International Congress on Nanotechnology (ICNT 2005) International Congress on Nanotechnology (ICNT 2005) October 31 October 31- -November 4, 2005, San Francisco, USA November 4, 2005, San Francisco, USA Nano Structured Interface between Nano Structured Interface between Gold Nanoparticles and Oxide and Gold Nanoparticles and Oxide and the Role in CO oxidation Role in CO oxidation the L. Guczi, A. Beck and K. Frey , A. Beck and K. Frey L. Guczi Chemical Research Center, Hungarian Academy of Chemical Research Center, Hungarian Academy of Sciences Sciences Institute of Isotopes, P. O. Box 77, H- -1525 Budapest, 1525 Budapest, Institute of Isotopes, P. O. Box 77, H HUNGARY HUNGARY 12/3/2005 ICNT-2005, San Francisco 1
BACKGROUND BACKGROUND Unique Unique electronic and chemical properties are electronic and chemical properties are known to develop in solid when its its dimensions dimensions known to develop in solid when reach the nanoscale nanoscale. . reach the C Changes hanges including discrete electronic structures, including discrete electronic structures, modified physical structures and altered chemical modified physical structures and altered chemical reactivity y, manifest themselves as new physical and , manifest themselves as new physical and reactivit chemical properties not observed in ‘ ‘bulk bulk’ ’ form of form of chemical properties not observed in the material. the material. 12/3/2005 ICNT-2005, San Francisco 2
Why to Use Model Catalysts ? Why to Use Model Catalysts ? oxidic support oxide layer active phase conducting substrate catalyst model catalyst single crystal 12/3/2005 ICNT-2005, San Francisco 3
Long range ordering: single crystals Short range ordering : nanoscale metal particles 12/3/2005 ICNT-2005, San Francisco 4
How to fabricate model nanoparticles ? Using pulsed laser deposition on a Si(100) single crystal Using pulsed laser deposition on a Si(100) single crystal („ „bottom up bottom up” ” approach) approach) ( Partial destroying thin films by e.g. implantation Partial destroying thin films by e.g. implantation („ „to top p down down” ” approach) approach) ( 12/3/2005 ICNT-2005, San Francisco 5
MAIN GOAL MAIN GOAL Nanosized gold particles interfaced with Nanosized gold particles interfaced with Fe 2 O 3 is highly active catalyst for CO Fe 2 O is highly active catalyst for CO 3 oxidation. oxidation. The present work is aimed at model modeling ing the the Au/ Au/FeO FeO x The present work is aimed at x interface to find out whether interface to find out whether FeO FeO x /SiO 2 /Si(100) substrate promotes Au nano- - x /SiO 2 /Si(100) substrate promotes Au nano particles through the Au/FeO x interface, or particles through the Au/FeO x interface, or the burried interface also affects the burried interface also affects iron oxide iron oxide by Au by Au particles. particles. the the electron structure, morphology and CO electron structure, morphology and CO oxidation are investigated oxidation are investigated 12/3/2005 ICNT-2005, San Francisco 6
Pulsed Laser Deposition (PLD) Pulsed Laser Deposition (PLD) Pulsed Laser Deposition (PLD) preparation Sample preparation Sample Guczi et al. Topics in Catal., 29 (2004) 129 J. Phys. Chem., (1997 ) J. Phys. Chem. B. , 101 (1997) 9973 J. Phys. Chem., (1997 ) 12/3/2005 ICNT-2005, San Francisco 7
Sample preparation (I) preparation (I) Sample J. Phys. Chem. B, 104 ( 2000) 3183 SiO 2 /Si(100) SiO 2 /Si(100) PLD of Fe PLD of Fe + O 2 + O PLD of Au PLD of Au FeO FeO x /SiO /SiO 2 /Si(100) /Si(100) nano Au/FeO x /SiO 2 /Si(100) nano Au/FeO x /SiO 2 /Si(100) 12/3/2005 ICNT-2005, San Francisco 8
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Composition and core level characteristics of PLD sample Binding Possible Au surface Energy (eV) chemical conc. (at/cm 2 ) state Au 0 Au 4f 7/2 : 84.0 Fe 3+ Fe 2p 3/2 : 710.9 (4.0 0.5) 10 15 O 1s: Fe-O 529.9 O 1s: -OH 531.5 O 1s: water 533.1 12/3/2005 ICNT-2005, San Francisco 11
Catalytic activity of PLD in CO oxidation at 523 K Catalytic activity of PLD in CO oxidation at 523 K Activity of PDL(I) mol CO 2 /mg Au / min Treatment As prepared 13.7 Oxidized 35.2 Reduced in H 2 2.2 Oxidation converts FeO(OH) species on the surface at the Oxidation converts FeO(OH) species on the surface at the gold/iron oxide interface (perimeter) FeO according to the gold/iron oxide interface (perimeter) FeO according to the following equations: following equations: 4 FeO(OH) 4 FeO + 4 FeO(OH) 4 FeO + + 2 H 2 + 2 H 2 O O (g) (g) + O + O 2 (g) (1) (1) (g) 2+ + 3+ + O (g) Fe Fe 2+ Fe + + O 2 + O Fe 3+ + O 2 - - (2) (2) 2 (g) (s) (s) where means an oxygen vacancy on the surface. where means an oxygen vacancy on the surface. 12/3/2005 ICNT-2005, San Francisco 12
Reaction (1) does not require Evidences Evidences oxidative atmosphere to remove Heating Heating in He in place of in He in place of water. the Au/FeO(OH) shows O 2 2 the Au/FeO(OH) shows O Reaction (2) occurs in the vicinity of no phase transition, only no phase transition, only the gold particles. Reactions (1) and some some water water desorption. desorption. (2) take place along the perimeter of No change in activity is No change in activity is the gold/iron oxide interface: XPS found found although although Au Au – results show that FeO species are vacancy pairs are vacancy pairs are created when after the oxidation the gold particles is partially covered by generated. generated. support species. If the support (FeO(OH)) If the support (FeO(OH)) O 2 - (s) species formed interact with alone is treated in O 2 alone is treated in O 2 iron ions formed in the vicinity of the there is no changes there is no changes gold particles neither in the Fe 2p B.E., neither in the Fe 2p B.E., nor in the catalytic nor in the catalytic - + Au + O 2 + Au O 2 (3) activity. activity. 12/3/2005 ICNT-2005, San Francisco 13
Au/FeO perimeter BE = 83.9 eV x O 2(g) Au - e - e 2+ O 2 3+ Surface: Fe Fe Bulk: Fe O + FeOOH 2 3 This effect is a consequence of the interface created during the treatment along the Au/Fe 2 O 3 perimeter. Catal Letter, 67, (2000) 117 Catal Letter, 67, (2000) 117 12/3/2005 ICNT-2005, San Francisco 14
Conclusion on Au nanoparticles deposited u nanoparticles deposited Conclusion on A onto Fe 2 O 3 /SiO 2 /Si(100) by PLD by PLD onto Fe 2 O 3 /SiO 2 /Si(100) The reactivity of the samples in the The reactivity of the samples in the CO CO oxidation oxidation decreases decreases in the sequence of in the sequence of Au/ /FeO FeO x /SiO 2 /Si Si(100)> (100)>FeO FeO x /SiO 2 /Si Si(100)> (100)> Au x /SiO 2 / x /SiO 2 / >Au Au/SiO /SiO 2 /Si Si(100)> (100)>Si(100). Si(100). > 2 / It was It was established that in developing the catalytic activity established that in developing the catalytic activity the gold metallic and the and the support amorphous with Fe with Fe the gold is is metallic support is is amorphous 2p B.E. of B.E. of 71 710 0. .8 8 eV eV B.E; B.E; 2p reaction occurs at reaction occurs at Au/FeOx interface along Au/FeOx interface along the perimeter of the perimeter of gold particles. gold particles. J. Phys. Chem. B., 104 ( 104 (2000 2000) 3183 ) 3183 J. Phys. Chem. B., 12/3/2005 ICNT-2005, San Francisco 15
Effect of gold particle size alone alone ? ? Effect of gold particle size 10 nm thick film was treated using implantation by Ar+ ions 10 nm thick film was treated using implantation by Ar+ ions at 40 keV energy at 40 keV energy 15 atom/cm atom/cm 2 dose (incident angle is 90 degree). and 10 15 and 10 dose (incident angle is 90 degree). 80 nm thick film was 80 nm thick film was used as reference used as reference - beam evaporation e - beam evaporation e SiO 2 /Si(100) 80nm Au/SiO 2 /Si(100) - beam evaporation e - beam evaporation e 10nm Au/SiO 2 /Si(100) Implantation by Ar Ar ions ions Implantation by nano Au/SiO 2 /Si(100) J. Am. Chem. Soc., 125 125 , 4332 (2003) , 4332 (2003) J. Am. Chem. Soc., 12/3/2005 ICNT-2005, San Francisco 16
CO oxidation as test reaction over 10 nm Au 10 nm Au CO oxidation as test reaction over film and Au nanoparticles and Au nanoparticles on SiO on SiO 2 /Si(100) film 2 /Si(100) 9 8 7 6 µmol/cm 2 "implanted" 5 Au/SiO 2 /Si(100) 4 3 2 "as deposited" Au/SiO 2 /Si(100) 1 0 0 1000 2000 3000 4000 5000 6000 sec Rate of CO oxidation on Au/SiO 2 /Si(100) substrate: small Au nano paticles are more active. 12/3/2005 ICNT-2005, San Francisco 17
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