Catalysis of Steam Reforming

Steam can be considered a cor-eactant of oxidation during rich-phases (lean in O2) [3-5], In oxy-steam conversion of propane, we showed (fig.l) that propane oxidation was catalyzed by platinum (between 200 and 350°C) while rhodium was the key-component in the catalysis of steam reforming (between 350 and 600°C). Ceria was an excellent promotor of steam reactions [3, 6], particularly when this reaction was carried out in the presence of oxygen. Therefore, the steam reforming activity is an excellent indicator of the rhodium surface state since the activity systematically decreases when the metallic rhodium area decreases [7]. On the other hand, oxidation activity is a more complex indicator of platinum surface state because there exists an optimum dispersion [8,9]. 

The understanding of the catalysis of steam reforming was achieved in parallel with the industrial developments described in Chapters 3, 4 and 5. The knowledge obtained from this research has been essential to strengthen the know-how gained from the process development and from the feedback from the industrial practice. It has provided a rational basis to cope with the secondary problems. The analysis has also demonstrated that the progress in catalysis to a large extent is related to the development of new characterisation techniques and new theoretical methods. This is an obvious field for collaboration between scientists in industry and in academia. 

Takahashi, K. Takezawa, N. Kobayashi, H., The mechanism of steam reforming of vehicles. Applied Catalysis 1982, 2, 363-366. 

Wang, X., Gorte, R. (2002). A study of steam reforming of hydrocarbon fuels on Pd/ceria. Appl. Catalysis A General 224,209-218. 

Graf, P.O., Mojet, B.L., van Ommen, J.G., and Lefferts, L. Comparative study of steam reforming of methane, ethane and ethylene on Pt, Rh and Pd supported on yttrium-stabilized zirconia. Applied Catalysis. A, General, 2007, 332 (2), 310. 

S. H. Clarke, A. L. Dicks, K. Pointon, T. A. Smith, and A. Swann. Catalytic aspects of steam reforming of hydrocarbons in internal reforming fuel cells. Catalysis Today 38,(1997)411 23. 

Hu, X., Lu, G. (2007). Investigation of steam reforming of acetic acid to hydrogen over Ni—Co metal catalyst. Journal of Molecular Catalysis A Chemical, 261, 43—48. 

Conant, T., Karim, A. and Datye, A. (2007) Coating of steam reforming catalysts in non-porous multi-channeled microreactors. Catalysis Today, 125, 11-15. 

De Lima, S. M., Da Silva, A. M., Da Costa, L. O. O., et al., 2009, "Study of catalyst deactivation and reaction mechanism of steam reforming, partial oxidation, and oxidative steam reforming of ethanol over Co/Ce02 catalyst". Journal of Catalysis, v. 268, n. 2, p.268-281. 

The reaction products H2 and CO are then oxidised to H2O and CO2 at the anode. Extensive research has been done on steam reforming catalysis. During steam reforming catalysis, steam to carbon ratios of approximately 2.5-3 are used which is more than the required stoichiometry so that the equilibrium of the water-gas shift reaction points to the right favouring H2 production and minimum carbon deposition. Figure 9.12 shows the reaction mechanism for SOFC utilising natural gas and steam. 

Uemiya, S., Brief review of steam reforming using a metal membrane reactor. Topics in Catalysis, 2004.29(1) 79-84. 

I.V. Yentekakis, Y. Jiang, S. Neophytides, S. Bebelis, and C.G. Vayenas, Catalysis, Electrocatalysis and Electrochemical Promotion of the Steam Reforming of Methane over Ni Film and Ni-YSZ cermet Anodes, Ionics 1, 491-498 (1995). 

Takanabe, K. Aika, K.-I. Inazu, K. T. B. Seshan, K. Lefferts, L., Steam reforming of acetic acid as a biomass derived oxygenate Bifunctional pathway for hydrogen formation over Pt/ZrOz catalysts. Journal of catalysis 2006,243(2), 263-269. 

As an application of Pt nanowires in heterogeneous catalysis, we performed preferential oxidation (PROX) of CO as a test reaction [32]. The PROX reaction is useful for PEM fuel cells for the selective removal of contaminating CO from hydrogen gas, because CO works as a strong catalyst poison for Pt electrode catalysts (Figure 15.24). H2 produced in steam-reforming and the water-gas shift reaction needs further to be purified in the PROX reaction to selectively oxidize a few% CO towards inert CO2 in a H 2-rich atmosphere, to reduce the CO content to <10ppm. Under the PROX conditions, the facile oxidation of H2 to H2O may also occur, thus the catalyst selectivity for CO oxidation over H2 oxidation is an... 

La2Cu04, Sr2Cu04. As we show in chapter 6, when a perovskite forms a composite or intergrowth with other structures, new compounds of interest in catalysis can be formed (such as in high-temperature superconducting copper oxides) and EM is used to determine the structures and properties of these complex compounds. The merits of using perovskites in steam reforming, membrane catalysis and fuel cells are discussed in chapter 6. 

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