effects of vanadia structure for dcb oxidation
TRANSCRIPT
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 !