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The Kinetic Mechanisms of NH3-SCR

over V2O5-WO3/TiO2, Fe- and Cu-Zeolite Catalysts

Enrico Tronconi and Isabella Nova

April 8th, 2016

Dipartimento

di Energia

2016 DOE-Crosscut Lean/Low-temperature Exhaust Emissions Reduction

Simulation Workshop, April 6-8, 2016, Ann Arbor, MI 48105

Enrico Tronconi

0 200 400 6000

100

200

300

400

500

600

700

alpha=0.6, exper.

alpha=0.8, exper.

alpha=0.6, model

alpha=0.8, model

alpha=1, exper.

alpha=1, model

NO

outlet conc., p

pm

Time, s

Experimental and simulated evolution of the NO

outlet concentration during

SCR reactor start-up and shut-down at

T = 360 °C. CNO0 = 560 ppm, AV = 33 Nm/h.

E. Tronconi, A. Cavanna, P. Forzatti, IEC Res. 37 (1998) 2341

NH3-SCR for stationary sources: Dynamic Modelling

Commercial catalysts:

V2O5–WO3/TiO2 extruded honeycombs

Operating temperatures: 300 – 400 °C

Chemistry: Standard SCR

2 NO + 2 NH3 + ½ O2 => 2 N2 + 3 H2O

Enrico Tronconi

Apply dynamic methods to analyze the steps of the NO-NO2/NH3 SCR

kinetic mechanism at low-T

catalyst bed

thermocouple capillaries

gas in: He, O2, H2O

corundum

NO,

NO2 in

NH3

in

gas out: to MS

+ UV analyzer

crushed monolith

Catalyst bed

Din =7 mm

h=10 mm

Wcat 80 mg

Commercial monolith

catalysts

V-WO3/TiO2,

Fe-zeolites,

Cu-zeolites

Microreactor

Dynamic runs

(e.g. step response, TPD, TPR, TPSR runs)

Analyzed reaction systems (+ O2 & H2O in He):

o NH3 (NO, N2O)

o NO2

o NO2 + NO

o NO2 + NH3

o NO2 + NH3 + NO

Lab scale tests in

microreactor afford:

• chemical regime

• fast transients

• isothermal operation

• N-balances

Also: FT-IR in-situ transient

reaction analysis, chemical

trapping, XAS….

Experimental approach: automotive applications

Enrico Tronconi

1. Nitrates

• NH4NO3 formation, decomposition: N2O

• NO reaction with NH4NO3: Fast SCR

• NH4NO3 effect on SCR activity: Enhanced SCR

• NO2 adsorption and reactivity of surface nitrates

2. Nitrites:

• NO oxidation and Standard SCR

3. Conclusions & Outlook

Outline

Enrico Tronconi

NH3-SCR kinetic

mechanisms: nitrates

Ammonium nitrate formation

Enrico Tronconi

150 200 250 300 350 400 450 500 550

NO2 SCR

Temperature, °C

Fast SCR

Standard SCR

150 200 250 300 350 400 450 500 550

Temperature, °C

Standard SCR

NO2 SCR

Fast SCR

150 200 250 300 350 400 450 500 550

0,0

0,2

0,4

0,6

0,8

1,0Fast SCR

Standard

SCR

NO

x c

on

ve

rsio

n

Temperature, °C

NO2 SCR

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,00

10

20

30

40

50

60

70

80

90

100

NO

x c

on

ve

rsio

n, %

NO2/NOx

T

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

NO2/NO

x

T

Effect of NO2: Standard, Fast & NO2 SCR reactions

Cu-zeolite Fe-zeolite V2O5-WO3/TiO2

GHSV =890’000 Ncc/(h*gap) NO2 = 500 ppm H2O = 3% O2 = 2%

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

NO2/ NO

x

T

GHSV =681’618 Ncc/(h*gap) NO2 = 500 ppm H2O = 8% O2 = 8%

GHSV =105’000Ncc/(h*gap) NO2 = 500 ppm H2O = 8% O2 = 2%

Enrico Tronconi

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

Nova, Tronconi et al., App.Cat.B: Env., 70 (2007) 80

NH3 + NO2 @ low T: Ammonium Nitrate! V2O5-WO3/TiO2

2000 4000 6000 8000

0

200

400

600

800

1000

1200

1400

1600

N-balance

NH3 = 1000 ppm

NO2 = 1000 ppm

N2O

N2

NH3

NO2

pp

m

Time (s)

T = 140°C

Evidence for AN deposition

in the line downstream from the reactor

(cold spot)

Enrico Tronconi

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

N2O + 2H2O

T

NH4NO3decomposition to N2O V2O5-WO3/TiO2

2000 4000 6000 8000

0

200

400

600

800

1000

1200

1400

1600

N-balance

NH3 = 1000 ppm

NO2 = 1000 ppm

N2O

N2

NH3

NO2

pp

m

Time (s)

T = 140°C

Nova, Tronconi et al., App.Cat.B:Env., 70 (2007) 80

Enrico Tronconi

200 250 300 350 400

0

100

200

300

400

500

NO NO2

Co

nce

ntr

atio

n (

pp

m)

Temperature (°C)

N2O

NH3

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

N2O + 2H2O

TPD after AN deposition:

T

NH4NO3decomposition to N2O V2O5-WO3/TiO2

2000 4000 6000 8000

0

200

400

600

800

1000

1200

1400

1600

N-balance

NH3 = 1000 ppm

NO2 = 1000 ppm

N2O

N2

NH3

NO2

pp

m

Time (s)

T = 140°C


Onset of N2O formation

at T = 210 – 230 °C

Enrico Tronconi

0

20

40

0

50

0

50

100

Wavenumbers (cm-1)

4000 3500 3000 2500 2000 1500 1000 5000

50

100

Catalyst after NH3+NO

2 @ 200°C

Catalyst after NH3+NO

2 @ 140°C

Fresh catalyst

Ammonium nitrate

IR Analyses :

@ 140°C: NH4NO3 is formed

and deposited onto

the catalyst

@ 200°C: NH4NO3 is formed but

not deposited onto the

catalyst

Tsublimation = 170°C

NH4NO3 HNO3 + NH3

Identification of NH4NO3 V2O5-WO3/TiO2


Enrico Tronconi

NH4NO3

NO2/NH3

catalyst

T<~170°C

NO2/NH3

catalyst

T>~170°C

(NH4NO3)

NH3 + HNO3

cold trap

NH4NO3

A cold trap was specifically designed to

quantify NH4NO3: the collected NH4NO3

agreed within 20% with the lack in the

N-balance

Sublimation/desublimation of NH4NO3 V2O5-WO3/TiO2

Enrico Tronconi

6000 8000 10000 12000 14000

0

200

400

600

800

1000

1200

NO2

NH3

pp

m

Time (s)

50

100

150

200

250

without catalyst100<T<200°C

T Tem

pera

ture

T > 100°C: NH4NO3 formation does not proceed in the gas phase

4000 6000 8000 10000 12000-200

0

200

400

600

800

1000

1200

1400

NH4NO

3

with catalyst

NH3

N2O

N2

NO2

pp

m

Time (s)

NH3 = 1000 ppm

NO2 = 1000 ppm

T = 200°C

Homogeneous formation of NH4NO3? V2O5-WO3/TiO2

Enrico Tronconi

• Formation of NH4NO3 at T<250 °C essentially identical

on Cu-CHA and on parent zeolite.

• Formation of NH4NO3

- not catalyzed by Cu

- T insensitive

NO2 SCR conditions

(Decreasing T steps)

150 200 250 300 350 400 450 500 550 600

0

20

40

60

80

100

NO

x Con

vers

ion,

%

Temperature

Cu-CHA

CHA parent

NH4NO3 formation on Cu-CHA: role of Cu

Enrico Tronconi

5500 6000 6500 7000 7500 8000 8500

0

100

200

300

400

500

NO2

NH3

N2C

on

ce

ntr

atio

n, p

pm

Time, s

NH4NO3 formation on Cu-zeolites: role of zeolite

Cu-BETA Cu-CHA Cu-SAPO

T=200°C

4500 5000 5500 6000

0

100

200

300

400

500

NO2

NH3

N2

Time, s

6000 6500 7000 7500 8000 8500

0

100

200

300

400

500

N2

Time, s

NO2

NH3

Q=250 Ncc/min

NH3 = NO2 = 500 ppm

H2O =5%, O2 =8%

NH4NO3 production: Cu-BETA > Cu-CHA ~ Cu-SAPO

2NO2 + 2NH3 → NH4NO3 + N2 + H2O

NH4NO3 Self poisoning

I. Nova, Europacat 2015, Kazan (RU)

Enrico Tronconi

10000 15000

0

100

200

300

400

500

600

N2C

on

ce

ntr

atio

n, p

pm

Time, s

NO2

NH3

NH4NO3 formation on parent zeolites: role of zeolite

BETA CHA SAPO

Q=250 Ncc/min

NH3 = NO2 = 500 ppm

H2O =5%, O2 =8%

Zeolite cage size: Cu-BETA > Cu-CHA ~ Cu-SAPO


NH4NO3 production: BETA > CHA ~ SAPO

2NO2 + 2NH3 → NH4NO3 + N2 + H2O

4500 5000 5500 6000

0

100

200

300

400

500

600

NO2

NH3

N2

Co

nce

ntr

atio

n, p

pm

Time, s

NH3

10000 15000 20000

0

100

200

300

400

500

600

Co

nce

ntr

atio

n,

pp

m

Time, s

NO2

NH3

T=120°C


NH4NO3 Self poisoning

Enrico Tronconi

100 200 300 400 500 600

0

100

200

300

SAPO

N2O

Pro

du

ctio

n, p

pm

Temperature, °C

BETA

CHA

Fast SCR

100 200 300 400 500 600

0

100

200

300

SAPO

CHA

N2O

Co

nce

ntr

atio

n, p

pm

Temperature, °C

BETA

NO2 SCR

N2O production: Cu-BETA > Cu-CHA > Cu-SAPO


N2O formation: role of zeolite


Zeolite cage size: Cu-BETA > Cu-CHA ~ Cu-SAPO Q=250 Ncc/min

NH3 = NO2 = 500 ppm

H2O =5%, O2 =8%

Enrico Tronconi

Parent increasing T Increasing vs

decreasing T steps Parent decreasing T

150 200 250 300 350 400 450 500 550 600

50

60

70

80

90

100

T

Co

nve

rsio

n N

H3, %

Temperature, °C

T

150 200 250 300 350 400 450 500 550 600

0

50

100

150

200

250

300

T

T

N2O

Co

nce

ntr

atio

n, p

pm

Temperature, °C

NOx conversion NH3 conversion N2O production

150 200 250 300 350 400 450 500 550 600

0

100

200

300

400

500

600

N2O

NH3

N2

Nbalance

NO

NO2

Co

nce

ntr

atio

n, p

pm

Temperature, °C

0

200

400

600

800

1000

1200

1400

1600

150 200 250 300 350 400 450 500 550 600

0

100

200

300

400

500

600

NO

NO2

Co

nce

ntr

atio

n, p

pm

Temperature, °C

0

200

400

600

800

1000

1200

1400

1600

Differences explained by AN accumulation – decomposition to N2O

150 200 250 300 350 400 450 500 550 600

50

60

70

80

90

100

T

T

Co

nve

rsio

n N

O2, %

Temperature, °C

NO2 SCR: Hysterisis on BETA parent

Q=250 Ncc/min

NH3 = NO2 = 500 ppm

H2O =5%, O2 =8%

Enrico Tronconi

NH3-SCR kinetic


Ammonium nitrate reaction with NO:

NO + AN NO2 + N2 + 2 H2O

Enrico Tronconi

5000 10000 15000

0

200

400

600

800

1000

1200

1400

NH3

NH4NO

3

Time (s)

NH3 = 1000 ppm

NO2 = 1000 ppm

N2

NO2

pp

m

T = 170°C, H2O = 1%, O2 = 0%

NH4NO3 formation

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

Reaction between NH4NO3 and NO 1/2 V2O5-WO3/TiO2

Enrico Tronconi

T = 170°C, H2O = 1%, O2 = 0%

NH4NO3 formation

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

5000 10000 15000

0

200

400

600

800

1000

1200

1400

NH3

NH4NO

3

NH3 = 1000 ppm

Time (s)

NH3 = 1000 ppm

NO2 = 1000 ppm

N2

NO2

NH3

pp

mReaction between NH4NO3 and NO 1/2 V2O5-WO3/TiO2

Enrico Tronconi

5000 10000 15000

0

200

400

600

800

1000

1200

1400

NH3

N2

NH4NO

3

NH3 = 1000 ppm

Time (s)

NH3 = 1000 ppm

NO2 = 1000 ppm

N2

NO2

NH3

NO

pp

m

NH3 = 1000 ppm

NO = 1000 ppm

Reaction between NH4NO3 and NO

T = 170°C, H2O = 1%, O2 = 0%

NH4NO3 formation

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

1/2 NH4NO3 + NO + NH3 3/2 N2 + 5/2 H2O


C.Ciardelli et al., Chem.Commun . 23 (2004) 2718

Enrico Tronconi

10000 15000

0

200

400

600

800

1000

1200

1400

NH4NO

3

NO2

NH3

pp

m

Time (s)

NH3 = 1000 ppm

NO2 = 500 ppm

NO = 500 ppm

NH4NO3 formation

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

“Fast” SCR

2NH3 + NO + NO2 → 2N2 + 3H2O

T = 170°C, H2O = 1%, O2 = 0%


Enrico Tronconi

10000 15000

0

200

400

600

800

1000

1200

1400

NH4NO

3

N2

NO

NO2

NH3

pp

m

Time (s)

NH3 = 1000 ppm

NO2 = 500 ppm

NO = 500 ppm

NH3 = 1000 ppm

NO = 500 ppm

T = 170°C, H2O = 1%, O2 = 0%

NH4NO3 formation

2NH3 + 2NO2 → N2 + NH4NO3 + H2O

“Fast” SCR

2NH3 + NO + NO2 → 2N2 + 3H2O

r FAST SCR r NH4NO3+NO

Reaction between NH4NO3 and NO

1/2 NH4NO3 + NO + NH3 3/2 N2 + 5/2 H2O

C.Ciardelli et al.,

Chem.Commun . 23 (2004) 2718


Enrico Tronconi

= 2 NH3 + NO2 + NO → 2 N2 + 3 H2O

2 NH3 + NO2

[NH4NO3]+ N2 + H2O 2 NH3 + 2 NO2

1

NO2 + N2 + 2 H2O

+ NO

2

N2O + 2 H2O

Fast SCR reaction = + 1 2

C.Ciardelli, I.Nova, E. Tronconi, D.Chatterjee, B. Bandl-Konrad; Chem. Commun. 2004, 2718

Fast SCR: sequential reaction scheme V2O5-WO3/TiO2

Enrico Tronconi

0

200

400

600

800

1000

1200

1400

NH3

N2NH

4NO

3

NH3 = 1000 ppm

NO2 = 1000 ppm

N2

NO2

NH3

NO

Co

nce

ntr

atio

n, p

pm

NH3 = 1000 ppm

NO = 1000 ppm

V2O5-WO3/TiO2

T=170°C, H2O=1%, O2=0%

0 2000 4000 8500 9000 9500

0

200

400

600

800

1000

1200

1400

NH3

NH4NO

3

Time (s)

NH3 = 1000 ppm

NO2 = 1000 ppm

N2

NO2

NH3

NO

Co

nce

ntr

atio

n (

pp

m)

NH3 = 1000 ppm

NO = 1000 ppmWO3/TiO2

NH4NO3 formation

2NH3 + 2 NO2→ NH4NO3+N2+H2O

NH4NO3 reduction by NO

NH4NO3 + NO N2 + NO2 + 2H2O

NH4NO3 formation

2NH3 + 2 NO2→ NH4NO3+N2+H2O

NH4NO3 reduction by NO

NH4NO3 + NO N2 + NO2 + 2H2O

200 250 300 350 400

0

100

200

300

400

500

NO NO2

Co

nce

ntr

atio

n (

pp

m)

Temperature (°C)

N2O

NH3

Role of Vanadium

Enrico Tronconi

2NO2 N2O4 HONO + HNO3

NH3ads

[NH4NO2] N2 + 2H2O

NH4NO3

NH3ads

2NO2 + 2NH3 NH4NO3 + N2 + H2O

NO

HONO + NO2 NH4NO3 + NO N2 + NO2 + 2H2O

2 NH3 + NO2 + NO 2 N2 + 3 H2O

[NH4NO2] N2 + 2H2O

NH3ads

NO-NO2/NH3

NO2/NH3

NH4NO3 NH3 + HNO3

I.Nova et al., Catal. Today, 114 (2006) 3

+ H2O

Chemistry of NO/NO2 – NH3 V2O5-WO3/TiO2

Enrico Tronconi

0 1000 2000 3000 4000

0

200

400

600

800

1000

1200

1400

1600

1800

HONO

HONO

NO2

NO

N2

NH3

Co

nce

ntr

atio

n, p

pm

Time, s

HNO3 = 50 ppm

NO = 1000 ppm

HNO3 = 50 ppm

NO = 1000 ppm

NH3 = 1500 ppm

a. u.

HNO3 +NO HONO + NO2

Converted NO Produced NO2

NO reduces HNO3,

but NH3 is necessary to arrive at N2

HNO3 +NO HONO + NO2

HONO + NH3 N2 + 2H2O

NO2 + NH3 ½ NH4NO3 + ½ N2

Conditions :

CO2 = 0 %; CH2O = 1%

CNH3 = 1500 ppm

CNO = 1000 ppm

Feed stream saturated

with HNO3 + H2O @ 42°C

T = 200 °C

I. Nova, C. Ciardelli, E. Tronconi, D. Chatterjee, B. Bandl-Konrad, Catal. Today, 114 (2006), 3

V2O5-WO3/TiO2 Fast SCR mechanism: NO + HNO3 reaction

Enrico Tronconi

Mcat = 0.021 g

(active ph. in crushed monolith)

GHSV= 205000 Ncc/(hg)

O2 = 0%, H2O = 1%

0 5000 10000 15000 20000 25000

0

200

400

600

800

1000

1200

N2

NO

NH3

N2

NH3

47

178

154

906

740

129

259

pp

m

Time (s)

NH3MS

NOMS

NO2MS

N2

N2O

NH3in

NOin

NO2in

429

NO2

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

0

200

400

600

800

1000

1200

269264

476

796

10001000

305

524

NH3

Time (s)

N2

NO2

NO

pp

m

1000

796

Fe-zeolite catalyst, T=170°C V-based catalyst, T=170°C

Mcat = 0.160 g

(crushed monolith)

GHSV= 45000 Ncc/(hg)

O2 = 0%, H2O = 1%

Results well explained in both cases by:

Stage I: 2 NO2 + 2 NH3 NH4NO3 + N2 + H2O

Stage II: NH4NO3 + NO NO2 + N2 + 2 H2O

Grossale et al., J. Catal. 256 (2008) 312 Ciardelli et al., Chem. Commun. (2004) 2718

NH4NO3 reactivity: Fe-zeolite vs. V-based catalyst

Enrico Tronconi

0 10000 20000 30000

0

200

400

600

800

1000

1200

N2

NO2

NO

1000

560

351

607

291

80

282

460

6176

460450

1000

500

Chem Com2 170 °C

pp

m

Time (s)

497

966NH3

0

50

100

150

200

250

300

350

400

450

500

550

Te

mp

era

ture

(°C

)

2NH3+2NO2 NH4NO3+N2+H2O

2NH3+ NO2 + NO2N2+3H2O NH4NO3+NON2+2H2O+NO2

2NH3+2NO2 NH4NO3+N2+H2O

Fe-Zeolite Steady state

0.080 g crushed Monolith

0.021 g active phase

72 Ncc/min

GHSV 207700 Ncc/(h g)

0% O2 1% H2O

• Same chemistry observed

over V-based catalyst

Grossale et al., J. Catal. 256 (2008) 312

T = 175°C

Role of NO + NH4NO3 in Fast SCR

Enrico Tronconi

12000 15000 18000 21000 24000 27000 30000

0

100

200

300

400

500

600

700

800

Co

nce

tra

tio

n, p

pm

Time

0

100

200

300

400

500

NH3 in

NH3

NO2

NO

T out react

Te

mp

era

ture

, °C

NO + NH4NO3 NO2 + N2 + 2 H2O

F. Marchitti, E. Barker Hemings, I. Nova, P. Forzatti, E. Tronconi, Journal of Emission Control Science and Technology, 2 (2016) 1

NO + NH4NO3 on Cu-CHA: stoichiometry

GHSV=100 k h-1; O2 = 8%v/v; H2O=5%v/v

NO = 500 ppm,

NH4NO3 = 100 ppm

T = 200 – 220 °C

Catalyst: commercial Cu-CHA

Feed = 500 ppm NO

+ 100 ppm AN

F

Enrico Tronconi

10000 20000 30000

0

100

200

300

400

500

600

700

800

900

200

400

600

Temperature

NO2

inNO

inNH3

in

N2

N2O

NO2

Co

nce

ntr

atio

n, p

pm

Time, s

NH3 NO

Te

mp

era

ture

, °C

NO «titration» of NH4NO3 deposited on Cu-CHA

Pilot#1 Powder - Run 3178

NO2 = 0-500 ppm; NH3 = 0-500 ppm; NO = 0-500 ppm; SV = 25000 h-1

T = 180 °C

N-Balance

Phase 2: AN generated in situ

NH3, NO2 are consumed, forming AN

N2 and N2O production is observed:

2NO2 + 2NH3 → AN + N2 + H2O lambda 6

3 NO2 + 4 NH3 → 7/2 N2 + 6H2O lambda 5

AN → N2O + 2H2O lambda 7

phase 2:

AN formation

phase 3:

AN reacts

with NO

Overall N balance % error = 3.5%

AN reacted = 0.0260 mmol

Compare with

AN deposited = 0.0231 mmol

(12.6% error)

16000 24000 32000

-0.06

0.00

0.06

0.0014

0.00070.0014

0.0017

0.0417

0.0817

0.00700.0081

0.05510.0523

0.0547

mm

ol

Time, s

0.0780

integrals

Phase 3: AN reaction with NO

N2 , NO2 and N2O are formed:

AN + NO → NO2 + N2 + 2 H2O lambda 1

NO2 + NO + 2 NH3 → 2 N2 + 3 H2O lambda 2

AN → N2O + 2H2O lambda 3

Enrico Tronconi

NH3-SCR kinetic


Ammonium nitrate as a booster:

Enhanced SCR reaction

Enrico Tronconi

10000 11000 12000 13000 14000

0

100

200

300

400

500

600

NOave

=140ppm

NO2ave

=180ppm

NOave

=320ppm

start feeding 500ppm NH3

start feeding 200ppm AN

NH3

NO2

NO

C

on

cen

tration

, p

pm

Time, s

1 2

NO2 “in situ” generation? Enhanced SCR

35

Stage 1 - NO oxidation by AN: NO + NH4NO3 → NO2 + N2 + 2 H2O

Test conditions:

GHSV = 75000 h-1;

NH3 = 0 - 500 ppm;

NO = 500 ppm;

O2 = 0% v/v

H2O = 5%

NH4NO3 = 200 ppm;

T = 190°C

AN rapidly oxidizes NO to NO2 on the SCR catalyst already at

low temperature: NO2 “on demand”

Catalyst: commercial Fe-BEA

Enrico Tronconi

10000 11000 12000 13000 14000

0

100

200

300

400

500

600

NOave

=140ppm

NO2ave

=180ppm

NOave

=320ppm

start feeding 500ppm NH3

start feeding 200ppm AN

NH3

NO2

NO

C

on

cen

tration

, p

pm

Time, s

1 2

NO2 “in situ” generation? Enhanced SCR

36

Stage 1 - NO oxidation by AN: NO + NH4NO3 → NO2 + N2 + 2 H2O

Stage 2 - Fast-SCR: __NO + NO2 + 2NH3 → 2N2 + 3H2O___

= E-SCR: 2NO + 2NH3 + NH4NO3 → 3N2 + 5H2O

Test conditions:

GHSV = 75000 h-1;

NH3 = 0 - 500 ppm;

NO = 500 ppm;

O2 = 0% v/v

H2O = 5%

NH4NO3 = ~ 200 ppm;

T = 190°C

AN rapidly oxidizes NO to NO2 on the SCR catalyst already at

low temperature: NO2 “on demand”

Catalyst: commercial Fe-BEA

Enrico Tronconi

20000 30000 40000 50000 60000 70000 80000

0.0

0.2

0.4

0.6

0.8

1.0

Fe-zeolite

NO

x c

on

ve

rsio

n

GHSV, h-1

Cu-zeolite

V-based

E-SCR vs. Std SCR

Experimental conditions:

NH3=NO= 500 ppm

O2=8%, H2O=0-10%

AN=200ppm

T = 200°C

European Patent EP 2 144 691 B1 (2008)

P. Forzatti, I.Nova, E.Tronconi, Angew. Chemie 121 (2009) 8516

Std. SCR

Enrico Tronconi

20000 30000 40000 50000 60000 70000 80000

0.0

0.2

0.4

0.6

0.8

1.0

Cu-zeolite

V-based

Fe-zeolite

NO

x c

on

ve

rsio

n

GHSV, h-1

Fe-zeolite

V-based


NH3=NO= 500 ppm

O2=8%, H2O=0-10%

AN=0 or 200ppm

T = 200°C

E-SCR vs. Std SCR

Std. SCR

+ 200 ppm

AN

European Patent EP 2 144 691 B1 (2008)

P. Forzatti, I.Nova, E.Tronconi, Angew. Chemie 121 (2009) 8516

Enrico Tronconi

100 150 200 250 300 350 400 450 500 550 600

0

10

20

30

40

50

60

70

80

90

100

110

E-SCR

100ppm

NO

x C

on

ve

rsio

n,

%

Temperature, °C

S-SCR

F-SCR 100NO2

Feed compositions: E-SCR = 500 ppm NO + 100 ppm AN vs. F-SCR = 400 ppm NO + 100 ppm NO2

Adding 100 ppm of AN is equivalent to replacing 100 ppm NO with NO2 AN = in situ DOC ?

Operating conditions: GHSV=75000h-1; NH3=500 ppm; NO=500/400 ppm; NO2=0/100ppm;

(H2O + 100/0 ppm NH4NO3)=5%v/v; O2=8%v/v

100 150 200 250 300 350 400 450 500 550 600

0

10

20

30

40

50

60

70

80

90

100

110

E-SCR

100ppm

NH

3 C

on

vers

ion

, %

Temperature, °C

S-SCR

F-SCR 100NO2

Commercial Fe-BEA E-SCR: effect of AN vs. effect of NO2

F. Marchitti et al., Journal of Emission Control Science and Technology, 2 (2016) 1

Enrico Tronconi

NH3-SCR kinetic


surface nitrates: storage and reactivity

Enrico Tronconi

-40 -20 0 20 40 60 80 100 120 140 160 180 200

0

200

400

600

800

1000

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

NO2 in

NO2

Time (sec)

NO

& N

O2 (

pp

m)

NO

NO

/

NO

2

2 NO2 + O2- → NO3- + NO2

-

NO2 + NO2- → NO3

- + NO

---------------------------------------------

3 NO2 + O2- → 2 NO3- + NO

NO/Δ NO2 = 1/3

On TiO2 : Despres et al., Appl. Catal. B 43 (2002) 389

On Al2O3: Apostolescu et al., Appl. Catal. B 51 (2004) 43

100 200 300 400 500

0

50

100

150

200

Co

nce

ntr

atio

n (

pp

m)

Temperature (°C)

NO2

O2 (a.u.)

Nitrate decomposition (TPD)

2NO3- 2NO2 + ½ O2 + O2-

Nitrate formation

NO2 storage mechanism similar to LNTs!

Max NO3- storage capacity = 0.20 mmol/g

NO/Δ NO2

Mechanism of nitrates storage from NO2 V2O5-WO3/TiO2

Enrico Tronconi

0 500 1000 1500 2000 2500 3000 3500 4000

-100

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NO

2 &

NO

(p

pm

)

Time (s)

NO

ou

t /(N

Oin 2-N

Oo

ut

2)

Fe-Zeolite Cu-zeolite

Reactions

Storage:

2 NO2 + H2O HNO2* + HNO3*

HONO* +NO2 HNO3* + NO

--------------------------------------------------------

3 NO2 + H2O 2HNO3* + NO

NO2

NO

NO2

NO

NO2 in NO2 in

• NO2 adsorbed as nitrate species

NO2 ads

(mmol/g)

Cu-Zeolite 0.87

Fe-Zeolite 0.50

Operating conditions:

NO2 = 1000 ppm

O2= 0%

H2O= 1%

T= 50-550°C

TPD ramp = 20 K/min

0 500 1000 1500 2000 2500 3000 3500 4000

-100

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NO

& N

O2 (

pp

m)

Time (s) N

Oo

ut /(

NO

in 2-N

Oo

ut

2)

NO/ΔNO2 NO/ΔNO2

Colombo, Nova, Tronconi, Catalysis Today 151 (2010) 223

NO2 Adsorption @ 50°C: Fe-zeolite vs. Cu-zeolite

Enrico Tronconi

Nitrates storage from NO2: role of the metal

100 200 300 400 500

0

25

50

75

100

NO CHA parent

NO2 CHA parent

400 °C342 °C

NO2 Cu-CHA

Co

nce

ntr

atio

n, p

pm

Temperature, °CNegligible nitrates storage on the

CHA parent zeolite

Nitrates are stored onto the Cu sites

Q=120 Ncc/min

Cin NO2 = 500ppm,

Cin H2O =0%, Cin O2 =0%

Heating rate=15°C/min

Pre-oxidized catalyst

TPD

CHA parent vs. Cu-CHA


Enrico Tronconi

100 200 300 400 500 600

0

20

40

60

80

100

120

140

160

NO2 Fe-ZSM-5

Co

nce

ntr

atio

n, p

pm

Temperature, °C

NO2 Cu-CHA

Nitrates stability: Cu-CHA vs. Fe-ZSM-5

NO2 ads. + TPD (He) ; Q = 120 Ncc/min; H2O = 0 %; O2 = 8 %;

NO2 = 500 ppm; NH3= 500 ppm; T = 120 °C + ramp 550 °C at 15 °C/min

Nitrates are more stable on Cu-CHA

Tads = 120°C

Fe-ZSM-5 = 22 mg

Cu-CHA = 16 mg

Enrico Tronconi

Q=120 Ncc/min

NO2 = 500ppm,

H2O =0%, O2 =0%

Heating rate=15°C/min

Pre-oxidized catalyst

100 200 300 400 500

0

10

20

30

40

50

60

70

SAPO

CHA

BETA

NO

2 c

on

ce

ntr

atio

n, p

pm

Temperature, °C

0 300 600 900 1200

0

100

200

300

400

500

600

NO

NO2

SAPO

SAPO

CHA

CHA

Concentr

ation, ppm

Time, s

BETA

BETANO

2in

Tads = 120°C TPD

Nitrates stability: Cu-CHA ≈ Cu-SAPO > Cu-BETA


Nitrates stability: Cu-CHA vs. Cu-SAPO vs. Cu-BEA

Zeolite cage size: Cu-BETA > Cu-CHA ~ Cu-SAPO

Enrico Tronconi

2400 2350 2300 2250 2200 2150 2100 2050 2000

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

min

8.59

2.51

1.88

1.67

1.46

0.10

IR S

ag

na

l

cm-1

2000 1975 1950 1925 1900 1875 1850 1825 1800

0.00

0.05

0.10

0.15

0.20

0.25

0.30

min

8.59

2.51

1.88

1.67

1.46

0.10

IR S

ag

na

lcm

-1

1800 1750 1700 1650 1600 1550 1500 1450 1400 1350 1300

0.0

0.2

0.4

0.6

0.8

min

8.59

2.51

1.88

1.67

1.46

0.10

IR S

ag

na

l

cm-1

0 2 4 6 8 10

0

500

1000

1500

2000

2500

3000

pp

m

Time, min

2400-2000 cm-1 2000-1800 cm-1 1800-1300 cm-1

T = 130 °C

NO2

O2=0%

H2O=0%

-1 0 1 2 3 4 5 6 7 8 9 10

0

20

40

0

2

4

6

8

0

1

2

3

4

5

Time, min

Pe

ak A

rea

Peak 1700-1510 cm-1

Pe

ak A

rea

Peak 1935-1810cm-1

Pe

ak A

rea

Peak 2230-2027 cm-1

1620 cm-1:

(+ 1574 cm-1)

Fe(III)-NO3

(stable)

2120 cm-1:

NO+ in cationic

position

1870 cm-1:

Fe(II)-NO

Peak area dynamics

Ruggeri, Sobalik, Nova, Tronconi,

Cat. Today, 184 (2012) 107

NO2 adsorption on Fe-ZSM-5: in situ FTIR

Enrico Tronconi

Peak area dynamics:

time resolved profiles

T = 120 °C

Enrico Tronconi

Volumetric flow = 75 Ncc/min

NO2 or NO = 500 ppm; H2O = 0%; O2 = 0%

Pre-treatment: 8 % O2 for 1hr at 500°C

0 10 20 30 40

0

2

4

6

8

Nitra

tes p

eak a

rea

Time, min

0

1

2

NO

+ p

ea

k a

rea

NO+

NO2 = 500 ppm

Nitrates

NO2 adsorption:

NO+ and nitrates are formed simultaneously:

2 NO2 NO+ + NO3-

M.P. Ruggeri et al., Appl.Catal.B: Environm., 166-167 (2015) 181-192

Dynamics of NOX adsorption on Cu-CHA: FTIR

Enrico Tronconi

Yeom et al.,

Catal.Tod., 136 (2008) 55

Rivallan et al., J.Catal. 264 (2009) 104 Iwasaki et al., J.Catal. 260 (2008) 205

NO+

NO3-

BaNa/Y

Fe-ZSM5

NO2 storage/FTIR Szanyi et al., Phys. Chem. Chem. Phys., 15 (2013) 2368

NO+ NO3

-

Fe-ZSM5

Cu-SSZ-13

Enrico Tronconi

10000 11000 12000 16000 17000 18000 19000 20000

0

100

200

300

400

500

600

700

800

900

1000

1100

0

50

100

150

200

250

300

350

400

450

500

550

600

Co

nce

ntr

atio

n, p

pm

Time, s

Temperature

NO sym

NO2 sym NH

3 sym

Te

mp

era

ture

, °C

4000 5000 9000 10000 11000 12000 13000

0

100

200

300

400

500

600

700

800

900

1000

1100

Co

nce

ntr

atio

n, p

pm

Time, s

NO sym

NO2 sym

NH3 sym

T=200°C T=120°C

NH3 is NOT able to reduce stored nitrates at T ≤ 200°C

Reduction of nitrates by NH3 ?

Cu-zeolite

M. Colombo, I. Nova, E. Tronconi, Cat. Today 197 (2012) 243

Enrico Tronconi

17000 17500 18000 18500 19000 19500

0

100

200

300

400

500

600

700

800

900

1000

Co

nce

ntr

atio

n, p

pm

Time, s

NOin

NO sym

NO2 sym

0 500 1000 1500 2000

0

200

400

600

800

1000

0

100

200

300

400

500

600

Ga

s c

on

ce

ntr

atio

n (

pp

m)

Time (sec)

Te

mp

era

ture

(°C

)

NO2 NO

NO3- + NO→ NO2 + NO2

-

NO2- + NO3

- → 2 NO2 + O2-

------------------------------------

2NO3- + NO → 3 NO2 + O2-

a) NO2 disproportionation &

nitrates formation

2 NO2 + O2- → NO3- + NO2

-

NO2 + NO2- → NO3

- + NO

-------------------------------------

3 NO2 + O2- → 2NO3- + NO

b) Nitrates reduction by NO

NO totally reduces stored nitrates

already at very low T

Reduction of nitrates by NO

T=200°C

Cu-zeolite

Enrico Tronconi

C.Ciardelli, I.Nova, E. Tronconi, D.Chatterjee, B. Bandl-Konrad, Chem. Commun. 2004, 2718

Fast SCR mechanism on V2O5-WO3/TiO2:

A. Grossale et al. J.Catal. 256(2008) 312

O. Kröcher et al. Catal. Reviews 50 (2008) 492

M. Colombo, I. Nova, E. Tronconi, Cat. Today 197 (2012) 243

2 NH3+NO2

[NH4NO3]+ N2 + H2O 2 NH3 + 2 NO2 1

NO2 + N2 + 2 H2O

+ NO 2

Fast SCR mechanism on Ba-Na Y zeolite:

Y. Yeom, E. Weitz et al., J. Catal. 235 (2005) 201 Fast SCR mechanism on Fe- and Cu-zeolites:

• Key intermediates are surface nitrates

formed by NO2 disproportionation

• Nitrates reduction by NO is the rds

at low T

• Redox properties not relevant J.S. McEwen, T. Anggara et al., Cat. Today 184 (2012) 129

slow

Mechanistic relevance of NO+nitrates reaction

Enrico Tronconi

50 100 150 200 250 300 350 400 450 500 550 600

0

20

40

60

80

100

NO

co

nve

rsio

n, %

Temperature, °C

A

A

Curve A (Fast SCR): Feed = 1% H2O, 0% O2, NH3= 1000 ppm, NO=NO2= 500 ppm + He

Grossale, et al. l, J. Catal.,

256 (2008) 312

Role of surface nitrates

Catalyst = Fe-zeolite

Enrico Tronconi

50 100 150 200 250 300 350 400 450 500 550 600

0

20

40

60

80

100

NO

co

nve

rsio

n, %

Temperature, °C

A

A

B

Curve A (Fast SCR): Feed = 1% H2O, 0% O2, NH3= 1000 ppm, NO=NO2= 500 ppm + He

Curve B: Feed = 1% H2O, 0% O2, NH3= 1000 ppm, NO= 1000 ppm + He

over catalyst pre-treated with NO2 (1000 ppm) + H2O (1 %) at 60 °C

Grossale, et al. l, J. Catal.,

256 (2008) 312

Role of surface nitrates

Catalyst = Fe-zeolite

Enrico Tronconi

0 50 100 150 200 250 300

0

10

20

30

40

50

60

70

80

90

100

NO

co

nve

rsio

n, %

NO+NH3+ nitrates

Fast SCR

V2O5/WO3/TiO2


TPR run: O2 =0% H2O= 3%; NO:NO2=500 ppm; NH3=1000 ppm; T-ramp=20K/min

TPSR run: NO2 adsorption: 1000 ppm at 50°C; T-ramp=20K/min; 1000 ppm NO:NH3

100 150 200 250

0

10

20

30

40

50

60

70

80

90

Fast SCR

NO

co

nve

rsio

n, %

Temperature (°C)

NO+NH3+nitrates

Cu-zeolite

Nova, et al. Cat. Today 114 (2006) 3

Role of surface nitrates on Cu-zeolite and V-based catalysts

Enrico Tronconi

T. Janssens, H. Falsig et al.,

ACS Catal. 5 (2015) 2832

Proposed mechanism

for Standard (and Fast SCR)

on Cu-CHA:

XAS +

EPR +

FTIR +

DFT

Mechanistic relevance of NO+nitrates reaction

Enrico Tronconi

NH3-SCR kinetic

mechanisms: nitrites

NO oxidation & Standard SCR reactions

Enrico Tronconi

Alternative pathways and intermediates:

D. Wang, L. Zhang, K. Kamasamudram, W. S. Epling,

ACS Catal. 3 (2013) 871

Standard SCR mechanism on Cu-SAPO-34:

Standard SCR mechanism on Cu-SSZ-13:

C. Paolucci, A. Verma, S. Bates,

et al., Angew. Chem. Int. Ed. 53 (2014) 11828-11833

In-situ

DRIFT

J. H. Kwak, J. H. Lee, S. D. Burton, A. S. Lipton, C. H. F. Peden, J. Szanyi

Angew. Chem. Int. Ed. 52 (2013) 9985

On Cu-SSZ-13:

In-situ

DRIFT

T. Janssens, H. Falsig et al., ACS Catal. 5 (2015) 2832

Standard (and Fast SCR)

on Cu-CHA:

XAS +

EPR +

FTIR +

DFT

XAS +

DFT

Mechanisms for NO - NH3-SCR

Enrico Tronconi

NO adsorption:

NO+ is formed before nitrates

Slower dynamics compared to NO2

adsorption

0 10 20 30 40 50

0

2

4

6

8

Nitra

tes p

ea

k a

rea

Time, min

0.0

0.5

1.0

1.5

2.0

2.5

NO

+ p

ea

k a

rea

NO+

NO = 500 ppm

Nitrates

Peak area dynamics:

time resolved profiles

T = 120 °C

Enrico Tronconi


NO2 or NO = 500 ppm; H2O = 0%; O2 = 0%

Pre-treatment: 8 % O2 for 1hr at 500°C

0 10 20 30 40

0

2

4

6

8

Nitra

tes p

eak a

rea

Time, min

0

1

2

NO

+ p

ea

k a

rea

NO+

NO2 = 500 ppm

Nitrates

NO2 adsorption:

NO+ and nitrates are formed

simultaneously


Dynamics of NOX adsorption on Cu-CHA: FTIR

Enrico Tronconi

Chemical trapping of NOx intermediates

Fe-ZSM-5 and Cu-CHA

• Provide (redox) active sites for NO oxidation and Standard SCR reaction

• Commercial catalysts

• Loaded 16 mg (up to 90 mg), mesh size 106-125 µm

BaO/Al2O3

• Chemical trap for NOx (see LNT literature)

• Prepared from Ba(CH3COO)2 via calcination

• Loaded 44 mg (up to 90 mg), mesh size 75-106 µm

Mechanical mixture: Me-zeolite + BaO/Al2O3

• Cu-CHA or Fe-ZSM-5: BaO/Al2O3 = 1:2.75 w/w

• Different particle sizes enable separation (sieving) of the two materials for ex situ IR analysis

to MS + UV

analyzers

NO2 or NO+O2 adsorption on:

Enrico Tronconi

100 200 300 400 500 600

0

10

20

30

40

50

60

70

80

NO

& N

O2 c

on

ce

ntr

atio

n, p

pm

Temperature, °C

NO2

NO

NO+O2 adsorption on Cu-CHA + BaO/Al2O3 @ 120°C

TPD

2000 1800 1600 1400 1200 1000

0.000

0.002

0.004

0.006

0.008

0.010

1820 cm-1

1430 cm-1

1540 cm-1

1640 cm-1

1380 cm-1

1270 cm-1

Ab

so

rba

nce

, a

. u

.

Wavenumber, cm-1

1090 cm-1

BaO/Al2O

3 from mechanical mixture

• TPD after NO+O2 adsorption onto mech. mixture shows equimolar

NO+NO2 evolution, typical of nitrites decomposition:

Ba(NO2)2 BaO + NO + NO2

• Ex situ IR analysis confirms formation of nitrites and nitrates on BaO

• Interaction between Cu-CHA and BaO mediated via gas phase

T. Selleri, M.P. Ruggeri, I. Nova, E. Tronconi, “Topics in Catalysis, in press (2016).

Enrico Tronconi

100 200 300 400 500 600

0

10

20

30

40

50

60

70

80

NO

& N

O2 c

on

ce

ntr

atio

n, p

pm

Temperature, °C

NO2

NO

Similar behaviors

NO+O2 adsorption + TPD on mech. mixture: Cu-CHA vs. Fe-ZSM-5

Solid lines = Cu-CHA + BaO/Al2O3

Dotted lines = Fe-ZSM-5 + BaO/Al2O3

Enrico Tronconi

100 200 300 400 500 600

-200

0

200

400

600

800

1000

1200

1400

Co

nce

ntr

atio

n, p

pm

Temperature, °C

NO2

NO

NO2 ads.TPD

Completely different decomposition profiles for intermediates from NO + O2 and

from NO2 rule out NO2/nitrates as intermediates in NO oxidation over Fe-ZSM-5

NITRATES NITRITES

NO+O2 vs. NO2 adsorption on Fe-ZSM-5 + BaO/Al2O3

NO + O2 ads. TPD

M. P. Ruggeri, T. Selleri, M. Colombo, I. Nova, E. Tronconi, J. Catal. 311 (2014) 266

Enrico Tronconi

BaO

CuII CuII O

II

NO

CuII CuI

O-NO+

HONO

O2 (+ NO ?)

H2O

Ba-NO2

NO+O2 adsorption on Cu-CHA+BaO/Al2O3: chemistry

Active sites for NO oxidation

= Cu dimers

A. A. Verma, S et al. J. Catal. 312 (2014)

Chemical trapping experiments prove that NO oxidative activation on Cu

results in formation of nitrite precursors, transferred and trapped onto BaO

M.P. Ruggeri et al., J. Catal. 311 (2014) 266; J. Catal. 328 (2015) 258

Enrico Tronconi

NH3*

CuII CuII O

II

NO

CuII CuI

O-NO+

HONO

O2 (+ NO ?)

H2O

N2 + H2O

Enrico Tronconi

Relevance to Std. SCR mechanism: NH3 as chemical trap ?

• Like BaO, adsorbed NH3 can intercept the reactive intermediate HONO,

but forming in this case unstable NH4NO2 «nitrite route»

• Limited formation of nitrates from NO + O2 in the presence of NH3 has been

reported on Cu-zeolites

D. Wang, L. Zhang, K. Kamasamudram, W. S. Epling, ACS Catal. 3 (2013) 871

I. Ellmers, R. Perez Velez, U. Bentrup, A. Bruekner, W. Gruenert, J Catal. 311 (2014) 199

NH4NO2

Enrico Tronconi

3500 3000 2500 2000 1500

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

5000 5200 5400 5600 5800 6000 6200 6400

Ar

NO + O2

Ar

20 minutes

40 minutes

53 minutes

66 minutes

Absorb

ance, a. u.

Wavenumber, cm-1

NH3 NO

in

NO

Time, s

N2

Concentr

ation, ppm

0

100

200

300

400

500

600

2200 2000 1800 1600 1400-0.05

0.00

0.05

0.10

0.15

Ar

NO + O2

Ar

20 minutes

40 minutes

53 minutes

66 minutes

Absorb

ance, a. u.

Wavenumber, cm-1

NH3

1630, 3340-3190 cm-1 : NH3 on Lewis sites

1440, 3270 cm-1: NH4+

3600 cm-1: Si-OH-Al band

3720 cm-1: Si-OH band

Peak identification for NH3 adsorption:


Operative Conditions:


NH3 = 500 ppm; H2O = 0%; O2 = 0%

NO+O2 on pre-adsorbed NH3 on Cu-CHA: in situ DRIFTS

Pre-treatment: 1000 ppm of NH3 for 1hr at 500°C

N2 formation due to NO + O2 reaction with NH3

Nitrates are formed only once NH3 is

completely depleted from the surface

NO + O2: Gas phase analysis (MS)

Enrico Tronconi

T = 120°C

Enrico Tronconi

General Conclusions and Outlook

• Many similar features observed in NH3-SCR chemistry over V-based, Fe- and Cu-

zeolite catalysts: no evidence for substantial differences in kinetic mechanisms

• Nitrates are crucial intermediates in NO2-related SCR reactions, but not in Std. SCR

• Different reactivities/kinetics correlate with stability of adsorbed species and/or with

steric effects due to zeolite structures.

• The available macroscopic observations of chemistry and kinetics can be used to

discriminate rival mechanistic proposals

• The presence of gaseous species in equilibrium with surface species (e.g. HNO3,

HONO) is relevant

• Detailed kinetic modelling in close adherence with realistic chemistry is possible

Enrico Tronconi

H2020 EU project HDGAS (2015-18):

“HD GAS engines integrated into vehicles”

FP7 EU project CO2RE (2012-16):

“CO2 REduction for long haul transport”

Acknowledgments

LABORATORY OF APPLIED

THERMODYNAMICS

http://www.corning.com/index.aspx

Enrico Tronconi

Catalysis at POLIMI

Thank you!

2016 doe-crosscut lean/low-temperature exhaust emissions ...€¦ · zeolite cage size: cu-beta...

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