Chemical Reaction Engineering Group (CREG) N01-Faculty of Chemical Engineering

Universiti Teknologi Malaysia UTM 81310 Johor Bahru, Johor Malaysia.

noraishah@cheme.utm.my 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.

noraishah@cheme.utm.my www.cheme.utm.my/staff/noraishah