Wrocław, September 20th, 2010 Mechanism of HCl oxidation (Deacon process) over RuO 2 Gerard Novell-Leruth

The Institute of Chemical Research of Catalonia

Scheme Deacon process Ruthenium Oxide Reactivity on RuO 2 (110) Microkinetic analysis Conclusions

The Chlorine Tree

The Production consumption per weight produced is near to iron and steel production. Chloroalkali process 2 NaCl + 2 H 2 O → Cl 2 + H NaOH kWh / ton of Chlorine Deacon Process 4 HCl + O 2 → 2 Cl H 2 O

Deacon process is: 4 HCl + O 2 → 2 Cl H 2 O ∆H = -114 kJ/mol Henry Deacon in 1874 (CuO 2 ) CuO 2 at ºC Kel-Chlor (NO,NO2, NOCl) Shell-Chlor (CuCl 2 -KCl/SiO 2 ) MT-Chlor (Cr 2 O 3 /SiO 2 ) Chlorine production

Deacon process is: 4 HCl + O 2 → 2 Cl H 2 O ∆H = -114 kJ/mol Henry Deacon in 1874 (CuO 2 ) CuO 2 at ºC Kel-Chlor (NO,NO2, NOCl) Shell-Chlor (CuCl 2 -KCl/SiO 2 ) MT-Chlor (Cr 2 O 3 /SiO 2 ) Sumitomo Chemicals RuO 2 /TiO 2 (rutile) High activity Low Temperature (300 ºC) Stability Production of 400 kton per year in a single reactor Chlorine production

Scheme Deacon process Ruthenium Oxide Reactivity on RuO 2 (110) Microkinetic analysis Conclusions

RuO 2 powder structure (100), (110), (001) and (101) are the common surfaces Show Ru cus atoms: Coordination 5 RuO 2 (110) is the most common surface (110)(101) (100)(001)

Different RuO 2 activities Different nature of the exposed sites i.e. nanoparticle structure N. López, J. Gómez-Segura, R. P. Marín, J. Pérez-Ramírez, J.Catal., 255, 2008, Faces γ / eV·Ǻ -2 Area / % > 1

RuO 2 (110) Deacon process is: HCl + ¼ O 2 → ½ Cl 2 + ½ H 2 O RuO 2 (110) is the most common surface

RuO 2 (110) Deacon process is: HCl + ¼ O 2 → ½ Cl 2 + ½ H 2 O RuO 2 (110) is the most common surface 5 Layers

RuO 2 (110) Deacon process is: HCl + ¼ O 2 → ½ Cl 2 + ½ H 2 O RuO 2 (110) is the most common surface 5 Layers Unit Cell

Computational details DFT (VASP) RPBE functional PAW pseudopotentials Cut-off of 400 eV

Scheme Deacon process Ruthenium Oxide Reactivity on RuO 2 (110) Microkinetic analysis Conclusions

O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* Common proposed mechanism

Oxygen adsorption O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* O 2 + 2* ↔ O 2c * E ads =-0.66 eV

O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* Oxigen dissociation O 2 ** ↔ 2 O c * E a =0.40 eV  E=-0.41 eV

HCl+*+O b * ↔ Cl c *+O b H* HCl+*+O c * ↔ Cl c *+O c H* HCl reaction O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* 1 reaction 2 configurations

HCl+*+O b * ↔ Cl c *+O b H* HCl+*+O c * ↔ Cl c *+O c H* HCl reaction O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* 1 reaction 2 configurations HCl* + Ob* ↔ Cl* + ObH* HCl* + Oc* ↔ Cl* + OcH* E a < 0.01 eV E a < 0.01 eV  E=-1.46 eV  E=-1.23 eV

O c H* + O c H* ↔ O c * + H 2 O c * O b H* + O c H* ↔ O b * + H 2 O c * HCl + *+O c H*↔ Cl*+H 2 O c * O b H*+O c H*↔ H 2 O b *+H 2 O c * O b H*+O c *↔ O b *+O c H* Water formation O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* 1 reaction 2 configurations

O c H* + O c H* ↔ O c * + H 2 O c * O b H* + O c H* ↔ O b * + H 2 O c * HCl + *+O c H*↔ Cl*+H 2 O c * O b H*+O c H*↔ H 2 O b *+H 2 O c * O b H*+O c *↔ O b *+O c H* Water formation O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2* 1 reaction 2 configurations O c H* + O c H* ↔ O c * + H 2 O c * O b H* + O c H* ↔ O b * + H 2 O c * E a = 0.38 eV E a = 0.24 eV  E= 0.24 eV  E=-0.11 eV

Water desorption H 2 O c * ↔ H 2 O + * E ads = eV O 2 +2*↔ O 2 ** O 2 **↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2*

Chlorine formation Cl c * + Cl c * ↔ Cl * E ads = eV O 2 +2*↔ O 2 ** O 2 +2*↔2O* HCl+*+O*↔Cl*+OH* OH*+OH*↔H 2 O*+O* H 2 O*↔H 2 O +* Cl*+Cl*↔Cl 2 +2*

Scheme Deacon process Ruthenium Oxide Reactivity on RuO 2 (110) Microkinetic analysis Conclusions

O * ↔ O 2 ** O 2 ** ↔ 2 O c * HCl + * + O b * ↔ Cl c * + O b H* HCl + * + O c * ↔ Cl c * + O c H* O c H* + O b H* ↔ H 2 O c * + O b * O c H* + O c H* ↔ H 2 O c * + O c * O c * + O b H* ↔ O c H* + O b * H 2 O c * ↔ H 2 O + * Cl c * + Cl c * ↔ Cl * Mechanism and reaction parameters E a / eV ΔE / eV < < < HCl + ¼ O 2 → ½ Cl 2 + ½ H 2 O RuO 2 (110)

Microkinetic modeling Differential-Algebraic Equation (DAE) system Temporal evolution of each species + Initial Conditions (P(HCl), P(O 2 )..) O * ↔ O 2 ** O 2 ** ↔ 2 O c * HCl + * + O b * ↔ Cl c * + O b H* HCl + * + O c * ↔ Cl c * + O c H* O c H* + O b H* ↔ H 2 O c * + O b * O c H* + O c H* ↔ H 2 O c * + O c * O c * + O b H* ↔ O c H* + O b * H 2 O c * ↔ H 2 O + * Cl c * + Cl c * ↔ Cl *

Transition State Theory (r=k·C R ) Static results as “batch reactor” Energy independent of the coverage Initial conditions P(HCl) = 2·10 5 Pa P(O 2 ) = 4·10 5 Pa T = 570 K Microkinetic modeling

Results: Cl 2 production vs T and t Initial Conditions: P(O 2 ) = 4·10 5 Pa P(HCl) = 2·10 5 Pa

Results: Presure vs Temperature Initial Conditions: P(O 2 ) = 4·10 5 Pa P(HCl) = 2·10 5 Pa Time = 1 s Experimental T regim P(O 2 ) P(HCl) P(Cl 2 ) P(H 2 O)

Results: P and Coverage vs time time / s Initial Conditions: P(O 2 ) = 4E5 Pa P(HCl) = 2E5 Pa T = 570 K P(O 2 ) P(HCl) P(Cl 2 ) P(H 2 O) θ(O b H) θ(O b ) θ(Cl c ) θ(O c )

Mechanism Our proposed mechanism contains the following elementary steps: O 2 +2*↔2O* HCl+O*+*↔OH*+Cl* OH*+OH*↔H 2 O+O* Cl*+Cl*↔Cl 2 +2* O * ↔ O 2 ** O 2 ** ↔ 2 O c * HCl + * + O b * ↔ Cl c * + O b H* HCl + * + O c * ↔ Cl c * + O c H* O c H* + O b H* ↔ H 2 O c * + O b * O c H* + O c H* ↔ H 2 O c * + O c * O c * + O b H* ↔ O c H* + O b * H 2 O c * ↔ H 2 O + * Cl c * + Cl c * ↔ Cl *

P(O 2 ) P(HCl) P(Cl 2 ) P(H 2 O) Variations at microkinetic models time / s P(O 2 ) P(HCl) P(Cl 2 ) P(H 2 O) Initial Conditions: P(O 2 ) = 4E5 Pa P(HCl) = 2E5 Pa T = 570 K Full Model Reduced Model

Mechanism Our proposed mechanism contains the following elementary steps: O 2 +2*↔2O* HCl+O*+*↔OH*+Cl* OH*+OH*↔H 2 O+O* Cl*+Cl*↔Cl 2 +2* O * ↔ O 2 ** O 2 ** ↔ 2 O c * HCl + * + O b * ↔ Cl c * + O b H* HCl + * + O c * ↔ Cl c * + O c H* O c H* + O b H* ↔ H 2 O c * + O b * O c H* + O c H* ↔ H 2 O c * + O c * O c * + O b H* ↔ O c H* + O b * H 2 O c * ↔ H 2 O + * Cl c * + Cl c * ↔ Cl *

Scheme Deacon process Ruthenium Oxide Reactivity on RuO 2 (110) Microkinetic analysis 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 !!!