Development of Pt/Zirconia

Catalyst for liquid phase HI

Decomposition Reaction in S-I

CycleDeepak Tyagi, Alisha Gogia, Salil Varma, A. K. Tripathi, S. R. Bharadwaj

Chemistry DivisionBhabha Atomic Research Centre, Mumbai

• Hydrogen as a future source of energy is a scenario of high probability and necessity, considering the ill-effects of fossil fuel based systems on the environment and also the depleting natural resources.

• The fast development of hydrogen based power sources like fuel cells will lead to more efficient and cleaner energy supply.

• For this to be economically feasible, large scale production of hydrogen has to be attained by environment friendly route.

Hydrogen as future fuelHydrogen as future fuel

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Origin Percent

Natural gas 48

Oil 30

Coal 18

Electrolysis 4

Total 100

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Today hydrogen is mainly produced from fossil resources.

In the long term, because ofincreasing energy demand,lack of fossil resourceslimitations on the release of green house gases

Water suitable raw materials for hydrogen production.

Production of Hydrogen:Production of Hydrogen:

The two processes that have the greatest likelihood of successful massive hydrogen production from water are (i) steam electrolysis (ii) thermochemical cycles.

This way hydrogen can be produced from water at temperatures much lower than the direct water decomposition at 3000 °C.

As heat can be directly used in thermochemical cycles, they have the potential of better efficiency than alkaline electrolysis.

The required thermal energy can be provided by nuclear reactor (CHTR).

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Production of Hydrogen from WaterProduction of Hydrogen from Water::

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Sulfur - Iodine Sulfur - Iodine

CycleCycle

Endothermic; T = 450 °CEndothermic; T = 870 °C

Exothermic; T = 120 °C

9I2 + SO2 + 16 H2O → (2HI + 10H2O + 8I2) + (H2SO4+ 4H2O)

Decomposition of hydriodic acid an integral part of Sulfur - Iodine and Magnesium – Iodine thermochemical cycle.

Homogeneous azeotrope in HI-H2O binary system and thermodynamically limited slow gaseous HI decomposition - highly energy consuming step.

1.The General Atomic Co. proposed use of phosphoric acid (Extractive Distillation) for concentration of the HI solution to obtain 99.7% molar HI vapour. But, concentration of recycled phosphoric acid consumes large amount of heat and electricity.

2.Employment of electro-electrodialysis concentration method and hydrogen permselective membrane reactor also reported by JAERI.

3.Reactive distillation - combining reaction and separation in a single step leading to overall shift of equilibrium towards production of I2 and H2. First reported by Roth et al in 1989.

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Hydriodic Acid Hydriodic Acid DecompositionDecomposition

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Catalyst reported for HI Catalyst reported for HI

decompositiondecompositionCeria IJHE 34(2009) 1688-

1695

Ni/Ceria IJHE 34(2009) 5637-5644

IJHE 34(2009)8792-8798

Ni/Alumina IJHE 34(2009) 4059-4056

Activated Carbon IJHE 34(2009) 4057-4064

Pt/Ceria IJHE 33(2008) 602 – 607

IJHE 33(2008) 2211-2217

Pt/Alumina Chinese chemical letters 20 (2009) 102-105

Pt/Ceria-Zirconia IJHE 35(2010) 445-451

“ D. R. O’keefe et al, Catalysis Reviews 22(3), 325-369 (1980)”

Objective of the present Objective of the present

WorkWork

• Develop Pt catalysts over Zirconia support (with different Pt loading)

• Demonstrate stability of the catalysts under the reaction conditions

• Evaluate activity of these catalysts for HI decomposition reaction

• Derive structure activity correlation for development of future catalysts

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Zirconium Hydroxide Gel

Dried at 100°C for 6h

Calcined at 350°C for 3h

Zirconia

(i) Add Chloroplatinic acid Dropwise With constant stirring(ii) Reduction by Hydrazine at RT(iii) Reduction by H2 flow at 300 °C

Platinum Zirconia Catalyst

Zirconyl Nitrate solution

NH4OH solution added dropwisewith constant stirring

Preparation of Preparation of CatalystCatalyst

Characterization:Characterization:

• XRD

• SEM

• FEG-SEM

• N2 Adsorption

• ICP OES

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X-Ray Diffraction:X-Ray Diffraction:

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10 20 30 40 50 60 70

020406080

100120

0.5 % Pt/ZrO2

Inte

ns

ity

10 20 30 40 50 60 70

020406080

100120

1 % Pt/ZrO2

10 20 30 40 50 60 70

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2 % Pt/ZrO2

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SEM & EDAX:SEM & EDAX:

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FEG-SEM:FEG-SEM:

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1% Pt/ZrO2 2% Pt/ZrO2

Adsorption and Desorption Adsorption and Desorption isotherms isotherms

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Pore Size Pore Size Distribution:Distribution:

1% Pt/ZrO2 2% Pt/ZrO2

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S. No

Sample Surafce Area

Pore Size

Pore Volume

1. ZrO2 108.64 3.62 0.1125

2. 1%Pt ZrO2 139.71 3.72 0.1573

3. 2%Pt ZrO2 133.47 3.72 0.1492

Surface Area:Surface Area:

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Activity & Stability of Activity & Stability of

CatalystsCatalysts50 ml of 27% HI + 250 mg of Catalyst

Heated for 2h at ~ 120oC

Filtered

Filtrate analyzed for presence of Pt by ICP-OES

&Used catalyst evaluated by XRD and

SEM.

Activity & Stability of Activity & Stability of CatalystsCatalysts

221

221 HIHI

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For liquid phase decomposition reaction, dissolution of

the I2 formed at catalyst surface into the iodide solution

as Ix- and continued intimate contact between HI and

catalyst maintains high reactivity levels even in presence

of I2.

Upto 50% conversion is reported by O’Keefe et al for 48h study at room temperature.

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Activity MeasurementActivity Measurement

H+ Titration I- Titration

Using Glass electrode Using Ag/AgCl electrode

Titration against NaOH Titration against AgNO3

NaOH was standardized using KHP

AgNO3 was standardized using NaCl

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Activity and stability of the Activity and stability of the

catalystscatalysts

S. No. Catalyst % Conversion

1. 0.5% Pt/ZrO2 13.9 %

2. 1% Pt/ZrO2 16.7 %

3. 2% Pt/ZrO2 18.5 %

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20 30 40 50 60 70

020406080

100120

Used 0.5% Pt/ZrO2

Inte

ns

ity

20 30 40 50 60 70

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100120

Used 1% Pt/ZrO2

20 30 40 50 60 70

0

20

40

60

80

100

Used 2% Pt/ZrO2

XRD Used Catalysts:XRD Used Catalysts:

Comparison with Pt/Carbon Comparison with Pt/Carbon catalystscatalysts

S. No.

Catalyst% Conversion(H+ Titration)

1 Pt/Gr 17.5 %

2 Pt/SBA 15.0 %

3 Pt/MCM-C 17.0 %

4 Pt/Zirconia 16.7 %

5 Pt/AC 12.1 %

6 Pt/FS-C 7.2 %

7 Blank 2.8 %

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ConclusionsConclusionsPt/Zirconia catalyst prepared was active for HI decomposition.

The percentage conversion is dependent on noble metal loading.

Catalyst prepared was found to be stable under liquid phase HI decomposition conditions.

Catalytic activity of Pt/Titania catalyst was better as compared to some of the Pt/C catalysts.

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