Vanadia Catalysts for Catalytic Oxidation of 1,2-Dichlorobenzene: Implication of

Vanadia Structure

Jen-Ray Chang

National Chung Cheng University

2

Motivations:

1. V2O5/TiO2: commercial catalysts for oxidative destruction of dioxins.

2. Drawbacks of TiO2 nano-particles: low thermal stability, low surface area, high cost.

3. Catalyst improvements: addition of MoO3, TiO2-SiO2 supports, vanadium alkoxide precursor

3

Research goals :

Fundamental understanding the role of MoO3, grafted TiO2, and vanadium precursor in affecting the vanadia structure and catalytic properties

OH

Cl

Cl

ClCl

H

Cl-HCl

V2O5 AirO2

H2O + CO + CO2 + HCl

ClCl

O

oxygen containing intermediate

O2partial oxidation product

O2

V2O5 AirO2O2

O2

4

How we approach:

1. Catalyst preparation

1. Role of MoO3: V2O5/TiO2, V2O5-MoO3/TiO2

2. Role of the grafted TiO2: TiO2-SiO2, SiO2

3. Effects of vanadia precursors: Conventional vanadia precursor, vanadium oxalate V(C2O4)2

Vanadium alkoxides, vanadium triisoperoxides VO(OC3H7)3

2. Catalyst characterization: Synchrotron PXRD, EXAFS, FT-IR

3. Catalytic properties : feed: air containing 1,2-dichlorobenzene (thiophene) reaction system: continuous fixed bed reactor

Role of MoO3 in affecting vanadia structure investigated by synchrotron PXRD

1.No V2O5 phase for fresh catalyst: MoO3 disperse vanadia2.Formation of MoV2O8 after reaction: confirm V-Mo bimetallic interaction

5 10 15 20 25 30 35 40 45 50 55-2000

0

2000

4000

6000

8000

10000

12000

14000

8 10 12 14 16 18

0

2000

4000

Inte

nsity

(a.u

.)

2 (=0.09537nm)

used V2O

5-MoO

3/TiO

2

0 10 20 30 40 50 60 70-4000

0

4000

8000

12000

MO3

TiO2

Inte

nsity

(a.u

.)

2

fresh V2O

5-MoO

3/TiO

2

freshV2O5/TiO2-MoO3: only TiO2, MoO3 phase

MoV2O8 peaks

6

VT , fresh V2O5/TiO2 VMoT , fresh V2O5/TiO2-MoO3 UVT, used V2O5/TiO2 UVMoT , used V2O5/TiO2-MoO3 SUVT, used V2O5/TiO2 with sulfur SUVMoT, used V2O5/TiO2-MoO3 with sulfur

1650 1600 1550 1500 1450-2.0

-1.9

-1.8

-1.7

-1.6

-1.5

-1.4

Ab

s

Wave number, cm-1

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(a)anatase TiO2, (b)VT, (C) VMoT, (d) UVT, (e) UVMoT, (f) SUVT, (g)SUVMoT

L

LB

B L+B

L

Role of MoO3 in affecting surface acidity investigated by FT-IR Sulfur containing feed

Fresh VMoT

MoO3 induce acid sites; similar to the adsorption SOx on TiO2 surface

SUVMoT

SUVT

7

50 100 150 200 250 300 350 400 450 500 550 600 650 700

0.00

0.03

0.06

0.09

450 500 550 600 650 700-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

400 410 420 430 440 450 460 470 480-0.003

-0.002

-0.001

0.000

H2

up

tak

e, a

rb

ita

ry

un

its

Temp, oC

VMoT:white, UVMoT:red, VT :yellow, UVT :green, MoO3 standard: blue

1. Decrease V2O5 cluster size; decrease Red. Temp. (600 → 560 ˚C)2.Formation of amorphous vanadia further decrease Red. Temp. (430 ˚C)

Role of MoO3 in affecting reduction temperature of vanadia

V2O5 clusterMoV2O8

Isolated andLayer V2O5

8

1. Partial oxidation is insignificant after 350 ˚C2. Total oxisation: VMoT(S) > VMoT> VT (S) > VT 3. SOx:increase frequency facto4. MoO3: increase both frequency and activation energy whereas the frequency factor enhancement is not as significant as SOx adsorption.

▼: VMoT (S) ♦: VMoT ▲: VT (S) ■: VT

Catalyst ko Eaapp(kJ)

VT 1826 34.4

VMoT 1958 31.5

VT(S) 2565 35.0

VMoT (S) 2836 32.2

Effects of MoO3 addition and SOx adsorption on DCB total oxidation

feed ： 1,2-dichlorobenzene (thiophene) in air; WHSV ： 0.2hr-

1 ; pressure ： 1 atm; temperature ：250-550 oC

0.0012 0.0014 0.0016 0.0018 0.0020 0.00220.0

0.5

1.0

1.5

2.0

2.5

3.0

Reaction Temperature ((K-1)

ln (

k)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

-3000

0

3000

6000

9000

12000

Inte

nsity

(a. u

.)

2 (=0.9537A)

TiO2

MoO3

MoV2O

8

VO2

UVMoT

Main role of MoO3

V2O5/TiO2 activity can be enhanced by adding MoO3 and introducing sulfur-containing compounds to the reaction system. MoO3 disperses vanadia and forms MoV2O8 during the reaction, which plays critical roles in the activity enhancement.

UVMoT

Chemical formula

TiO2 MoO3 MoV2O8 VO2

Space group

I 41/a m d P b n m C 2 P 2/m

a, Ǻ 3.7836(5) 3.9612(3) 19.415(3) 9.046(7)

b, Ǻ 3.78362 13.868(1) 3.6254(6) 5.792(4)

c, Ǻ 9.5096(2) 3.6959(3) 4.1170(7) 4.561(4)

Crystal Weight Fraction

0.759(1) 0.123(2) 0.108(3) 0.0096(2)

Crystalline size, nm

39 27 26 2430 wt % amorphous phase V2O5

10

Role of the grafted TiO2 in affecting vanadia structure investigated by synchrotron PXRD and EXAFS

V2O5(A)/SiO2: VO(OC3H7)3

grafted on SiO2 then calcined at 450oCTiO2-SiO2: TiO(OC3H7)3

grafted on SiO2 then calcined at 450oCV2O5

(A)/TiO2-SiO2:VO(OC3H7)3 grafted on TiO2-SiO2 then calcined at 450oC

5 10 15 20 25 30 35

0

1000

2000

3000

4000

5000

6000

Inte

ns

ity

2

V2O5(A)/SiO2

V2O5(A)/TiO2-SiO2

V2O

5

TiO2

wavelength: 0.9537A

1. Apparance of anatase characteristic peaks TiO2 layer or clusters (about 5nm) formed on SiO2

2. No V2O5 characteristic peaks for V2O5(A)/TiO2-SiO2 and V2O5

(A)/SiO2 structure need to be characterized by EXAFS

11

Role of the grafted TiO2 in affecting vanadia structure investigated by EXAFS

0 1 2 3 4 5 6-6

-4

-2

0

2

4

6

Fo

uri

er

Tra

ns

form

R(0.1nm)

TiO2-SiO2 Anatase

Ti edge KWE=3Phase corrected by TiOf

Ti-OTi-O-Ti

4.27

1.933.78

3.04

Ti-O

2nd TiO shell contribution is insignificant suggesting formation of layer or isolated TiO2

Morphology of grafted-TiO2 on SiO2: clusters (d 5 nm)

12

1 2 3 4 5-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Fo

uri

er T

ran

sfo

rm

R(0.1nm)

V2O

5

(A)/SiO2

V2O

5

(A)/TiO2-SiO2 V2O5

Role of grafted TiO2 (1): morphology of vanadia characterized by EXAFS

V=OV-O

V-O-V

V-edge KWE=2Phase corrected by VO

Grafted TiO2 anchor vanadia from migration leading to a formation of Isolated vanadia species or rather small V2O5 clusters.

1.576

3.428

3.0801.879

13

Role of grafted TiO2 (2): surface acidity characterized by FT-IR

1700 1650 1600 1550 1500 1450 1400 1350 1300

-0.05

0.00

0.05

0.10

0.15

0.20

0.25L

V2O

5

(A)/SiO2

A

bs

orb

an

ce

wavenumber (cm-1)

SiO2(Q30)

V2O

5

(A)/TiO2-SiO2

L

L+BB

V2O5/SiO2 : vanadia block Lewis acid sites of silicaV2O5/TiO2-SiO2: vanadia anchoring on TiO2, hence no Lewis acid sites of SiO2 was covered.

14

Role of grafted TiO2 (3): catalytic properties characterized by total oxidation of 1,2 dichlorobenzene

150 200 250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1,2

-dic

hlo

rob

en

zen

e c

on

ve

rsio

n

reaction temperature(oC)

V2O5(A)/SiO2

V2O5(A)/TiO2-SiO2

150 200 250 300 350 400 450 500 550 6000.8

0.9

1.0

se

lec

tiv

ity

to

CO

plu

s C

O 2reaction temperature(oC)

V2O5(A)/SiO2

V2O5(A)/ TiO2-SiO2

1. Conversion is dominated by vanadia dispersion, while surface acidity influence total oxidation selectivity.2. Catalytic oxidation properties are improved by vanadia-TiO2 interactions.

feed ： 1,2-dichlorobenzene in air; WHSV ： 0.2hr-1 pressure ： 1 atm; temperature ： 250-550 oC

15

V2O5/TiO2-SiO2 structure proposed by EXAFS

0 1 2 3 4 5

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

Four

ier T

rans

form

R(0.1nm)

(a)

Shell Na Rb 1000×Δσ2c ΔE0d EXAFS optimal bond

distances (Å) (Å2) (eV) reference

V15-O16 1.0 1.6±0.1 -4±2 -2±2 V-O 1.68V15-O14,17,18 3.0 1.8±0.1 9±4 12±2 V-O 1.86

V15-O11 1.0 2.5±0.2 31±18 -8±6 V-O 2.59V15-Ti13 1.0 3.2±0.1 3±5 1±3 V-Ti 3.28V15-O2,4 2.0 3.3±0.1 5±4 5 V-O 3.34

V

Ti

O

O

TiO

OO

O

16

Morphology of vanadia on TiO2-SiO2 and SiO2

V2O5(A)/TiO2-SiO2: isolated VOx or layer V2O5 covered on TiO2

V2O5(A)/SiO2: V2O5 clusters to SiO2

Role of the grafted-TiO2

Anchor vanadia precursors (VO(OC3H7)3 thereby increasing vanadia dispersion and surface acidity

OVSiTi

V2O5(A)/TiO2-SiO2

V2O5(A)/SiO2

17

Effect of V precursor (1): morphology of vanadia characterized by EXAFS

V2O5(A)/TiO2-SiO2:VO(OC3H7)3 grafted on TiO2-SiO2 then calcined at 450oC

V2O5(C)/TiO2-SiO2:V(C2O4)2 impregnated in TiO2-SiO2 followed with calcination at 450oC

0 1 2 3 4 5-3

-2

-1

0

1

2

3

Fo

uri

er

Tra

ns

form

R (0.1nm)

V2O5(C)/ TiO2-SiO2

V2O5(A)/ TiO2-SiO2

V2O5

V edge KWE=3Phase corrected by VO

V2O5(A)/TiO2-SiO2 presents higher vanadia dispersion as opposed to

V2O5(C)/TiO2-SiO2

1.576

3.428

3.0801.879

18

Effect of V precursor (2):catalytic properties characterized by total oxidation of 1,2 dichlorobenzene

150 200 250 300 350 400 450 500 550 6000.0

0.2

0.4

0.6

0.8

1.0

1,2

-dic

hlo

rob

en

ze

ne

co

nv

ers

ion

reaction temperature(oC)

V2O5(A)/TiO2-SiO2

V2O5(C)/TiO2-SiO2

V2O5(A)/TiO2-SiO2 presents higher initial activity in comparing with

V2O5(C)/TiO2-SiO2 whereas lower as temperature was elevated.

feed ： 1,2-dichlorobenzene in air; WHSV ： 0.2hr-1 pressure ： 1 atm; temperature ： 250-550 oC

19

Thermal stability of V2O5(A)/TiO2-SiO2

Characterized by EXAFS

0 1 2 3 4 5-3

-2

-1

0

1

2

3

Fo

uri

er

Tra

ns

form

R (0.1nm)

V2O5(A)/ TiO2-SiO2 fresh

V2O5(A)/ TiO2-SiO2 300oC used

V edge KWE=3Phase corrected by VO

1. Growth of V2O5 clusters was observed for V2O5(A)/TiO2-SiO2 as reaction

temperature elevated to 300 oC 2. Catalysts prepared from alkoxides present higher vanadia dispersion whereas its thermal stability is lower.

20

Thermal stability of V2O5(C)/TiO2-SiO2

Characterized by EXAFS

V edge KWE=3Phase corrected by VO

No significant morphology change for V2O5(C)/TiO2-SiO2 after reaction

temperature elevated to 300 oC

Prepared from conventional V precursor-vanadium oxalate V(C2O4)2

21

Morphology: VO(OC3H7)3: V2O5

(A)/TiO2-SiO2; isolated VOx or layer V2O5 depositeded on TiO2 V(C2O4)2: V2O5

(C)/TiO2-SiO2; small V2O5 clusters bonded to SiO2 and TiO2 Reactivity: Initial Activity: V2O5

(A)/TiO2-SiO2 > V2O5(C)/TiO2-SiO2

Thermal stability: V2O5(C)/TiO2-SiO2 > V2O5

(A)/TiO2-SiO2

Effects of vanadia precurosrs

OVSiTi

V2O5(A)/TiO2-SiO2

V2O5(C)/TiO2-SiO2

22

Acknowledgements

Hwo–Shuenn Sheu, Jyh-Fu LeeNational Synchrotron Radiation Research Center, Taiwan

Hsi-Yen ChangDepartment of Chemical Engineering, National Chang Kung University

Shin-Guang ShyuInstitute of Chemistry, Academia Sinica, Nankan

Chia-Gin HungDepartment of Chemical Engineering, National Chung Cheng University

23

THANKS FOR

YOUR ATTENTION !