J. Phys. Chem. 1995,99, 10294-10298
10294
Infrared Study of Ozone Adsorption on Ti02 (Anatase) K. M. Bulanin? J. C. Lavalley,**$and A. A. Tsyganenkot Institute of Physics, St. Petersburg University, St. Petersburg, 198904, Russia, and URA CNRS 414, ISMRA, Universitt de Caen, 14050, Caen, Cedex, France Received: November 28, 1994; In Final Form: April IO, 199.5@
Ozone adsorption at 77 K on titania (anatase) surface dehydrated at different temperatures or preexposed to pyridine, acetonitrile, and CO has been studied by infrared spectroscopy in order to characterize ozone interaction with Lewis acid sites of different strength. With weaker sites, ozone molecules form coordinative complexes bound via the terminal oxygen atom. The observed vibrational frequencies (about 1145 and 990 cm-I), as well as the isotopic shifts observed for ozone enriched by '*O, reveal a strong distortion of the molecule in this complex. No molecular adsorption of ozone on strong Lewis sites was detected. Data obtained provide evidence for ozone dissociation on these sites. Formation of atomic oxygen is suggested. It participates in oxidation of CO on the Ti02 surface.
Introduction Ozone adsorption has practically not been studied by means of IR spectroscopy so far. After the first attempts which have shown a possibility of detecting the bands of ozone molecules adsorbed on Mg0,1-2a thorough investigation of ozone interaction with silica surface was reported in our previous paper.3 Frequency shift of surface hydroxyl groups demonstrated the basic character of ozone, comparable with that of CO. Frequencies of ozone forming a hydrogen bond with the OH groups were found to be almost coinciding with those of ozone in liquid or dissolved states or of physically adsorbed ozone on methoxylated silica surface. From the comparison of the half-width values of the v3 mode bands for different isotopic modifications, it was concluded that interaction with the proton OH groups occurs rather via the terminal oxygen atom than via the central atom of the 0 3 triangle, so that the symmetry of the adsorbed molecule is likely to be lowered from C2" to C,. The basic character of ozone should manifest itself in its interaction with the surface acid sites, such as the Lewis sites of metal oxides. To observe the two ozone stretching bands, the oxide should be transparent enough up to about 1000 cm-I or lower. It is also desirable for the Lewis sites to be more or less homogeneous to avoid complications due to ozone interaction with sites of different strength. For these reasons, titania (anatase) was chosen as the adsorbent. Lewis acidity of titania has been characterized by adsorption of ammonia and ~ y r i d i n e . ~More - ~ recent data on C07-9 and N29 adsorption have shown that two types of acid sites of different strength are present on the surface. A number of Lewis acid sites already arise after desorption of coordinatively bonded water on evacuation at room temperature. Pumping at higher temperature results in the increase of their number, whereas their strength is slightly enhanced. Less abundant strong Lewis sites appear after dehydroxylation at about 723 K or higher, and as follows from the position of the adsorbed CO and N2 bands, they present a substantially greater electron-accepting ability or acidity, as compared with the previous ones. Thus, by choosing the conditions of Ti02 pretreatment, it seems possible to elucidate ozone interaction with Lewis acid sites of different strength .
* To whom correspondence
' St. Petersburg University. 4 @
should be addressed.
ISMRA, Universite de Caen. Abstract published in Advance ACS Absrracrs, June 1, 1995
In order to gain more information on the nature of ozone adsorption sites, additional experiments have been carried out involving poisoning of certain sites by preliminary adsorption of bases, like acetonitrile and pyridine whose adsorption was previously studied on titania.5,'0 CO coadsorption with ozone has been studied in two ways, with different sequences of gases in contact with the surface, in order to see the competitive occupation of the same sites.
Experimental Section The stainless steel cell for studying the infrared spectra of adsorbed species at liquid nitrogen temperature has been described elsewhere." Ozone was prepared from gaseous I6O2 or its mixtures with 1 8 0 2 in an electric discharge and manipulated as previously r e p ~ r t e d . ~ Ti02 powder, anatase (BTP Tioxide Ltd., 86 m2/g), was pressed into 10-50 mg/cm2 pellets and pretreated at 773 K in vacuum and then in the presence of 10-20 Torr of 0 2 to oxidize the organic impurities and to prevent the reduction of titanium. Oxygen was changed 3-5 times before cooling to room temperature and final evacuation. To achieve the complete hydration of the surface, samples were brought into contact with 5-7 Torr of water vapor; most of that was then removed up to a residual pressure of about 0.1 Torr at room temperature. Then the sample volume was closed, and the cell was cooled with liquid nitrogen. Prolonged evacuation at 300 K or higher temperature was performed for partial dehydration of the surface. Before recording the spectra, about 0.5 Torr of helium was always introduced into the sample containing volume of the cell to improve the thermal contact of the sample with the cold environment. Spectra were recorded with a Nicolet FTIR 710 spectrometer with 2 cm-I resolution. To eliminate the bulk absorption of the oxide, the spectra of the cooled pretreated samples were usually subtracted from those after exposure to ozone.
Results Effect of Surface Dehydration. Ozone adsorption was studied on anatase at three different stages of the surface dehydration: (i) completely hydrated, (ii) well pumped at 300 K ( P < low4Torr), and (iii) evacuated at 773 K. In each case, the spectrum of carbon monoxide adsorbed at 77 K was recorded
0022-3654/95/2099-10294$09.00/0 0 1995 American Chemical Society
Ozone Adsorption on Ti02 (Anatase)
J. Phys. Chem., Vol. 99, No. 25, 1995 10295 0
R
tf: mP
c
H Q
I HAVENUHBER I CM-1 I
adsorbed at 77 K on Ti02 (anatase) cooled after pumping off the excess of water vapor up to 0.1 Torr at 300 K (1) or evacuated for 20 min at 300 K ( 2 ) and at 773 K ( 3 ) . Curves 2 and 3 were registered after removal of weakly sorbed ozone by pumping at about 100 K for 5 min.
Figure 1. IR spectra of
j60j
for the surface characterization, and then CO was removed at 300 K from the sample moved to the warm part of the cell. After that, a new background spectrum of the cooled sample was registered, and ozone was let into the cell. The results are presented in Figure 1. In accordance with the earlier result^,^ CO adsorption on the completely hydrated titania surface does not reveal any Lewis acidity; the only v(C0) band observed arises at 2150 cm-I and is due to an interaction with the OH groups. Ozone adsorption on such a sample (Figure 1, curve 1) results in the appearance of a strong band at 1034 cm-I, accompanied by an %40 times less intense one at 1108 cm-I. In the OH stretching region, the shoulder at 3735 cm-' and the band at 3680 cm-' decrease in intensity, and a perturbed v(0H) band appears at about 3570 cm-I. Prolonged evacuation of the Ti02 sample at 300 K removes a part of coordinatively adsorbed molecular water, as shown by the intensity decrease of the bending vibration band at 1620 cm-' . CO introduction on such a sample leads to the appearance of a band at 2178 cm-I, revealing the creation of weak Lewis acid sites. The spectrum of ozone on such a sample presents a new couple of bands at 1140.5 and 1001 cm-', the lowfrequency band being about 1.7 times stronger than the other. These bands resist pumping at about 100 K while their maxima become shifted to 1142 and 995 cm-I. By contrast, the bands due to weakly adsorbed ozone at 1108 and 1034 cm-' almost completely disappear (Figure 1, curve 2). The 1142 and 995 cm-' bands disappear after evacuation at 150 K. If the temperature of the sample pretreatment is raised to 773 K, the intensity of the 2178 cm-' band due to coordinatively bonded CO increases, and a new band characterizing molecules adsorbed on strong acid sites arises at about 2210 cm-I. No new bands, however, appear in the spectrum of adsorbed ozone on such a sample (Figure 1, curve 3) although the intensity of the above two bands due to the strongIy heId 0 3 molecules increases greatly; their position becomes shifted to 1147 and 989.5 cm-' after evacuation at 100 K. Significant changes also occur after ozone adsorption in the OH stretching region. The spectrum of surface OH groups of anatase outgassed at 773 K consists of narrow bands at 3725 and 3680 cm-I and a broader one about 3485 cm-I. In the presence of ozone, the former two bands disappear, and a new band of perturbed OH groups appears at about 3570 cm-I.
Figure 2. IR spectrum of I6O3adsorbed at 77 K on Ti02 (anatase) pretreated at 773 K, before (1) and after adsorption of acetonitrile and evacuation at 300 K ( 2 ) .
Almost exactly the same shift to 3570 cm-' was noted after introduction of an excess of C0.7 Effect of Acetonitrile or F'yridine Preadsorption. The influence of preadsorbed CH3CN on ozone adsorption on titania activated at 773 K is illustrated in Figure 2. After acetonitrile adsorption and removal of the excess adsorbate by pumping at 300 K, two bands arise in the C-N stretching region at 2305 and 2279 cm-'. Subsequent ozone adsorption at 77 K, besides the bands of physisorbed ozone, results in the appearance of two bands at 1134 and 1001 cm-I, much less intense as compared with those of ozone alone adsorbed on the same sample. In accordance with earlier reported data,"5 pyridine adsorption at 300 K, followed by pumping at 423 K, gives rise on titania activated at 773 K to coordinatively bonded molecules characterized by a strong band at 1609 cm-'. Adsorption of ozone at 77 K on a such pyridine-pretreated sample gives rise, as in the case of preadsorbed acetonitrile, to much weaker absorptions at 1130-1121 and 1014 cm-'. These experiments evidence that preadsorption of acetonitrile or pyridine almost prevents the formation of strongly bonded 0 3 species, confirming it results from the interaction of ozone with Lewis acid sites. Coadsorption of Ozone with CO. Two kinds of experiments have been carried out, according to whether CO or O3 has been adsorbed first. After CO adsorption on Ti02 pretreated at 773 K, removal of the gas phase by short pumping, and admitting helium into the cell, the spectrum shows two v(C0) bands at 2208 cm-' (weak) and 2180 cm-' (strong and narrow), characterizing CO adsorption on the two types of surface coordinatively unsaturated Ti"' ions. Prolonged pumping at about 100 K (Figure 3, curve 1) decreases the intensity of the lower v(C0) band by a factor of 2.5-3, while the band maxima are shifted to 221 1 and 2189 cm-' as a result of changes in the lateral interactions between the adsorbed molecules.I2 The intensity of the high-frequency v(C0) band remains constant, showing that the strong Lewis acid sites are still completely blocked by the adsorbed CO. Data on ozone adsorption on such a sample are presented in Figure 3. Immediately after ozone admission and appearance of the adsorbed ozone bands, the intensity of the two v(C0) bands does not change, while their maximum shifts somewhat toward lower wavenumbers. This shift increases with time, and after several minutes, the bands reach 2207 and 2180 cm-I, exactly the wavenumbers observed at saturating CO coverage. Mean-
Bulanin et al.
10296 J. Phys. Chem., Vol. 99, No. 25, 1995 N 4
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URVENUIIBER
( CM-1 )
Figure 3. IR spectrum of Ti02 (anatase)pretreated at 7 7 3 K after CO adsorption and evacuation at about lOOK (l), 20 min after 77 K ( 2 ) and 60 min later ( 3 ) .
I6O3 addition
at
W
c
2 00
2150
ZiOO
Figure 4. IR spectra of isotopically mixed water vapor at 373 K.
0 3
2650
ZbOO
I h J
"
WAVENUMBER (CM-1 )
with 68% (1) and 3 2 8 ( 2 ) of I8O, adsorbed at 77 K on Ti02 (anatase) evacuated after contact with
while, the intensities of both these bands decrease gradually, and a band due to molecular CO:! at 2342 cm-l appears and begins to grow (Figure 3, curve 2 and 3). Somewhat unexpected was the almost linear growth of the v(C02) band against the decrease of the high-frequency v(C0)component at about 2210 cm-'. CO addition at 80 K to the sample with preliminary adsorbed ozone results in a rapid decrease of the bands intensity at 1145 and 988 cm-I and the appearance of bands due to CO absorption at 2206 and 2178 cm-l and C02 formation at about 2250 cm-'. Immediately after CO addition, the intensity of the band at 1034 cm-I due to weakly bonded ozone grows dramatically and then gradually diminishes. Adsorption of Isotopically Substituted Ozone Molecules. Additional information on the nature of adsorbed complexes could be drawn from the isotopic shifts and the multiplicity of bands due to isotopic substitution. For this purpose, adsorption of I8O3 and isotopically mixed ozone with the 160:180 ratios close to 1:2 and 2:l has been studied on the anatase sample evacuated at 300 K, Le., when the bands of strongly held ozone are sharp enough and their position is less dependent on the coverage. The results are presented in Figure 4. Because of the low transparency of the sample below 1000 cm-I, it was not possible to study the splitting of the low-frequency band at about 995 cm-l, but the spectrum in the range of the 1143 cm-l band was reasonably well resolved. Instead of a single band at this position, a triplet with two new components at 1112 and
1080 cm-I is observed after adsorption of ozone prepared from a mixture of 68% 1 6 0 2 and 32% of l S 0 2 and removal of the most of weakly bonded ozone. No new bands were found after adsorption of ozone prepared from of a mixture with 68% of I8O2 and 32% of 1602, but the intensities of the bands were redistributed so that the low-frequency peak became most intense. The maximum at 1063 cm-I can be removed simultaneously with the bands due to weakly bound ozone and is, evidently, due to the v1 160180180 mode, enhanced because of the symmetry lowering. One can only detect a small downward shift of all the three bands for the 68% I8O mixture. When using pure I8O3, only one band was found at 1080 cm-' in this region. A more complicated structure could be seen simultaneously in the range of the v1 v3 combination mode. For pure l 6 0 3 and l 8 0 3 molecules, single bands appear at about 2136 and 1994 cm-', while in the spectra of isotopic mixtures, at least four more bands are observed at about 2108, 2074, 2052, and 2022 cm-' (Figure 4).
+
Discussion Weakly Bound Ozone. Positions of the bands due to ozone weakly bound to the surface of titania are practically the same as for ozone solution in liquid oxygen or for ozone adsorbed on Si02. Simultaneous perturbation in the spectrum of the surface OH groups shows that at least a fraction of the weakly
Ozone Adsorption on Ti02 (Anatase) bound ozone molecules form H bonds with surface OH groups. The intensities of the bands at 1106 and 1034 cm-I show, however, no correlation with the amount of perturbed OH groups, and like for SiOz, we have to assume that the bands due to H-bonded and physisorbed ozone molecules superimpose and could not be resolved also for this adsorbent. The band of perturbed OH groups at 3570 cm-I evidently corresponds to the more intense band of type I1 H
Ti
/'\ Ti
isolated hydroxyls at 3680 cm-', which are restored after the removal of weakly bound ozone, or may be partly due to the type 1 H
0 I
Ti
groups at 3735 cm-'. The resulting frequency shift by 110165 cm-I upon ozone adsorption is close to that observed after CO adsorption on anatase (120 cm-I). This confirms our conclusion about basic properties of ozone with a protonaccepting ability close to that of C0.3 Greater shift values as compared with that of silanol groups perturbed by ozone (80110 cm-I 3, reflect the higher acidity of titania surface hydroxyls, by comparison to that of the Si-OH groups. Strong Molecular Adsorption. Experiments on ozone coadsorption with strong bases like pyridine or acetonitrile, as well as with a weaker base like CO, provide evidence that the bands due to strongly adsorbed ozone at 1147- 1137 and 1002989 cm-I result from molecules bond to coordinatively unsaturated TirVions, which act as surface Lewis acid sites, or at least to those that account for the band of adsorbed CO at 2178 cm-'. The two bands are attributed to the two stretching fundamentals of the ozone molecules, shifted by about 35-50 cm-l with respect to their positions for the free molecules in the gas phase. It is remarkable that even the absolute values of the shift of each band is not less than the CO frequency shift (35 cm-') caused by CO adsorption on the same sites, despite the about twice lower values of the O3 frequencies. The two O3 bands move in opposite directions, so that their separation increases by almost 100 cm-', from about 60 cm-I for gas to 157.5 cm-I for ozone strongly held on the sample pretreated at 773 K. Adsorption also causes great change in the two bands intensity ratio. The intensity of the V I band for gaseous ozone is 4% or less of that of the v3 band,I3 only about 0.7% for ozone dissolved in liquid oxygen,13and about 2.5% for ozone weakly adsorbed on titania. By contrast, for ozone chemisorbed on anatase, the high-frequency band intensity is up to 60% of that of the low-frequency one, the intensities of the two bands becoming thus very close. More information about ozone perturbation on adsorption could be obtained from the isotopic splitting data. The free C2,, ozone molecule has two equivalent oxygen atoms, and in the different combinations of I6O and I8O,six modifications of 0 3 are possible, so that each band of ozone molecule is split into six more or less well-separated components. For the free 160180160 and 180160180 molecules, the V I modes have almost the same frequencies, and one could expect for slightly perturbed ozone molecules, in the V I region, the presence of five bands, not less than 10 cm-' apart, when the mixture contains all the isotopic varieties. If the molecule symmetry is lost, the two terminal oxygen atoms become nonequivalent, and up to eight modifications
J. Phys. Chem., Vol. 99, No. 25, 1995 10297 should be distinguishable in the mixture. However, in the observed spectra of isotopically enriched ozone, only three maxima separated by 30 cm-' were detected in the range of the YI band. It is almost exactly the kind of splitting expected for a dioxygen fragment, if it has frequency in this region. However, the splitting of the V I v3 combination band into at least five maxima confirms that the adsorbed species is still the three-atomic ozone molecule. We have thus to conclude that the adsorbed ozone molecules are distorted in such a manner that two atoms participate in the high-frequency vibration, while the low-frequency one is influenced by the substitution of the third atom, and thus, the combination mode will be sensitive to the masses of all the three atoms. It could happen if the adsorbed 0 3 molecule becomes almost linear, and the V I band corresponds to the symmetric vibration of two terminal atoms with respect to the motionless central one, similar to the V I mode of C02. However, for such a case, the symmetric stretching mode should have lower frequency than the asymmetric one and a have very low intensity, which is completely inconsistent with the experimental data. The only other possible explanation is that the two 0-0 stretching vibrations are almost completely uncoupled because the molecule is bent, and the two 0-0 bonds have essentially different force constants. This could occur if the adsorbed molecule is attached to the surface site via one of its terminal atoms, which practically does not participate in the high-frequency vibration of the O=O fragment, in a structure like
+
o=o
-Ti
P
-
The difference in frequency between the two stretching modes should increase, each becoming localized on one 0-0 bond and being sensitive to the isotopic substitution of the considered pair of atoms. A slight downward shift of all the three isotopic components of the high-frequency band on the increasing " 0 3 content in the isotopic mixture may be interpreted as a result of the intensity redistribution between unresolved constituents, corresponding to substitution of the attached to the surface oxygen atom. A tendency of the ozone molecule to interact with the cations via one of the terminal oxygen atoms was also found in a recent ab initio study of ozone complexes with Li+ ionsI4 and is in agreement with the geometry found for hydrogen-bonded complexes, both in matricesI5 and on the silica ~ u r f a c e . ~ The above form of molecular ozone adsorption is certainly associated with the weaker Lewis sites characterized by the band of adsorbed CO at 2178 cm-I. (i) Both the ozone bands and the latter v ( C 0 ) band do not appear after adsorption on a fully hydrated sample, and arise after dehydration at 300 K, when the 2210 cm-I v(C0) band is still absent. (ii) The intensities of the ozone bands increase with the pretreatment temperature, while the position of each band shifts with respect to the frequency found for the free molecule. This shift may be due to the growing strength of Lewis acid sites on dehydration or results from lateral interactions, which also accounts for the increasing coverage dependence of the band maxima positions. Exactly the same occurs for the v ( C 0 ) band at 2178 cm-'. (iii) After ozone adsorption on the sample with preadsorbed CO, the bands of strongly held ozone immediately appear upon ozone admittance, whereas the 2210 cm-' band of adsorbed CO remains unchanged.
Bulanin et al.
10298 J. Phys. Chem., Vol. 99, No. 25, 1995
Ozone Interaction with Strong Lewis Sites, Decomposition, and CO Oxidation by Ozone. The results do not explain how ozone molecules interact with the strong Lewis sites characterized by the v(C0)band at 2210 cm-' since we were not able to detect a new pair of bands due to ozone adsorbed on these sites. It is worth to note that a molecule like nitrogen shows a much greater frequency shift on interaction with these strong Lewis sites.9 It is unlikely that ozone does not interact with such sites or, if it does, shows exactly the same spectral characteristics as the molecules adsorbed on the weaker sites. The results obtained in this work enable us to suggest the following answer consistent with most of the data at our disposal. Ozone adsorption on the stronger Lewis sites should lead to a further distortion of the molecule until it becomes unstable and dissociates into a free oxygen molecule and a surface oxygen atom, which remains attached to the titanium ion:
o=o
0 3
-Ti-
0
-I -I 0
-Ti-
0+02
-Ti-
The oxygen atom can react with the next ozone molecule to form two more 0 2 molecules; if the temperature is high enough for its migration, recombination of two oxygen atoms is also possible. These two mechanisms of ozone decomposition were suggested by GolodetsI6 to explain the kinetics of this process, but the author has neither discussed the nature of the active sites nor suggested any idea about the state of atomic oxygen on the oxide surfaces. The proposed mechanism implies that upon ozone adsorption at the surface with the strong Lewis sites some molecules should readily dissociate with the formation of molecular oxygen. Atomic oxygen formed on the surface in the reaction of ozone with the strong Lewis sites should easily react with other molecules such as CO to form adsorbed oxidized species. Indeed, C02 was formed on titania when CO was coadsorbed. One should take into account that COz at 77 K has practically zero vapor pressure and can scarcely move from one surface site to another. That is why appearance of the linearly adsorbed C02 band, on CO addition at 77 K to the sample with preadsorbed ozone, can be considered as evidence for CO reaction with the surface atomic oxygen; the fact that other forms of C02 adsorption such as carbonate-like or bicarbonate species do not appear in this conditions suggests that the CO?; molecule is attached to the same titanium ion the atomic oxygen is bound to. At higher temperatures, linearly bound molecular COz will be desorbed or will form carbonatelike surface species on other surface sites, and the strong Lewis sites will be free for the next ozone molecule. This make possible the catalytic CO oxidation on the strong Lewis acid sites on titania. In the experiment with ozone adsorption after CO,the C02 band does not appear immediately after ozone addition at 77 K to the sample, because the strong Lewis acid sites were saturated by CO. The correlation found between the further gradual growth of the v(CO2)band and the decrease of the v(C0) band at 2210 cm-' also testifies for the above mechanism of CO oxidation on the strong Lewis acid sites.
Conclusion Low-temperature ozone adsorption on titania has been studied by means of IR spectroscopy. The spectra obtained for the
samples dehydrated at different temperatures reveal at least three forms of ozone adsorption on TiOz: (i) weakly bonded molecules that form hydrogen bonds with OH groups or are physically adsorbed at the surface, (ii) molecules adsorbed on the weaker Lewis acid sites which arise on Ti02 evacuated at 300 K and account for the band of adsorbed CO at 2178 cm-', and (iii) products of ozone interaction with the stronger Lewis acid sites responsible for the 2210 cm-I band of adsorbed CO. Experiments with site poisoning by pyridine, acetonitrile, and CO show that, with weaker sites, ozone molecules form coordinative complexes characterized by bands at 1145 and 990 cm-' , Adsorption of isotopically substituted ozone mixtures with different I8O contents confirms the assignment of these bands to molecular ozone. The frequency shifts with respect to positions of the band maxima in gaseous, liquid, or dissolved ozone are greater than those known from the literature for any observed or calculated ozone complexes. An increased separation between the frequencies of the two stretching modes as well as the values of isotopic shifts observed for ozone enriched by I8O reveal strong distortion of molecules bound to the surface titanium ions by one of the terminal oxygen atoms. No molecular adsorption of ozone on the strong Lewis sites was detected. The data obtained provide evidence for ozone dissociation on these sites with the formation of atomic oxygen, which participates in the catalytic reactions of ozone decomposition or CO oxidation on TiOz.
Acknowledgment. The authors acknowledge the help of J. Lamotte and N. Tsyganenko for technical assistance. Part of this work was supported by the RFFI (Russian Foundation for Fundamental Investigations)under Grant 94-03-08550-a. K.M.B. is grateful to the Ministere des Affaires Etrangkres FranGais for a grant. References and Notes (1) Alekseev, A. V.; Babaeva, M. A,; Bystrov, D. S.; Tsyganenko, A. A.; Yushkov, V. A. All-Union symposium on photochemical processes in the Earth atmosphere. Moscow, 1986; Tchemogolovka, 1986; p 27. (2) Alekseev, A. V.; Babaeva, M. A.; Bystrov, D. S.; Tsyganenko, A. A.; Yushkov, V. A. In Photochemical processes in the Earth atmosphere; Nauka: Moscow, 1990; p 20 (in Russian). (3) Bulanin, K. M.; Alekseev, A. V.; Bystrov, D. S.; Lavalley, J. C.; Tsyganenko, A. A. J. Phys. Chem. 1994, 98, 5100. (4) Tret'yakov, N. E.; Filimomov, V. N. Kinet. Katal. 1973, 14, 803. (5) Morterra, C.; Ghiotti, G.; Garrone, E.; Fisicaro, E. J. Chem. SOC., Faraday Trans. 1 1980, 76, 2102. (6) Tsyganenko, A. A.; Pozdnyakov, D. V.; Filimonov, V. N. J . Mol. Struct. 1975, 29, 299. (7) Rodionova, T. A.; Tsyganenko, A. A,; Filimonov, V. N. Adsorbtsiya i adsorbenrj, No 10, Kiev; Naukova Dumka, 1982; p 33 (Russian). (8) Morterra, C.; Garrone, E.; Bolis, V.; Fubini.B. Spectrochim. Acta 1987, 43A, 1577. (9) Zverev, S. M.; Smimov, K. S.; Tsyganenko, A. A. Kinet. Katal. 1988, 29, 1439. (10) Mortena, C.; Chiorino, A,; Boccuzzi, F.; Fisicaro, E. Z. Phys. Chem. (Munich) 1981, 124, 211. (11) Babaeva. M. A.; Bystrov, D. S.; Kovalgin, A. Yu.; Tsyganenko, A . A. J. Catal. 1990, 123, 396. (12) Tsyganenko, A. A,; Denisenko, L. A,; Zverev, S. M.; Filimonov, V. N. J. Catal. 1985, 94, 10. (13) Zittel, P. F. J. Phys. Chem. 1991, 95, 6802. (14) Snyder, G.; Sapse, D. Chem. Phys. Lett. 1994, 218, 312. (15) Andrews, L.; Withnall, R.; Hunt, R. D. J. Phys. Chem. 1988, 92, 78. (16) Golodets, G . I. Heterogeneous Catalytic Reactions Involving Molecular Oxygen; Kiev. Naukova Dumka, 1977. JP943 148B
