Consideration of literature indicated that the following components would be required for a low temperature TMO catalyst: ⢠Pd as it is the most active metal.
The role of the Pd(0)/PdO redox cycle and balance of support acidity and oxygen mobility in achieving lower temperature methane oxidation Ahmed Ibrahim Osman Dr. Jillian Thompson
Methane
As a fuel CH4 + 2O2 CO2 + 2H2O ΔH°= -802.3 kJmol-1 1. Abundant in land/sea reserves 2. Clean (compared to other fossil fuels) 3. Very high energy on combustion
Methane
As a fuel CH4 + 2O2 CO2 + 2H2O ΔH°= -802.3 kJmol-1 1. Abundant in land/sea reserves 2. Clean (compared to other fossil fuels) 3. Very high energy on combustion However… C-H bond extremely stable meaning complete combustion requires very high temperatures (>1000 °C).
Methane
As a pollutant Low temperature: Incomplete combustion to CH4 and CO
As a fuel CH4 + 2O2 CO2 + 2H2O ΔH°= -802.3 kJmol-1 1. Abundant in land/sea reserves 2. Clean (compared to other fossil fuels) 3. Very high energy on combustion However… C-H bond extremely stable meaning complete combustion requires very high temperatures (>1000 °C).
CH4 + H2O CO + 3H2 ΔH°= -185 kJmol-1 High temperature: Formation of NOx species N2 + O2 NOx
Methane
As a pollutant Low temperature: Incomplete combustion to CH4 and CO
As a fuel CH4 + 2O2 CO2 + 2H2O ΔH°= -802.3 kJmol-1 1. Abundant in land/sea reserves 2. Clean (compared to other fossil fuels) 3. Very high energy on combustion However… C-H bond extremely stable meaning complete combustion requires very high temperatures (>1000 °C).
CH4 + H2O CO + 3H2 ΔH°= -185 kJmol-1 High temperature: Formation of NOx species N2 + O2 NOx Catalytic combustion
CH4 + 2O2 CO2 + 2H2O • Improved exploitation of methane reserves as a fuel • Reduction in pollution from road vehicles
Aims and Objectives of this work are: • To prepare stable catalysts from a range of
components, derived from the literature, for low temperature total methane oxidation (TMO) • Test the activity of these catalysts and use basic characterisation to understand the importance of each component
Motivation from literature Consideration of literature indicated that the following components would be required for a low temperature TMO catalyst: • Pd as it is the most active metal • An acidic support
• An oxygen carrier • Pt to stabilise the Pd References: 1- W. Lin, Y.X. Zhu, N.Z. Wu, Y.C. Xie, I. Murwani, E. Kemnitz, Applied Catalysis B: Environmental 50 (2004) 59-66. 2- R. Burch, F.J. Urbano, Applied Catalysis A: General 124 (1995) 121-138. 3- S.S. Carstens JN, Bell AT, Journal of Catalysis 176 (1998) 136-142.
Motivation from literature Consideration of literature indicated that the following components would be required for a low temperature TMO catalyst: • Pd as it is the most active metal • An acidic support
• An oxygen carrier
5%Pd, 2%Pt, X%TiO2, /ZSM-5
• Pt to stabilise the Pd References: 1- K. Persson, A. Ersson, K. Jansson, N. Iverlund, S. Jaras, Journal of Catalysis 231 (2005) 139-150. 2- W. Lin, Y.X. Zhu, N.Z. Wu, Y.C. Xie, I. Murwani, E. Kemnitz, Applied Catalysis B: Environmental 50 (2004) 59-66. 3- O. M'Ramadj, D. Li, X. Wang, B. Zhang, G. Lu, Catalysis Communications 8 (2007) 880-884.
Some important publications using similar catalysts 1000
T10%
T10% / Space velocity
900
Space Velocity *100
800 700 600 500 400 300 200 100 0 Lopez
References:
Zhou
Lin
M'Ramadi
Janbey
Our work
Papers
1- R. Ramírez-López, I. Elizalde-Martinez, L. Balderas-Tapia, Complete catalytic oxidation of methane over Pd/CeO2– Al2O3: The influence of different ceria loading, Catalysis Today, 150 (2010) 358-362. 2- R. Zhou, B. Zhao, B. Yue, Applied Surface Science 254 (2008) 4701-4707. 3- W. Lin, Y.X. Zhu, N.Z. Wu, Y.C. Xie, I. Murwani, E. Kemnitz, Applied Catalysis B: Environmental 50 (2004) 59-66. 4- O. M'Ramadj, D. Li, X. Wang, B. Zhang, G. Lu, Catalysis Communications 8 (2007) 880-884. 5- A. Janbey, W. Clark, E. Noordally, S. Grimes, S. Tahir, Chemosphere 52 (2003) 1041-1046.
Activity Data - 5%Pd, 2%Pt, X%TiO2 on ZSM-5(80) 100
Conversion of Methane, %
0% 80
5% 10%
60
17.50% 25%
40
35% 46.50% 20
68% 83%
0 200
250
300
350
400
450
Reaction Temperature
At high and low TiO2 loading the reaction is limited by mass transfer. Activity increased with increasing TiO2 loading but then decreased.
500
550
Optimum activity 70
Conversion of Methane, %
60
50
40
30
20
10
0 0
10
20
30
40
50
60
TiO2, wt%
The activity reached a maximum when the TiO2 loading was 17.5%.
70
80
90
Proposed role of each component
XRD Analysis – PdO peak 0% 5%
Intensity (a.u.)
10% 25% 46.50% 68% 83%
32
34
2θ(°)
36
TCD signal
TPR Analysis
-20
80
180
280
380
480
580
Temperature °C
TiO2 peak at 480ᴼC, decreasing to the range of 220 to 420 °C for all the catalysts with TiO2 Low TiO2 loading – PdO peak only Medium TiO2 – positive PdO and negative beta hydride are present. High TiO2 loading - less PdO – and this is supported by XRD
TCD signal
TPR Analysis
-20
80
180
280
380
480
580
TCD signal
Temperature °C 17.5% -20
80
180
280 Temperature °C
380
480
580
The importance of the interaction between all phases 100 90
% Conversion of Methane
80 70 60 50 40 30 20 10 0 200
300
400
500
Temperature °C
Figure 6: The effect of metal loading for 17.5%TiO2 (0.05 g), 5 wt% Pd, 2 wt% Pt, H-ZSM-5(80) with 17.5 wt% TiO2 () and Cat 12 (0.05 g), 1 wt% Pd, 0.4 wt% Pt, H-ZSM-5 with 18.6 wt% TiO2 (). The bed for the diluted catalyst consisted of 17.5%TiO2 (0.01 g) and H-ZSM-5(80) (0.04 g) ().
Stability Test 70
60
% conversion of methane
50
40
30
20
10
0 0
10
20
30
40
50
Time on stream [h]
Figure 7: Comparison of the stability of 17.5%TiO2, (), 25%TiO2 () and 7% Pd catalyst () all prepared with sonication and 17.5%TiO2 prepared without sonication ().
60
SEM analysis
0%TiO2
5%TiO2
17.5%TiO2
46.5%TiO2
83%TiO2
Mechanically mixed
The activity reached a maximum when the TiO2 loading was 17.5%.
Conclusion 1- Natural gas is considered as an alternative to petroleum for the production of synthetics fuels and also a robust catalyst. 2- The acidity of the support increases the electrophilicity of the Pd(0) species thereby facilitating its reoxidation. 3- the presence of the oxygen carrier ensures a supply of oxygen as well as improving oxygen mobility for both the oxidation and reduction processes. 4- The presence of Pt and use of sonication in catalyst preparation results in a highly stable catalyst. 5- By optimising the acidity and oxygen supply a catalyst which shows high
activity for the TMO at 200 °C can be obtained, one of the lowest reported temperatures.
Acknowledgements Professor David Rooney Dr Jillian Thompson Dr Jehad Abu-Dahrieh Dr Teresa Curtin Dr Fathima Laffir
Further readings A.I. Osman, J.K. Abu-Dahrieh, F. Laffir, T. Curtin, J.M. Thompson, D.W. Rooney, A bimetallic catalyst on a dual component support for low temperature total methane oxidation, Applied Catalysis B: Environmental, 187 (2016) 408418. http://www.sciencedirect.com/science/article/pii/S 0926337316300200
