carbon dioxide reduction with hydrogen using photonanocatalyst · water splitting . monolith...
TRANSCRIPT
Chemical Reaction Engineering Group (CREG) N01-Faculty of Chemical Engineering
Universiti Teknologi Malaysia UTM 81310 Johor Bahru, Johor Malaysia.
[email protected] www.cheme.utm.my
Carbon Dioxide Reduction with Hydrogen Using Photonanocatalyst
Nor Aishah Saidina Amin
Presentation Outline
• Background of Study • Research Scope • Methodology • Results and Discussions • Conclusions • Acknowledgement
Global anthropogenic greenhouse gas emissions broken down into 8 different sectors. [http://en.wikipedia.org/wiki/Greenhouse_gas]
Majour contributors
Background
• Energy consumption has been increasing with world population
• Fossil fuels are the main source of energy supply
• Reserves of fossil fuel is fossil depleting Combustion of fossil fuels generates greenhouse CO2
Background
Fossil fuel Combustion
Greenhouse
Gas CO2 Energy
Crisis and Global
Warming
How?
(i) How CO2 can be re-utilized easily and efficiently (ii)How CO2 can be recycled or converted to fuels
Mitigation of Greenhouse Gas CO2
6
Conversion of Carbon Dioxide
Biological (EtOH, sugar, CH3COOH)
Electrochemical (EtOH, HCOOH,
CO)
Photocatalysis (CO, CH4, HC,
MeOH, HCOOH)
Thermal reforming
Plasma reforming
Reforming (CO, H2)
Recycling of CO2 to Fuels
• Required higher temperature and pressure
• Thus, instability of catalysts and uneconomical
• Required electricity for the process
• Required high voltage and cause fouling on electrode surface
• Required biocatalyst
• Required very specific conditions
• Specific bioreactors
• Short life time of biocatalyst
• Workable under solar energy
• Economical process
• Required normal temp and pressure
• Sustainable process
• High stability of catalysts 6
Semiconductor Material
Photocatalytic Reactor
Reducing Agent
Photocatalysis System
Efficient Phototechnology for CO2 Reduction
• Higher photonic Efficiency, • higher illumination area
• Have good photoactivity • Higher charger production • Lower charges recombination
• Can easily be oxidized • Can reduced CO2 • Can help to produce • desire products
Hydrogen Reductant
Plasmonic PhotoCatalysts
Monolith Photoreactor
What we are Offering??
9
Hydrogen Reducing Agent
,2 2 2CO H CO + H Ohv catalyst+ → (RWGS reaction)
,2 2 2 4 22CO +6H C H + 4H Ohv catalyst→
,2 2 2 6 22CO +7H C H + 4H Ohv caalyst→
,2 2 3 6 23CO +9H C H +6H Ohv catalyst→
,2 2 3 8 23CO +10H C H + 6H Ohv catalyst→
Single step F-T process
• Hydrogen is good reducing agent for CO2 conversion via RWGS reaction
• Syngas (CO and H2) can be used for F-T process
• CO2 reduction with H2 can also be produced hydrocarbons in single step.
• H2 for CO2 reduction can be obtained from water splitting
Monolith Photoreactor √ It has microchannels of
different shape and sizes √ Light distribution is
effective over the catalyst surface.
√ Larger surface area to reactor volume.
√ Catalyst loading is higher with enhanced stability.
√ Very suitable for systems operating in gas- solids.
√ Larger conversion with improved selectivity.
√ Higher quantum efficiency
√ Higher light distribution over the catalyst
Monolith
10
Honeycomb, foam or fibers structure Channels have square, circular, and triangular Density varies from 9 to 600 cells per square inch
(CPSI) Higher void fraction (65 to 91 %) compared to
packed bed catalyst (36 to 45 %)
11
LSPR of Au
(a)
(b)
Plasmonic Au/TiO2 Photonanocatalyst
TiO2
When the incident light is (in the range of LSPR) absorbed by Au- metal NPs, electric filed (e-/h+ ) is produced (Fig. a)
Plasmonic electrons are transferred to TiO2 CB band for its activation (Fig. B)
Efficient separation of electrons Efficient CO2 reduction via SPR
effect Higher efficiency for trapping
electrons Au can enhance efficiency under
UV and visible light
Schematic of Monolith Reactor
Experimental Rig
Experimental Setup
Monoliths
Catalyst Preparation and Coating
Hydrolysis
Au-loading
Dip-coating
Drying and Calcination
Ti (C3H7O)4 + isopropanol
Acetic acid + isopropanol
Gold chloride + isopropanol
Aging
Monolith
Calcined at 500oC for 5h @ 5oC/min
Dried at 80 oC for 24 h
SEM and TEM Analysis
• Uniform coating of catalysts over the monolith surface
• TiO2 particles are spherical in shape and uniform size
• Au/TiO2 have mesoporous structure
TEM images of Au/TiO2 exhibit uniform particle size and mesoporous structure of TiO2
TiO2 d-spacing confirmed anatase TiO2.
TEM (Au/TiO2) SEM
TiO2 Au/TiO2
Front view Side View
10 20 30 40 50 60 70 80
Inte
nsity
(a.u
)
2-Theta (degree)
TiO2
0.2% Au-TiO2
0.3% Au-TiO2
0.5% Au-TiO2
0.0 0.2 0.4 0.6 0.8 1.0
0
20
40
60
80
100
120
140
160
Relative pressure (P/Po)
Vol
ume
adso
rbed
(cm
3 /g a
t STP
)
TiO2
0.3 wt.% Au/TiO2
0.5 wt.% Au/TiO2
200 300 400 500 600 700 800
Abso
rbanc
e (a.u
)
Wavelength (nm)
TiO2
0.3% Au/TiO2
0.5% Au/TiO2
(a) (b)
(c)
XRD
UV-Vis
BET
XRD, BET and UV-Vis Analysis
Plasmon effect
(a) Anatase phase in TiO2 and Au/TiO2 samples
(b) N2 adsorption-desoprtion plots show isothersms of type IV, confirming mesoporous materials of TiO2 and Au/TiO2
(c) UV-Visible analysis confirmed Plasmonic effect in Au/TiO2 catalyst
A
A A A
A=anatase
Summary of Analysis
Element B.E (eV) State Ti2p 459.50
465.20
Ti4+
Au4f 83.86
88.12
Au
O1s 530.72
532.94
O-O
O-H C1s 284.60
286.05
C-C
C-O
Catalysts
BET surface area
(m2/g)
BJH adsorption
surface area (m2/g)
BJH pore volume
(cm3/g)
Crystallite size (nm)
Band gap energy
(eV)
TiO2 43 52 0.134 19 3.12 0.3 wt.% Au- TiO2
46 58 0.23 17 3.03
0.5 wt.% Au-TiO2
47 74 0.24 18 2.93
Au has no effect on BET surface area
Au has no effect on Crystallite size
Band gap energy shifted to visible region in Au/TiO2
Gold was present over TiO2 in metal state
Table 1
Table 2
Nanocatalyst
• Plasmonic Au/TiO2 registered significantly enhanced CO production activity over irradiation time
• Optimum Au-loading of 0.5%Au was determined
• Maximum yield of CO was 12445 µmole g-catal.-1
• Steady sate process achieved after 2h of i di i i
0 2 4 6 8 10
0
2000
4000
6000
8000
10000
12000
14000
16000
Yield
of C
O (µ
mole
g-ca
tal.-1
)
Irradiation time(h)
TiO2
0.2% Au-TiO2
0.3% Au-TiO2
0.5% Au-TiO2
0.7% Au-TiO2
0 2 4 6 8 100
2
4
6
8
10
12
14
16
18
20
22
24
Yie
d of
CH
4 (µ
mol
e g-
cata
l.-1)
Irradiation time (h)
TiO2
0.2% Au-TiO2
0.3% Au-TiO2
0.5% Au-TiO2
0.7% Au-TiO2
CO production CH4 production
(a) Maximum production of CH4 initially (b) CH4 production decreased due to photo-
oxidation back into CO2 by O2 produced over catalyst surface
(c) Saturation of catalyst sites with intermediate species or deactivation of catalyst
(d) photo-reduction of products back to CO2.
(a) (a)
Photoactivity Test of Continuous CO2 Reduction to CO
Fig. Effects of Au-loading and irradiation time on CO2 reduction with H2 at CO2/H2 ratio 1.0, molar flow rate 20 mL/min, and temperature 100oC; (a) CO production, (b) CH4 production.
Summary of Results
C2H4 C2H6 CH4 CO0
20
40
60
80
100
Selec
tivity
(%)
Products
TiO2
0.5 wt.% Au/TiO2
(b)
TiO2 0.2% Au-TiO2 0.3% Au-TiO2 0.5% Au-TiO2 0.7% Au-TiO20
500
1000
1500
2000
2500
3000
3500
4000
4500
Yield
rate
(µm
ole g
-cat
al-1 h
-1)
Photocatalysts
CH4
CO
(a)
Fig. (a ) Yield rates of products over Au/TiO2 catalysts
Fig. (b) Selectivity of products over Au/TiO2 catalysts.
318 fold
0.5% Au/TiO2
TiO2
CO selectivity 92% to 99%
Catalyst Stability Test
a= CO production
(a) In the cyclic runs over prolonged irradiation time, higher stability of catalysts
(b) In second and third cycles, photoactivity slightly reduced (c) Decreased in photoactivity of Au/TiO2 catalyst was possibly due to active
sites blockage with intermediate species.
0 2 4 6 8 10
0
2000
4000
6000
8000
10000
12000
14000
Yie
ld o
f C
O (
ppm
)
Irradiation time (h)
Cycle R-1 Cycle R-2 Cycle R-3
0 2 4 6 8 100
1
2
3
4
5
6
7
8
0 2 4 6 8 10
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Yie
ld o
f CH
4 (pp
m)
Irradiation time (h)
Cycle R-1 Cycle R-2 Cycle R-3
Yie
ld o
f C2H
6 (pp
m)
Irradiation time (h)
Cycle R-1 Cycle R-2 Cycle R-3
b= hydrocarbons production
CH4 C2H6
Conclusions Enhanced efficiency of monolith photoreactor for CO2
reduction to fuels Efficient CO2 reduction with H2 to CO and HCs over
Au/TiO2. Yield of CO production over Au/TiO2 increased to 318
times higher than TiO2 Selectivity of CO production reached above 99% by Au Enhanced Au/TiO2 activity was due to plasmonic effect Efficient trapping of electrons and inhibited charges
recombination by Au-metal Tests revealed prolonged stability of Au/TiO2 in cyclic
runs.
Acknowledgements
Ministry of Higher Education (MOHE) Malaysia for financial
support under NanoMite LRGS (Long-term Research Grant
Scheme , Vot 4L839),
Universiti Teknologi Malaysia (UTM) for the RUG (Research
University Grant, Vot 02G14) and
FRGS (Fundamental Research Grant Scheme, Vot 4F404).
THANK YOU FOR YOUR ATTENTION
Chemical Reaction Engineering Group (CREG) N01-Faculty of Chemical Engineering
Universiti Teknologi Malaysia UTM 81310 Johor Bahru, Johor Malaysia.
[email protected] www.cheme.utm.my/staff/noraishah