Effect of water in direct methane dehydroaromatization over 3%Mo/HZSM-5 under supersonic jet expansion condition B.S. Liu a, L. Li a, C.T. Au c, A.S.-C. Cheung a* a The University of Hong Kong, Pokfulam Road, Hong Kong, China c Hong Kong Baptist University, Kowloon Tong, Hong Kong, China

Acknowledgements: The work was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7015/07P). Prof. Bingsi Liu, Tianjin University, China Drs. Joanne W.H. Leung and Lynn L. Li, HKU Prof. C.T. Au, Hong Kong Baptist University

I. Introduction Energy Petroleum Coal Syngas Chemicals Aromatics Hydrogen Fuel cell NH 3

CH 4 Mo/HZSM o C C 6 H 6 C 7 H 8 C 10 H 8 + H2H2 The catalyst Mo/HZSM-5 needs to be activated during the induction period: H 2 O (< 2%) +

Problems ? (1) Activation of catalyst in induction period. (2) Carbon deposition over catalyst Non-traditional procedure CH 4 only ? Membrane reactor Supersonic jet expansion CH 4 + H 2 O ?

II. Experiment CH 4 dehydro-aromatization apparatus is coupled to a Time-of-flight (TOF) mass spectrometer. CH 4 dehydroaromatization apparatus – catalytic reaction TOF – detect and monitor reagents (CH 4, H 2 O) and reacted species (eg. C 10 H 8 ) etc.. Ionization of species by a pulsed laser (266 nm; 13 mJ) CH 4 dehydro-aromatization apparatus is coupled to a Time-of-flight (TOF) mass spectrometer. CH 4 dehydroaromatization apparatus – catalytic reaction TOF – detect and monitor reagents (CH 4, H 2 O) and reacted species (eg. C 10 H 8 ) etc.. Ionization of species by a pulsed laser (266 nm; 13 mJ)

Fig.1 Apparatus for CH 4 dehydroaromatization II. Experiment

III. Results and discussion Fig.2 Product distribution at different time on stream 1. Investigation on catalyst activation – CH 4

Effect of water during CH 4 dehydroaromatization (after the induction period) Fig.4 Effect of water on Mo/ZSM-5 catalyst; (A) 1.4%H 2 O; (B) 2.0%H 2 O; (C) Relative stability of catalyst.

Investigation on catalyst activation – CH 4 + H 2 O Figure 5 Direct addition of water in induction period of CH 4 dehydroaromatic reaction NO C 10 H 8 formation

Properties of coke under condition of H 2 O/CH 4 co-feed Fig.6 TPO profiles of used catalyst Fig.7 Amorphous carbon deposition over Mo 2 C particle. (TEM).

Fig.8 Carbon 1s XPS spectra used 3%Mo/HZSM-5 at different condition.

Fig.11 Mo 3d XPS spectra of 3%Mo/HZSM-5 samples 6. Properties of Mo 2 C at different H 2 O/CH 4 co-feed by XPS

VI. Conclusion: 1.Direct dehydroaromatization of methane over 3%Mo/HZSM-5 forms naphthalene under the supersonic jet expansion condition. In this work, the gas mixture exited from reaction zone was analyzed directly using TOF-MS. 2. An appropriate amount of steam co-addition to methane feed over Mo/HZSM-5 can improve the stability of catalyst. Carbon deposition was reduced with increasing steam concentration.

The results of TPO, XPS and HRTEM image demonstrate that the carbon deposition is basically amorphous in structure during the H 2 O/CH 4 reaction but the formation of graphite carbon when CH 4 was used only. 4. Addition of excess water (> 2%) led to the deactivation of Mo 2 C/HZSM-5 catalyst and the destruction of Mo 2 C.