Selective Catalytic Selective Catalytic Reduction of NOReduction of NOxx-- and briefly about its deactivationand briefly about its deactivation

Marie Louise Dahl ThomsenMarie Louise Dahl Thomsen

April 17, 2006April 17, 2006

Power PlantsPower Plants

OverviewOverview

Why DeNoWhy DeNoxx and SCR catalysts and SCR catalysts Why clean the flue gasWhy clean the flue gas SCR catalysts mechanismsSCR catalysts mechanisms Placement of SCR catalystPlacement of SCR catalyst Deactivation caused by alkali metals, Deactivation caused by alkali metals,

especially potassiumespecially potassium Research results of deactivationResearch results of deactivation Proposal of minimum deactivationProposal of minimum deactivation

Why DeNOx and SCR Catalysts?Why DeNOx and SCR Catalysts?

NONOxx is air polluting is air polluting

NONOxx is the sum of nitrogen oxides which is the sum of nitrogen oxides which

are NO, Nare NO, N22O and NOO and NO22

Typically 90-95% NOTypically 90-95% NOxx-components in the -components in the

flue gas will be in form of NO. flue gas will be in form of NO. The form NThe form N22O is hardly not there. O is hardly not there.

Why clean the flue gas?Why clean the flue gas?

Acid rain:Acid rain:

2 NO (g) + O2 NO (g) + O22 (g) → 2 NO (g) → 2 NO2 2 (g)(g)

2 NO2 NO22(g) + H(g) + H22O(l) ↔ HNOO(l) ↔ HNO33(aq)+HNO(aq)+HNO22(aq)(aq)

SOSO22 + ½ O + ½ O22 → SO → SO33

SOSO33 + H + H22O → HO → H22SOSO44

Nitrogen oxides can react with the sun Nitrogen oxides can react with the sun and become to ozone:and become to ozone:

NONO22 + UV-sunlight → NO + O + UV-sunlight → NO + O

OO22 + O → O + O → O33 (ozone) (ozone)

Log Angeles, California

Beijing, China

Mexico City

Smog = Ozone

Daily cycle of pollutant concentrationDaily cycle of pollutant concentration

NONOxx is bad for our health is bad for our health

It is observed that NOIt is observed that NOxx gases weaken our gases weaken our

immune defense by especially getting immune defense by especially getting virus.virus.

NONOxx gases are also a reason to other gases are also a reason to other

illnesses as pneumonia and allergy. illnesses as pneumonia and allergy. (Topsøe, 1997) (Topsøe, 1997)

Catalysts in generalCatalysts in general

The most common definition of a catalyst The most common definition of a catalyst is that a catalyst makes a reaction go is that a catalyst makes a reaction go faster without being used. faster without being used.

Not always true Not always true → deactivation→ deactivation Most used SCR catalyst:Most used SCR catalyst:

VV22OO55-WO-WO33-TiO-TiO22

Developed of the Japanese in 1977 Developed of the Japanese in 1977 (Topsøe, 1997, 1998) (Topsøe, 1997, 1998)

WOWO3 3 has many has many advantagesadvantages

WOWO33 makes the catalyst stronger makes the catalyst stronger

WOWO33 increases the active sites increases the active sites

Forzatti et al, 1999

SCR CatalystsSCR Catalysts

Morsing et al, 2003

Heterogenic catalystHeterogenic catalyst Adsorptions mechanismAdsorptions mechanism Elay-Rideal mechanismElay-Rideal mechanism Langmuir-Hinshelwood mechanismLangmuir-Hinshelwood mechanism

Jacobsen et al, 2002

SCR catalyst reactionsSCR catalyst reactions

6 NO + 4 NH6 NO + 4 NH33 → 5 N → 5 N22 + 6 H + 6 H22OO

6 NO6 NO22 + 8 NH + 8 NH33 → 7 N → 7 N22 + 12 H + 12 H22OO

OO22 makes the reaction faster makes the reaction faster

4 NO + 4 NH4 NO + 4 NH33 + O + O22 → 4 N → 4 N22 + 6 H + 6 H22O O

No ammonia out so only add 80-90% No ammonia out so only add 80-90% NHNH33

Bosch and Janssen, 1988

Me=Vanadium or Me=Vanadium or TungstenTungsten

Pritchard et al, 1995

Site NomenclatureSite Nomenclature

5

4

3

Acid site

Redox site

Surface hydroxyl groups

Reduced vanadium cations

V OH

V O

V OH

V

(1)(1) NH NH33 + V + V5+5+-OH -OH ↔ ↔ V-ONHV-ONH44

(2)(2) V-ONH V-ONH44 + V=O + V=O ↔↔ V-ONH V-ONH33-V-V4+4+-OH-OH(3)(3) NO + V-ONHNO + V-ONH33-V-V4+4+-OH -OH →→ N N22 + H + H22O + VO + V5+5+-OH -OH

+ V+ V4+4+-OH-OH

(4)(4) 2V 2V4+4+-OH -OH ↔↔ H H22O + VO + V3+3+ + V=O + V=O(5)(5) O O22 + 2V + 2V3+3+ →→ 2V=O 2V=O(6)(6) H H22O + VO + V5+5+-OH -OH ↔↔ V V5+5+-OH-OH33O O [Dumesic et al, 1996][Dumesic et al, 1996]

Proposed reaction mechanismProposed reaction mechanism

H

H O

NN

NH3

N+

H

H

H

H

OO

V-

V-

O

NO(g)

OHOH

VV

O

OOH

V

OV

OOH

V

OV

H

H O

NN

H

H

ONN

OHOH

VV

O

H2O

O

V

O

V1/2 O2

OO

V-

V-

O

Topsøe et al, 1997, 1998Topsøe et al, 1997, 1998

So far we knowSo far we know

NHNH33 adsorbs on Bronsted acid sites to adsorbs on Bronsted acid sites to

give NHgive NH44 species, and on Lewis sites to species, and on Lewis sites to

give coordinated NHgive coordinated NH33 species species

NO does not adsorb on VNO does not adsorb on V22OO55

Each NEach N22 molecule contains one N from molecule contains one N from

NO and one from NHNO and one from NH33 (Elay-Rideal (Elay-Rideal

mechanism)mechanism)

Common for SCR Common for SCR catalystscatalysts

Works in temperatures between 300-Works in temperatures between 300-400C400C

Need a high specific surface area Need a high specific surface area (high porosity)(high porosity) Lose activity over time because of ex. Lose activity over time because of ex.

poison, fouling or sintring.poison, fouling or sintring. Need to be changed, because they Need to be changed, because they

deactivatedeactivate

Site Nomenclature for SCR placementSite Nomenclature for SCR placement

AH = Air preHeaterAH = Air preHeater ESP = ElectroStatic PrecipitatorESP = ElectroStatic Precipitator H-ESP = High temperature ESPH-ESP = High temperature ESP FGD = Flue Gas DesulphurizationFGD = Flue Gas Desulphurization GGH = Gas-Gas HeaterGGH = Gas-Gas Heater SCR = Reactor for SCRSCR = Reactor for SCR

Placement of SCR Placement of SCR catalystcatalyst

Soud and Fukasawa, 1996

Chen et al, 1990

Alkali metals are among the strongest poisons.

The strength of the poison follows the order of basicity:

Cs2O > Rb2O > K2O > Na2O > Li2O

Deactivation of SCR catalysts, Deactivation of SCR catalysts, caused by potassiumcaused by potassium

StudstrupværketStudstrupværket

Cofiring of coal and Cofiring of coal and

strawstraw

After 2860 hours – After 2860 hours –

The SCR catalystThe SCR catalyst

deactivate with 35 %deactivate with 35 %

Technical University of Technical University of DenmarkDenmark

Flue gas with KClFlue gas with KCl

After 1100 hours – After 1100 hours –

The SCR catalystThe SCR catalyst

deactivate with about 50deactivate with about 50%%Yuanjing Zeng et al, 2005

RegenerationRegeneration

Left: Deactivated

SCR catalyst

Right: Regenerated

SCR catalyst

http://www.envica.com/de/index.php

Proposal: Inert layer may Proposal: Inert layer may helphelp

The layer could be metal-oxides ex: AlThe layer could be metal-oxides ex: Al22OO33, TiO, TiO22 and ZrO and ZrO22

Conclusion Conclusion

SCR catalysts remove NOSCR catalysts remove NOxx from flue gas from flue gas

We care about the environmentWe care about the environment SCR catalysts deactivate over time SCR catalysts deactivate over time

caused potassium and also alkali metals caused potassium and also alkali metals in generalin general

Still need research in SCR catalystsStill need research in SCR catalysts

ReferencesReferences

Bosch, H., F. Janssen, “Catalytic Reduction of Nitrogen Oxides. A review Bosch, H., F. Janssen, “Catalytic Reduction of Nitrogen Oxides. A review on the Fundamentals and Technology”, Catal.Today, 2, 369 (1988)on the Fundamentals and Technology”, Catal.Today, 2, 369 (1988)

Chen, J.P., Yang, R.T.,”Mechanism of Poisoning the VChen, J.P., Yang, R.T.,”Mechanism of Poisoning the V22OO55/TiO/TiO22 Catalyst Catalyst

for the Reduction of NO by NHfor the Reduction of NO by NH33”, J.Catal. 125, 411-420 (1990) ”, J.Catal. 125, 411-420 (1990)

Christensen, K.A., M., Livbjerg, H., “The Combustion of Straw – Christensen, K.A., M., Livbjerg, H., “The Combustion of Straw – Submicron Aerosol Particles and Gas Pollutants” J. Aerosol Sci., Vol. 26 Submicron Aerosol Particles and Gas Pollutants” J. Aerosol Sci., Vol. 26 suppl., pp s173-s174 (1995)suppl., pp s173-s174 (1995)

Dumesic, J. A., Topsøe, N., Y., Topsøe, H., Chen, Y., Slabiak, T. Dumesic, J. A., Topsøe, N., Y., Topsøe, H., Chen, Y., Slabiak, T. “Kinetics of Selective Catalytic Reduction of Nitric Oxides by Ammonia “Kinetics of Selective Catalytic Reduction of Nitric Oxides by Ammonia over Vanadia/Titania”, J. Catal. 163, 409-417 (1996)over Vanadia/Titania”, J. Catal. 163, 409-417 (1996)

Folkedahl, B.C., Zygarlicke, C.J., Gosnold, W.D., “Biomass Impacts on Folkedahl, B.C., Zygarlicke, C.J., Gosnold, W.D., “Biomass Impacts on SCR Performance”, EERC Proposal No. 2002-0017 (2001)SCR Performance”, EERC Proposal No. 2002-0017 (2001)

Forzatti, P. Lietti L., “Catalyst Deactivation” Catal. Today 52, 165-181 Forzatti, P. Lietti L., “Catalyst Deactivation” Catal. Today 52, 165-181 (1999)(1999)

ReferencesReferences

Forzatti, P. Lietti L., “Recent Advances in De-NOxing Catalysis for Forzatti, P. Lietti L., “Recent Advances in De-NOxing Catalysis for Stationary Application” Heter. Chem. Rev., 3(1), 33 (1996)Stationary Application” Heter. Chem. Rev., 3(1), 33 (1996)

Huges, R., “Deactivation of Catalysts” Academic Press, 1984Huges, R., “Deactivation of Catalysts” Academic Press, 1984 Jacobsen, Claus J.H., Schmidt, Iver, Boisen, Astrid, Johannsen, Kim, Jacobsen, Claus J.H., Schmidt, Iver, Boisen, Astrid, Johannsen, Kim,

“Katalytisk Kemi – Et Spørgsmål om miljø og Ressourcer” Haldor Topsøe “Katalytisk Kemi – Et Spørgsmål om miljø og Ressourcer” Haldor Topsøe A/S (2002)A/S (2002)

Morsing, P., Slabiak, T., “SCR DeNOMorsing, P., Slabiak, T., “SCR DeNOxx”, Haldor Topsøe A/S, Denmark, ”, Haldor Topsøe A/S, Denmark, November (2003)November (2003)

Pritchard, S., Difrancesco, C., Kaneko, S., Kobayashi, N., Suyama, K., Pritchard, S., Difrancesco, C., Kaneko, S., Kobayashi, N., Suyama, K., Lida, K., “Optimizing SCR Catalyst Design and Performance for Coal-Lida, K., “Optimizing SCR Catalyst Design and Performance for Coal-Fired Boilers”, Presented at EPA/ERPI 1995 Joint Symposium on Fired Boilers”, Presented at EPA/ERPI 1995 Joint Symposium on Stationary Combustion Nox Control, May 16-19 (1995)Stationary Combustion Nox Control, May 16-19 (1995)

Topsøe, Nan-Yu, “Catalysis for NOTopsøe, Nan-Yu, “Catalysis for NOxx abatement – Selective Catalytic abatement – Selective Catalytic Reduction of NOReduction of NOxx by Ammonia. Fundament and Industrial aspects” pages by Ammonia. Fundament and Industrial aspects” pages 125-134, December (1997)125-134, December (1997)

ReferencesReferences

Topsøe, Nan-Yu, “Infrared Spectroscopic Investigations on Environmental Topsøe, Nan-Yu, “Infrared Spectroscopic Investigations on Environmental DeNODeNOxx and Hydrotreating Catalyst”, The Haldor Topsøe Research and Hydrotreating Catalyst”, The Haldor Topsøe Research

Laboratories, Lyngby, Denmark (1998)Laboratories, Lyngby, Denmark (1998) Sloss, L.L., “NOSloss, L.L., “NOxx Emissions from Coal Combustion”, IEA Coal Research, Emissions from Coal Combustion”, IEA Coal Research,

London, UK (1991)London, UK (1991) Soud, H.N., Fukasawa, K., “Developments in NOSoud, H.N., Fukasawa, K., “Developments in NOxx Abatement and Abatement and

Control”, IEACR/89, IEA Coal Research, London, UK (1996)Control”, IEACR/89, IEA Coal Research, London, UK (1996) Yuanjing Zeng, Jensen A.D., Johnsson J.E., “Deactivation of VYuanjing Zeng, Jensen A.D., Johnsson J.E., “Deactivation of V22OO55-WO-WO33--

TiOTiO22 SCR catalyst at a biomass-fired combined heat and power plant”, SCR catalyst at a biomass-fired combined heat and power plant”,

Technical University of Denmark, 2005Technical University of Denmark, 2005 http://www.iea.org/Textbase/stats/oecdcountryresults.asp?

oecd=Denmark&SubmitB=Submit http://www.envica.com/de/index.php