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Hydrodechlorination catalytic activity of gold nanoparticles supported on TiO2 modified SBA-15 investigated by IR spectroscopy
Journal of Molecular Structure 924–926 (2009) 355–357
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Hydrodechlorination catalytic activity of gold nanoparticles supported on TiO2 modified SBA-15 investigated by IR spectroscopy I. Hannus a,*, M. Búza a, A. Beck b, L. Guczi b, G. Sáfrán c a
Department of Applied and Environmental Chemistry, University of Szeged, Rerrich B. tér 1, Szeged H-6720, Hungary Institute of Isotopes of the Hungarian Academy of Sciences, P.O. Box 77, Budapest H-1525, Hungary c Research Institute for Technical Physics and Materials Science, HAS, Konkoly Thege Miklós út 29/33, H-1525 Budapest, Hungary b
a r t i c l e
i n f o
Article history: Received 7 November 2008 Received in revised form 3 December 2008 Accepted 5 December 2008 Available online 24 December 2008 Keywords: Hydrodechlorination Au nanoparticles IR spectroscopy Carbon tetrachloride
a b s t r a c t The hydrodechlorination catalytic activity of gold nanoparticles on SBA-15 silica modified by TiO2 promoters has been investigated. Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used in the hydrodechlorination of CCl4 as model compound. The IR spectroscopic experimental results showed that the gold nanoparticles have higher catalytic activity, than platinum ones. The two samples were tested also in CO oxidation, in which Au/TiO2/SBA-15 possess also somewhat higher activity than Pt/TiO2. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction Some of the chlorinated organic compounds are widely used commercially, because of their advantageous chemical/physical properties or having toxicity for pestiferous living substances. However, most of them are environmental pollutants. Emitted into the atmosphere they are responsible for diminishing the ozone layer in the stratosphere. Therefore, a lot of effort is devoted to finding proper solutions to decompose these chemicals in environment-friendly ways. Nobel metals on different carriers play very important role in catalytic hydrodechlorination of these compounds. No such own activity of Au was reported, but improved selectivity and activity could be obtained by supported alloyed type and core/shell AuPd bimetallic particles in dichlorodifluoromethane and trichloroethene hydrodechlorination, respectively, compared to the monometallic Pd analogues [1–3]. We report here on the preparation of Au/TiO2 nanostructures in mesoporous SBA-15 silica and their performance in hydrodechlorination reactions of carbon tetrachloride. 2. Experimental 2.1. Materials TiO2 (5 wt%) was introduced into SBA-15 via surface hydroxyls initiated hydrolysis of Ti-isopropoxide in anhydrous ethanol sus* Corresponding author. E-mail address: [email protected] (I. Hannus). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.12.030
pension of SBA-15 followed by calcination at 873 K. Gold was deposited on the TiO2/SBA-15 at pH 2 by adsorption of Au colloid (dAu = 2.7 ± 0.9 nm) reduced from HAuCl4 by NaBH4 and stabilized by polyvinylalcohol [4]. The Au loading was 2.5 wt% according to ICP-MS analysis. Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used in the hydrodechlorination of CCl4 as model compound. Pt/TiO2 was synthetised by the adsorption of Pt colloid (dPt = 3.2 ± 1.4 nm) formed from PtCl4 by reduction/stabilization with tannic acid + Na-citrate, on TiO2 Degussa P25 at pH 2. The Pt content was 1.9 wt% as determined by ICP-MS. 2.2. Experimental methods IR spectroscopic self-supporting wafer technique was employed for catalytic hydrodechlorination measurements. The wafers (10 mg/cm2) were prepared from the powdered catalysts and placed into the sample holder of the in situ IR cell. During the pretreatment process when the wafer was heated to 673 K for 1 h in oxygen followed by evacuation at the same temperature for 2 h the organic compounds (remaining reducing and stabilizing agents) could be removed. This oxidized sample was reduced in H2 (26.6 kPa at 473 K). After this treatment the sample was cooled to room temperature and the background spectrum of the catalyst was recorded. For hydrodechlorination experiments the pretreated catalyst wafers were loaded with 1.33 kPa of reactant carbon tetrachloride at room temperature. Both the surface species and the gas-phase products were analysed as the reaction proceeded under
I. Hannus et al. / Journal of Molecular Structure 924–926 (2009) 355–357
various experimental conditions. Spectra were run on a Mattson Genesis 1 FTIR spectrometer (lithium tantalate detector), with a resolution of 2 cm 1. For a spectrum 16 scans were accumulated [5]. The two samples (60–60 mg) were tested also in CO oxidation reaction in a flow reactor with QMS analysis after calcination at 673 K in 20% O2 in He mixture for 1 h to remove the organic residues, in case of Pt/TiO2 followed by reduction at 673 K in H2 for 1 h to rereduce platinum. The temperature programmed CO + O2 reaction was performed with a 55 ml/min gas flow of 0.54% CO and 9.1% O2 in He with 4 K/min ramp rate. Both Au/TiO2/SBA-15 and Pt/TiO2 were investigated after CO oxidation test in a JEOL 3010 high resolution transmission electron microscope (HRTEM) of 0.17 nm point resolution operating at 300 kV. The TEM specimens were prepared by dripping and drying the aqueous suspensions of the samples on carbon-coated microgrids. The gold and platinum particle size distributions were determined by measuring 200–300 metal particles. 3. Results The two catalysts were derived from Au and Pt colloids of 2.7 ± 0.9 nm and 3.2 ± 1.4 nm mean diameters, respectively. After the calcination/reduction pretreatment and CO oxidation catalytic test the Au and Pt particle size did not change, it was 2.9 ± 1.0 and 3.2 ± 1.3 nm, respectively. This suggests that the particles were stable against sintering. Fig. 1 shows TEM micrographs of the Au/TiO2/ SBA-15 (a) and Pt/TiO2 (b) samples after the CO oxidation test. The metal particles appear as dark contrast features on the mesoporous SiO2 and nonporous TiO2 support particles, respectively. Assuming spherical metal particles (that is in agreement with TEM images) and taking into account the metal loadings and particle sizes of the two samples, the relative number of the surface metal atoms in Au/TiO2/SBA-15 and Pt/TiO2 after pretreatments is Aus/ Pts = 1.5. This value will be helpful in comparison of catalytic activities in CCl4 hydrodechlorination and CO oxidation. Hydrodechlorination reaction takes place when CCl4 reacts on noble metal containing catalyst [6]. This reaction was investigated in the presence of hydrogen using IR spectroscopy. 3.1. IR spectra of adsorbed phase in the hydrodechlorination reaction Fig. 2 shows the spectra of CCl4 + H2 mixture adsorbed on Au nanoparticles in mesoporous silicate (Au/TiO2/SBA-15). The band near 2050 cm 1 is due to adsorbed CO on gold nanoparticles. It is
0.25 d c
Absorbance
356
b
a
2500
2000
1500
1000
500
Wavenumber (1/cm) Fig. 2. IR spectra of adsorbed and reacted CCl4 on Au nanoparticles in mesoporous silicate as catalyst; CCl4 adsorbed at room temperature (a), at 373 K (b), at 473 K (c) and at 573 K (d).
assumed that the oxygen appearing in CO originates from the framework of the support [7]. 3.2. IR spectra of the gas phase in the hydrodechlorination reaction Under the given experimental conditions the main products were methane and HCl being typical of the hydrodechlorination of carbon tetrachloride. As it is seen in Fig. 3 the characteristic absorptions of methane appeared in the CAH stretching region, at 3050 cm 1, and CAH deformation region, at 1300 cm 1. The bands centered at 2880 cm 1 are attributed to the characteristic vibration of HCl. In the CACl stretching vibration region of the spectra the absorption of the starting material (carbon tetrachloride) is seen at 800 cm 1. The CACl stretching vibration of chloroform is also visible at 780 cm 1. IR spectroscopy indicated that chloroform is an intermediate product of a consecutive transformation, because its characteristic absorptions at 1210 cm 1 (due to CAH deformation vibration) and at 780 cm 1 (due to CACl vibration) passed through a maximum. The starting material carbon tetrachloride is not visible at 573 K only chloroform exists (Fig. 3/c). At 673 K the chloroform also disappeared and practically the final products methane and HCl are only visible at the spectrum (Fig. 3/d).
Fig. 1. TEM image of Au/TiO2/SBA-15 (a) and Pt/TiO2 (b) after CO oxidation test.
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I. Hannus et al. / Journal of Molecular Structure 924–926 (2009) 355–357
100
d
b
CO conversion, %
Absorbance
c
80
60
40
20
Pt/TiO2
0.5
Au/TiO2 /SBA-15
0
a 300
4000
3500
3000
2500
2000
1500
1000
320
340
360
380
400
420
440
Temperature, K
500
Wavenumber (1/cm)
Fig. 5. CO oxidation activity of the two samples.
Fig. 3. Infrared gas-phase spectra of the products of carbon tetrachloride reacted over Au nanoparticles in mesoporous silicate catalyst; at 373 K (a), 473 K (b), 573 K (c) and 673 K (d).
0.5
The catalytic activity of Au/TiO2/SBA-15 in CCl4 hydrodechlorination is higher than that of Pt/TiO2 sample even if we refer it to one surface metal atoms. In the Au containing sample the number of surface metal atoms was 1.5 times higher than in the Pt containing one. 3.3. Activity in CO oxidation reaction
d Absorbance
As a comparison the two samples were tested also in CO oxidation (see Fig. 5), in which Au/TiO2/SBA-15 posses also somewhat higher activity than Pt/TiO2. 4. Conclusion
c
b
a 4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (1/cm) Fig. 4. Infrared gas-phase spectra of the products of carbon tetrachloride reacted over Pt nanoparticles on TiO2 support; at 373 K (a), 473 K (b), 573 K (c) and 673 K (d).
In spite of the hydrogen atmosphere applied in these experiments a small amount of oxygen containing intermediate product, phosgene (usually observed in inert or oxidative medium) was also detected (C@O vibration at 1830 and CACl vibration at 850 cm 1), see on Fig. 3/b. The carbon monoxide originated from the decomposition of phosgene can adsorb on gold nanoparticles and give an intensive band at 2050 cm 1 (see on Fig. 2/b,c and d). Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used. The IR spectra of adsorbed CCl4 on Pt-containing catalyst were very similar to that on Au-containing one. The adsorbed CO on platinum nanoparticles is also visible at 2050 cm 1. Infrared gas-phase spectra of carbon tetrachloride reacted over Pt nanoparticles on TiO2 support show lower hydrodechlorination catalytic activity than over Au nanoparticles. As can be seen on Fig. 4, final products (methane, HCl) were observed at higher temperature, at 573 K, than in the case of gold catalyst. Starting material carbon tetrachloride was remained at 673 K over Pt nanoparticles in contrary over Au ones.
The hydrodechlorination catalytic activity of gold nanoparticles on SBA-15 silica modified by TiO2 promoters has been investigated. Infrared spectroscopic experiments proved that the final products are methane and HCl in the hydrodechlorination reaction of carbon tetrachloride. Beside the final products, CHCl3 as intermediate product was formed as well. Its intensity goes through a maximum. The catalytic activity of Au/TiO2/SBA-15 in CCl4 hydrodechlorination is higher than that of Pt/TiO2 sample even if we refer it to one surface metal atoms. In the Au containing sample the number of surface metal atoms was 1.5 times higher than in the Pt containing one. In the former case at 673 K there is no reactant carbon tetrachloride in the gas phase, the reaction is complete. Acknowledgement This work was performed with the help of Grant OTKA T049564, Hungary. References [1] R.W.J. Scott, O.M. Wilson, S.K. Oh, E.A. Kenik, R.M. Crooks, J. Am. Chem. Soc. 126 (2004) 15583. [2] M. Bonarowska, J. Pielaszek, V.A. Semikolenov, Z. Karpinski, J. Catal. 209 (2002) 528. [3] M.O. Nutt, K.N. Heck, P. Alvarez, M.S. Wong, Appl. Catal. B Environ. 69 (2006) 115. [4] A. Beck, A. Horváth, Gy. Stefler, R. Katona, O. Geszti, Gy. Tolnai, L.F. Liotta, L. Guczi, Catal. Today 139 (2008) 180. [5] I. Hannus, Zs. Kropok, J. Halász, J. Mol. Struct. 834-836 (2007) 236. [6] B. Imre, I. Hannus, I. Kiricsi, J. Mol. Struct. 744–747 (2005) 501. [7] J. Halász, B. Imre, I. Hannus, Appl. Catal. A General 271 (2004) 47.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Hydrodechlorination catalytic activity of gold nanoparticles supported on TiO2 modified SBA-15 investigated by IR spectroscopy I. Hannus a,*, M. Búza a, A. Beck b, L. Guczi b, G. Sáfrán c a
Department of Applied and Environmental Chemistry, University of Szeged, Rerrich B. tér 1, Szeged H-6720, Hungary Institute of Isotopes of the Hungarian Academy of Sciences, P.O. Box 77, Budapest H-1525, Hungary c Research Institute for Technical Physics and Materials Science, HAS, Konkoly Thege Miklós út 29/33, H-1525 Budapest, Hungary b
a r t i c l e
i n f o
Article history: Received 7 November 2008 Received in revised form 3 December 2008 Accepted 5 December 2008 Available online 24 December 2008 Keywords: Hydrodechlorination Au nanoparticles IR spectroscopy Carbon tetrachloride
a b s t r a c t The hydrodechlorination catalytic activity of gold nanoparticles on SBA-15 silica modified by TiO2 promoters has been investigated. Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used in the hydrodechlorination of CCl4 as model compound. The IR spectroscopic experimental results showed that the gold nanoparticles have higher catalytic activity, than platinum ones. The two samples were tested also in CO oxidation, in which Au/TiO2/SBA-15 possess also somewhat higher activity than Pt/TiO2. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction Some of the chlorinated organic compounds are widely used commercially, because of their advantageous chemical/physical properties or having toxicity for pestiferous living substances. However, most of them are environmental pollutants. Emitted into the atmosphere they are responsible for diminishing the ozone layer in the stratosphere. Therefore, a lot of effort is devoted to finding proper solutions to decompose these chemicals in environment-friendly ways. Nobel metals on different carriers play very important role in catalytic hydrodechlorination of these compounds. No such own activity of Au was reported, but improved selectivity and activity could be obtained by supported alloyed type and core/shell AuPd bimetallic particles in dichlorodifluoromethane and trichloroethene hydrodechlorination, respectively, compared to the monometallic Pd analogues [1–3]. We report here on the preparation of Au/TiO2 nanostructures in mesoporous SBA-15 silica and their performance in hydrodechlorination reactions of carbon tetrachloride. 2. Experimental 2.1. Materials TiO2 (5 wt%) was introduced into SBA-15 via surface hydroxyls initiated hydrolysis of Ti-isopropoxide in anhydrous ethanol sus* Corresponding author. E-mail address: [email protected] (I. Hannus). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.12.030
pension of SBA-15 followed by calcination at 873 K. Gold was deposited on the TiO2/SBA-15 at pH 2 by adsorption of Au colloid (dAu = 2.7 ± 0.9 nm) reduced from HAuCl4 by NaBH4 and stabilized by polyvinylalcohol [4]. The Au loading was 2.5 wt% according to ICP-MS analysis. Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used in the hydrodechlorination of CCl4 as model compound. Pt/TiO2 was synthetised by the adsorption of Pt colloid (dPt = 3.2 ± 1.4 nm) formed from PtCl4 by reduction/stabilization with tannic acid + Na-citrate, on TiO2 Degussa P25 at pH 2. The Pt content was 1.9 wt% as determined by ICP-MS. 2.2. Experimental methods IR spectroscopic self-supporting wafer technique was employed for catalytic hydrodechlorination measurements. The wafers (10 mg/cm2) were prepared from the powdered catalysts and placed into the sample holder of the in situ IR cell. During the pretreatment process when the wafer was heated to 673 K for 1 h in oxygen followed by evacuation at the same temperature for 2 h the organic compounds (remaining reducing and stabilizing agents) could be removed. This oxidized sample was reduced in H2 (26.6 kPa at 473 K). After this treatment the sample was cooled to room temperature and the background spectrum of the catalyst was recorded. For hydrodechlorination experiments the pretreated catalyst wafers were loaded with 1.33 kPa of reactant carbon tetrachloride at room temperature. Both the surface species and the gas-phase products were analysed as the reaction proceeded under
I. Hannus et al. / Journal of Molecular Structure 924–926 (2009) 355–357
various experimental conditions. Spectra were run on a Mattson Genesis 1 FTIR spectrometer (lithium tantalate detector), with a resolution of 2 cm 1. For a spectrum 16 scans were accumulated [5]. The two samples (60–60 mg) were tested also in CO oxidation reaction in a flow reactor with QMS analysis after calcination at 673 K in 20% O2 in He mixture for 1 h to remove the organic residues, in case of Pt/TiO2 followed by reduction at 673 K in H2 for 1 h to rereduce platinum. The temperature programmed CO + O2 reaction was performed with a 55 ml/min gas flow of 0.54% CO and 9.1% O2 in He with 4 K/min ramp rate. Both Au/TiO2/SBA-15 and Pt/TiO2 were investigated after CO oxidation test in a JEOL 3010 high resolution transmission electron microscope (HRTEM) of 0.17 nm point resolution operating at 300 kV. The TEM specimens were prepared by dripping and drying the aqueous suspensions of the samples on carbon-coated microgrids. The gold and platinum particle size distributions were determined by measuring 200–300 metal particles. 3. Results The two catalysts were derived from Au and Pt colloids of 2.7 ± 0.9 nm and 3.2 ± 1.4 nm mean diameters, respectively. After the calcination/reduction pretreatment and CO oxidation catalytic test the Au and Pt particle size did not change, it was 2.9 ± 1.0 and 3.2 ± 1.3 nm, respectively. This suggests that the particles were stable against sintering. Fig. 1 shows TEM micrographs of the Au/TiO2/ SBA-15 (a) and Pt/TiO2 (b) samples after the CO oxidation test. The metal particles appear as dark contrast features on the mesoporous SiO2 and nonporous TiO2 support particles, respectively. Assuming spherical metal particles (that is in agreement with TEM images) and taking into account the metal loadings and particle sizes of the two samples, the relative number of the surface metal atoms in Au/TiO2/SBA-15 and Pt/TiO2 after pretreatments is Aus/ Pts = 1.5. This value will be helpful in comparison of catalytic activities in CCl4 hydrodechlorination and CO oxidation. Hydrodechlorination reaction takes place when CCl4 reacts on noble metal containing catalyst [6]. This reaction was investigated in the presence of hydrogen using IR spectroscopy. 3.1. IR spectra of adsorbed phase in the hydrodechlorination reaction Fig. 2 shows the spectra of CCl4 + H2 mixture adsorbed on Au nanoparticles in mesoporous silicate (Au/TiO2/SBA-15). The band near 2050 cm 1 is due to adsorbed CO on gold nanoparticles. It is
0.25 d c
Absorbance
356
b
a
2500
2000
1500
1000
500
Wavenumber (1/cm) Fig. 2. IR spectra of adsorbed and reacted CCl4 on Au nanoparticles in mesoporous silicate as catalyst; CCl4 adsorbed at room temperature (a), at 373 K (b), at 473 K (c) and at 573 K (d).
assumed that the oxygen appearing in CO originates from the framework of the support [7]. 3.2. IR spectra of the gas phase in the hydrodechlorination reaction Under the given experimental conditions the main products were methane and HCl being typical of the hydrodechlorination of carbon tetrachloride. As it is seen in Fig. 3 the characteristic absorptions of methane appeared in the CAH stretching region, at 3050 cm 1, and CAH deformation region, at 1300 cm 1. The bands centered at 2880 cm 1 are attributed to the characteristic vibration of HCl. In the CACl stretching vibration region of the spectra the absorption of the starting material (carbon tetrachloride) is seen at 800 cm 1. The CACl stretching vibration of chloroform is also visible at 780 cm 1. IR spectroscopy indicated that chloroform is an intermediate product of a consecutive transformation, because its characteristic absorptions at 1210 cm 1 (due to CAH deformation vibration) and at 780 cm 1 (due to CACl vibration) passed through a maximum. The starting material carbon tetrachloride is not visible at 573 K only chloroform exists (Fig. 3/c). At 673 K the chloroform also disappeared and practically the final products methane and HCl are only visible at the spectrum (Fig. 3/d).
Fig. 1. TEM image of Au/TiO2/SBA-15 (a) and Pt/TiO2 (b) after CO oxidation test.
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I. Hannus et al. / Journal of Molecular Structure 924–926 (2009) 355–357
100
d
b
CO conversion, %
Absorbance
c
80
60
40
20
Pt/TiO2
0.5
Au/TiO2 /SBA-15
0
a 300
4000
3500
3000
2500
2000
1500
1000
320
340
360
380
400
420
440
Temperature, K
500
Wavenumber (1/cm)
Fig. 5. CO oxidation activity of the two samples.
Fig. 3. Infrared gas-phase spectra of the products of carbon tetrachloride reacted over Au nanoparticles in mesoporous silicate catalyst; at 373 K (a), 473 K (b), 573 K (c) and 673 K (d).
0.5
The catalytic activity of Au/TiO2/SBA-15 in CCl4 hydrodechlorination is higher than that of Pt/TiO2 sample even if we refer it to one surface metal atoms. In the Au containing sample the number of surface metal atoms was 1.5 times higher than in the Pt containing one. 3.3. Activity in CO oxidation reaction
d Absorbance
As a comparison the two samples were tested also in CO oxidation (see Fig. 5), in which Au/TiO2/SBA-15 posses also somewhat higher activity than Pt/TiO2. 4. Conclusion
c
b
a 4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (1/cm) Fig. 4. Infrared gas-phase spectra of the products of carbon tetrachloride reacted over Pt nanoparticles on TiO2 support; at 373 K (a), 473 K (b), 573 K (c) and 673 K (d).
In spite of the hydrogen atmosphere applied in these experiments a small amount of oxygen containing intermediate product, phosgene (usually observed in inert or oxidative medium) was also detected (C@O vibration at 1830 and CACl vibration at 850 cm 1), see on Fig. 3/b. The carbon monoxide originated from the decomposition of phosgene can adsorb on gold nanoparticles and give an intensive band at 2050 cm 1 (see on Fig. 2/b,c and d). Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO2 catalyst was used. The IR spectra of adsorbed CCl4 on Pt-containing catalyst were very similar to that on Au-containing one. The adsorbed CO on platinum nanoparticles is also visible at 2050 cm 1. Infrared gas-phase spectra of carbon tetrachloride reacted over Pt nanoparticles on TiO2 support show lower hydrodechlorination catalytic activity than over Au nanoparticles. As can be seen on Fig. 4, final products (methane, HCl) were observed at higher temperature, at 573 K, than in the case of gold catalyst. Starting material carbon tetrachloride was remained at 673 K over Pt nanoparticles in contrary over Au ones.
The hydrodechlorination catalytic activity of gold nanoparticles on SBA-15 silica modified by TiO2 promoters has been investigated. Infrared spectroscopic experiments proved that the final products are methane and HCl in the hydrodechlorination reaction of carbon tetrachloride. Beside the final products, CHCl3 as intermediate product was formed as well. Its intensity goes through a maximum. The catalytic activity of Au/TiO2/SBA-15 in CCl4 hydrodechlorination is higher than that of Pt/TiO2 sample even if we refer it to one surface metal atoms. In the Au containing sample the number of surface metal atoms was 1.5 times higher than in the Pt containing one. In the former case at 673 K there is no reactant carbon tetrachloride in the gas phase, the reaction is complete. Acknowledgement This work was performed with the help of Grant OTKA T049564, Hungary. References [1] R.W.J. Scott, O.M. Wilson, S.K. Oh, E.A. Kenik, R.M. Crooks, J. Am. Chem. Soc. 126 (2004) 15583. [2] M. Bonarowska, J. Pielaszek, V.A. Semikolenov, Z. Karpinski, J. Catal. 209 (2002) 528. [3] M.O. Nutt, K.N. Heck, P. Alvarez, M.S. Wong, Appl. Catal. B Environ. 69 (2006) 115. [4] A. Beck, A. Horváth, Gy. Stefler, R. Katona, O. Geszti, Gy. Tolnai, L.F. Liotta, L. Guczi, Catal. Today 139 (2008) 180. [5] I. Hannus, Zs. Kropok, J. Halász, J. Mol. Struct. 834-836 (2007) 236. [6] B. Imre, I. Hannus, I. Kiricsi, J. Mol. Struct. 744–747 (2005) 501. [7] J. Halász, B. Imre, I. Hannus, Appl. Catal. A General 271 (2004) 47.