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Propane steam reforming reaction over supported Rh and Ru catalysts

Florou Alexandra

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Summary

Interest in hydrogen (H2) as a potential energy carrier has increased significantly in recent decades as a result of the rapid development of fuel cell technology, which is an environmentally friendly method for distributed electricity generation, both for mobile and stable applications. H2 is the fuel of the PEM-fuel cells and can be produced via steam reforming of various compounds, such as liquefied petroleum gas (LPG). LPG is a mixture of mainly propane (C3H8) and butane (C4H10), in concentrations that vary according to their source, and can be easily obtained following widely established methods for its transport and storage. The main object of this study is the synthesis, characterization and optimization of catalytic materials and their evaluation for the propane steam reforming reaction. The optimal catalysts developed were also studied for their catalytic performance in the presence of butane in the gas stream at concentrations similar to those found in the actual LPG mixture. Τhe effect of the calcination temperature (400-800 °C) of the carrier (Al2O3) on the activity of Rh catalysts, as well as the effect of the promotion of Ru/TiO2 catalysts with a small amount of alkali (K, Na, Cs, Li) was examined. The effect of composite metal oxides (10%Gd2O3-TiO2, 10%Y2O3-TiO2, 10%La2O3-TiO2, 10%CeO2-TiO2 and 10%La2O3-Al2O3, 10%Sm2O3-Al2O3, 10%Y2O3-Al2O3, 10%TiO2-Al2O3, Gd2O3-Al2O3) as carries as well as the effect of the Gd2O3 content (0 wt.%,5 wt.%,10 wt.%,20 wt.%) on the activity of Rh catalysts were also studied and discussed. Finally, the effect of the various operating parameters on the catalytic performance of 0.5%Rh/TiO2 under realistic reaction conditions was investigated in the present study. In particular, the effect of the steam to carbon ratio (H2O/C), the gas hourly space velocity, and the reaction time by conducting long-term catalytic stability experiments was investigated. Results showed that the calcination of the Al2O3 carrier leads to an improvement in catalytic performance. Optimal results were obtained for Rh catalyst supported on Al2O3 carrier calcined at 600 °C. The addition of a small amount of alkali on Rh/TiO2 catalysts leads to an increase of the reaction rate compared to the unpromoted sample, with the exception of Na addition. Highest activity was obtained over the Li-promoted Ru/TiO2 catalyst. The deposition of La2O3 and Ce2O3 to a TiO2 carrier improves the activity of Rh, contrary to the deposition of Gd2O3 or Y2O3 leading to lower catalytic activity. The performance of Rh is significantly increased when dispersed on carries of various composite metal oxides (10%MxOy-Al2O3), with Gd2O3-Al2O3 and La2O3-Al2O3 carriers being the most suitable for the propane steam reforming reaction. An increase of the Gd2O3 content on the Al2O3 surface cannot improve catalytic behavior. Regarding the effect of operating reaction conditions, it was found that the efficiency of Rh/TiO2 catalyst is enhanced by decreasing GHSV and/or increasing the H2O/C ratio. The variation of GHSV does not affect significantly the selectivity toward reaction products. The catalyst exhibits excellent response in abrupt changes of H2O/C ratio at constant temperature, without being deactivated or leading to a decrease of H2 selectivity following successive changes of feed composition. Finally, Rh/TiO2 catalyst exhibits excellent stability at 500 and 550 °C under realistic reaction conditions and is therefore a promising catalyst for H2 production through the reaction of LPG steam reforming.

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