Catalytic conversion of propane to hydrogen in microstructured reactors

A microstructured reactor has been fabricated from the high temperature alloy Fecralloy (72.6% Fe, 22% Cr, 4.8% Al). The reactor was oxidized at high temperature to form a porous layer of α-Al2O3 on the surface of the channels and subsequently impregnated with Rh. The reactor was tested for partial oxidation (POX) and oxidative steam reforming (OSR) of propane at 1 bar and in the temperature range 500–1000 °C. The results were compared to those obtained from equivalent experiments using reactors made of pure Rh or from oxidized Fecralloy reactors without catalyst or impregnated with Ni. OSR gives higher yields of hydrogen than POX for the Rh/Al2O3/Fecralloy system. Formation of H2, CO, CO2 and H2O by gas phase reactions does not seem to play a dominating role below 1000 °C. Small amounts of methane and ethene were detected at the highest temperatures. The Rh/Al2O3/Fecralloy reactor gives higher selectivities to hydrogen as compared to the reactor made of Rh, indicating that having the catalyst dispersed on a porous layer in the microchannels is beneficial. Changing the residence time by changing the feed rate influenced conversions and selectivities differently for Rh/Al2O3/Fecralloy and for Al2O3/Fecralloy without any Rh. Deactivating including coke formation was not observed for the Rh/Al2O3/Fecralloy system under the conditions applied. Results from Ni/Al2O3/Fecralloy are more ambiguous, and it appears that sintering effects, oxidation of Ni or possibly loss of material occur in this system. Microstructured Fecralloy foils were prepared in the same way as used for the reactors in order to characterize the resulting oxide layer and the impregnated catalyst. XRD, SEM/EDX and XPS measurements confirm the existence of an α-Al2O3 layer. XPS furthermore confirms the presence of metallic Rh, while Ni appears to be present as both metal and oxide.

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