or
H2O. The IR cell was made of quartz, and the temperature of
the cell was controlled by liquid nitrogen and electrical heating.
Details of the cell are shown in ref 14. The cell was connected
to a closed-circulation glass system. The IR spectra were
obtained by JASCO 7300 FT-IR with a MCT detector at 4 cm-1
of resolution. Sixty-four scans were collected to obtain each
spectrum. The TPD spectra were measured by mass spectrom-
eter (ANELVA AQA-100 MPX).
appearance of three bands in Figure 2 indicated the formation
of water-like species; bands at 1604, 1411, and 1186 cm-1 were
assigned to bending (δ) modes of H2O, HOD, and D2O,
respectively.30 The source of oxygen of the water is probably
the surface lattice oxygen of ZrO2 since O2 contamination was
carefully eliminated by passing through a Pd tube before
introduction. It is concluded, therefore, that the molecular
hydrogen was cleaved on Ru particles and spilled over onto
ZrO2 support to form hydroxyl species similar to the structure
of water, and that any Ru-H species were not observed by FT-
IR under the experimental conditions.
Results and Discussion
Worley et al.32,33 have reported an IR study of H2 adsorption
on Rh(2.2 wt %)/Al2O3 at pressures between 110 and 8000 Torr,
which showed that rapid dissociation of H2 on Rh sites produced
Rh-H (2013 cm-1) and the counterpart H atoms spilling over
onto the Al2O3 support. The spilled H atoms were found to
combine with surface hydroxyl groups on the support to produce
H2O species (δ(H2O) at 1618 cm-1). The production mechanism
of H2O on Rh/Al2O3 was based on the concomitant decrease of
the bands due to the isolated hydroxyl groups on the Al2O3
support when the bands of Rh-H species (2013 cm-1) and H2O
(1618 cm-1) grew in intensity. However, in this study, no
significant decrease of the isolated OH groups on ZrO2 in
IR Spectra of H2 Adsorbed on Ru/ZrO2. IR spectra of
hydrogen species adsorbed on Ru(2.0 wt %)/ZrO2 are shown
in Figure 1. H2 (100 Torr) was at first introduced at 123 K, and
the sample was gradually warmed in the presence of H2. A band
at around 1600 cm-1 began to emerge at 233 K (not shown)
with a broad band at 2500-3800 cm-1, and increased in
intensity with the temperature. The latter band was assigned to
the stretching mode of hydrogen-bonded OH groups. The band
near 1600 cm-1 could be attributable to Zr-H species formed
by heterolytic dissociative adsorption on ZrO2, forming Zr-H
and O-H species.28 The another possibility was the stretching
mode of Ru-H species. If so, the band is assigned to the

Hydrogen Adsorption on Ru/ZrO2
J. Phys. Chem. B, Vol. 103, No. 16, 1999 3231
Figure 3. (A) TPD spectra of D2 and D2O from deuterium-adsorbed Ru/ZrO2. Deuterium was adsorbed under 100 Torr of D2 at room temperature
for 1.5 h, and the thermal desorption was started with a heating rate of 4 K min-1. (B) The open circles show the integrated peak intensity of the
δ(D2O) band due to D2O-like species on ZrO2 at each temperature. The solid circles show the diminution of the peak intensity of that at each
temperature. The sample was gradually warmed from room temperature under evacuation after D2 adsorption (100 Torr) for 1.5 h at room temperature.
intensity was observed, and a different mechanism for the
formation of the H2O-like species on ZrO2 should be considered.
TPD Study. TPD spectra were measured to examine the
desorption behavior of the H2O-like species on ZrO2. Figure
3A shows the TPD spectra of D2 and D2O from Ru(2.0 wt %)/
ZrO2 after D2 adsorption (100 Torr) at room temperature. The
thermal desorption was started from room temperature with a
heating rate of 4 K min-1. A clear desorption peak of D2
centered at ca. 370 K was observed. The TPD spectrum of D2O
(m/e ) 20) above 473 K in Figure 3 A is due to the desorption
of D2O from the glass tube of circulation system because a
similar peak of D2O also appeared in a blank test. The TPD
peak of D2 (m/e ) 4) at 370 K is expected to be derived from
Ru-D or the D2O-like species, although the former was not
observed by IR. The following experiment was made in order
to clarify the assignment of this peak. The open circles in Figure
3B show the integrated peak intensities of the δ(D2O) band due
to the D2O-like species on ZrO2 in IR spectra measured during
the heating procedure under vacuum. Monotonic decrease of
the integrated intensity of δ(D2O) was observed. The solid
circles in Figure 3B were the difference between the integrated
intensities and the neighboring integrated intensities, to simulate
a TPD spectrum. The temperatures of the solid circles were
plotted at the center between two temperatures of neighboring
open circles. D2 was used in order to avoid the interference of
atmospheric H2O (1500-1700 cm-1). The feature of the solid
circles in Figure 3B is in reasonable agreement with the TPD
peak of D2 (m/e ) 4) in Figure 3A. Therefore, the TPD peak
of D2 at 370 K was attributed to the D2O-like species.
To study the hydrogen species on Ru particles, a TPD
experiment was carried out from a lower temperature. H2 (100
Torr) was introduced at room temperature, and the sample was
cooled to 85 K under gaseous H2 followed by evacuation. The
TPD spectra are shown in Figure 4. Some desorption peaks of
H2 (not shown) due to molecularly adsorbed H2 were observed
between 100 and 180 K. The peak of H2 (m/e ) 2) at around
370 K corresponds to the H2O-like species previously shown
in Figure 3, parts A and B. The peak at around 280 K may be
assigned to H2 desorption from Ru particles because H2 desorbs
from a H-covered Ru(001) surface at around 300 K.34 These
results indicate that the H2O (D2O)-like species on ZrO2 desorbs

3232 J. Phys. Chem. B, Vol. 103, No. 16, 1999
Ishikawa et al.
Figure 4. TPD spectra of H2 and H2O from hydrogen-adsorbed Ru/
ZrO2. Hydrogen was adsorbed under 100 Torr of H2 at room
temperature for 1.5 h, and it was cooled down to 85 K under gaseous
H2, followed by the thermal desorption started with a heating rate of 4
K min-1
.
not as H2O (D2O) but as H2 (D2) probably via inverse spillover
to Ru particles.
Comparison of the H2O-like and Adsorbed H2O Species.
The comparison between the H2O-like species and H2O on ZrO2
produced by H2 and H2O adsorption on Ru/ZrO2 was next
examined. Figure 5 shows IR spectra of H2O adsorbed on Ru/
ZrO2 by introduction of various amounts of H2O at room
temperature. H2O was supplied stepwise to the sample several
times, and the gaseous H2O was evacuated in Figure 5e. Both
OH stretching (ν(OH)) and bending (δ(H2O)) bands of adsorbed
H2O appeared more intensely than those of the H2O-like species
in Figure 1; the peak intensity of the δ(H2O) band of H2O
species was about four times larger than that of the H2O-like
species at their saturation coverages (Figure 5e). If it is assumed
that the infrared absorption coefficients of the bands of the H2O-
like and H2O species are the same, the amount of the H2O-like
species is about 1/4 of the adsorbed H2O at room temperature.
Figure 6 shows the time courses of amounts of the H2O-like
and H2O species on Ru/ZrO2 under evacuation after H2 and H2O
were adsorbed to the saturation, respectively, at room temper-
ature. Integrated intensities of the δ(H2O) bands of the H2O-
like and H2O species are plotted against the evacuation time.
As mentioned above, saturation coverages of these species are
clearly different. A small part of H2O species desorbed in the
initial 10 min under vacuum from Ru/ZrO2, while the H2O-
like species did not desorb under the same condition. The
frequency shifts of the both δ(H2O) bands are plotted as a
function of the peak intensity (amount of adsorption) for both
species in Figure 7A. Although both bands blue-shifted with
increasing coverage, the δ(H2O) band of the H2O-like species
always appeared at higher frequency than that of H2O species
at the same coverage. The difference of the H2O-like and H2O
species in δ(H2O) bands was also observed in fwhm (full width
at half-maximum) as shown in Figure 7B. As the peak intensity
of the δ(H2O) band of the H2O-like species increased, the fwhm
sharply decreased. On the other hand, fwhm of the δ(H2O) band
of H2O species remained unchanged for all coverages. These
results may suggest some difference in nature between both
species although they give very similar IR spectra.
Figure 5. FT-IR spectra of H2O adsorbed on Ru/ZrO2 by introduction
of (a) 1.54 mmol, (b) 3.08 mmol, (c) 4.62 mmol, and (d) 7.70 mmol
of H2O, and after evacuation of (e), (d).
Figure 6. The time courses of the peak intensities of the δ(H2O) band
due to H2O-like species on ZrO2 and that due to adsorbed H2O formed
by introduction of H2O on Ru/ZrO2, both under evacuation at room
temperature. Evacuation was started after the amount of adsorption of
both H2 and H2O was saturated on Ru/ZrO2: solid circles and solid
squares represent H2O and H2O-like species, respectively.
The adsorption and desorption processes of H2 on Ru/ZrO2
are shown in Scheme 1. When H2 is introduced on Ru/ZrO2, it
adsorbs dissociatively on Ru particles,20 and spilled over onto
ZrO2 to form the H2O-like species. It is suggested from the broad
and low-frequency shifted ν(OH) band that the H atoms of the
H2O-like species are hydrogen-bonded to other neighboring O
atoms of ZrO2. When the H-covered Ru/ZrO2 is heated under
evacuation, the hydrogen of the H2O-like species desorbed as
H2sprobably through Ru particles.

Hydrogen Adsorption on Ru/ZrO2
J. Phys. Chem. B, Vol. 103, No. 16, 1999 3233
TABLE 1: Summary of the Head of Adsorption of H2O-
and D2O-like Species on ZrO2 Support and the Activation
Energy for Spillover of H and D Species from Ru Particles
onto ZrO2 of 2.0 wt % Ru/ZrO2
surface species
Q (kJ mol-1
)
E (kJ mol-1
)
H2O-like species
D2O-like species
134 ( 11
172 ( 11
28.6 ( 3.2
36.6 ( 5.6
SCHEME 2. Energy Diagram for H2 Adsorption on Ru/
a
ZrO2
Figure 7. (A) Comparison of the change of frequencies of the δ(H2O)
bands depending on the peak intensities between H2O and H2O-like
species on Ru/ZrO2. (B) Comparison of the change of FWHM of δ-
(H2O) bands depending on the peak intensities between H2O and H2O-
like species on Ru/ZrO2. Open circles correspond to spectra of H2O
species shown in Figure 5, and open triangles to those measured during
evacuation at room temperature. Solid circles were plotted for H2O-
like species during the adsorption experiment shown in Figure 1.
SCHEME 1. Hydrogen Adsorption and Desorption
Processes on Ru/ZrO2
a The energy values are presented in kJ mol-1. *From reference 34.
An energy diagram for H2 adsorption on Ru/ZrO2 is shown
in Scheme 2. The activation energy for hydrogen adsorption
on a Ru surface is considered to be very small because H2
readily adsorbs dissociatively on a Ru surface even at low
temperature.20 Values of 134 ( 11 and 28.6 ( 3.2 kJ mol-1 in
Scheme 2 correspond to the heat of adsorption to form the H2O-
like species on ZrO2 support (Q) and the activation energy for
hydrogen to spill over from Ru to ZrO2 (E), respectively, which
were obtained in this study. It was reported that the activation
energy for desorption of H2 from Ru(001) single-crystal surface
was 92 kJ mol-1 at low coverage as derived from TPD data
using Redhead’s method.35 Feulner et al. also reported by TPD
study that the desorption energy of hydrogen from Ru(001)
surface decreased, roughly linearly with coverage, from ca. 120
to 90 kJ mol-1 34
Comparing these reports with the results in
.
Energy Diagram for H2 and D2 Adsorption on Ru/ZrO2.
The adsorption isotherms of H2 on Ru(2.0 wt %)/ZrO2 were
measured at various temperatures (Figure 8S (A)), in which the
integrated peak intensities of the δ(H2O) bands of the H2O-like
species were used. The heat of adsorption to form the H2O-like
species was obtained by the Clausius-Clapeyron equation
(Figure 8S (B)). The heat of adsorption was estimated to be
134 ( 11 kJ mol-1 at the integrated peak intensity of 0.02.
Similarly, the heat of adsorption of deuterium was estimated to
this study, the difference of energy between Ru-H species and
the H2O-like species is supposed to be relatively small, and
estimated to be about 10-60 kJ mol-1
.
We have previously reported the isotope exchange reaction
between molecular D2 and OH species on ZrO2 by FT-IR.36 In
that study, the initial activation energies for isotope exchange
reaction of terminal and bridging OH groups were estimated as
35 and 41 ( 4 kJ mol-1, respectively, on ZrO2. The activation
energies were attributed to the migration process of the cleaved
D atoms to the OH species.36 The activation energy for spillover
of D atoms on Ru/ZrO2 obtained in the present study (36.6 (
5.6 kJ mol-1) and that of migration of D atoms on ZrO2 (35
and 41 ( 4 kJ mol-1) are very close, which is consistent with
the picture that H or D atoms spill over from Ru particles to
ZrO2 support to form the H2O- or D2O-like species.
be 172 ( 11 kJ mol-1
.
The activation energy for the formation of the H2O-like
species was obtained from the initial rates under 100 Torr of
H2 at various temperatures. The activation energy was estimated
between 313 and 393 K to be 28.6 ( 3.2 kJ mol-1 according
to the Arrhenius equation (Figure 9S). The activation energy
for the formation of the D2O-like species was 36.6 ( 5.6 kJ
mol-1, which was measured between 273 and 373 K. These
activation energies may be attributed to the barriers for hydrogen
and deuterium to spill over from Ru particles onto ZrO2 support,
respectively. The obtained heats of adsorption and activation
energies for adsorption of hydrogen and deuterium on Ru/ZrO2
are summarized in Table 1. Isotope effect can be confirmed
from these results.
Adsorption Site of the H2O-like Species on ZrO2 Support.
The adsorption site of the H2O-like species on the ZrO2 support
is discussed. ZrO2 was prepared by calcination at 973 K, and
the monoclinic structure was confirmed by XRD. The fringe
spacings of monoclinic ZrO2 (m-ZrO2) are observed as the (111)
surface (far predominant) by HRTEM (high-resolution transmis-
sion electron microscopy).37 Three kinds of sites exist on the

3234 J. Phys. Chem. B, Vol. 103, No. 16, 1999
Ishikawa et al.
(111) surface of m-ZrO2, which was demonstrated by computer-
izing molecular simulations37 and these sites are shown as
follows.
References and Notes
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Xin, Q., Eds.; Stud. Surf. Sci. Catal. 1997, 112, 1.
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It is supposed that H atoms which spill over from Ru particles
onto ZrO2 support seem to be favorable to coordinate with O
atoms of ZrO2 lattice on site A among the three, because divalent
coordination unsaturation is required to form two O-H bonds.
The H2O-like species has hydrogen-bond interaction with the
adjacent oxygen atoms because the IR peak of the stretching
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particles because a rapid isotope exchange reaction from the
H2O-like species to the D2O-like species was observed when
D2 molecules were introduced to the H2O-like species on Ru/
ZrO2 at room temperature.
At this moment, we cannot clearly suggest why not -OH
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ZrO2 support and why the H2O-like species desorbs not as H2O
but as H2. It is still an open question for future work.
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ZrO2 (Figure 10S (A)). Similarly, although the bands of H2O-
like species appeared, no peak emerged in the blank test without
the introduction of H2 (Figure 10S (B)). This result leads us to
firmly conclude that the H2O-like species is derived from the
introduction of pure H2.
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Conclusion
The introduction of H2 (D2) on Ru(2.0 wt %)/ZrO2 produced
two IR bands at 1600 (1190) cm-1 and at about 3400 (2300)
cm-1. The band at about 3400 (2300) cm-1 was assigned to
the stretching mode of hydroxyl bond and the band at 1600
(1190) cm-1 was to δ(H2O) (δ(D2O)) mode which was
confirmed by the experiment with a mixture of H2 and D2. When
H2 was introduced on Ru/ZrO2, hydrogen adsorbed dissocia-
tively on the Ru surface and spilled over from Ru particles onto
the ZrO2 support to form the H2O-like species. Hydrogen atoms
of the H2O-like species on the support desorbed as H2 molecules
when evacuated at higher temperature. Clear differences of the
H2O-like species formed by H2 adsorption from adsorbed H2O
molecules on Ru/ZrO2 were demonstrated by comparing IR
spectra of both species. The heat of hydrogen (deuterium)
adsorption on ZrO2 support was calculated to be 134 ( 11 (172
( 11) kJ mol-1 and the activation energy for hydrogen
(deuterium) to spill over from Ru particles onto ZrO2 support
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24, 225.
(30) H2O and D2O belong to C2V and HDO to Cs point groups. Although
the symmetry numbers are different, they all have three vibrational modes:
symmetric and asymmetric stretching modes and one bending mode.
Therefore, three bands observed in Figure 2 were reasonably assigned to
the bending modes of H2O (1604 cm-1), HDO (1411 cm-1), and D2O (1186
cm-1), respectively. They appear at 1595, 1402, and 1178 cm-1 when they
are in gas phase.31
(31) Shimanouchi, T. In Tables of Molecular Vibrational Frequencies
Consolidated Volume 1; Nat. Stand. Ref. Data Ser., National Bureau of
Standards (U.S.), 1972, p 39.
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8881.
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T. Surf. Sci. 1978, 71, 599.
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was estimated to be 28.6 ( 3.2 (36.6 ( 5.6) kJ mol-1
.