HORIZON 2020 EUROPEAN UNION FUNDING FOR RESEARCH & INNOVATION

MATERIALS FOR SELECTIVE CATALYTIC REDUCTION OF NOX WITH NH3 AT HALDOR TOPSOE

6/30/2015

2

Introduction Environmental Challenges – NOx

• NOx = NO + NO2

• A major portion of the worldwide NOx emissions comes from

mobile sources (transport)

• Of the mobile sources the major contribution is from diesel

engines

• Harmful because:

– NOx + VOC + sunlight smog

– Formation of HNO3 – acid rain

Off-road

mobile (22%)

On-road

mobile (34%)

Non-mobile

sources

(44%)

US NOx sources

EPA, National Air Quality and Emissions Trends Report, 1999

Engine Air/Fuel ratio Catalyst / System

Gasoline = 1.0 TWC

Diesel > 1.0 LNT, SCR etc.

6/30/2015

3

Introduction Legislation and development

• Regulations are becoming increasingly more stringent

• Similar trends are seen in almost all parts of the world

• Exhaust after-treatment systems are required

• Diesel particulate filters, diesel oxidation catalysts and SCR catalyst

NOx

(g/kWh)

PM

(g/kWh)

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0 1 2 3 4 5 6 7 8 9 10

EU2

EU3

EU4 EU5 EU6

Engine

Tuning

DOC (oxidation catalyst)

CxHy + O2 → CO2 + H2O

2 CO + O2 → 2 CO2

2 NO + O2 → 2 NO2

DPF (diesel particulate filter)

C + O2 → CO2

C + 2 NO2 → CO2 + 2 NO

SCR (selective catalytic reduction)

4 NO + 4 NH3 + O2 → 4 N2 + 6 H2O

2 NO + 2 NO2 + 4 NH3 → 4 N2 + 6 H2O

Urea Diesel

DOC DPF ASC Z-SCR

NOx PM HC CO NH3 NOx PM HC CO NOx PM HC CO NOx PM HC CO

NO2 NO2 NO2

6/30/2015

5

Materials for SCR

Precious

metals e.g. Pt

Vanadium

based

Metal-zeolites

Temperature

range

Low temperature

(2-300°C)

Medium temperature

(250-450°C)

Low-high

temperature

(150-600°C)

Comments • expensive,

• sensitive to

poisons e.g.

sulfur

• Inexpensive,

• sulfur tolerant,

• but potassium

sensitive,

• health issues(?)

• Sensitive to H2O

at high T

• HC-tolerant?

• S-tolerant?

0

20

40

60

80

100

150 250 350 450 550 Temperature (°C)

NO

x c

on

ve

rsio

n (

%)

V-SCR FeZ-SCR CuZ-SCR

Zeolites on different scales

• mm-μm range

– 10-3-10-6 m

m-mm range

– 1-10-3 m μm-Å range

– 10-6-10-10 m

Crystalline aluminosilicates

What is a Zeolite?

Crystalline microporous aluminosilicates

• Tetrahedrally coordinated [SiO4]4-

Si

3 4 6 8

• Brønsted acid site

OSi

OSi

OSi

OSiSi

OSi

OAl

OSi

OSiSi

H+AlIII, +H+

-SiIV

• Exchange with metal ions

OSi

OAl

OSi

OSiSi

-H+

OSi

OAl

OSi

OSiSi

H+Cu+

Cu

Haldor Topsøe has a strong history in understanding SCR mechanism

6/30/2015

A consistent SCR reaction scheme

NH3 SCR

NO + NO2 + 2NH3 2N2 + 3H2O

3NO + O2+ 2NH3 NO2 + 2N2 + 3H2O

4NO + 4NH3 + O2 4N2 + 6H2O

• Fast SCR is a part of standard SCR

• Cu is reduced and oxidized in the catalytic sample

• NO is required in both oxidation and reduction

• Oxidation of Cu requires NO and O2

• Reduction of Cu requires NO and NH3

Cu2+-NO3- is the most likely formed species in oxidation

of Cu+ by NO and O2

+O2(g)

ΔE = -0.69 eV

+NO(g)

ΔE = -0.77 eV ΔE = -1.49 eV

ΔE = 0.68 eV

DFT

On the oxidation!

Nitrateformation evidenced by IR and XAS • IR and XAS : shows Cu2+-NO3

-

formation

A complete catalytic cycle

Experimental evidence by FTIR, XAS and EPR

a) 1000 ppm NO/10% O2

b) 1200 ppm NH3 /1000 ppm NO

c) 1000 ppm NO/10% O2

A consistent reaction scheme

NH3 SCR

NO + NO2 + 2NH3 2N2 + 3H2O

3NO + O2+ 2NH3 NO2 + 2N2 + 3H2O

4NO + 4NH3 + O2 4N2 + 6H2O

• NO is required in both oxidation and reduction

• Oxidation of Cu requires NO and O2

• Reduction of Cu requires NO and NH3

• Fast SCR is a part of standard SCR

Summary

We have constructed a consistent NH3 SCR mechanism for Cu-zeolites

• Based on results from DFT, EPR, EXAFS and FTIR

NOx

(g/kWh

)

PM

(g/kWh)

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0 1 2 3 4 5 6 7 8 9 10

EU2

EU3

EU4 EU5 EU6

Engine

Tuning

This knowledge enables us to press the right pedals for finding better materials for future SCR catalysts