62 nd OSU International Symposium on Molecular Spectroscopy

62 nd OSU International Symposium on Molecular Spectroscopy CH 4/CO 2 reforming over La 2 Ni. O 4 and 10%Ni. O/Ce. O 2 La 2 O 3 catalysts under the condition of supersonic jet expansion via cavity ring down spectroscopic analysis B. S. Liu 3, Ling Li 1, J. W-H Leung 1, C. T. Au 2 and A. S. -C. Cheung 1 1 2 3 Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China Department of Chemistry and Centre for Surface Analysis and Research, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China Department of Chemistry, Tianjin University, Tianjin 300072, P. R. China

62 nd OSU International Symposium on Molecular Spectroscopy Outline Ø Introduction Ø Experimental Details Ø Results and Discussion Ø Conclusion

62 nd OSU International Symposium on Molecular Spectroscopy Introduction Ø Methane is available in huge quantity, besides burning, there are many way to utilize it. CO 2 reforming : CH 4 + CO 2 catalyst 2 CO +2 H 2 Synthesis gas CO + 3 H 2 Synthesis gas Steam reforming: CH 4 + H 2 O Coupling reaction: CH 4 + CH 4 Aromatization: n. CH 4 C 2 H 6 + etc… C 6 H 6 , C 10 H 8 + …

62 nd OSU International Symposium on Molecular Spectroscopy Ø Numerous studies on CH 4/CO 2 reforming reaction using various Ni-based catalysts. cat. CH 4 + CO 2 → 2 CO +2 H 2 Problems: Synthesis gas (i) Low yield ( ~55%) (ii) Carbon deposit (~after 1 hour)

62 nd OSU International Symposium on Molecular Spectroscopy Our studies: Ø Study CH 4/CO 2 reforming at a short time scale of ca. 10 -3 s using supersonic free jet expansion. Ø Investigate the change in reactants (CH 4 and CO 2), product (CO) and associated-product (H 2 O) by cavity ring-down spectroscopy. Ø Compare the performance of two catalysts: La 2 Ni. O 4 and 10% Ni. O/Ce. O 2 -La 2 O 3 catalysts Ø Investigate reverse-water-gas-shift (RWGS) reaction over La 2 Ni. O 4 catalyst during CH 4/CO 2 reforming Associated reaction: CO 2 + H 2 CO + H 2 O

62 nd OSU International Symposium on Molecular Spectroscopy Part I Cavity ring down spectroscopic study of CH 4/CO 2 reforming over La 2 Ni. O 4 and 10 % Ni. O/Ce. O 2 -La 2 O 3 catalysts

62 nd OSU International Symposium on Molecular Spectroscopy Nd: YAG Laser Experimental setup for studying CH 4/CO 2 reforming using supersonic jet expansion and cavity ring down spectroscopy

62 nd OSU International Symposium on Molecular Spectroscopy Experimental Conditions v Pump laser Nd: YAG laser output 532 nm, 400 m. J, 10 Hz v Pulsed dye laser Wavelength range : 610 – 710 nm 50 m. J (using DCM and LDS 698 dye) v Raman shift tube Gas: Hydrogen (~120 psi, 2 nd order Stoke line) Wavelength range: 1. 2 -1. 5 m (near IR region) Energy: < ~ 1 m. J v Detector In. Ga. As photodiode- near IR region

62 nd OSU International Symposium on Molecular Spectroscopy Vibration-rotational absorption lines in the near infrared spectral region as detected in CRDS analysis. Spectral Molecul Point Group Vibrational region (cme symmetry transition 1) Rotational transition CH 4 Td 7480 -7500 J = 0 (Q branch) H 2 O C 2 v 7485. 1 63, 3 – 51, 4 CO 2 D h 6357 - 6370 R(12) – R(34) CO C h 6357 - 6368 3 -0 R(1) – R(4)

62 nd OSU International Symposium on Molecular Spectroscopy CRDS spectra of CH 4/CO 2 reforming reaction CRDS signal of CH 4 consumption ( ) and water formation ( ) recorded over La 2 Ni. O 4 at different temperatures.

62 nd OSU International Symposium on Molecular Spectroscopy CRDS signals of CO 2 ( ) consumption and CO ( ) formation observed over (i) La 2 Ni. O 4 and (ii) 10%Ni. O/Ce. O 2 -La 2 O 3, respectively in different temperature.

62 nd OSU International Symposium on Molecular Spectroscopy CRDS spectra of CO ( ), CO 2 ( ), CH 4( )and H 2 O ( ) over catalysts at 700 o. C at different time on stream. La Ni. O 2 4 10% Ni. O/Ce. O 2 -La 2 O 3

62 nd OSU International Symposium on Molecular Spectroscopy Conversion of CH 4 ( ) and CO 2 ( ) over La 2 Ni. O 4 and conversion of CH 4 ( ) and CO 2 ( ) over 10%Ni. O/Ce. O 2 -La 2 O 3 , estimated based on peak areas. (Inset is the conversion of CH 4 and CO 2 observed over 10%Ni. O/Ce. O 2 -La 2 O 3 on a conventional reactor under the same condition).

62 nd OSU International Symposium on Molecular Spectroscopy v We found that La 2 Ni. O 4 is superior to 10% Ni. O/Ce. O 2 La 2 O 3 in performance v Initial conversion (jet condition) of CH 4 and CO 2 is 68% and 82% for La 2 Ni. O 4 catalyst 48% and 75% for 10% Ni. O/Ce. O 2 -La 2 O 3 Traditional condition: 58% and 71% for 34% and 50% for La 2 Ni. O 4 catalyst 10% Ni. O/Ce. O 2 -La 2 O 3 v We also observed an increase in H 2 O signal with time-onstream, which could be a result of the RWGS reaction being favorable under jet condition

62 nd OSU International Symposium on Molecular Spectroscopy Part II Time of flight mass spectroscopic study of CH 4/CO 2 reforming over La 2 Ni. O 4 and 10 % Ni. O/Ce. O 2 -La 2 O 3 catalysts

62 nd OSU International Symposium on Molecular Spectroscopy Schematic diagram of CH 4/CO 2 reforming under supersonic jet expansion via time of flight mass spectroscopy

62 nd OSU International Symposium on Molecular Spectroscopy Experimental Details (i) Background pressure source chamber ~ 5 10 -6 torr ionization chamber ~ 3 10 -6 torr (ii) Backing pressure = 6 atm (iii) Ionization Laser Nd: YAG laser, 10 Hz, 266 nm (5 -6 m. J) (iv) Detector Microchannel plate (MCP)

62 nd OSU International Symposium on Molecular Spectroscopy TOF-MS signals of products at 620 o. C: (a) exposure to CH 4 for 5 min, (b) exposure to CH 4 for 30 min, (c) exposure to CO 2 for 5 min, and (d) exposure to CH 4/ CO 2 (1: 1) for 5 min.

62 nd OSU International Symposium on Molecular Spectroscopy HRTEM images of carbon deposition on (a) La 2 Ni. O 4 (b) 10%Ni. O/Ce. O 2 -La 2 O 3

62 nd OSU International Symposium on Molecular Spectroscopy Conclusion v CH 4/CO 2 reforming over La 2 Ni. O 4 and 10% Ni. O/Ce. O 2 La 2 O 3 catalysts under the condition of supersonic jet expansion were studied via direct monitoring of the reactants and products using CRDS. v Vibration-rotational absorption lines of CH 4, H 2 O, CO 2 and CO molecules were recorded in the near infrared spectral region. v It was also found that the associated reverse water-gas shift (RWGS) reaction affected significantly the H 2/CO product ratio, over the catalysts during CH 4/CO 2 reforming.

62 nd OSU International Symposium on Molecular Spectroscopy Acknowledgements The work described here was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7101/02 P).