Upload
philip-r-davies
View
136
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Presented at the 2013 ISSC 19 meeting in Nottingham, 27th March 2013
Citation preview
ISSC 19 27th March 2013 1
Surface Science &catalysis Cardiff Catalysis Institute
STM & XPS studies of the chemistry of oxygen and HCl at Cu(100)
& Cu(100)/Au surfaces.
Hatem Altass, Albert F. Carley, Philip R. Davies & Robert J. Davies
Cardiff Catalysis Institute, School of Chemistry, Cardiff University
ISSC 19 27th March 2013 2
Surface Science &catalysis Cardiff Catalysis Institute
Production: 42 Mt per annum. ~50% incorporated in product. Waste: HCl & Cl‾
Deacon process
4HCl + O2 2Cl2 + 2H2OCu based catalyst 450 °C
Chlorine in the chemical industry
Polychlorinateddibenzo-furans (PCDF)
• Toxic, t½ > 100 years
• Combustion products, 99% anthropogenic
• Formation: heterogeneous catalysis by fly ash (carbon nanoparticles)
• Strong correlation with Cu content & oxygen
PCDD and PCDF formation
ISSC 19 27th March 2013 3
Surface Science &catalysis Cardiff Catalysis Institute
Cu(110) HCl & O2
19.6 nm
2HCl (g) + Cu-O(a) CuCl2(a) + H2O(g)HCl(g) Cl(a) + ½H2(g)
31-10-00#100 28.5 nm
200 nm
28.5 nm
“A Low Energy Pathway to CuCl2 at Cu(110) Surfaces.” Albert F. Carley, Philip R. Davies, K R. Harikumar, R V. Jones. PCCP 11 (2009) 10899
ISSC 19 27th March 2013 4
Surface Science &catalysis Cardiff Catalysis Institute
• Does the nature of the substrate affect the reaction mechanism?
Cu(100) vs Cu(110)• Does the concentration of O(a) affect the chloride?
(√2x√2)R45 vs (√2x2√2)R45 θ < 1 vs θ > 1
• Cu(100) vs Cu(100)/Au
Aims of the investigation:
ISSC 19 27th March 2013 5
Surface Science &catalysis Cardiff Catalysis Institute
0 100 200 3000
100000000000000
200000000000000
300000000000000
400000000000000
500000000000000
600000000000000
700000000000000
800000000000000
Exposure /L
conc
entra
tion
/cm
-2
Surface concentration of Cl(a) as a function of exposure to HCl
(√2x√2)R45 Cl 6.73x1014 cm-2
Cu(100) / HCl
198.1
(σCu = 1.53 x1015 cm-2)
ISSC 19 27th March 2013 6
Surface Science &catalysis Cardiff Catalysis Institute
0 500 1000 1500 20000
100000000000000
200000000000000
300000000000000
400000000000000
500000000000000
600000000000000
700000000000000
800000000000000
Exposure /L
O(a)
/cm
-2
540 532536 528
Cu(100) / O2 θ ~ 1
(√2x2√2)R45
(√2x√2)R45 σO= 7.21x1014 cm-2
ISSC 19 27th March 2013 7
Surface Science &catalysis Cardiff Catalysis Institute
σO = 1.25x1015 cm-2
(√2x2√2)R45
Cu(100) / O2 @ 250 oC
ISSC 19 27th March 2013 8
Surface Science &catalysis Cardiff Catalysis Institute
0 20 40 60 80 100 120 1400
100000000000000200000000000000300000000000000400000000000000500000000000000600000000000000700000000000000800000000000000900000000000000
1000000000000000
Exposure /LSurfa
ce co
ncen
trati
on /c
m-2
1x10-8 mbar 4.5x10-9 mbar 5x10-8 mbarσO = 5.21x1014 cm-2
Cl(a)
O(a)
2Cl(a) : 1 H2O(g)
Unsaturated surface
HCl(g) + O(a) OH(a) + Cl(a)OH(a) + HCl(g) H2O(g) + Cl(a)
Saturated surface
2HCl(g) + O(a) H2O(g) + 2Cl(a)
Reaction of HCl with low coverage O(a)
ISSC 19 27th March 2013 9
Surface Science &catalysis Cardiff Catalysis Institute
Replacement of (√2x√2)R45
Cl(a)(√2x√2)R45
O(a)(√2x2√2)R45
ISSC 19 27th March 2013 10
Surface Science &catalysis Cardiff Catalysis Institute
The reaction of HCl with Cu(100)/O(a) (√2x2√2)R45
Increasing HCl exposure
STM recorded during exposure to HCl
ISSC 19 27th March 2013 11
Surface Science &catalysis Cardiff Catalysis Institute
0 50 100 150 200 250 3000
200000000000000
400000000000000
600000000000000
800000000000000
1000000000000000
1200000000000000
O(a)
2 Cl(a) : 1 H2O(g)
Exposure to HCl /L
Surf
ace
conc
entr
ation
/cm
-2
Reaction of HCl with O(a) at o ~ 1σO = 7.22x1014 cm-2
Cl(a)
ISSC 19 27th March 2013 12
Surface Science &catalysis Cardiff Catalysis Institute
Reaction of HCl with O(a) at o ~ 1
(√2x2√2)R45 O(a)
(√2x√2)R45Cl(a)
CuCl(a) multilayer
ISSC 19 27th March 2013 13
Surface Science &catalysis Cardiff Catalysis Institute
θo> 1Cu(100) / O2(g) & 250 oC
σO = 1.25x1015 cm-2
70 L2x10-8 mbar
HCl
(√2x2√2)R45 O(a)
ISSC 19 27th March 2013 14
Surface Science &catalysis Cardiff Catalysis Institute
160 L HCl room temperatureσCl = 1.24x1015 cm-2
72 L HCl
90 L HCl
σO = 5.27x1014
σO = 1.25x1015
σCl = 1.24x1015
CuClislands
ISSC 19 27th March 2013 15
Surface Science &catalysis Cardiff Catalysis Institute
Cu(100) /AuReactions with HCl & O2
ISSC 19 27th March 2013 16
Surface Science &catalysis Cardiff Catalysis Institute
/nm
/Å
1.8 Å
4.3x1014 cm-2
/nm
/Å
1.9 Å
5.9 x1014 cm-2 1.7 x1015
cm-2
Au-Cu surface alloys (Cu3Au – ordered alloy)
Cu-Au alloy
Increasing Au at a Cu(100) surface
ISSC 19 27th March 2013 17
Surface Science &catalysis Cardiff Catalysis Institute
Cl 2p
x 102
120
130
140
150
160
170
CPS
208 204 200 196 192Binding Energy (eV)
Cl 2p199.2
Auo Au 4f 7/2 = 84.00 eVAuCu3 Au 4f 7/2 = 84.37 eV (shifts higher with lower Au concentration )Kuhn M., Sham T.K. Journal: Phys. Rev. B 49, 1647 (1994)
5.9x1014 cm-2
4.3x1014 cm-2
Au = 5.9x1014 cm-2
XPSCu/Au
ISSC 19 27th March 2013 18
Surface Science &catalysis Cardiff Catalysis Institute
nm
Å
1.9 Å
1.9 Å
Before HClσAu = 7.8 x1014
cm-2
Effect of HCl on Cu/Au surface alloys
ISSC 19 27th March 2013 19
Surface Science &catalysis Cardiff Catalysis Institute
Gold
x 103
10
15
20
25
30
35
40
45
50
CP
S
88 84 80 76 72 68 64Binding Energy (eV)
After HClBefore HCl
Cu3p1/2,3/2
Binding energy (eV)
Cl
x 102
115
120
125
130
135
140
145
150
CP
S
208 204 200 196 192 188Binding Energy (eV)
Binding energy (eV)
Cl 2p199.5
85.4 eV
σAu = 7.8 x1014 cm-2 Exposure to HCl
XPS data
ISSC 19 27th March 2013 20
Surface Science &catalysis Cardiff Catalysis Institute
a b
c d
0 L 50 L
150 L 200 Lc(2x2)-Cl
5.2 Å 5.2 Å
(σAu = 7.8 x1014 cm-2)Dealloying of Au/Cu on exposure to HCl
ISSC 19 27th March 2013 21
Surface Science &catalysis Cardiff Catalysis Institute
De-alloying of Au-Cu
Cu(100)
Cu/Au
Cu-Cl
Cu(100)
Cu/Au
HClAu
• Island fragmentation, step growth• Formation of Cu(100) c(2x2) Cl• Cu-Au dealloying
ISSC 19 27th March 2013 22
Surface Science &catalysis Cardiff Catalysis Institute
Gold
x 103
10
15
20
25
30
35
40
45
50
CP
S
88 84 80 76 72 68 64Binding Energy (eV)
Cl
x 102
115
120
125
130
135
140
145
150
155
160
165
CP
S
212 208 204 200 196 192 188Binding Energy (eV)
AfterHCl
BeforeHCl
Cu 3p1/2,3/2
Binding energy (eV)
Cl 2p1/2,3/2
Binding energy (eV)
σAu = 1.72x1015 cm-2, Exposure to HCl
XPS data
199.2
ISSC 19 27th March 2013 23
Surface Science &catalysis Cardiff Catalysis Institute
a b
σAu = 1.72x1015 cm-2, Exposure to HCl
ISSC 19 27th March 2013 24
Surface Science &catalysis Cardiff Catalysis Institute
Au (1x1)
σAu = 1.72x1015 cm-2, Exposure to HCl
XPS data
ISSC 19 27th March 2013 25
Surface Science &catalysis Cardiff Catalysis Institute
De-alloying of Au-Cu
Cu/Au
Cu(100)
HCl
Au
• Island fragmentation, step growth• Formation of Cu(100) c(2x2) Cl• Cu-Au dealloying
Cu(100)
Cu-ClAu
ISSC 19 27th March 2013 26
Surface Science &catalysis Cardiff Catalysis Institute
• Does the nature of the substrate affect the reaction mechanism? Cu(100) vs Cu(110) V. similar behaviour, but only stable chlorides on
Cu(100)
• Does the O(a) concentration affect the chloride? (√2x√2)R45 – Rapid reaction c(2x2) Cl
(√2x2√2)R45 – “Slower” Cl(a) multilayer.
θo > 1 (√2x2√2)R45 CuCl clusters
Conclusions
ISSC 19 27th March 2013 27
Surface Science &catalysis Cardiff Catalysis Institute
• Cu(100) vs Cu(100)/Au
Au and Cl environment suggest some interaction although STM evidence is for CuCl.
For low Au coverages ordered Cu(100)-Cl structures form
High Au coverages CuCl islandsAu overlayer
Conclusions
ISSC 19 27th March 2013 28
Surface Science &catalysis Cardiff Catalysis Institute
Funded by EP/I038748/1Saudi Arabian Government PhD scholarship
ISSC 19 27th March 2013 29
Surface Science &catalysis Cardiff Catalysis Institute
0 500 1000 1500 20000
100000000000000
200000000000000
300000000000000
400000000000000
500000000000000
600000000000000
700000000000000
800000000000000
Exposure /L
O(a
) /c
m-2
Cu(100) / O2 Room temperature
ISSC 19 27th March 2013 30
Surface Science &catalysis Cardiff Catalysis Institute
Missing Cu row
Cu(100) (√2x2√2)R45 O(a)
ISSC 19 27th March 2013 31
Surface Science &catalysis Cardiff Catalysis Institute
a b c
d e f