Mechanism of HCl oxidation (Deacon process) over RuO 2

Wrocław, September 20th, 2010

Mechanism of HCl oxidation (Deacon process) over RuO2

Gerard Novell-Leruth

The Institute of Chemical Research of Catalonia

Scheme

• Deacon process

• Ruthenium Oxide

• Reactivity on RuO2(110)

• Microkinetic analysis

• Conclusions

The Chlorine Tree

The Chlorine Tree

The Production consumption per weight produced is near to iron and steel production.

• Chloroalkali process2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH3600 -3300 kWh / ton of Chlorine• Deacon Process4 HCl + O2 → 2 Cl2 + 2 H2O

Deacon process is:4 HCl + O2 → 2 Cl2 + 2 H2O ∆H = -114 kJ/mol

Henry Deacon in 1874 (CuO2) CuO2 at 400-450 ºC

• Kel-Chlor (NO,NO2, NOCl) • Shell-Chlor (CuCl2-KCl/SiO2)• MT-Chlor (Cr2O3/SiO2)

Chlorine production

Deacon process is:4 HCl + O2 → 2 Cl2 + 2 H2O ∆H = -114 kJ/mol

Henry Deacon in 1874 (CuO2) CuO2 at 400-450 ºC

• Kel-Chlor (NO,NO2, NOCl) • Shell-Chlor (CuCl2-KCl/SiO2)• MT-Chlor (Cr2O3/SiO2)

Sumitomo Chemicals

RuO2/TiO2 (rutile)High activityLow Temperature (300 ºC)Stability Production of 400 kton per year in a single reactor

Chlorine production

Scheme

• Deacon process

• Ruthenium Oxide



• Conclusions

RuO2 powder structure

(100), (110), (001) and (101) are the common surfacesShow Rucus atoms: Coordination 5RuO2(110) is the most common surface

(110)(101)(100)(001)

Different RuO2 activitiesDifferent nature of the exposed sites i.e. nanoparticle structure

20 30 40 50 60 70

111

00222

0

210

211

200

101

used

Inte

nsity

/ a.

u.

2 / degree

fresh

110

310 11

230

1

110

101

100

20 30 40 50 60 70

111

00222

0

210

211

200

101

used

Inte

nsity

/ a.

u.

2 / degree

fresh

110

310 11

230

1

110

101

100

N. López, J. Gómez-Segura, R. P. Marín, J. Pérez-Ramírez, J.Catal., 255, 2008, 29-39

Faces γ / eV·Ǻ-2 Area / %

110 0.041 43

101 0.051 42

100 0.047 14

001 0.075 > 1

RuO2 (110)

Deacon process is:HCl + ¼ O2 → ½ Cl2 + ½ H2O

RuO2(110) is the most common surface

RuO2 (110)



5 Layers

RuO2 (110)



5 Layers

Unit Cell

Computational details

•DFT (VASP)

•RPBE functional

•PAW pseudopotentials

•Cut-off of 400 eV

Scheme

• Deacon process

• Ruthenium Oxide



• Conclusions

O2+2*↔ O2**O2**↔2O*HCl+*+O*↔Cl*+OH*OH*+OH*↔H2O*+O*H2O*↔H2O +*Cl*+Cl*↔Cl2+2*

Common proposed mechanism

Oxygen adsorption


O2 + 2* ↔ O2c*

Eads=-0.66 eV


Oxigen dissociationO2** ↔ 2 Oc*

Ea=0.40 eVDE=-0.41 eV

HCl+*+Ob* ↔ Clc*+ObH*HCl+*+Oc* ↔ Clc*+OcH*

HCl reaction


1 reaction 2 configurations

HCl+*+Ob* ↔ Clc*+ObH*HCl+*+Oc* ↔ Clc*+OcH*

HCl reaction



HCl* + Ob* ↔ Cl* + ObH* HCl* + Oc* ↔ Cl* + OcH* Ea < 0.01 eV Ea < 0.01 eV

DE=-1.46 eV DE=-1.23 eV

OcH* + OcH* ↔ Oc* + H2Oc*ObH* + OcH* ↔ Ob* + H2Oc*

HCl + *+OcH*↔ Cl*+H2Oc*ObH*+OcH*↔ H2Ob*+H2Oc*ObH*+Oc*↔ Ob*+OcH*

Water formation



OcH* + OcH* ↔ Oc* + H2Oc*ObH* + OcH* ↔ Ob* + H2Oc*

HCl + *+OcH*↔ Cl*+H2Oc*ObH*+OcH*↔ H2Ob*+H2Oc*ObH*+Oc*↔ Ob*+OcH*

Water formation



OcH* + OcH* ↔ Oc* + H2Oc* ObH* + OcH* ↔ Ob* + H2Oc*Ea = 0.38 eV Ea = 0.24 eVDE= 0.24 eV DE=-0.11 eV

Water desorption

H2Oc* ↔ H2O + *

Eads= -0.90 eV


Chlorine formation

Clc* + Clc* ↔ Cl2 + 2 *

Eads= -1.56 eV

O2+2*↔ O2**O2+2*↔2O*HCl+*+O*↔Cl*+OH*OH*+OH*↔H2O*+O*H2O*↔H2O +*Cl*+Cl*↔Cl2+2*

Scheme

• Deacon process

• Ruthenium Oxide



• Conclusions

O2 + 2 * ↔ O2**O2

** ↔ 2 Oc*

HCl + * + Ob* ↔ Clc* + ObH*HCl + * + Oc* ↔ Clc* + OcH*OcH* + ObH* ↔ H2Oc* + Ob*OcH* + OcH* ↔ H2Oc* + Oc*Oc* + ObH* ↔ OcH* + Ob*H2Oc* ↔ H2O + *Clc* + Clc* ↔ Cl2 + 2 *

Mechanism and reaction parameters

Ea / eV ΔE / eV < 0.01 -0.66 0.38 -0.76 < 0.01 -1.46 < 0.01 -1.23 0.38 0.27 0.24 -0.11 0.55 -0.01 0.90 0.90 1.56 1.56

HCl + ¼ O2 → ½ Cl2 + ½ H2O

RuO2(110)

Microkinetic modeling

Differential-Algebraic Equation (DAE) system

Temporal evolution of each species

+Initial Conditions (P(HCl), P(O2)..)

O2 + 2 * ↔ O2**O2

** ↔ 2 Oc*

HCl + * + Ob* ↔ Clc* + ObH*HCl + * + Oc* ↔ Clc* + OcH*OcH* + ObH* ↔ H2Oc* + Ob*OcH* + OcH* ↔ H2Oc* + Oc*Oc* + ObH* ↔ OcH* + Ob*H2Oc* ↔ H2O + *Clc* + Clc* ↔ Cl2 + 2 *

•Transition State Theory (r=k·CR)

•Static results as “batch reactor”

•Energy independent of the coverage

•Initial conditions P(HCl) = 2·105 Pa P(O2) = 4·105 Pa T = 570 K

Microkinetic modeling

Results: Cl2 production vs T and t

Initial Conditions:P(O2) = 4·105 PaP(HCl) = 2·105 Pa

Results: Presure vs Temperature

Initial Conditions:P(O2) = 4·105 PaP(HCl) = 2·105 PaTime = 1 s

Experimental T regim

P(O2)

P(HCl)P(Cl2)

P(H2O)

Results: P and Coverage vs time

time / s

Initial Conditions:P(O2) = 4E5 PaP(HCl) = 2E5 PaT = 570 K

P(O2)

P(HCl)P(Cl2) P(H2O)

θ(ObH)

θ(Ob)

θ(Clc)

θ(Oc)

Mechanism

Our proposed mechanism contains the following elementary steps:

O2+2*↔2O*

HCl+O*+*↔OH*+Cl*

OH*+OH*↔H2O+O*

Cl*+Cl*↔Cl2+2*

O2 + 2 * ↔ O2**O2

** ↔ 2 Oc*

HCl + * + Ob* ↔ Clc* + ObH*HCl + * + Oc* ↔ Clc* + OcH*

OcH* + ObH* ↔ H2Oc* + Ob*OcH* + OcH* ↔ H2Oc* + Oc*Oc* + ObH* ↔ OcH* + Ob*H2Oc* ↔ H2O + *

Clc* + Clc* ↔ Cl2 + 2 *

P(O2)

P(HCl)P(Cl2) P(H2O)

Variations at microkinetic models

time / s

P(O2)

P(HCl)P(Cl2) P(H2O)

Initial Conditions:P(O2) = 4E5 PaP(HCl) = 2E5 PaT = 570 K

Full Model

Reduced Model

Mechanism

Our proposed mechanism contains the following elementary steps:

O2+2*↔2O*

HCl+O*+*↔OH*+Cl*

OH*+OH*↔H2O+O*

Cl*+Cl*↔Cl2+2*

O2 + 2 * ↔ O2**O2

** ↔ 2 Oc*

HCl + * + Ob* ↔ Clc* + ObH*HCl + * + Oc* ↔ Clc* + OcH*

OcH* + ObH* ↔ H2Oc* + Ob*OcH* + OcH* ↔ H2Oc* + Oc*Oc* + ObH* ↔ OcH* + Ob*H2Oc* ↔ H2O + *

Clc* + Clc* ↔ Cl2 + 2 *

Scheme

• Deacon process

• Ruthenium Oxide



• Conclusions

Conclusion

• Mechanism of the global process

• The bridge Oxygen acts as a reservoir of H

• Microkinetic model with DFT results

• Discussion of species in the process as function of the reaction conditions

Acknowledgements

THANKS FOR

YOUR ATTENTION !!!

Mechanism of HCl oxidation (Deacon process) over RuO 2

Documents

Transcript of Mechanism of HCl oxidation (Deacon process) over RuO 2