Partial oxidation of fuels on noble metals is key to producing (1) syngas and hydrogen for a potential hydrogen economy from fossil fuels and biomass derivatives and (2) alkenes, such as ethylene which is the basic unit for polyethylene. The former process requires C-C bond cleavage, whereas the latter (oxidative) dehydrogenation. The best catalyst for the latter process is platinum [1]. Using DFT, we examined various C2Hx and C2HxO species on Pt(111) and Pt(211). We find that all the C2HxO species are more stable than the reference state (CH2CH3ad + Oad), especially the species containing less than three H atoms (herein ‘ad' stands for adsorbed species). In addition, we calculated the barriers of several key reactions including ethane dehydrogenation, C-O association and C-C cleavage. CCH3 and CCH2, which are the most abundant surface species under typical reaction conditions [2-4], are important links between inter-conversions of C2Hx and C2HxO. Finally, we studied the influence of high O coverage on some reactions. This is typical under combustion conditions and upstream in the partial oxidation reactor. The barriers of dehydrogenation and C-O coupling reaction change slightly, while the barriers of C-C cleavage reaction increase significantly and the barrier of 1, 2-H shift between CH2CH2 and CH3CH decrease dramatically. Results of DFT are input into microkinetic models and comparison to various experimental data is conducted. Finally, the comparison of ethane to methane chemistriesy will be compared.

References:

[1] A.S. Bodke, D.A. Olschki, L.D. Schmidt, E. Ranzi, Science 285, 712 (1999).

[2] S. G. Podkolzin, R. Alcalá, J. A. Dumesic, J. Mole. Catal. A 218, 217 (2004).

[3] P. S. Cremer, X. C. Su, Y. R. Shen, G. A. Somorjai, J. Am. Chem. Soc. 118, 2942 (1996).

[4] S. Azad, M. Kaltchev, D. Stacchiola, G. Wu, W. T. Tysoe, J. Phys. Chem. B 104, 3107 (2000).