Jackson S.D., Hargreaves J.S.J. Metal Oxide Catalysis
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184 4 Resonance Raman Spectroscopy – Θ-Al
2
O
3
-Supported Vanadium Oxide Catalysts
V
=
O. This is an indication that the V
–
O
–
Al interface bond is much easier to
reduce than the V
=
O bond.
The hydrogen - reduction of VO
x
/ θ - Al
2
O
3
samples with intermediate VO
x
density
(1.2 and 4.4 V nm
− 2
) was studied by both UV and visible Raman spectroscopy. As
an example, the Raman spectra of 1.2 V samples reduced by hydrogen at different
temperatures are shown in Figure 4.4 . For the oxidized sample, the V
=
O stretch-
ing band is observed at different Raman shifts in the UV (1021 cm
− 1
) and visible
(1034 cm
− 1
) excited Raman spectra. This is explained in the previous section in
terms of selective resonance enhancement, monovanadate and polyvanadate
species being resonance enhanced in UV Raman and visible Raman, respectively.
When the 1.2 V sample was treated in hydrogen, the Raman intensity from surface
VO
x
species decreased at both excitation wavelengths. There is a slight and gradual
red shift of the band due to V
=
O in the visible Raman spectra as a function of
reduction temperature, from 1034 to 1023 cm
− 1
. The bands due to VO
x
species
totally disappear in the visible Raman spectra after hydrogen reduction at 873 K,
consistent with previous visible Raman studies [26, 33 – 39] . However, Raman
bands are still observable at 870, 910 (shoulder) and 1021 cm
− 1
in the UV Raman
spectra, even after hydrogen treatment at 973 K. This apparent difference between
the two excitation wavelengths suggests that the VO
x
species detected by visible
Raman are much easier to reduce than those detected by UV Raman, that is,
polyvanadate is more easily reduced than monovanadate. Considering the struc-
tural differences between monovanadate and polyvanadate species, it is reasonable
to deduce that the V
–
O
–
Al bond is more diffi cult to reduce than the V
–
O
–
V bond.
Figure 4.4 Raman spectra of 1.2 V sample reduced by
hydrogen at different temperatures: (a) UV ( λ
excitation
= 244 nm;
(b) visible ( λ
excitation
= 488 nm).
4.2 Structure of Al
2
O
3
-Supported Vanadia Catalysts 185
The new UV Raman band centered at 870 cm
− 1
, similar to the band observed on
samples with lower vanadia loadings after high temperature hydrogen treatment,
may be attributed to reduced VO
x
species. This broad feature is also observed on
VO
x
/ θ - Al
2
O
3
samples with higher VO
x
density (4.4, 8 and 14.2 V nm
− 2
) after hydro-
gen - reduction at high temperatures. However, as the size and proximity of poly-
vanadate species increases with loading, the VO
x
/ θ - Al
2
O
3
samples become more
easily reduced as evidenced by a more pronounced weakening of the Raman bands
due to surface oxide vanadia species in both UV and visible Raman spectra after
hydrogen - reduction at high temperatures. This model is also consistent with the
quantitative results from H
2
- TPR (not shown here) where the vanadium average
oxidation state decreases with increasing surface VO
x
density.
To aid the interpretation of the Raman spectra from V/ θ - Al
2
O
3
samples reduced
by hydrogen at high temperatures, both UV and visible Raman spectra of different
bulk VO
x
compounds, V
2
O
5
, V
6
O
13
, VO
2
and V
2
O
3
, were measured in fl owing
helium at room temperature. In the UV Raman spectra, all the bulk VO
x
samples
produce a broad band in the range 400 – 600 cm
− 1
, due to V
2
–
O and V
3
–
O bridging
modes. A band at 875 cm
− 1
, which can be assigned to V
–
O
–
V stretching, is
observed in the spectra of all bulk VO
x
except for V
2
O
5
. This band becomes broader
following the sequence V
6
O
13
, VO
2
and V
2
O
3
, resulting in a feature similar to the
870 cm
− 1
band observed on V/ θ - Al
2
O
3
samples reduced by hydrogen at high tem-
peratures. In the Raman shift range near 1000 cm
− 1
, where V
=
O stretching usually
appears, the four VO
x
compounds exhibit Raman bands at different wavenumbers.
In the visible Raman spectral region (830 – 1080 cm
− 1
), Raman bands are detectable
only for V
2
O
5
and V
6
O
13
. Since H
2
- TPR and in situ UV - Vis DRS of VO
x
/ θ - Al
2
O
3
samples reduced in hydrogen indicate the presence of V
3+
/V
4+
species after high -
temperature reduction [53] , we suggest that the new UV Raman band observed
from V/ θ - Al
2
O
3
samples centered at ca 870 cm
− 1
after high - temperature hydrogen
treatment is due to reduced VO
x
species, similar to V
2
O
3.
UV Raman spectra after re - oxidation of reduced V/ θ - Al
2
O
3
samples show very
similar features to those of freshly calcined samples, indicating that the reduction
of V/ θ - Al
2
O
3
samples is reversible. However, additional visible Raman spectra of
the re - oxidation process are highly desirable, as they may provide information on
the redox behavior of polyvanadate species.
4.2.2
Summary
The structures of VO
x
species on θ - Al
2
O
3
under both oxidizing and reducing
atmospheres have been investigated by multi - wavelength Raman spectroscopy
together with H
2
- TPR and in situ UV - Vis DRS techniques. The multi - wavelength
Raman method enables selective identifi cation of three different vanadia species:
isolated VO
x
species are resonance enhanced by UV excitation while polymerized
VO
x
and V
2
O
5
by visible excitation. The study of reduced V/ θ - Al
2
O
3
samples sug-
gests that UV Raman is more powerful than conventional visible Raman for
studies of reduced metal oxide catalysts. This is mainly due to a combination of
186 4 Resonance Raman Spectroscopy – Θ-Al
2
O
3
-Supported Vanadium Oxide Catalysts
decreased self - absorption and resonance enhancement in UV Raman. These
results suggest that a complete structural characterization of supported metal
oxide catalysts requires a multi - wavelength excitation approach in Raman spec-
troscopy.
4.3
Quantifi cation of Surface VO
x
Species on Supported Vanadia Catalysts
For supported vanadia catalysts, the distribution of different vanadia species, i.e.
monovanadate, polyvanadate and V
2
O
5
, on the support depends upon vanadia
coverage and the method of preparation. This distribution presents diffi culties in
the identifi cation of the active and selective sites for catalytic reactions. Quantita-
tive information on the speciation of surface vanadia is an important tool for
understanding structure/function relationships for these catalysts. Qualitative
determination of the three vanadia species is accessible by several techniques such
as Raman, UV - Vis, NMR spectroscopies and others [4] . However, quantifi cation
of the individual vanadia species is more diffi cult because these techniques only
provide information about the mixture as a whole. The previous sections on multi -
wavelength Raman spectroscopic studies of V/Al
2
O
3
catalysts show the possibility
of selectively detecting different vanadia species via different laser excitations,
which makes the quantifi cation of the individual VO
x
species possible using multi -
wavelength Raman spectroscopy. Because supported vanadia has high absorbance
in the UV region and sometimes in the visible region, the self - absorption effect
[54] greatly affects the measured Raman intensity. Consequently, quantifi cation of
surface vanadia species requires a correction to the measured intensities to account
for self - absorption. Either internal or external standards can be employed for this
purpose [54 – 56] . The external standardization method for solid samples which
absorb radiation makes use of the diffuse refl ectance of the samples to correct the
measured Raman intensity [54 – 56] . Thus, the combination of multi - wavelength
Raman spectroscopy and UV - visible diffuse refl ectance spectroscopy of V/Al
2
O
3
samples can be applied for quantifi cation of different vanadia species.
The measured Raman intensity ψ
∞
can be corrected using the equation [54]
I
R
RR
c
=
−
+
()
[]
∞
∞
∞∞
ψ
1
1
(4.1)
where I
c
is the corrected Raman intensity and R
∞
is the diffuse refl ectance at the
wavelength of the Raman scattered radiation. Several restrictions apply when
using Equation 4.1 as outlined elsewhere [54] . Briefl y, the scattering coeffi cient of
the sample must not change among a series of sample measurements; the sample
must not be too strongly absorbing; and the diffuse refl ectance R
∞
must be identi-
cal at the excitation wavelength and the wavelength of the Raman bands.
Since only the UV Raman spectra (Figure 4.1 ) give measurable information for
all V/ θ - Al
2
O
3
samples (0.01 – 14.2 V nm
− 2
), the diffuse refl ectance spectra (Figure
4.2 ) are combined with UV Raman spectra for the correction of self - absorption.
Figure 4.5 a presents the corrected and uncorrected Raman intensities of VO
x
(band at ca 1015 ∼ 1026 cm
− 1
) as a function of surface VO
x
concentration. At VO
x
concentrations < 1 mol% (1.2 V nm
− 2
) (see inset in Figure 4.5 a), the corrected inten-
sity is linearly proportional to the surface VO
x
concentration, in agreement with
the results from the internal standardization using θ - Al
2
O
3
[54] . The corrected
intensity versus VO
x
concentration is no longer linear as the VO
x
concentration
increases to 1 mol% and above. This non - linearity is not due to the breakdown of
the three requirements for using Equation 4.1 .
Figure 4.5 (a) Uncorrected and UV - Vis diffuse refl ectance -
corrected Raman band intensity of surface vanadia species
(band at ∼ 1015 cm
− 1
) as a function of surface VO
x
concentration in V/ θ - Al
2
O
3
system. (b) Amount of
monovanadate as a function of surface VO
x
density.
(c) Distribution of monovanadate, polyvanadate and
crystalline V
2
O
5
as a function of surface VO
x
density.
4.3 Quantifi cation of Surface VO
x
Species on Supported Vanadia Catalysts 187
188 4 Resonance Raman Spectroscopy – Θ-Al
2
O
3
-Supported Vanadium Oxide Catalysts
The linear relationship between corrected Raman intensity and VO
x
concentra-
tion in the concentration range 0.01 – 0.14 mol% with both internal and external
standards suggests the presence of one type of surface VO
x
species, namely mon-
ovanadate. This is consistent with the selective detection of monovanadate by UV
Raman [25] . The linearity also suggests that the Raman cross - section of monovana-
date is essentially constant as the monovanadate concentration changes more than
10 - fold. Thus, the non - linear behavior at VO
x
concentrations higher than 0.14 mol%
is unlikely to be due to a change in the Raman cross - section of monovanadate. At
VO
x
concentrations of 1 mol% and above, a mixture of different VO
x
species exists
on the Al
2
O
3
support and only a fraction of the vanadia species (monovanadate)
are detected by UV Raman spectroscopy. Therefore the plot in Figure 4.5 a is not
expected to be linear. Under these circumstances, the plot in Figure 4.5 a would
be indicative only of the concentration of monovanadate species detected by UV
resonance Raman spectroscopy. The amount of this species increases at low
surface VO
x
concentration and decreases at high VO
x
concentrations as shown in
Figure 4.5 b.
The amounts of polyvanadate and crystalline V
2
O
5
can now be obtained since
the amounts of total vanadium and monovanadate are known. It is also known
that the relative Raman cross - section of V
2
O
5
and dispersed VO
x
is about 10 for
visible Raman measurements [56] . With this knowledge, the individual amounts
of polyvanadate and V
2
O
5
can be calculated based upon fi tting visible Raman peaks
from V/ θ - Al
2
O
3
samples [25] (assuming the amount of V
2
O
5
and polyvanadate can
be represented by the peak areas at 995 and ∼ 1030 cm
− 1
, respectively). The distribu-
tion of the three VO
x
species is plotted as a function of surface VO
x
density as
shown in Figure 4.5 c. It is seen that (a) monovanadate species predominate on
the surface at low vanadia loadings, (b) polyvanadate species predominate at inter-
mediate vanadia loadings and (c) there is a mixture of monovanadate, polyvanadate
and V
2
O
5
on the support surface at intermediate and high vanadia loadings.
Quantifi cation greatly aids the understanding of the catalytic contributions of
different vanadia species during catalytic reactions. For example, our preliminary
activity test over these supported VO
x
catalysts showed that the 1.2 V/ θ - Al
2
O
3
sample exhibits better stability than higher loading catalysts for butane dehydro-
genation in dilute feed [57] . The explanation is that the monovanadate species (ca
50% on the surface) dilute the polyvanadate species so that the two - dimensional
coke species responsible for catalyst deactivation are less likely to form [40, 57] .
Our quantifi cation result clearly supports the general assumption that for sup-
ported VO
x
catalysts, polyvanadates and V
2
O
5
predominate on the support surface
with increasing VO
x
loading. However, we should point out that this method has
limitations. Figure 4.6 shows two distinct UV Raman bands centered at 997 cm
− 1
and 1015 cm
− 1
for the 0.16 V/ θ - Al
2
O
3
sample. They are attributed to V
=
O stretching
vibrations from two distinct vanadyl species. The relative intensities of the two
bands changes as a function of excitation wavelength, indicating that there are at
least two different types of isolated monovanadate species in the 0.16 V sample.
This is likely due to the fact that isolated vanadate species are bonded to distinct
sites on the alumina surface, and these species would be expected to possess
correspondingly distinct electronic absorption wavelengths. Thus, selective
resonance - enhanced Raman measurements will be able to distinguish different
subsets of monovanadate species using suitable excitation wavelengths. This will
also be true for V/ θ - Al
2
O
3
samples with a mixture of different VO
x
structures
(monovanadates, polyvanadates and V
2
O
5
). Therefore, it may be possible to map
out VO
x
species with a distribution of sizes and coordination geometries by
employing as many excitation wavelengths as possible in a Raman study. Cur-
rently, it appears that the Raman measurements using 244 and 488 nm excitation
represent only a subset of monovanadates and polyvanadates, respectively, and the
quantifi cation of VO
x
species obtained from these two excitations is a simplifi ed
model. This two - excitation - wavelength - based quantifi cation can be considered as
the fi rst step in the approach to a complete quantifi cation of VO
x
.
4.3.1
Summary
A combination of UV - Vis DRS and UV and visible Raman spectroscopy allow
quantifi cation of surface VO
x
species in V/ θ - Al
2
O
3
samples with different VO
x
densities. It is shown that monovanadate species are the predominant species on
the surface at low surface VO
x
density but they decrease in fraction and quantity
Figure 4.6 UV Raman spectra ( λ
excitation
= 220 nm, 287 nm) of
dehydrated 0.16 V sample and θ - alumina. Two distinct Raman
bands at 997 cm
− 1
and 1015 cm
− 1
for the 0.16 V sample are
attributed to V
=
O stretching vibrations from two distinct
vanadyl species. A broad band at ∼ 897 cm
− 1
can be assigned
to V
–
O
–
Al stretching vibrations.
4.3 Quantifi cation of Surface VO
x
Species on Supported Vanadia Catalysts 189
190 4 Resonance Raman Spectroscopy – Θ-Al
2
O
3
-Supported Vanadium Oxide Catalysts
as the surface VO
x
density increases. Polyvanadate and crystalline V
2
O
5
dominate
at intermediate and high surface VO
x
density. The three vanadia species co - exist
on the sample even at the highest VO
x
density (which is almost two monolayers
in coverage). The quantitative information gained assists the determination of the
specifi c catalytic contributions by these different vanadia species. It is also appar-
ent that a complete quantifi cation of surface VO
x
species in a heterogeneous sup-
ported VO
x
catalyst by Raman spectroscopy requires measurements using as many
laser excitation wavelengths as possible.
4.4
Conclusion
This short chapter has illustrated the application of Raman spectroscopic tech-
niques to the elucidation of structure – activity relationships in the V// θ - Al
2
O
3
system. This system, in which a number of different VO
x
species with differing
catalytic activity exist, provides a useful case study to illustrate the power of Raman
spectroscopy. Examples have been chosen that demonstrate the utility of applica-
tion of the multi - wavelength method to the determination of the simultaneous
presence of isolated, polymerized and V
2
O
5
species. Furthermore, combination of
UV - Vis DRS and UV - Vis Raman spectroscopy has been demonstrated to be very
powerful in the quantifi cation of such species, which is a key requirement in the
elucidation of their respective catalytic activity. In summary, the power of multiple
Raman techniques can be seen from the examples given, which go a long way
towards the development of a detailed understanding of the catalytic activity of
these systems. Further exciting developments in the application of Raman spec-
troscopy can be anticipated.
Acknowledgements
This work was fi nancially supported by ATHENA and the Chemical Sciences,
Geosciences and Biosciences Division, Offi ce of Basic Energy Sciences, Offi ce of
Science, US Department of Energy under Grant No. DE - FG02 - 97ER14789. The
Athena project is funded by the Engineering & Physical Sciences Research Council
(EPSRC) of the UK and Johnson Matthey plc.
References 191
1 Bond , G.C. and Tahir , S.F. ( 1991 )
Vanadium oxide monolayer catalysts:
preparation, characterization and
catalytic activity . Applied Catalysis , 71 ( 1 ),
1 – 31 .
2 Reddy , B.N. , Reddy , B.M. and
Subrahmanyam , M. ( 1991 ) Dispersion
and 3 - picoline ammoxidation
investigation of vanadium oxide/
aluminum oxide (V2O5/a - Al2O3)
catalysts . Journal of the Chemical
Society, Faraday Transactions , 87 ( 10 ),
1649 – 55 .
3 Deo , G. , Wachs , I.E. and Haber , J. ( 1994 )
Supported vanadium oxide catalysts.
Molecular structural characterization
and reactivity properties . Critical
Reviews in Surface Chemistry , 4 ( 3 & 4 ),
141 – 87 .
4 Wachs , I.E. and Weckhuysen , B.M.
( 1997 ) Structure and reactivity of surface
vanadium oxide species on oxide
supports . Applied Catalysis A: General ,
157 ( 1 – 2 ), 67 – 90 .
5 Banares , M.A. and Wachs , I.E. ( 2002 )
Molecular structures of supported metal
oxide catalysts under different environ-
ments . Journal of Raman Spectroscopy ,
33 ( 5 ), 359 – 80 .
6 Weckhuysen , B.M. and Keller , D.E.
( 2003 ) Chemistry, spectroscopy and the
role of supported vanadium oxides in
heterogeneous catalysis . Catalysis Today ,
78 ( 1 – 4 ), 25 – 46 .
7 Went , G.T. , Oyama , S.T. and Bell , A.T.
( 1990 ) Laser Raman spectroscopy of
supported vanadium oxide catalysts .
Journal of Physical Chemistry , 94 ( 10 ),
4240 – 6 .
8 Deo , G. and Wachs , I.E. ( 1991 )
Predicting molecular structures of
surface metal oxide species on oxide
supports under ambient conditions .
Journal of Physical Chemistry , 95 ( 15 ),
5889 – 95 .
9 Vuurman , M.A. and Wachs , I.E. ( 1992 )
In situ Raman spectroscopy of alumina -
supported metal oxide catalysts . Journal
of Physical Chemistry , 96 ( 12 ), 5008 – 16 .
10 Wachs , I.E. ( 1996 ) Raman and IR studies
of surface metal oxide species on oxide
supports: supported metal oxide catalysts .
Catalysis Today , 27 ( 3 – 4 ), 437 – 55 .
11 Olthof , B. , Khodakov , A. , Bell , A.T. and
Iglesia , E. ( 2000 ) Effects of Support
Composition and Pretreatment Conditions
on the Structure of Vanadia Dispersed on
SiO
2
, Al
2
O
3
, TiO
2
, ZrO
2
, and HfO
2
. Journal
of Physical Chemistry B , 104 ( 7 ), 1516 – 28 .
12 Argyle , M.D. , Chen , K.D. , Bell , A.T. and
Iglesia , E. ( 2002 ) Effect of catalyst
structure on oxidative dehydrogenation of
ethane and propane on alumina - supported
vanadia . Journal of Catalysis , 208 ( 1 ),
139 – 49 .
13 Cortez , G.G. and Banares , M.A. ( 2002 ) A
Raman Spectroscopy Study of Alumina -
Supported Vanadium Oxide Catalyst
during Propane Oxidative Dehydrogenation
with Online Activity Measurement . Journal
of Catalysis , 209 ( 1 ), 197 – 201 .
14 Khodakov , A. , Olthof , B. , Bell , A.T. and
Iglesia , E. ( 1999 ) Structure and catalytic
properties of supported vanadium oxides:
support effects on oxidative dehydro-
genation reactions . Journal of Catalysis ,
181 ( 2 ), 205 – 16 .
15 Christodoulakis , A. , Machli , M. ,
Lemonidou , A.A. and Boghosian , S.
( 2004 ) Molecular structure and reactivity
of vanadia - based catalysts for propane
oxidative dehydrogenation studied by in
situ Raman spectroscopy and catalytic
activity measurments . Journal of Catalysis ,
222 ( 2 ), 293 – 306 .
16 Xiong , G. , Li , C. , Li , H.Y. , Xin , Q. and
Feng , Z.C. ( 2000 ) Direct spectroscopic
evidence for vanadium species in
V - MCM - 41 molecular sieve characterized
by UV resonance Raman spectroscopy .
Chemical Communications (Cambridge,
United Kingdom) , 8 , 677 – 8 .
17 Chua , Y.T. , Stair , P.C. and Wachs , I.E.
( 2001 ) A comparison of ultraviolet and
visible raman spectra of supported metal
oxide catalysts . Journal of Physical
Chemistry B , 105 ( 36 ), 8600 – 6 .
18 Wachs , I.E. , Jehng , J. - M. , Deo , G. ,
Weckhuysen , B.M. , Guliants , V.V. ,
Benziger , J.B. and Sundaresan , S. ( 1997 )
Fundamental studies of butane oxidation
over model - supported vanadium oxide
References
192 4 Resonance Raman Spectroscopy – Θ-Al
2
O
3
-Supported Vanadium Oxide Catalysts
catalysts: molecular structure - reactivity
relationships . Journal of Catalysis , 170 ( 1 ),
75 – 88 .
19 Kanervo , J.M. , Harlin , M.E. , Krause , A.O.I.
and Banares , M.A. ( 2003 ) Characterization
of alumina - supported vanadium oxide
catalysts by kinetic analysis of H2 - TPR
data . Catalysis Today , 78 ( 1 – 4 ) 171 – 80 .
20 Koranne , M.M. , Goodwin , J.G. Jr and
Marcelin , G. ( 1994 ) Characterization of
silica - and alumina - supported vanadia
catalysts using temperature programmed
reduction . Journal of Catalysis , 148 ( 1 ),
369 – 77 .
21 Harlin , M.E. , Niemi , V.M. and Krause ,
A.O.I. ( 2000 ) Alumina - supported
vanadium oxide in the dehydrogenation of
butanes . Journal of Catalysis , 195 ( 1 ), 67 – 78 .
22 Harlin , M.E. , Niemi , V.M. , Krause ,
A.O.I. and Weckhuysen , B.M. ( 2001 )
Effect of Mg and Zr Modifi cation on the
activity of VOx/Al
2
O
3
catalysts in the
dehydrogenation of Butanes . Journal of
Catalysis , 203 ( 1 ), 242 – 52 .
23 Gao , X. , Jehng , J. - M. and Wachs , I.E.
( 2002 ) In situ UV - vis - NIR diffuse
refl ectance and raman spectroscopic
studies of propane oxidation over ZrO
2
-
supported vanadium oxide catalysts .
Journal of Catalysis , 209 ( 1 ), 43 – 50 .
24 Wachs , I.E. , Chen , Y. , Jehng , J. - M. ,
Briand , L.E. and Tanaka , T. ( 2003 )
Molecular structure and reactivity of the
Group V metal oxides . Catalysis Today ,
78 ( 1 – 4 ) 13 – 24 .
25 Gao , X. , Banares , M.A. and Wachs , I.E.
( 1999 ) Ethane and n - butane oxidation
over supported vanadium oxide catalysts:
an in situ UV - visible diffuse refl ectance
spectroscopic investigation . Journal of
Catalysis , 188 ( 2 ), 325 – 31 .
26 Ruitenbeek , M. , Van Dillen , A.J. , de
Groot , F.M.F. , Wachs , I.E. , Geus , J.W.
and Koningsberger , D.C. ( 2000 ) The
structure of vanadium oxide species on .
gamma - alumina; an in situ X - ray
absorption study during catalytic
oxidation . Topics in Catalysis , 10 ( 3 – 4 )
241 – 54 .
27 Wachs , I.E. and Chan , S.S. ( 1984 ) In situ
characterization of small vanadium oxide
(V
2
O
5
) crystallites supported on titanium
dioxide (anatase) . Applied Surface Science ,
20 ( 1 – 2 ), 181 – 5 .
28 Wachs , I.E. , Jehng , J. - M. , Deo , G. ,
Weckhuysen , B.M. , Guliants , V.V. and
Benziger , J.B. ( 1996 ) In situ Raman
spectroscopy studies of bulk and surface
metal oxide phases during oxidation
reactions . Catalysis Today , 32 ( 1 – 4 ,
Proceedings of the 5th European
Workshop Meeting on Selective
Oxidation by Heterogeneous Catalysis,
1995), 47 – 55 .
29 Sun , Q. , Jehng , J. - M. , Hu , H. Herman ,
R.G. , Wachs , I.E. and Klier , K. ( 1997 ) In
situ Raman spectroscopy during the partial
oxidation of methane to formaldehyde over
supported vanadium oxide catalysts .
Journal of Catalysis , 165 ( 1 ), 91 – 101 .
30 Mul , G. , Banares , M.A. , Cortez , G. Garcia ,
van der Linden , B. , Khatib , S.J. and
Moulijn , J.A. ( 2003 ) MultiTRACK and
operando Raman - GC study of oxidative
dehydrogenation of propane over alumina -
supported vanadium oxide catalysts .
Physical Chemistry Chemical Physics , 5 ( 20 ),
4378 – 83 .
31 Banares , M.A. , Cardoso , J.H. , Agullo -
Rueda , F. , Correa - Bueno , J.M. and Fierro ,
J.L.G. ( 2000 ) Dynamic states of V - oxide
species: reducibility and performance for
methane oxidation on V2O5/SiO2 catalysts
as a function of coverage . Catalysis Letters ,
64 ( 2 – 4 ) 191 – 6 .
32 Christodoulakis , A. , Machli , M. ,
Lemonidou , A.A. and Boghosian , S. ( 2004 )
Molecular structure and reactivity of
vanadia - based catalysts for propane
oxidative dehydrogenation studied by in
situ Raman spectroscopy and catalytic
activity measurements . Journal of Catalysis ,
222 ( 2 ), 293 – 306 .
33 Argyle , M.D. , Chen , K.D. , Iglesia , E. and
Bell , A.T. ( 2005 ) In situ UV - visible
spectroscopic measurements of kinetic
parameters and active sites for catalytic
oxidation of alkanes on vanadium oxides .
Journal of Physical Chemistry B , 109 ( 6 ),
2414 – 20 .
34 Sullivan , V.S. , Jackson , S.D. and Stair , P.C.
( 2005 ) In situ ultraviolet Raman spec-
troscopy of the reduction of chromia on
alumina catalysts . Journal of Physical
Chemistry B , 109 ( 1 ), 352 – 6 .
35 Li , C. ( 2003 ) Identifying the isolated
transition metal ions/oxides in molecular
sieves and on oxide supports by UV
References 193
resonance Raman spectroscopy . Journal
of Catalysis , 216 ( 1 – 2 ), 203 – 12 .
36 Gao , X. and Wachs , I.E. ( 2000 )
Investigation of surface structures of
supported vanadium oxide catalysts by
UV - vis - NIR diffuse refl ectance spec-
troscopy . Journal of Physical Chemistry B ,
104 ( 6 ), 1261 – 8 .
37 Weckhuysen , B.M. , De Ridder , L.M. and
Schoonheydt , R.A. ( 1993 ) A quantitative
diffuse refl ectance spectroscopy study of
supported chromium catalysts . Journal of
Physical Chemistry , 97 ( 18 ), 4756 – 63 .
38 Li , C. and Stair , P.C. ( 1996 ) An advance
in Raman studies of catalysts: ultraviolet
resonance Raman spectroscopy . Studies
in Surface Science and Catalysis , 101 (11th
International Congress on Catalysis –
40th Anniversary, 1996, Pt B), 881 – 90 .
39 Li , C. and Stair , P.C. ( 1997 ) Ultraviolet
Raman spectroscopy characterization of
coke formation in zeolites . Catalysis
Today , 33 ( 1 – 3 ), 353 – 60 .
40 Chua , Y.T. and Stair , P.C. ( 2000 ) A novel
fl uidized bed technique for measuring
UV Raman spectra of catalysts and
adsorbates . Journal of Catalysis , 196 ( 1 ),
66 – 72 .
41 Xie , S. , Iglesia , E. and Bell , A.T. ( 2000 )
Effects of hydration and dehydration on
the structure of silica - supported vanadia
species . Langmuir , 16 ( 18 ), 7162 – 7 .
42 Xie , S. , Iglesia , E. and Bell , A.T. ( 2001 )
Effects of temperature on the Raman
spectra and dispersed oxides . Journal of
Physical Chemistry B , 105 ( 22 ), 5144 – 52 .
43 Dupuis , A.C. , Haija , M. Abu , Richter , B. ,
Kuhlenbeck , H. and Freund , H.J. ( 2003 )
V
2
O
3
(0 0 0 1) on Au(1 1 1) and W(1 1 0):
growth, termination and electronic
structure . Surface Science , 539 ( 1 – 3 ),
99 – 112 .
44 Xiong , G. , Li , C. , Feng , Z.C. , Ying , P.L. ,
Xin , Q. and Liu , J.K. ( 1999 ) Surface
coordination structure of molybdate with
extremely low loading on gamma -
alumina characterized by UV resonance
Raman spectroscopy . Journal of Catalysis ,
186 ( 1 ), 234 – 7 .
45 Xiong , G. , Feng , Z. , Li , J. , Yang , Q. ,
Ying , P. , Xin , Q. and Li , C. ( 2000 ) UV
resonance Raman spectroscopic studies
on the genesis of highly dispersed
surface molybdate species on .gamma. -
alumina . The Journal of Physical Chemistry
B , 104 ( 15 ), 3581 – 8 .
46 Stair , P.C. and Li , C. ( 1997 ) Ultraviolet
Raman spectroscopy of catalysts and
other solids . Journal of Vacuum Science
and Technology. A, Vacuum, Surfaces,
and Films , 15 ( 3, Pt 2 ), 1679 – 84 .
47 Tian , H. , Ross , E.I. and Wachs , I.E. ( 2006 )
Quantitative determination of the
speciation of surface vanadium oxides and
their catalytic activity . Journal of Physical
Chemistry B , 110 ( 19 ), 9593 – 600 .
48 Catana , G. , Rao , R.R. , Weckhuysen , B.M. ,
Van Der Voort , P. , Vansant , E. and
Schoonheydt , R.A. ( 1998 ) Supported
vanadium oxide catalysts: quantitative
spectroscopy, preferential adsorption of
V4+/5+;, and Al
2
O
3
coating of zeolite Y .
Journal of Physical Chemistry B , 102 ( 41 ),
8005 – 12 .
49 Wu , Z. , Kim , H. - S. , Stair , P.C. , Rugumini ,
S. and Jackson , S.D. ( 2005 ) On the structure
of vanadium oxide supported on aluminas:
UV and visible Raman spectroscopy, UV -
visible diffuse refl ectance spectroscopy, and
temperature - programmed reduction
studies . Journal of Physical Chemistry , 109,
2793 – 800 .
50 Gerrard , D.L. and Maddams , W.F. ( 1981 )
Resonance Raman spectrum of degraded
poly(vinyl chloride). 3. Background studies .
Macromolecules , 14 ( 5 ), 1356 – 62 .
51 Magg , N. , Giorgi , J.B. , Schroeder , T. ,
Baeumer , M. and Freund , H. - J. ( 2002 )
Model catalyst studies on vanadia particles
deposited onto a thin - fi lm alumina
support. 1. structural characterization .
Journal of Physical Chemistry B , 106 ( 34 ),
8756 – 61 .
52 Yamaguchi , T. , Kimura , Y. and Hirota , N.
( 1998 ) Solvation state selective excitation
in resonance Raman spectroscopy. II.
Theoretical calculation . Journal of Chemical
Physics , 109 ( 20 ), 9084 – 95 .
53 Wu , Z. , Stair , P.C. , Rugmini , S. and
Jackson , S.D. ( 2007 ) Raman spectroscopic
study of V/ θ - Al
2
O
3
catalysts: quantifi cation
of surface vanadia species and their
structure reduced by hydrogen . Journal of
Physical Chemistry C , (in press).
54 Cavani , F. , Cortelli , C. , Frattini , A. ,
Panzacchi , B. , Ravaglia , V. , Trifi ro , F. ,
Fumagalli , C. , Leanza , R. and Mazzoni , G.
( 2005 ) A new approach to the charac-