chemistry of oxygen and hcl at cu(100) & cu(100)/au surfaces

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



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



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



• 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:



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)



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



σO = 1.25x1015 cm-2

(√2x2√2)R45

Cu(100) / O2 @ 250 oC



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)



Replacement of (√2x√2)R45

Cl(a)(√2x√2)R45

O(a)(√2x2√2)R45



The reaction of HCl with Cu(100)/O(a) (√2x2√2)R45

Increasing HCl exposure

STM recorded during exposure to HCl



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)



Reaction of HCl with O(a) at o ~ 1

(√2x2√2)R45 O(a)

(√2x√2)R45Cl(a)

CuCl(a) multilayer



θo> 1Cu(100) / O2(g) & 250 oC

σO = 1.25x1015 cm-2

70 L2x10-8 mbar

HCl

(√2x2√2)R45 O(a)



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



Cu(100) /AuReactions with HCl & O2



/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



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



nm

Å

1.9 Å

1.9 Å

Before HClσAu = 7.8 x1014

cm-2

Effect of HCl on Cu/Au surface alloys



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



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



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



Gold

x 103

10

15

20

25

30

35

40

45

50

CP

S


Cl

x 102

115

120

125

130

135

140

145

150

155

160

165

CP

S


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



a b




Au (1x1)


XPS data



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



• 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



• 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



Funded by EP/I038748/1Saudi Arabian Government PhD scholarship



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



Missing Cu row

Cu(100) (√2x2√2)R45 O(a)



a b c

d e f

chemistry of oxygen and hcl at cu(100) & cu(100)/au surfaces

Education

cu100 surface

heterogeneous catalysis

surface concentration

hcl exposure issc

cla issc

hcl o2issc

hcl gold

cuau dealloying issc