Synthesis, Characterization and Catalytic Activity of Ru-N-C Hy-brid Nanocomposite for Ammonia Dehydrogenation

Thesis for the Degree of Master

Nguyen Thi Bich Hien

Advisor: Dr. Chang Won Yoon

Fuel cell Research Center,Korea Institute of Science and Technology,

Clean Energy and Chemical Engineering Korea University of Science and Technology,

May 21, 2015

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Contents

Introduction and research objectives

Experimental

Results and discussion

Conclusions

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2

3

4

3

1Introduction

Contents

4

IntroductionIntroduction: Hydrogen as a future energy carrier

Searching for renewable energiesSolar

energy

Biomass en-ergy

Wind energy

Geother-mal en-

ergy

Hydro-gen en-ergy

Exhaust of fossil fuel & environmental hazards

http://www.britannica.com/

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Introduction: Why hydrogen storage important?

Methane

Wind

Solar

Electrolysis

Reformer

Water

Oxygen

HydrogenStorage

Hydrogen

Fuel cell

Hydrogen production

Hydrogen utilization

Hydrogen Economy

Hydrogen Economy Hydrogen

storage

Renewables energy

5

6

Introduction: Hydrogen Storage Technology

Hydrogen storage

Physical-based Chemical-based

Com-pressed-

GasLiquid

Cryo-ad-sorption

Metal hy-drides

Chemical hydrides

NH3NH3BH3 HCOOH CH3OH etc.

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Introduction: Ammonia as hydrogen career

Dehydrogenation

High hydrogen density (17.8wt%)

Carbon-free chemical energy

Developed technology for synthesis (Haber-Bosch process)

Solid ammine complexes

The capital and operating cost of the NH3 facility cheaper than H2 (20.2 M$ & 63.2 M$, respectively).

7J. Mater. Chem., 2008, 18, 2304–2310

NH3 Dehydrogenation Requires “Catalysts”

Thermodynamically, 98-99% conversion of ammonia to hydrogen is possible at temperatures as low as 425 °C.

2NH3 3H2 + N2 H △ = 46kJ/mol Ammonia decomposi-

tion

It is necessary to develop the catalyst for ammonia dehydrogenation 8

450 475 500 525 550

0

20

40

60

80

100

Temperature (oC)

NH

3 c

onve

rsio

n (%

)

No catalyst

Literature Precedents: Controlling Factors

2NH3 3H2 + N2 H △ = 46kJ/mol Ammonia decomposi-

tion

(1) Influence of Metals:

Ru

Ru > Rh > Ni > Pd Pt > Fe≒

RhNiPd, Pt

S.F. Yin et al., Appl. Catal. A 277 (2004) 1-9S.F. Yin et al., Appl. Catal. 244 (2004) 384-396

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Literature Precedents: Controlling Factors

2NH3 3H2 + N2 H △ = 46kJ/mol Ammonia decomposi-

tion

(2) Influence of Supports:

J. Mater. Chem. A, 2014, 2, 9185–919210

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Rate Determining Step (recombinative desorption of N)

Literature Precedents: Controlling Factors

Chem. Chem. Phys., 2011, 13, 12892–12899 Lee, J.H at all, Inorg. Chim. Acta 2014, 422, 3-7.

Increase electron den-sities of metal

N, K doping ba-sic support

Enhance recombinative desorption of N

(3) Influence of Dopant:

Schematic diagram of synthetic proce-dure of Fe–N–C

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Catalyst Design: “Ru-N-C Hybrid Materials”

Metal : Ru – highly activity for ammonia decomposition

Support : black C sphere – cheap & high surface areas

Promoter : N – increase electron density of metal

N-doped Carbon as supports

Ru

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2 Experimental

Contents

▪ Preparation Catalyst

▪ Reaction design

Experimental – Preparation of catalyst

1 Gram

black C RuCl3.xH20

0.25 Gram

dicyanamide

1 Gram

20 ml H2O

100oC4h

550oC, 4 h in N2ICP

Ru-N-C

0.97 wt%

Ru-C 0.88 wt%

Ru3+ chelated composites

Ru-N-C nanocomposite

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NC RuC RuCN

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Reaction conditionsCatalyst : 100mg, Reduction : 50% H2/N2, 550 , 1h; NH℃ 3 purity :10%, flow rate : 37 mL/min, Temp. : 400 - 550℃ ℃

2NH3 3H2 + N2 H △ = 46kJ/mol Ammonia decomposi-

tion

Experimental – Ammonia cracking process

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Contents

Results & Discussion

▪ Characterization results

▪ Catalytic activity

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Ru-N-C

a

b

aCharacterization: Morphological analysis

17N-containing helped metal dispersion

5nm

20 nm

Hollow graphitized structure

Aggregation Ru

Ru-C

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TEM image & EDX spectrum of Ru-N-C and elements mapping

Characterization: Morphological analysis

Ru, C, and N were well dispersed over the catalyst 18

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25.2°: Carbon sphere

Characterization: XRD

Scherrer equation

Ru particles size (nm)

Ru-N-C 1.3

Ru-C 5.1 19

101

002

Ru

102

110 10

3210

002

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BET surface area, pore size, pore volume of the Ru-based catalysts

Catalyst

BET Surface

Areaa

(m2g-1)

Pore Sizea

(nm)

Pore Volumea

(cm3g-1)

Ru-N-C 898 4.7 1.05

Ru-C 1,110 5.4 1.57 aDetermined by physical adsorption using N2

Surface area of Ru-N-C smaller than Ru-CA slight reduction of the pore size and pore volume in Ru-N-C

Characterization: Textural Properties

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Graphitic

C-O

Graphitic

C(sp2)-N

C(sp3)-N

NitrilePyrrolic

Pyridinic

Characterization: XPS analysis (C1s & N1s)Ru-C

390 400 410

1680

1700

1720

1740

1760

1780

Binding energy (eV)

Inte

nsi

ty (

a.u

.)

N1s

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Ru-N-C

N atoms were introduced into the graphitic structure upon pyrolysis.

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Ru-C

Ru-N-C

Ru 3d

Ru 3d

Characterization: XPS analysis (Ru3p & Ru3d)

Ru-N-C

Ru-C

RuO2

RuO2·xH2O

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RuO2

RuO2·xH2O

Ru-N-C appeared at lower binding energy compared to that of Ru-C the incorporated nitrogen atoms donated electron density into the Ru active sites.

281.1

280.9

23 The activity of Ru-N-C > Ru-C> N-C

Catalytic activity: Influence of temperatureNH3 conversion

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95%GHSV: 7,448 mLg-1h-1

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GHSV 400 oC 450 oC 500 oC 550 oC

2,234 0 44.7 97.7 99.7

4,469 0 27.8 86.8 99.2

7,448 0 0 55.9 94.5

11,172 0 0 31.2 81.5

Catalytic activity: Influence of GHSV & Temp .

500 oC

450 oC

400 oC

550 oC

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GHSV (mLg-1h-1)

NH3 conversion of Ru-N-C increased as GHSV decreased H2 release properties improved as temperature increased

99.7%

81.5%

500 oC; GHSV = 7.448 mLg-1h-1

79%

61%

36% 19%

Catalytic activity: Long-Term Stability

Initially, NH3 conversion started at 79% for Ru-N-C and 19% for Ru-C, a significant difference by 60%.

After 80h, Ru-N-C slightly decreased by 18% while Ru-C increase by 20% Hypothesis: The reactant NH3 acted as a N-doping agent in Ru-C

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HAADF STEM images of Ru-C following the long-tem sta-bility test for 80 h and elemental mapping

Post-analysis of the spent-catalyst:

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Nitrogen0.82wt%

The reactant NH3 acted as a N-doping agent in Ru-C

b) c)

Post-analysis of the spent-catalyst: Continued

Ru-N-C

Fresh

a)

b) c)

d)

Ru-C

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Fresh after reaction for 80 h

Fresh after reaction for 80 h

The graphitic hollow structure are stable during long term reaction. Ruthenium particles in Ru-N-C slightly agglomerated even after 80 hours.

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The improved activity for H2-release from NH3 over Ru-N-C may originate from the incorporation of N species that contributed to:

• The formation of the small-sized Ru nanoparticles by initially anchoring the Ru3+ precursor to prevent them from sintering

• Enhancing the thermal stability of the catalyst

• Increasing the Ru electron density induced by the interaction between Ru & N

Summary

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Contents

Conclusions3

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• The simple synthetic strategy presented herein provides an economical route for large-scale production of the highly active Ru-N-C catalyst.

• The Ru-N-C catalyst displayed excellent performance for NH3 dehydrogenation with high stability.

• The incorporated nitrogen atoms were proposed to play pivotal roles in: Generating uniformly distributed, small-sized Ru nanoparticles. Improving the thermal stability of the catalyst. Donating electron density to Ru via electronic interactions between Ru and N.

The as-developed Ru-N-C hybrid nanocomposite is thus applicable for on-site hy-drogen production from ammonia with relevant catalyst optimization, and further provides insight for the development of various M-N-C catalysts (M = transition metals) for a number of chemical transformations.

Conclusions

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ACKNOWLEDGEMENTThanks to:Advisor: Prof. Yoon Chang Won

Committee members:Prof. Ham Hyung ChulProf. Kim Jin Young

All group members current and past, friends and family:Dr. Kim Young Jeon, Dr. Park Nan Hee, Dr. Lee Jin Hee, Dr. Jeon Mina, Muhammad Ridwan, Kim Hyo Young.

All of our laboratory’s facilities: stations, chemicals,…

For their help and support me during my re-search period in the past 2 years! 30

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Contents

BACKUP SLIDES4

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Benefits of hollow carbon doped N

Hollow nanostructures: Low density High surface-to-volume ration Shell permeability

Hollow carbon nanospheres: Cheap, nontoxic Good chemical stability Good Electrical conductivity- chemical inertness

Carbon nanomaterials with nitrogen: Increase the surface polarity Enhance electrical conductivity & surface basic sites and electron- donor tendency of the carbon matrix

Chem. Commun., 2014, 50, 329

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• Pyridinic N bonds with two C atoms at the edges or defects of graphene and contributes one p electron to the π system; sp2 hybridized

Lowest barrier for electron transfer; coordinate with transition metals.

• Pyrrolic N refers to N atoms that contribute two p electrons to the π system; sp3 hybridized

Nitrogen bonding configurations

Journal of Catalysis 239 (2006) 83–96

ACS Catal. 2012, 2, 781−794

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Ru-N-C indicated reasonable stability up to 500 °C while the decomposition of Ru-C was initiated at 380 °C

The TGA pattern of Ru-C-N and Ru-C.

Characterization: Thermal stability

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380 °C

500 °C

heat 10 °C/min, un-der N2

0 200 400 600 8000

20

40

60

80

100W

eigh

t los

s (%

)

Temperature (oC)

FWHM of D band

FWHM of G band

ID/IG

Ru-C 157.8 100.5 1.15

Ru-C-N 190.1 109.3 1.09

Result & Discussion RAMAN

The ID/IG values of N-C support < C a more graphitic structure & increase the ratio of sp2 to sp3 bonds.

Increase FWHM of D peak increase defect due to N doped on carbon

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Dicyandiamide, 5g +H3B─NH3, 0.25g

+Carbon black, 5g

+RuCl3.xH2O, 0.25g

1) Oil bath 80oC, 6h

2) 550oC, N2

Ru-N-B-C

1) Oil bath 80oC, 6h

2) 550oC, N2

N-B-C

N-B-C, 1g

Y. Wang et al. Chem. Sci. 2011, 2, 446-450.

+ Boron

J. Mater. Chem. A, 2014, 2, 16645–16651

Synthesis of Boron Nitrogen co-doped carbon

RESEARCH PLAN

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BmimPF6, 0.50g

Dicyandiamide, 5g +

+Carbon black, 5g

Y. Zhang et al. J. Am. Chem. Soc. 2010, 132, 6294-6295.

+RuCl3.xH2O, 0.25g

1) Oil bath 80oC, 6h

2) 550oC, N2

Ru-N-P-C

N-P-C, 1g

1) Oil bath 80oC, 6h

2) 550oC, N2

N-P-C

Synthesis of Doped Ru-NP-C

RESEARCH PLAN