Efficient Sm modified Mn/TiO2 catalysts for selective

catalytic reduction of NO with NH3 at low temperature

Lijun Liu, Sheng Su*, Limo He, Mengxia Qing, Kai Xu,

Jun Xu, Song Hu, Yi Wang, Jun Xiang*

State Key Laboratory of Coal Combustion (SKLCC)

Huazhong University of Science & Technology (HUST)

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CONTENTS

Research background01

Experimental02

Conclusions04

Results and discussion03

Research background

current position

300-420℃

new location

100-150℃solution

present problem

abrasion caused by fly ash

deactivation caused by alkali metal

high conversion of SO2 to SO3

new problem

excellent low-temperature

SCR activity

good resistance to H2O and

SO2

meet

BoilerStack

novel

SCR

catalyst

Catalyst design

Mn[1]-Sm/TiO2[2]MnOx has excellent low

temperature SCR activity

TiO2-supported MnO2

catalysts showed more

promising SCR activity

Sm can prevent transition

from Mn4+ to Mn3+

Experimental

Propose

[1] D.A. Peña, B.S. Uphade, P.G. Smirniotis, J. Catal. 221 (2004) 421-431.

[2] P.G. Smirniotis, P.M. Sreekanth, D.A. Peña, R.G. Jenkins, Ind. Eng. Chem. Res. 45 (2006) 6436-6443.

Catalytic activity test

Schematic diagram of the experimental system.

Test condition

Simulated flue gas:

500 ppm NO, 500 ppm NH3, 5% O2, 5%

H2O(when used), 100 ppm SO2(when

used) and N2 as balance

Total flow rate: 1L/min

Particle size: 40-60 mesh

Gas hourly space velocity: 60000 h-1

NOx conversion =[NOx]in − [NOx]out

[NOx]in× 100%

N2 selectivity = [NOx]in + [NH3]

in− [NOx]out − [NH3]

out− 2[N2O]

out[NOx]in + [NH3]

in− [NOx]out − [NH3]

out×

100%

Experimental

Characterization

Physicochemical properties

XRD BET XPS NH3-TPD H2-TPR

Reaction mechanism

in situ DRIFTS

Catalytic performance

Results and discussion

100 150 200 250 30040

50

60

70

80

90

100

N2 s

ele

cti

vit

y (

%)

Temperature (℃) 20Mn/TiO2

20Mn-10Sm/TiO2

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

70

80

90

SO2 offH

2O off

H2O on

SO2 on

H2O off

NO

x c

on

vers

ion

(%

)

Reaction time (h)

20Mn/TiO2

20Mn-10Sm/TiO2

H2O on

NOx conversion N2 selectivity Resistance to H2O and SO2

100 150 200 250 30010

20

30

40

50

60

70

80

90

NO

x c

on

vers

ion (

%)

Temperature (℃) 20Mn-5Sm/TiO

2

20Mn-10Sm/TiO2

20Mn-20Sm/TiO2

20Mn/TiO2

50% → 85% at 120 °C

Optimum loading : 10% Higher N2 selectivity

Over 95% at 80-150 °C

85% → 70% for Mn-Sm

80% → 55% for Mn

Specific surface area: BET

The surface areas of Mn-Sm/TiO2 catalysts increased in the presence of Sm ;

The doped Sm could promote the dispersion of manganese oxide

Results and discussion

catalystBET surface area

(m2/g)

pore volume

(cm3/g)

average pore size

(nm)

TiO2 50.45 0.24 19.41

20Mn/TiO2 43.67 0.34 31.55

20Mn-5Sm/TiO2 45.93 0.30 26.24

20Mn-10Sm/TiO2 47.69 0.33 27.38

20Mn-20Sm/TiO2 38.40 0.29 30.67

Crystal structure: XRD

Results and discussion

Diffraction peaks of TiO2 are observed

20 30 40 50 60 70 80

◆

▼

◆◆◆

▼▼▼▼

▼▼

▼

▼

▼

▼

▼

TiO2

20Mn/TiO2

20Mn-5Sm/TiO2

20Mn-10Sm/TiO2

20Mn-20Sm/TiO2

Inte

nsi

ty (

a.u

.)

2 Theta (degree)

▼

◆

Anatase TiO2

Rutile TiO2

No Mn and Sm species are detected

Strong interaction between Mn and Ti

Pure TiO2

Supported TiO2

Oxidation state and surface atomic concentrations: XPS

660 655 650 645 640 635

Mn 2p3/2

Mn 2p1/2

Mn-Nitrate (644.3)

Mn4+

(642.4)

Mn3+

(641.4)

20Mn-10Sm/TiO2

Mn-Nitrate (643.6)

Mn 2p3/2

Mn 2p1/2

Mn4+

(642.2)

Inte

nsi

ty (

a.u.)

Binding energy / eV

Mn3+

(641.2)

20Mn/TiO2

535 530

Oα (532.1)

Oβ (529.9)

20Mn-10Sm/TiO2

O 1s

O 1s

Oα (531.6) O

β (530.0)

Inte

nsi

ty (

a.u.)

Binding energy / eV

20Mn/TiO2

catalyst

surface atom concentration

Mn4+/Mn3+ Mn4+/Mn Mn/Ti Oα/Oβ Oα/O

20Mn/TiO2 2.08 36.81% 0.21 0.38 27.75%

20Mn-10Sm/TiO2 2.46 41.57% 0.43 0.54 35.10%

The presence of Sm could inhibit the crystallization of manganese oxide ;

Mn could incorporate into lattice structure of TiO2;

The addition of Sm could promote the surface active oxygen species.

Results and discussion

Acidity: NH3-TPD

50 100 150 200 250 300 350

TC

D s

ign

als

(a.u

.)

Temperature / oC

20Mn/TiO2

20Mn-10Sm/TiO2

20Mn-20Sm/TiO2

190314

Redox property: H2-TPR

100 150 200 250 300 350 400 450

Mn2O

3 to MnO

TC

D s

ign

als

(a.u

.)

Temperature / oC

20Mn/TiO2

20Mn-10Sm/TiO2

20Mn-20Sm/TiO2

344

311

321

410

427

MnO2 to Mn

2O

3

Lewis acid site might not be the main factor in low-

temperature NH3-SCR of NOx over these catalysts.

The reducibility may be play an important

role in low-temperature SCR activity.

Results and discussion

Reaction of NH3 with pre-adsorbed NO + O2: In situ DRIFTS

Results and discussion

The bridging nitrates are the main active nitrate

species;

The SCR reactions over the Mn/TiO2 catalyst can

proceed through L−H mechanism.

The bridging nitrates were not formed on the surface

of Mn-Sm/TiO2 catalyst;

The SCR reactions over the Mn-Sm/TiO2 catalyst can

not happen via L−H mechanism.

Mn/TiO2 Mn-Sm/TiO2

1750 1500 1250 1000

1606

Ab

sorb

ance

(a.

u.)

Wavenumber / cm-1

NO+O2

4

6

60

90 min

NH3

0.02

a

1750 1500 1250 1000

1267

1553

Abso

rbance (

a.u

.)

Wavenumber / cm-1

NO+O2

30

60 min

NH3

0.02 bBridging nitrate

Disappear

Bidentate nitrate

Stable

Reaction of NO + O2 with pre-adsorbed NH3: In situ DRIFTS

Results and discussion

All bands of coordinated NH3, NH4+ and -NH2

species disappeared gradually after exposure to

NO + O2;

The SCR reactions over the Mn/TiO2 catalyst can

proceed through E−R mechanism.

The reaction of preadsorbed NH3 with NO + O2 on

Mn-Sm/TiO2 catalyst was significantly faster than that

over Mn/TiO2 catalyst;

The Sm modified catalyst possessed more –NH2

species than Mn/TiO2 catalyst.

Mn/TiO2 Mn-Sm/TiO2

1750 1500 1250 1000

1560

Abso

rban

ce (

a.u.)

Wavenumber / cm-1

NO+O22

60

120 min

NH3

0.02

1267

b

1750 1500 1250 1000

NO+O2

90 min

14

8

Abso

rban

ce (

a.u.)

Wavenumber / cm-1

0.02

NH3

1606

1267a

Nitrate

NH3-NH2NH3

Bidentate nitrate

-NH2 -NH2NH3

NH3 ad-species disappear

NH3 ad-species disappear

Adsorption and reaction of NH3 + NO + O2: In situ DRIFTS

Results and discussion

The co-existence of the NH3 ad-species and NOx ad-

species are observed;

The reactive bridging nitrate and the –NH2 and NH4+

intermediates are all absent.

The adsorption of NO can not happen in the

presence of NH3;

The formed –NH2 species quickly reacted with

gaseous NO to produce N2 and H2O.

Mn/TiO2 Mn-Sm/TiO2

1750 1500 1250 1000

1151

12041292

148515411559

1600

Ab

sorb

an

ce (

a.u

.)

Wavenumber / cm-1

2

4

8

30

60 min

0.02 a

1750 1500 1250 1000

1595

Abso

rban

ce (

a.u.)

Wavenumber / cm-1

2

50

10

30

60 min

0.02

1415

1192 b

No –NH2 species

NitrateNH3 NH3

No bridging nitrate

and –NH2 species

NH3

NH3

Conclusions

The best 20Mn-10Sm/TiO2 catalyst achieved almost 85% NO conversion with a

GHSV of 60000 h-1 at 120 °C;

The SCR reaction mechanism changed by inhibiting the formation of bridging

nitrate in the presence of Sm and the reactions can proceed only through Eley-

Rideal mechanism;

The presence of Sm can improve the dispersion of manganese oxide and the

relative concentration of surface oxygen (Oα);

The enhanced oxygen transport after introduction of Sm boost the reaction rate.

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